Design optimization method of super-long pile in super-thick soft soil layer wharf

Abstract

The application relates to a design optimization method for an ultra-long pile of an ultra-thick soft soil layer wharf, and belongs to the technical field of port hydraulic structures and deep soft soil foundation treatment. In view of the problem that, in an ultra-thick soft soil layer, an ultra-long pile is caused by unknown deep layer side friction and large deviation between a horizontal displacement zero point and an imaginary embedded point, the method establishes a layered pile soil model, sets a layered side friction correction coefficient for a soil layer with a depth of 50m below a mud surface λ i , calculates single-pile bearing capacity and pile side friction contribution rate, adjusts a pile end elevation or increases a pile diameter when the contribution rate is insufficient, compares the horizontal displacement zero point with the imaginary embedded point, establishes a deviation degree R , when the deviation degree is greater than 0.5 R , corrects soil spring stiffness when the deviation degree is greater than 1, and iteratively converges through an equivalent constraint stiffness reduction factor δ ; when the bearing capacity deviation is greater than 15% through static load or high strain detection, the correction coefficient is proportionally corrected. The method is mainly used for design optimization of heavy-load high-pile structures, reduces material waste, and guarantees construction and operation safety.

Description

Technical Field

[0001] This invention belongs to the technical field of port hydraulic engineering and deep soft soil foundation treatment. More specifically, this invention relates to a method for optimizing the design of ultra-long piles for wharves in ultra-thick soft soil layers. Background Technology

[0002] Nearshore isolated plant sites, offshore energy projects, and large-scale marine engineering equipment projects often require dedicated wharves. These wharves, in addition to accommodating ship berthing and component transfer, must also withstand heavy loads from large cranes, roll-on / roll-off vehicles, and temporary stacking during construction. When the wharf foundation is located in a deep soft soil area, the superstructure often contains silt or soft plastic cohesive soil, with a soft soil layer thickness reaching 20-80 meters and an effective bearing layer depth generally between 50-120 meters. In such cases, steel pipe piles often exhibit friction-type long piles with side friction as the primary load-bearing source, with single pile lengths exceeding 60 meters, representing a typical stress problem for ultra-long steel pipe piles.

[0003] Current port engineering pile foundation design typically relies on the m-method, the hypothetical fixed point method, and the formula for calculating the vertical bearing capacity of a single pile, all recommended by the code. These methods are relatively mature under conditions of ordinary soft soil and conventional pile lengths, but for the design of ultra-long piles in ultra-thick soft soil layers, direct application will result in significant deviations in stress assessment.

[0004] Regarding vertical bearing capacity, for ultra-long piles exceeding 60m in length, a large number of piles need to penetrate deep soft soil layers. The stress characteristics of the soil lateral to the pile in areas deeper than 50m below the mud surface differ significantly from those in shallow soil layers. Current specifications lack clear provisions on the mechanism of pile side friction in deep soil layers, failing to provide methods for calculating side friction parameters for deep soft soil, nor offering correction coefficients that consider depth effects. Existing designs typically extend the skin friction parameters of shallow soil empirically to deeper layers, or directly adopt the same standard values ​​for side friction as those for shallow layers. However, practical engineering experience shows that the degree of development of pile side friction in deep soft soil under long-term loading differs significantly from that in shallow highly compressible soft soil. If shallow specification values ​​are uniformly applied, they often do not match the actual pile-soil interaction state, making it difficult to accurately predict the ultimate bearing capacity of a single pile.

[0005] Regarding horizontal stress, the stress state of ultra-long steel pipe piles under heavy and horizontal loads is more complex. The current m-method assumes that the soil's horizontal resistance coefficient increases linearly with depth, and the calculated hypothetical embedment depth can well reflect the pile's stress characteristics in conventional pile length designs. However, in ultra-long pile designs, actual stress analysis reveals a significant deviation between this hypothetical embedment depth and the actual zero-point depth of horizontal displacement. The location of the maximum bending moment and the inflection point of the pile under the hypothetical embedment assumption do not correspond to the bending moment distribution under actual deep stress conditions. This discrepancy means that the horizontal displacement and internal force distribution of the pile calculated solely using standard methods cannot accurately reflect the stress state of ultra-long piles in deep soft soil layers.

[0006] Because the characteristics of deep side friction and horizontal stress differ significantly from those of shallow soft soil, and existing standards and methods do not provide specific treatment measures for ultra-long piles, engineering practice often encounters problems such as large deviations between calculated and measured values ​​of the vertical bearing capacity of a single pile, and underestimation of the calculated horizontal displacement. The root cause of these problems lies in the current design process's failure to incorporate the values ​​of deep side friction and the zero-point offset of horizontal displacement into a unified calculation system for closed-loop verification, leading to separate judgments and design gaps between different disciplines. While simply increasing the pile diameter or length can alleviate the exceedance of individual indicators to some extent, it often fails to fundamentally solve the problem of distortion in deep stress. Accurately assessing the interaction between deep piles and soil, and integrating the correction of deep side friction and the zero-point offset of horizontal displacement into the design verification process, is a crucial technical challenge that urgently needs to be addressed in the design of ultra-long piles for ultra-thick soft soil wharves. Summary of the Invention

[0007] The purpose of this invention is to provide an optimized design method for ultra-long piles in wharves located in ultra-thick soft soil layers. This method aims to overcome the shortcomings of existing standard methods in calculating ultra-long piles, such as excessive deviations in vertical bearing capacity due to the mixing of deep and shallow layer side friction values, and distortions in horizontal internal forces caused by the offset between the zero point of horizontal displacement and the hypothetical anchoring point, leading to inaccurate assessment of deep stress. This invention incorporates deep side friction correction, horizontal displacement zero-point deviation verification, and feedback from field measurement data into a unified calculation process. This ensures that, while meeting bearing capacity, displacement, and stability requirements, it avoids material waste and construction risks caused by simply increasing pile diameter, pile length, or the number of piles.

[0008] To address the aforementioned problems and achieve the objectives and other advantages of this invention, a design optimization method for ultra-long piles in ultra-thick soft soil layers of wharves is provided. The thickness of the soft soil layer in the wharf foundation is 20-80m, and the effective bearing layer depth is 50-120m. The ultra-long steel pipe piles have a length of 60-130m, a diameter of 1.0-2.0m, and a length-to-diameter ratio of 40-110. The method includes the following steps: Preliminary determination of pile length, pile diameter, and number of piles; Based on geological survey data, a layered pile-soil model was established to obtain the standard values ​​of pile side friction resistance for each soil layer in the 0-50m range below the mud surface. qfik For areas 50m below the mud surface, sections are divided based on the physical and mechanical properties of the soil layers, and a correction factor for the side friction resistance of each layer is set. l i Among them, for those with a natural water content greater than the liquid limit, a porosity greater than 1.0, and a compressibility coefficient greater than 0.5 MPa -1 And in conventional soft soil sections where the SPT blow count is less than 4, l i Take a value of 0.8-1.1; for standard penetration tests (SPT) blow counts greater than 8 blows and compressibility coefficients less than 0.1 MPa. -1 Or deep improved soil layers with a compression modulus greater than 15 MPa, l i Take 1.05-1.50; for soil layers with weak interlayers not less than 0.5-1.0m thick, or those affected by construction disturbance and soil displacement, l i Take 0.6-1.0; according to the formula Calculate the ultimate vertical bearing capacity of a single pile Q uk ,in, qfik For the first i Standard value of side skin friction of piles u i For the first i Perimeter of pile layer, l i For the first i Effective length of pile side, a p This is the reduction factor for pile end resistance. q pk This is the standard value of pile end resistance. A p The area at the pile tip; and according to the formula Calculate the contribution rate of pile side friction or f ;when or f When the bearing capacity is less than 70%, the pile tip elevation is compared with the effective bearing layer depth. If the pile tip elevation is shallower than the effective bearing layer depth, the pile tip elevation is adjusted downwards to within the effective bearing layer, and the pile diameter or the number of piles is increased before recalculating the vertical ultimate bearing capacity of the single pile. Q uk and the contribution rate of pile side friction or f The steps continue until the desired result is achieved. or f Not less than 70%; Based on the soil layer division and pile-soil parameters provided by the layered pile-soil model, an overall pile-soil spring model of the wharf was established, and a three-dimensional pile-soil interaction model was also established; the depth of the hypothetical embedded point was obtained. h f The depth of the zero point of horizontal displacement calculated by the three-dimensional pile-soil interaction model. z 0 and the depth of the imaginary embedded point h f deviation R Deviation R The calculation formula is: R = z 0 / h f ;when R When the value is <1.2 or >2.8, a review is performed. This review involves correcting the soil spring stiffness and soil layer boundary parameters in the overall pile-soil spring model of the wharf; extracting the maximum bending moment point based on the bending moment curve distributed along the depth of the pile; and addressing any deviations that cannot be corrected after the review. R It falls within the range of 1.5-2.5 and the point of maximum bending moment cannot be located in h f If the location is nearby, it is determined that the structure itself has insufficient stiffness; When the structure is determined to have insufficient rigidity, adjustments are made to the pile diameter, wall thickness, number of piles, or pile location, and the aforementioned verification steps are repeated until the deviation is correct. R The value falls within the range of 1.5-2.5 and the point of maximum bending moment is located at... h f Nearby; if the requirements still cannot be met after adjustment, then based on the degree of deviation. R Establish equivalent constraint stiffness reduction factor d ;like R When the value is greater than 2.8, the equivalent constraint stiffness reduction factor is... d Take 0.6-0.8; if R When <1.2, the equivalent constraint stiffness reduction factor d Take 1.2-1.4; if R If the value is within the range of 1.2-2.8, the original calculation parameters of the overall pile-soil spring model of the wharf will be directly used as the basis for subsequent calculations; when the equivalent constraint stiffness reduction factor is used... d At that time, the equivalent constraint stiffness reduction factor d Used to determine the original stiffness of the soil springs in the area 50m below the mud surface in the integral pile-soil spring model of the wharf. K 原始 Perform multiplication correction; the formula for multiplication correction is as follows: K 修正 = d × K 原始The corrected soil spring stiffness is then re-substituted into the overall pile-soil spring model of the wharf for calculation, and the calculation is iterated repeatedly until the equivalent constraint stiffness reduction factor obtained from two adjacent calculations is obtained. d If the rate of change is less than 5%, and the difference between the recalculated overall pile-soil spring model of the wharf and the three-dimensional pile-soil interaction model at the maximum displacement and the maximum bending moment is less than 5%, then convergence is determined. The measured bearing capacity obtained from static load tests or high strain tests is compared with the ultimate vertical bearing capacity of a single pile. Q uk Comparison, when the vertical ultimate bearing capacity of a single pile Q uk When the deviation from the measured bearing capacity exceeds 15%, a proportional correction is applied; the proportional correction includes correction for the corresponding coefficients of the source of deviation at the pile tip or pile side; when the deviation mainly originates from the pile tip, the pile tip resistance reduction factor is applied. a p According to the formula Make corrections. a p,old and a p,new These are the reduction factors for pile end resistance before and after the correction, respectively, and the correction factor is used as the reference. a p,new As the reduction factor for pile end resistance in subsequent calculations, and the corrected a p,new The value is limited to the range of 0.6-1.0; when the deviation mainly originates from the pile side, the correction factor for side skin friction is... l i According to the formula Make corrections. l i,old and l i,new These are the correction factors for side friction resistance before and after the correction, respectively, and the correction factor after the correction is... l i,new The values ​​are limited to the range of values ​​for the corresponding section; repeat the above calculation until the deviation between the calculated bearing capacity and the measured bearing capacity does not exceed 15%; Output the final design scheme, which includes pile diameter, pile length, number of piles, wall thickness, and pile end elevation.

[0009] Preferably, in the aforementioned optimization method for the design of ultra-long piles for wharves in ultra-thick soft soil layers, the specific method for determining whether the deviation mainly originates from the pile tip or pile side is as follows: extract the calculated value of the pile axial force distribution along the depth output from the overall pile-soil spring model or the three-dimensional pile-soil interaction model of the wharf, and the measured value of the pile axial force distribution along the depth obtained by actual measurement; calculate the absolute value of the difference between the calculated value and the measured value of the axial force at each depth; and calculate the sum of the absolute values ​​of the axial force differences at all depths. When the absolute value of the difference at the pile tip accounts for 60% or more of the sum of the absolute values ​​of the differences, it is determined that the deviation mainly originates from the pile tip; when the absolute value of the difference at the pile tip accounts for less than 60% of the sum of the absolute values ​​of the differences, it is determined that the deviation mainly originates from the pile side.

[0010] Preferably, in the aforementioned method for optimizing the design of ultra-long piles for wharves in ultra-thick soft soil layers, when adjusting the pile diameter, wall thickness, number of piles, or pile location, an equivalent constraint stiffness reduction factor is used. d The linkage optimization relationship between pile diameter, pile length, and single pile steel quantity is controlled; multiple pile diameter schemes are established under the same pier, the same load combination, and the same geological profile, and the foundation sensitivity relationship between pile diameter, pile length, and single pile steel quantity is set. The foundation sensitivity relationship is defined as the increase rate of pile length required to meet bearing capacity and stability when the pile diameter is reduced by 0.1m, and the steel weight of a single steel pipe pile is reduced by 2-4%; when the equivalent constraint stiffness reduction factor... d A low value of 0.6-0.8 is selected to indicate weak deep confinement, and the pile length increase rate is forcibly set to the upper limit of 5%; when the equivalent confinement stiffness reduction factor... d When the pile length is within the range of 1.2-1.4, the lower limit of 2% is selected for the pile length increase rate. The maximum pile driving length of the piling vessel is used as a hard constraint condition. When the adjusted pile length exceeds the maximum pile driving length of the piling vessel, the next scheme with a larger pile diameter is directly locked and the subsequent calculations are re-executed. If the next scheme with a larger pile diameter still cannot meet the bearing capacity and stability requirements, the step of increasing the number of piles is returned, and the process of adjusting the pile diameter, wall thickness, number of piles, or pile position is re-executed. If, after multiple rounds of the above-mentioned adjustments, the current design scheme still cannot meet the bearing capacity and stability requirements, the current adjustment process is terminated, and local foundation treatment or isolation measures are taken to meet the design requirements.

[0011] Preferably, in the aforementioned design optimization method for ultra-long piles in ultra-thick soft soil layers, the method further includes verification of the additional lateral action of adjacent dike settlement. The specific steps for verifying the additional lateral action of adjacent dike settlement are as follows: when the final settlement of the adjacent dike is not less than 0.2m, and the distance between the pile foundation and the dike side edge is less than twice the thickness of the soft soil layer, the additional lateral earth pressure generated by the consolidation of the dike is directly superimposed onto the outer boundary conditions of the three-dimensional pile-soil interaction model through mathematical vector decomposition; the additional bending moment generated after superposition is vector superimposed with the original horizontal load bending moment; for the peak bending moment in the deep soft soil area 50m below the mud surface, a double-layer data threshold is set. When the superimposed bending moment exceeds the threshold, the excess additional bending moment value is converted into a bending moment-force value. The equivalent conversion formula is converted into an additional horizontal concentrated force, which is then applied to the pile-soil spring node at the corresponding depth in the overall pile-soil spring model of the wharf. For inclined piles or side piles near the dike, the negative bending moment distribution curve under superimposed load is extracted. The peak value of the negative bending moment appearing in the depth range directly below the dike edge is taken as the control condition, and the peak value of the negative bending moment is compared with the design allowable negative bending moment value. If it exceeds the allowable value, the pile diameter or wall thickness of the inclined pile or side pile is increased and adjusted, and the check of the additional lateral action on the settlement of the adjacent dike is re-executed. If the peak value of the negative bending moment of the inclined pile or side pile still exceeds the design allowable value after multiple rounds of adjustment, the current adjustment process is terminated, and isolation measures or measures to control the settlement of the dike during the construction stage are adopted.

[0012] Preferably, the design optimization method for ultra-long piles in ultra-thick soft soil wharves further includes a coupled verification of the long-term durability and buckling stability of the ultra-long steel pipe piles; an algorithm for the stiffness attenuation coefficient of the pile section is constructed based on the design service life of the steel pipe piles; a stiffness attenuation coefficient that evolves with time is applied to the section stiffness of the pile element in the three-dimensional pile-soil interaction model; when the stiffness attenuation coefficient decays to a preset warning threshold, the overall pile-soil spring model of the wharf and the three-dimensional pile-soil interaction model simultaneously switch to the buckling stability master control verification mode; the buckling stability master control verification mode means that in subsequent design calculations, the pile buckling stability coefficient is used as the primary control indicator, and the pile diameter, wall thickness, number of piles or pile position are adjusted to ensure that the pile buckling stability coefficient meets the design requirements, and is satisfied with the design requirements. The required pile buckling stability coefficient is used as one of the verification bases for the final design scheme. Corrosion protection measures are designed for the steel pipe piles in the splash zone, water level fluctuation zone, underwater zone, and mud zone. The splash zone adopts heavy-duty anti-corrosion coating, the water level fluctuation zone and underwater zone adopt a combination of coating and sacrificial anode cathodic protection, and the mud zone is equipped with cathodic protection within 20-40m below the mud surface. The annual average corrosion rate of unprotected steel pipe piles is estimated at 0.2-0.6mm / a, and the corrosion allowance is taken as 1-4mm. The effective wall thickness after corrosion is obtained by subtracting the corrosion allowance from the initial wall thickness of the steel pipe pile. The effective wall thickness after corrosion is used to replace the initial wall thickness in the buckling stability check to ensure that the maximum combined stress of the section does not exceed 0.85 times the design allowable value. The final design scheme also includes anti-corrosion measures.

[0013] Preferably, in the design optimization method for ultra-long piles of wharves in ultra-thick soft soil layers, a convergence gradient threshold is set during the iterative process; after each iteration update of the soil spring stiffness in the overall pile-soil spring model of the wharf, the current equivalent constraint stiffness reduction factor is calculated. d Compared with the previous round of equivalent constraint stiffness reduction factor d The normalized gradient is used to determine the equivalent constraint stiffness reduction factor when the normalized gradient is less than the convergence gradient threshold. d Under this condition, convergence has been achieved and the iteration has ended; when the normalized gradient is always greater than or equal to the convergence gradient threshold and the equivalent constraint stiffness reduction factor is applied... d Continuous deviation is determined by the degree of deviation R The determined equivalent constraint stiffness reduction factor d When the value range is selected, it is determined that the deep soil constraint characteristics have high nonlinearity, triggering the recalibration of the deep soil constitutive parameters in the three-dimensional pile-soil interaction model based on field geological data, and restarting the repeated iteration process.

[0014] Preferably, in the aforementioned method for optimizing the design of ultra-long piles for wharves in ultra-thick soft soil layers, the equivalent constraint stiffness reduction factor is applied. dIn the coordinated optimization process involving pile diameter and pile length, a safety margin for the construction-deployable pile length is set. When the difference between the design pile length output under each candidate pile diameter scheme and the maximum pile length that can be driven by the piling vessel is less than the safety margin for the construction-deployable pile length, the equivalent constraint stiffness reduction factor is directly applied. d Substituting the convergence value into the long-term cross-sectional stiffness attenuation coefficient of the pile body under the current pile diameter scheme, the equivalent constraint stiffness reduction factor under long-term service conditions is calculated. d The degradation trajectory; when the pile buckling stability redundancy is lower than the design standard under the degradation trajectory, skip the current pile diameter scheme and directly lock the next larger pile diameter scheme; if the next larger pile diameter scheme still cannot meet the long-term stability requirements, return to the step of increasing the number of piles, and re-execute the process of adjusting the pile diameter, wall thickness, number of piles, or pile position; if the long-term stability requirements still cannot be met after multiple rounds of adjustment, terminate the current adjustment process, and take local foundation treatment or set up isolation measures to meet the long-term stability requirements; at the same time, the hook capacity of the piling vessel is not less than the weight of a single pile. W p The maximum pile length is 1.10 times that of the design pile, and the maximum pile driving length of the pile frame is 3-8m with a safety margin relative to the equivalent length of the designed pile, so as to ensure that the construction feasibility and long-term stability meet the constraints at the same time; the final design scheme also includes pile driving control standards.

[0015] Preferably, in the aforementioned design optimization method for ultra-long piles in ultra-thick soft soil wharves, when applying a section stiffness attenuation coefficient to the pile element in the three-dimensional pile-soil interaction model, the deviation degree is used as the criterion. R Based on the deviation degree R The magnitude of the attenuation rate of the cross-sectional stiffness attenuation coefficient is modulated by partitioning; the attenuation rate includes a lower limit and an upper limit. Taking the lower limit means that the cross-sectional stiffness attenuation coefficient degrades according to the reference degradation rate, which is the ratio obtained by dividing the corrosion allowance by the design service life; taking the upper limit means that the cross-sectional stiffness attenuation coefficient degrades at a preset multiple of the reference degradation rate; when the deviation is... R When the coefficient of stiffness attenuation is greater than 2.8, the attenuation rate of the cross-sectional stiffness attenuation coefficient takes the lower limit value in the region above the hypothetical fixed point and the upper limit value in the deep soft soil region below the hypothetical fixed point; when the deviation... R When the value is ≤2.8, the attenuation rate of the cross-sectional stiffness attenuation coefficient is taken as the lower limit in both the region above the hypothetical fixed point and the deep soft soil region below the hypothetical fixed point.

[0016] Preferably, in the aforementioned design optimization method for ultra-long piles in ultra-thick soft soil wharves, after the additional lateral earth pressure generated by the consolidation of the dike body is superimposed onto the outer boundary conditions of the three-dimensional model, an active feedback suppression mechanism for the additional bending moment is executed. The specific execution steps of the active feedback suppression mechanism for the additional bending moment are as follows: extracting the peak negative bending moment of the inclined piles adjacent to the dike body or the side piles close to the dike body under superimposed load in the three-dimensional pile-soil interaction model; when the peak negative bending moment exceeds a preset proportion of the design allowable value, triggering virtual unloading of the additional lateral earth pressure, generating an equivalent normal resistance force in the opposite direction and proportional in magnitude to the additional earth pressure within a preset depth range below the mud surface of the three-dimensional pile-soil interaction model; superimposing the equivalent normal resistance force into the three-dimensional pile-soil interaction model. The actual stress state of the inclined piles or side piles after the superimposed calculation is dynamically evaluated, and the stress or displacement value under the actual stress state after the superimposed calculation is compared with the design allowable value of the negative bending moment control condition. When the stress or displacement value is greater than the design allowable value, it is determined that the current pile type parameters do not meet the requirements, and the process returns to adjust the pile diameter or wall thickness of the inclined piles or side piles, and the active feedback suppression mechanism for the additional bending moment is re-executed. When the stress or displacement value is less than or equal to the design allowable value, it is determined that the current pile type parameters meet the requirements. If the stress or displacement value is still greater than the design allowable value after multiple rounds of adjustment, the current adjustment process is terminated, and isolation measures or measures to control settlement during the construction stage of the embankment are adopted.

[0017] Preferably, in the aforementioned design optimization method for ultra-long piles at wharves in ultra-thick soft soil layers, the equivalent constraint stiffness reduction factor... d During the iterative correction process, a multi-parameter auxiliary judgment mechanism is set up. This mechanism simultaneously extracts the axial force normalization sequence, bending moment normalization sequence, and soil strength normalization sequence at various depths below the mud surface from the three-dimensional pile-soil interaction model; and calculates the equivalent constraint stiffness reduction factor. d First correlation index with the standardized sequence of pile axial forces, equivalent constraint stiffness reduction factor d The second correlation index with the standardized bending moment sequence, and the equivalent constraint stiffness reduction factor. d A third correlation index between the soil strength standardization sequence and the soil strength standardization sequence; when any one of the first, second, and third correlation indices shows a negative correlation, and the absolute value of the negative correlation exceeds a preset negative correlation threshold, the current equivalent constraint stiffness reduction factor is determined. d The effectiveness is questionable, and the equivalent constraint stiffness reduction factor is forcibly frozen. dThe iterative update process involves: after freezing, comparing the actual distribution values ​​of axial force and bending moment extracted from the three-dimensional pile-soil interaction model at the freezing point with the calculated values ​​of axial force and bending moment obtained from the overall pile-soil spring model of the wharf, and then calculating a new equivalent constraint stiffness reduction factor that can eliminate this deviation. d Theoretical value, and the new equivalent constraint stiffness reduction factor. d The theoretical value serves as the new equivalent constraint stiffness reduction factor. d Initial value; reduce the new equivalent constraint stiffness factor. d Theoretical values ​​are limited by deviation. R The corresponding equivalent constraint stiffness reduction factor d Within the value range, if the new equivalent constraint stiffness reduction factor d Theoretical value exceeds deviation R The corresponding equivalent constraint stiffness reduction factor d If the value range is specified, then the deviation must be taken. R The corresponding equivalent constraint stiffness reduction factor d The boundary limits of the range of values ​​are used as new equivalent constraint stiffness reduction factors. d Initial value, restart stiffness backoff correction closed loop; the specific steps of stiffness backoff correction closed loop are: reconstruct the equivalent constraint stiffness reduction factor d Initial values ​​are input into the overall pile-soil spring model of the wharf. The stiffness values ​​of the soil springs in the area 50m below the mud surface are recalculated and updated according to the multiplication correction formula. The calculation results of the updated overall pile-soil spring model of the wharf are then compared with the calculation results of the three-dimensional pile-soil interaction model. If the difference between the overall pile-soil spring model of the wharf and the three-dimensional pile-soil interaction model at the maximum displacement and maximum bending moment does not meet the requirement of less than 5%, the equivalent constraint stiffness reduction factor is adjusted repeatedly. d And recalculate the soil spring stiffness until the current step. d Compared to the previous round d When the rate of change is less than 5%, and the difference between the overall pile-soil spring model and the three-dimensional pile-soil interaction model at the maximum displacement and maximum bending moment is less than 5%, the convergence condition is deemed met. Simultaneously, the current multi-parameter auxiliary judgment results are stored as historical working condition markers in the working condition memory of the design optimization method, so that the equivalent constraint stiffness reduction factor can be directly retrieved during subsequent design of wharf pile foundations under similar geological conditions. d The initial value is obtained, thereby improving the versatility and iterative calculation efficiency of the ultra-long pile design optimization method under different geological profiles.

[0018] The present invention has at least the following beneficial effects: This invention establishes a layered pile-soil model and introduces a layered side skin friction correction coefficient. l iDifferentiated values ​​were used for soil layers deeper than 50m below the mud surface, which effectively overcame the defect of directly applying shallow friction parameters to deep layers in existing specifications. This significantly improved the calculation accuracy of the vertical ultimate bearing capacity of ultra-long steel pipe piles in deep soft soil and avoided over-design or safety hazards caused by improper values ​​of deep friction.

[0019] This invention sets the contribution rate of pile side friction during the bearing capacity calculation process. or f The control target of no less than 70% ensures that the ultra-long piles rely primarily on side skin resistance for bearing capacity, avoiding the risk of insufficient bearing capacity caused by excessive reliance on pile end resistance. Furthermore, the system proactively corrects for deviations exceeding 15% between calculated and tested bearing capacity. l i The pile end resistance reduction coefficient and pile length or diameter are used to ensure that the design scheme remains consistent with the actual project.

[0020] This invention establishes a joint verification mechanism between a quay integral pile-soil spring model and a three-dimensional pile-soil interaction model, enabling precise extraction of the zero-point depth of horizontal displacement of ultra-long piles in deep soft soil. z 0 and the point of maximum bending moment, and will z 0 and the standard hypothetical embedment depth h f deviation R By controlling the value within the range of 1.5-2.5, the systematic deviation of the standard m-method in the horizontal stress analysis of ultra-long piles was effectively corrected, providing a reliable basis for the accurate assessment of the internal forces and displacements of the pile body.

[0021] This invention sets a deviation degree R The review threshold, when R When the value is less than 1.2 or greater than 2.8, the soil spring stiffness and soil layer boundary parameters are automatically corrected. If the correction is ineffective, the structure itself is deemed to have insufficient stiffness. The deep stress state is improved by adjusting the pile diameter, wall thickness, number of piles or pile position. This effectively avoids material waste caused by blindly enlarging the pile size and improves the rationality and economy of the design scheme.

[0022] This invention is based on the degree of deviation R Dynamically establish the equivalent constraint stiffness reduction factor d The original stiffness of the soil spring in the area 50m below the mud surface was corrected by multiplication, and the result was obtained through repeated iterations. d With a change rate of less than 5% and a difference of less than 5% between the maximum displacement and maximum bending moment of the two models, the consistency between the spring stiffness value of the deep soil and the response of the three-dimensional model is ensured, which significantly improves the convergence efficiency and calculation accuracy of the horizontal stress analysis of ultra-long piles.

[0023] This invention verifies the calculated bearing capacity through on-site static load tests or high-strain test results. When the deviation exceeds 15%, a proportional correction is performed, and targeted adjustments are made to the sources of deviation at the pile end and pile side. At the same time, the correction coefficient is strictly limited to a reasonable range, so that the theoretical calculation value and the measured data are in high agreement, which greatly enhances the engineering reliability of the design scheme.

[0024] This invention sets a 60% difference criterion as the main source of deviation, using the proportion of the difference in axial force at the pile end to the sum of the absolute values ​​of the total pile difference as the criterion. This allows the proportional correction to accurately pinpoint the dominant position of the deviation, effectively reducing repeated calculations caused by unclear deviation sources and significantly improving the efficiency and accuracy of model parameter correction.

[0025] This invention establishes a basic sensitivity relationship between pile diameter, pile length, number of piles, wall thickness, and steel content per pile. For every 0.1m decrease in pile diameter, a quantitative rule guides the coordinated optimization by increasing pile length by 2-5% and decreasing steel content by 2-4%. This is further supported by an equivalent constraint stiffness reduction factor. d The high and low values ​​respectively control the upper and lower limits of the pile length increase rate, so that the optimization direction can be accurately matched with the strength of deep constraints, and the bearing capacity and material economy are coordinated and unified.

[0026] This invention uses the maximum pile driving length of the piling vessel as a rigid constraint condition. When the pile length exceeds the equipment capacity, it actively locks in the next larger pile diameter scheme. When multiple adjustments still cannot meet the bearing capacity requirements, it adopts local foundation treatment or sets up isolation measures. This effectively avoids the problem of the design calculation value being out of sync with the actual construction capacity and ensures the feasibility of the design scheme.

[0027] This invention vector decomposes and superimposes the additional lateral earth pressure generated by the settlement of the adjacent embankment, and sets a double-layer data threshold for the area 50m below the mud surface. The excess bending moment is converted into an additional horizontal concentrated force and fed back to the m-method model for secondary verification. At the same time, the negative bending moment peak near the edge of the embankment is used as the control condition for the side piles. This effectively makes up for the deficiency of conventional design in ignoring the additional effect of embankment settlement and ensures the safety of the pile body under stress during operation.

[0028] This invention provides a sufficient protective barrier for the stress safety of the side piles under complex load combinations by comparing the peak negative bending moment of the inclined piles or the side piles close to the embankment under superimposed loads with the design allowable negative bending moment value. When the limit is exceeded, the pile diameter or wall thickness is adjusted in time. When multiple rounds of adjustment are ineffective, isolation measures or settlement control during the construction stage of the embankment are adopted. This avoids the risk of pile cracking or failure caused by local bending moment exceeding the limit.

[0029] This invention constructs an algorithm for the stiffness attenuation coefficient of the pile body section based on the design service life of the steel pipe pile, and simulates the degradation process of stiffness over time in a three-dimensional model. When the attenuation reaches a preset warning threshold, it automatically switches to the buckling stability master control verification mode, and takes the pile body buckling stability coefficient as the primary control indicator and verifies it before strength. This fundamentally solves the long-term instability risk caused by the degradation of cross-sectional stiffness due to long-term corrosion.

[0030] This invention designs anti-corrosion measures for steel pipe piles according to the splash zone, water level fluctuation zone, underwater zone, and mud zone, and determines the corrosion allowance based on the corrosion rate and design service life. The effective wall thickness after corrosion is directly substituted into the buckling stability check to ensure that the maximum combined stress of the section does not exceed 0.85 times the design allowable value. This establishes a direct coupling between durability design and structural bearing capacity, avoiding the problem of insufficient long-term bearing capacity caused by wall thickness reduction.

[0031] This invention reduces the equivalent constraint stiffness by using an equivalent constraint stiffness reduction factor. d During repeated iterations, a convergence gradient threshold is set for each adjacent iteration. d The normalized gradient of the value is monitored in real time. When the gradient is less than a threshold, convergence is determined and the iteration is terminated, effectively avoiding the influence of... d The infinite loop caused by continuous fluctuations improves the convergence speed and computational efficiency of the iterative process.

[0032] This invention addresses the issue of the normalized gradient continuously exceeding the limit and d When the model deviates from the ideal range, the constraint characteristics of the deep soil are determined to be highly nonlinear, triggering a recalibration of the constitutive parameters of the deep soil in the 3D model based on field geological data. This ensures that the model can withstand complex geological conditions. d It can reconverge to a reasonable physical range, improving the adaptability of the design optimization method under special geological conditions.

[0033] This invention sets a safety margin for the length of piles that can be driven during construction by optimizing the linkage between pile diameter and pile length. When the difference between the designed pile length and the maximum pile length that the piling vessel can drive is less than the safety margin, [the following will occur]. d The convergence value is substituted into the long-term section stiffness attenuation coefficient to calculate the degradation trajectory. When the pile buckling stability redundancy under the degradation trajectory is lower than the design standard, the scheme is skipped and a larger pile diameter is locked, which effectively ensures that the design scheme achieves the optimal balance between construction feasibility and long-term service stability.

[0034] This invention optimizes the pile diameter and pile length by simultaneously considering that the lifting capacity of the piling vessel hook is not less than the weight of a single pile. W pThe maximum pile driving length of the pile frame is 1.10 times that of the design pile driving length, and a safety margin of 3-8m is left relative to the design pile driving equivalent length. This allows the rigid constraints of the construction equipment and the flexible optimization of the structural design to form a closed loop of mutual correction, avoiding the problem that the design scheme cannot be implemented or the construction risk is significantly increased due to ignoring the construction capacity boundary.

[0035] This invention establishes a cross-sectional stiffness attenuation coefficient and an equivalent constraint stiffness reduction factor during the pile stiffness attenuation process. d The temporal coupling relationship, and the deviation under the current operating condition. R Using the zero-point deviation rate as a benchmark, the attenuation rate is modulated in different zones. The lower limit of the attenuation rate is taken in the area above the hypothetical embedment point and near the mud surface, while the upper limit of the attenuation rate is taken in the deep soft soil area below the hypothetical embedment point. This creates a synergistic deterioration judgment mechanism between the stiffness degradation rate caused by corrosion and the insufficient constraint of deep soil, which significantly improves the identification accuracy of pile instability risk in deep soft soil areas under long-term service conditions.

[0036] This invention extracts the peak negative bending moment of inclined piles or side piles under superimposed loads and sets a preset ratio to trigger virtual unloading. It generates an equivalent normal resistance force opposite to the direction of the additional earth pressure within a preset depth range below the mud surface. This resistance force is superimposed on a three-dimensional model to dynamically evaluate the stress or displacement value under the actual stress state and compare it with the design allowable value. Through a cyclic feedback mechanism, the structural dimensions are gradually brought closer to the optimal control range, effectively avoiding material waste caused by blindly increasing the size, while ensuring the safety of the structure under complex load combinations.

[0037] This invention reduces the equivalent constraint stiffness by using an equivalent constraint stiffness reduction factor. d During the iterative correction process, a multi-parameter auxiliary judgment mechanism is set up, and the axial force normalization sequence, bending moment normalization sequence, and soil strength normalization sequence are extracted to calculate... d The correlation index between the sequences is frozen when any index shows a negative correlation and its absolute value exceeds a threshold. d Iterate and reconstruct using the deviation back calculation d The initial values ​​effectively avoid the shortcomings of relying solely on numerical convergence metrics while ignoring physical matching, significantly improving... d The physical rationality of the values ​​and the reliability of the design results.

[0038] This invention, through d After freezing, a new theoretical calculation is performed based on the measured axial force and bending moment distribution. d The values ​​are then adjusted through a closed-loop correction cycle until the convergence condition is met. Simultaneously, the current multi-parameter auxiliary judgment results are stored as historical working condition markers in the working condition memory bank, providing directly callable data for subsequent wharf pile foundation design under similar geological conditions. dThe initial value reference significantly reduces the number of iterations and computation time, effectively improving the versatility and efficiency of the ultra-long pile design optimization method under different geological profiles.

[0039] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0040] Figure 1 Flowchart of the optimization method for designing ultra-long piles for wharves in ultra-thick soft soil layers; Figure 2 A schematic diagram showing the pile-soil interaction and control depth of ultra-long piles in ultra-thick soft soil layers; Figure 3 A graph showing the sensitivity relationship between pile diameter, pile length, and steel consumption per pile; Figure 4 A schematic diagram for verifying the additional lateral effect of adjacent dike settlement on ultra-long piles; Figure 5 This is a schematic diagram of the durable zonal corrosion protection design for ultra-long steel pipe piles. Detailed Implementation

[0041] The present invention will now be described in further detail so that those skilled in the art can implement it based on the description.

[0042] This invention provides a design optimization method for ultra-long piles in wharfs with ultra-thick soft soil layers. The thickness of the soft soil layer in the wharf foundation is 20-80m, and the effective bearing layer depth is 50-120m. The ultra-long steel pipe piles have a length of 60-130m, a diameter of 1.0-2.0m, and a length-to-diameter ratio of 40-110. The method includes the following steps: Preliminary determination of pile length, pile diameter, and number of piles; Based on geological survey data, a layered pile-soil model was established to obtain the standard values ​​of pile side friction resistance for each soil layer in the 0-50m range below the mud surface. qfik For areas 50m below the mud surface, sections are divided based on the physical and mechanical properties of the soil layers, and a correction factor for the side friction resistance of each layer is set. l i Among them, for those with a natural water content greater than the liquid limit, a porosity greater than 1.0, and a compressibility coefficient greater than 0.5 MPa -1 And in conventional soft soil sections where the SPT blow count is less than 4, l i Take a value of 0.8-1.1; for standard penetration tests (SPT) blow counts greater than 8 blows and compressibility coefficients less than 0.1 MPa. -1 Or deep improved soil layers with a compression modulus greater than 15 MPa, l iTake 1.05-1.50; for soil layers with weak interlayers not less than 0.5-1.0m thick, or those affected by construction disturbance and soil displacement, l i Take 0.6-1.0; according to the formula Calculate the ultimate vertical bearing capacity of a single pile Q uk ,in, qfik For the first i Standard value of side skin friction of piles u i For the first i Perimeter of pile layer, l i For the first i Effective length of pile side, a p This is the reduction factor for pile end resistance. q pk This is the standard value of pile end resistance. A p The area at the pile tip; and according to the formula Calculate the contribution rate of pile side friction or f ;when or f When the bearing capacity is less than 70%, the pile tip elevation is compared with the effective bearing layer depth. If the pile tip elevation is shallower than the effective bearing layer depth, the pile tip elevation is adjusted downwards to within the effective bearing layer, and the pile diameter or the number of piles is increased before recalculating the vertical ultimate bearing capacity of the single pile. Q uk and the contribution rate of pile side friction or f The steps continue until the desired result is achieved. or f Not less than 70%; Based on the soil layer division and pile-soil parameters provided by the layered pile-soil model, an overall pile-soil spring model of the wharf was established, and a three-dimensional pile-soil interaction model was also established; the depth of the hypothetical embedded point was obtained. h f The depth of the zero point of horizontal displacement calculated by the three-dimensional pile-soil interaction model. z 0 and the depth of the imaginary embedded point h f deviation R Deviation R The calculation formula is R = z 0 / h f ;when RWhen the value is <1.2 or >2.8, a review is performed. This review involves correcting the soil spring stiffness and soil layer boundary parameters in the overall pile-soil spring model of the wharf; extracting the maximum bending moment point based on the bending moment curve distributed along the depth of the pile; and addressing any deviations that cannot be corrected after the review. R It falls within the range of 1.5-2.5 and the point of maximum bending moment cannot be located in h f If the location is nearby, it is determined that the structure itself has insufficient stiffness; When the structure is determined to have insufficient rigidity, adjustments are made to the pile diameter, wall thickness, number of piles, or pile location, and the aforementioned verification steps are repeated until the deviation is correct. R The value falls within the range of 1.5-2.5 and the point of maximum bending moment is located at... h f Nearby; if the requirements still cannot be met after adjustment, then based on the degree of deviation. R Establish equivalent constraint stiffness reduction factor d ;like R When the value is greater than 2.8, the equivalent constraint stiffness reduction factor is... d Take 0.6-0.8; if R When <1.2, the equivalent constraint stiffness reduction factor d Take 1.2-1.4; if R If the value is within the range of 1.2-2.8, the original calculation parameters of the overall pile-soil spring model of the wharf will be directly used as the basis for subsequent calculations; when the equivalent constraint stiffness reduction factor is used... d At that time, the equivalent constraint stiffness reduction factor d Used to determine the original stiffness of the soil springs in the area 50m below the mud surface in the integral pile-soil spring model of the wharf. K 原始 Perform multiplication correction; the formula for multiplication correction is as follows: K 修正 = d × K 原始 The corrected soil spring stiffness is then re-substituted into the overall pile-soil spring model of the wharf for calculation, and the calculation is iterated repeatedly until the equivalent constraint stiffness reduction factor obtained from two adjacent calculations is obtained. d If the rate of change is less than 5%, and the difference between the recalculated overall pile-soil spring model of the wharf and the three-dimensional pile-soil interaction model at the maximum displacement and the maximum bending moment is less than 5%, then convergence is determined. The measured bearing capacity obtained from static load tests or high strain tests is compared with the ultimate vertical bearing capacity of a single pile. Q uk Comparison, when the vertical ultimate bearing capacity of a single pile Q uk When the deviation from the measured bearing capacity exceeds 15%, a proportional correction is applied; the proportional correction includes correction for the corresponding coefficients of the source of deviation at the pile tip or pile side; when the deviation mainly originates from the pile tip, the pile tip resistance reduction factor is applied.a p According to the formula Make corrections. a p,old and a p,new These are the reduction factors for pile end resistance before and after the correction, respectively, and the correction factor is used as the reference. a p,new As the reduction factor for pile end resistance in subsequent calculations, and the corrected a p,new The value is limited to the range of 0.6-1.0; when the deviation mainly originates from the pile side, the correction factor for side skin friction is... l i According to the formula Make corrections. l i,old and l i,new These are the correction factors for side friction resistance before and after the correction, respectively, and the correction factor after the correction is... l i,new The values ​​are limited to the range of values ​​for the corresponding section; repeat the above calculation until the deviation between the calculated bearing capacity and the measured bearing capacity does not exceed 15%; Output the final design scheme, which includes pile diameter, pile length, number of piles, wall thickness, and pile end elevation.

[0043] Current port engineering pile foundation design codes typically fail to differentiate between shallow and deep soil skin friction when calculating the bearing capacity of ultra-long steel pipe piles. Instead, they directly apply the standard value of shallow soil skin friction to the soil deeper than 50m below the mud surface, leading to significant discrepancies between the calculated vertical ultimate bearing capacity of a single pile and actual engineering measurements. Furthermore, the m-method recommended in the codes assumes that the horizontal resistance coefficient of the soil increases linearly with depth, resulting in an inaccurate assumption of the embedded point depth. h f The actual horizontal displacement zero point depth calculated from the 3D solid model z There is a systematic offset between 0 and 0, making it difficult for conventional methods to accurately predict the horizontal stress and bending moment distribution of ultra-long piles in deep soft soil.

[0044] To address the aforementioned shortcomings, this solution proposes a design optimization method that integrates vertical bearing capacity correction, horizontal displacement zero-point deviation correction, and measurement data back-substitution within a unified process.

[0045] This plan first proposes candidate pile lengths, diameters, and numbers based on the magnitude of the engineering load, the geological distribution in the site survey data, the maximum pile length and lifting capacity of the piling vessel, and experience from similar projects. The purpose of this step is to provide reasonable initial input for subsequent fine-tuning and to avoid the initial plan deviating too much from the actual situation.

[0046] Subsequently, a layered pile-soil model was established based on geological survey data. Based on the soil layer types, bottom depths of each layer, and physical and mechanical properties such as natural water content, void ratio, and SPT blow count revealed by the borehole columnar section, the soil beneath the mud surface was divided into several independent horizontal layers, and each layer was assigned corresponding parameters such as thickness, unit weight, compression modulus, cohesion, and internal friction angle. The layered pile-soil model serves as the foundational data framework for subsequent bearing capacity and deformation analysis. Based on the layered pile-soil model's division of the soil layers, combined with recommended values ​​in current port engineering pile foundation specifications, recommended values ​​in the geological survey report, and back-calculated values ​​from on-site pile test data, the standard values ​​of pile side friction resistance for each soil layer in the 0-50m range below the mud surface were comprehensively determined.

[0047] For the pile side soil at or below 50m below the mud surface, this scheme introduces a layered side skin friction correction coefficient. l i Layered side friction correction coefficient l i Differential values ​​are assigned based on the physical and mechanical properties of the soil layer. This applies when the section exhibits a natural water content greater than the liquid limit, a void ratio greater than 1.0, and a compressibility coefficient greater than 0.5 MPa. -1 Furthermore, for conventional soft soil sections with a standard penetration test (SPT) blow count below 4, the correction factor for layered side friction is... l i Take a value between 0.8 and 1.1. This applies when the section exhibits a standard penetration test (SPT) blow count greater than 8 and a compressibility factor less than 0.1 MPa. -1 Or, for deep improved soil layers with a compression modulus greater than 15 MPa, the correction factor for layered side friction resistance. l i Take 1.05-1.50. When there are weak interlayers with a thickness of not less than 0.5-1.0m, construction disturbances, and soil displacement effects in this section, the layered side friction correction coefficient is used. l i Take a value of 0.6-1.0. Correction factor for layered side friction. l i The purpose is to correct the application deviation of the standard empirical values ​​in deep soft soil.

[0048] After determining the parameters for each layer, it is necessary to obtain the parameters required for the calculation. Among these, the standard values ​​of pile side skin friction for each soil layer in the 0-50m range below the mud surface are required. qfik The standard value of pile end resistance is determined by combining the recommended values ​​in the current port engineering pile foundation specifications, the recommended values ​​in the geological survey report, and the back-calculated values ​​from the same site test pile data. q pk Based on the recommended value of the soil bearing capacity at the pile tip in the survey report, and in conjunction with the values ​​for similar soil layers in the current port engineering pile foundation code, the pile tip resistance reduction factor was verified and determined. a pIn the initial calculation stage, a value of 0.6-1.0 can be used; when the deviation between the calculated bearing capacity and the tested bearing capacity exceeds 15%, return to the layered pile-soil model for readjustment. a p And the corrected a p The value is strictly limited to the range of 0.6-1.0.

[0049] Then follow the formula Calculate the ultimate vertical bearing capacity of a single pile Q uk .in, qfik For the first i Standard value of side skin friction of piles u i For the first i Perimeter of pile layer, l i For the first i Effective length of pile side, a p This is the reduction factor for pile end resistance. q pk This is the standard value of pile end resistance. A p The area at the pile tip is used. The contribution rate of pile side skin friction is also calculated. or f Its calculation formula is Calculate the contribution rate of pile side friction. or f The purpose is to determine whether the bearing mode of ultra-long piles is mainly based on side skin resistance, and or f It should not be less than 70%, and preferably not less than 85%.

[0050] When the calculated contribution rate of pile side friction or f When the percentage is less than 70%, it indicates that the pile side skin friction is not playing a major role, and the pile body relies excessively on the pile end resistance. In this case, bearing capacity adjustment should be performed by comparing the pile end elevation with the effective bearing layer depth. If the pile end elevation is shallower than the effective bearing layer depth, the pile end elevation should be adjusted downwards to within the effective bearing layer, while simultaneously increasing the pile diameter or the number of piles. Simply adjusting the pile end elevation downwards will increase the proportion of pile end resistance, potentially further reducing the contribution rate of pile side skin friction. or f Therefore, while adjusting the pile tip elevation, it is necessary to increase the pile diameter or the number of piles to increase the pile side surface area, thereby increasing the total pile side friction resistance and the contribution rate of pile side friction resistance. or f The final result should meet the requirement of not less than 70%. The aforementioned calculation of the ultimate vertical bearing capacity of the single pile should then be repeated. Q uk and the contribution rate of pile side friction orf The steps continue until the contribution rate of pile side friction is satisfied. or f Not less than 70%. This step ensures that the ultra-long piles rely primarily on pile side friction for load bearing, thereby increasing the load-bearing safety redundancy.

[0051] After the bearing capacity meets the requirements, the horizontal stress and deformation verification stage begins. Based on the soil layer division and pile-soil parameters provided by the layered pile-soil model, a comprehensive pile-soil spring model for the wharf is established. This model discretizes the piles into beam elements, sets soil springs along the horizontal direction at the pile nodes, and sets axial springs at the pile ends for calculating the overall internal forces of the structure. Simultaneously, a three-dimensional pile-soil interaction model is established. This model uses solid elements to simulate the soil, considering the nonlinear characteristics of the soil and the friction and separation effects at the pile-soil contact surface. The hypothetical embedment depth calculated according to the port engineering pile foundation code is obtained. h f The actual horizontal displacement zero-point depth calculated by the three-dimensional pile-soil interaction model. z 0 and the depth of the imaginary embedded point h f deviation R Its calculation formula is R = z 0 / h f The purpose of this step is to determine whether the hypothetical fixed point assumed by the specification is applicable to the actual stress conditions of ultra-long piles.

[0052] When deviation R When the value is <1.2 or >2.8, a review is performed. The review involves correcting the stiffness values ​​of the soil springs in the area 50m below the mud surface and the boundary parameters of the soil layers in the overall pile-soil spring model of the wharf. The maximum bending moment point is extracted based on the bending moment curve distributed along the depth of the pile. If the deviation cannot be corrected after the review... R It falls within the range of 1.5-2.5, and the point of maximum bending moment cannot be located at the hypothetical fixed point depth. h f If the location is nearby, the structure is determined to have insufficient stiffness. The maximum bending moment point mentioned here is located at the depth of the hypothetical fixed point. h f Nearby refers to the depth between the point of maximum bending moment and the depth of the imaginary fixed point. h f The difference is within the acceptable tolerance range for engineering. Specifically, this tolerance range is determined by... z 0 / h f The reasonable stress range corresponding to the ratio control interval of 1.5-2.5 is determined. This applies when the location of the maximum bending moment is close to the depth of the hypothetical fixed point. h fWhen the offset exceeds the reasonable stress range corresponding to the ratio control interval, it is determined that the maximum bending moment point cannot be located at the hypothetical fixed point depth. h f Nearby. At this point, adjustments need to be made to the pile diameter, wall thickness, number of piles, or pile location, and the aforementioned verification steps should be repeated until the deviation is correct. R The bending moment falls within the range of 1.5-2.5 and the point of maximum bending moment is located at the depth of the imaginary fixed point. h f nearby.

[0053] If the above horizontal stress conditions still cannot be met after adjusting the pile dimensions, then the deviation should be considered. R The value of is used to establish the equivalent constraint stiffness reduction factor. d When the deviation R When the value is greater than 2.8, the equivalent constraint stiffness reduction factor is... d A value of 0.6-0.8 is used to reduce the original stiffness of the soil springs in the area 50m below the mud surface in the overall pile-soil spring model of the wharf. When the deviation... R When <1.2, the equivalent constraint stiffness reduction factor d A value of 1.2-1.4 is used to amplify the original stiffness of the soil spring in this area. When the deviation... R When the value is between 1.2 and 2.8, the original calculation parameters of the overall pile-soil spring model of the wharf are directly used as the basis for subsequent calculations. When the equivalent constraint stiffness reduction factor is used... d At that time, it is used to perform a multiplicative correction on the original stiffness. The formula for calculating the multiplicative correction is as follows: K 修正 = d × K 原始 This step involves dynamically adjusting the soil spring stiffness to approximate the calculated response of the overall pile-soil spring model of the wharf to a three-dimensional pile-soil interaction model, thereby correcting the shortcomings of the hypothetical fixed point assumption in the horizontal stress analysis of ultra-long piles. This correction process needs to be repeated continuously until the equivalent constraint stiffness reduction factor obtained from two adjacent calculations is obtained. d The rate of change is less than 5%, and the difference between the recalculated overall pile-soil spring model and the three-dimensional pile-soil interaction model at the maximum displacement and maximum bending moment is less than 5%, indicating that convergence has been achieved.

[0054] Finally, the measured bearing capacity and calculated bearing capacity obtained from static load tests or high strain tests are compared. Q uk A comparison is made. When the deviation between the calculated bearing capacity and the measured bearing capacity exceeds 15%, a proportional correction is applied. If the deviation mainly originates from the pile end, the pile end resistance reduction factor is adjusted. a p Make corrections; the parameter was previously denoted as... a p,old The corrected version is denoted asa p,new According to the formula Make corrections, and use the corrected version. a p,new As the reduction factor for pile end resistance in subsequent calculations, and a p,new The value is strictly limited to the range of 0.6-1.0. If the deviation mainly originates from the pile side, the correction coefficient for the layered side friction is... l i Make corrections; the parameter was previously denoted as... l i,old The corrected version is denoted as l i,new According to the formula Make corrections, and l i,new The value of is strictly limited to the original value range of the corresponding section. If the correction value calculated by the above formula exceeds the boundary of the corresponding interval, the boundary limit value of that interval is forcibly taken to eliminate extreme value error. The aforementioned bearing capacity calculation is repeated until the deviation between the calculated bearing capacity and the measured bearing capacity does not exceed 15%.

[0055] At this point, the entire design optimization process is complete. The final output of pile diameter, pile length, number of piles, wall thickness, and pile end elevation is the result obtained after verification through all the aforementioned steps. This final design scheme must simultaneously meet the following conditions: the contribution rate of pile side skin friction is not less than 70%, and the deviation between the calculated bearing capacity and the measured bearing capacity does not exceed 15%; deviation degree R The bending moment falls within the range of 1.5-2.5 and the point of maximum bending moment is located at the depth of the imaginary fixed point. h f Nearby; Equivalent constraint stiffness reduction factor d The rate of change is less than 5%, and the difference between the overall pile-soil spring model and the three-dimensional pile-soil interaction model at maximum displacement and maximum bending moment is less than 5%. The final design scheme output after these verifications meets the design requirements for bearing capacity, deformation, and stability. Furthermore, the final design scheme also includes pile layout, pile side skin friction correction parameters, and parameters for each soil layer. l The value table and internal force displacement control points are as follows. z 0 / h f Complete design outputs, including values ​​and pile driving control standards.

[0056] This scheme introduces a correction factor for the side friction resistance at a depth of 50m below the mud surface. l i This method corrects the calculation deviation caused by the mismatch between the values ​​of side friction resistance in deep soil and those in shallow soil. The method establishes a deviation degree... R and equivalent constraint stiffness reduction factor dThe dynamic correction mechanism corrects the systematic offset between the hypothetical fixed point and the actual zero point of horizontal displacement under the assumption of the m-method. Finally, the scheme uses field test data to recalculate parameters, achieving a closed-loop unification between the theoretical model and actual geological conditions. This scheme effectively improves the problem of inaccurate deep stress assessment caused by the limitations of standard methods in the design of ultra-long piles, and can avoid material waste and construction risks caused by simply increasing the pile diameter, pile length, or number of piles while ensuring structural safety.

[0057] In another scheme, the specific method for determining whether the deviation mainly originates from the pile tip or pile side in the optimization method for the design of ultra-long piles in ultra-thick soft soil layer wharf is as follows: extract the calculated value of the pile axial force along the depth distribution output by the overall pile-soil spring model or three-dimensional pile-soil interaction model of the wharf, and the measured value of the pile axial force along the depth distribution obtained by actual measurement, calculate the absolute value of the difference between the calculated value and the measured value of the axial force at each depth, and calculate the sum of the absolute values ​​of the axial force difference at all depths. When the absolute value of the difference at the pile tip accounts for 60% or more of the sum of the absolute values ​​of the difference, it is determined that the deviation mainly originates from the pile tip. When the absolute value of the difference at the pile tip accounts for less than 60% of the sum of the absolute values ​​of the difference, it is determined that the deviation mainly originates from the pile side.

[0058] Before performing the aforementioned proportional correction steps, it is necessary to obtain measured axial force data for comparison. This measured axial force data can be obtained by pre-embedding strain gauges at different depths of the ultra-long steel pipe pile and simultaneously collecting strain values ​​at each depth section during the static load test, or by installing distributed fiber optic sensors inside the pile to obtain the axial force distribution throughout the pile. The method for determining the source of deviation extracts the calculated value of the pile axial force distribution along depth from the overall pile-soil spring model or the three-dimensional pile-soil interaction model of the wharf, as well as the measured value of the pile axial force distribution along depth obtained by the above methods. The calculated value and the measured value are compared point by point at the same depth position, and the absolute value of the difference between the calculated value and the measured value of the axial force at each depth is calculated. Then, the sum of the absolute values ​​of the axial force differences at all depths is accumulated, and this sum is used as the overall benchmark for measuring the axial force deviation distribution of the entire pile. Based on this, by statistically analyzing the proportion of the absolute value of the difference in depth at the pile tip to the total absolute value of the difference in axial force, 60% is used as the quantitative judgment threshold. When the absolute value of the difference at the pile tip reaches 60% or more, the judgment deviation mainly comes from the pile tip; otherwise, the judgment deviation mainly comes from the pile side.

[0059] This determination method transforms the judgment of deviation sources from qualitative and vague subjective experience judgment to quantitative numerical analysis based on the comparison of measured and calculated data. It provides clear judgment criteria, making the selection of correction objects in the proportional correction process more targeted. It avoids repeated trial calculations or blind adjustments caused by inaccurate judgment of deviation sources, effectively reduces the number of correction iterations, improves the efficiency and accuracy of calculation model parameter correction, and makes the corrected bearing capacity calculation results closer to the engineering measured results, thereby enhancing the reliability of the final design scheme in actual engineering.

[0060] In another approach, the optimization method for designing ultra-long piles for wharves in ultra-thick soft soil layers utilizes an equivalent constraint stiffness reduction factor when adjusting the pile diameter, wall thickness, number of piles, or pile location. d The linkage optimization relationship between pile diameter, pile length, and single pile steel quantity is controlled; multiple pile diameter schemes are established under the same pier, the same load combination, and the same geological profile, and the foundation sensitivity relationship between pile diameter, pile length, and single pile steel quantity is set. The foundation sensitivity relationship is defined as the increase rate of pile length required to meet bearing capacity and stability when the pile diameter is reduced by 0.1m, and the steel weight of a single steel pipe pile is reduced by 2-4%; when the equivalent constraint stiffness reduction factor... d A low value of 0.6-0.8 is selected to indicate weak deep confinement, and the pile length increase rate is forcibly set to the upper limit of 5%; when the equivalent confinement stiffness reduction factor... d When the pile length is within the range of 1.2-1.4, the lower limit of 2% is selected for the pile length increase rate. The maximum pile driving length of the piling vessel is used as a hard constraint condition. When the adjusted pile length exceeds the maximum pile driving length of the piling vessel, the next scheme with a larger pile diameter is directly locked and the subsequent calculations are re-executed. If the next scheme with a larger pile diameter still cannot meet the bearing capacity and stability requirements, the step of increasing the number of piles is returned, and the process of adjusting the pile diameter, wall thickness, number of piles, or pile position is re-executed. If, after multiple rounds of the above-mentioned adjustments, the current design scheme still cannot meet the bearing capacity and stability requirements, the current adjustment process is terminated, and local foundation treatment or isolation measures are taken to meet the design requirements.

[0061] In the process of correcting the stiffness of deep soil springs, the equivalent constraint stiffness reduction factor is used. d The value can clearly indicate the actual constraint strength of the deep soil on the ultra-long pile. However, simply modifying the soil spring stiffness cannot directly complete the pile type design optimization from the source. How to... dThe main technical challenge lies in converting the deep mechanical indicators into a basis for adjusting pile dimensions and effectively linking them with the capabilities of construction equipment. Without a unified linkage mechanism, designers are prone to relying solely on experience to enlarge the pile diameter or increase the wall thickness to ensure safety, resulting in a significant increase in steel consumption. Alternatively, increasing the pile diameter may cause the pile length to exceed the driving depth allowed by the ship machinery, making the designed pile type unfeasible.

[0062] To address the aforementioned challenges and improve design efficiency and quality, this scheme first establishes pile diameter, pile length, and the weight of steel in a single steel pipe pile as unified, interconnected variables. Under the same wharf pier, load combination, and geological profile conditions, multiple candidate schemes with different pile diameters are simultaneously established for comparison. During the comparison process, a foundation sensitivity relationship is pre-defined between pile diameter, pile length, and the amount of steel in a single pile. This relationship is specifically defined as follows: for every 0.1m decrease in pile diameter, to meet the same vertical bearing capacity and structural stability requirements, the required increase in pile length is between 2-5%, while the weight of steel in a single steel pipe pile decreases accordingly by 2-4%. For example, when the pile diameter decreases from 1.6m to 1.5m, 1.4m, and 1.3m, the longest pile length can increase from approximately 96m to approximately 99m, 102m, and 106m, respectively, while the amount of steel in a single pile can decrease from approximately 86t to approximately 83t, 80t, and 78t, respectively.

[0063] In specific control measures, the constraint state of deep soil is used as the first screening criterion. When the equivalent constraint stiffness reduction factor... d When the value is in the lower range of 0.6-0.8, it means that the actual constraint effect of the deep soil on the pile is weak. At this time, the structure is more sensitive to the pile length. Therefore, the upper limit of the pile length increase rate of 5% is forcibly selected for compensation. Conversely, when the equivalent constraint stiffness reduction factor is in the lower range of 0.6-0.8, it means that the actual constraint effect of the deep soil on the pile is weak. At this time, the structure is more sensitive to the pile length. Therefore, the upper limit of the pile length increase rate of 5% is forcibly selected for compensation. d The value is in the higher range of 1.2-1.4, indicating that the deep soil has a good embedment effect and the pile body is under ideal stress. At this time, the lower limit of the pile length increase rate of 2% can be selected for optimization, so as to exchange a small increase in pile length for a significant reduction in steel consumption.

[0064] Complete the above based on d After the initial dimensions for factor control are selected, a hard constraint check on the construction capacity must be performed on the selected pile length. The maximum pile length that the on-site piling vessel can drive is used as a rigid constraint. If the currently optimized pile length value exceeds the maximum pile length allowed by the on-site piling equipment, the next candidate scheme with a larger pile diameter is directly locked, and then all subsequent dimension calculations and constraint checks are re-executed.

[0065] If, after gradually increasing the pile diameter according to the aforementioned steps, the next larger pile diameter scheme still cannot meet the requirements of vertical bearing capacity and overall stability, then the path of simply relying on increasing the pile diameter is abandoned, and the process of increasing the number of piles is reversed, restarting the multi-round adjustment process of pile diameter, wall thickness, number of piles, or pile location. During this multi-round structural dimension adjustment process, if the bearing capacity and stability requirements still cannot be met by increasing the number of piles, adjusting pile locations, or carrying out local foundation treatment, then the current adjustment process is terminated, and local foundation treatment or isolation measures are implemented to meet the design requirements.

[0066] Taking a practical application of an isolated wharf project as an example, the equivalent constraint stiffness reduction factor was obtained through preliminary iterative calculations. d A value of 0.65 indicates poor lateral confinement capacity of deep soft soil, failing to provide sufficient embedded support. Therefore, the pile length increase rate for every 0.1m decrease in pile diameter was forcibly set to a maximum limit of 5%. After adjusting the linkage between pile diameter and pile length, although steel consumption became more economical, the pile length, when increased to 102m, exceeded the maximum effective pile driving length of the on-site piling vessel. Subsequently, based on the hard constraint conditions, a scheme with a larger pile diameter was directly locked in. After enlarging the pile diameter again, the pile length was simultaneously reduced to within the allowable range of the equipment. Ultimately, a pile layout scheme was successfully output under the premise of meeting the deep constraint requirements and construction equipment limitations, effectively avoiding the construction failure caused by blindly pursuing a small pile diameter, or the waste of steel caused by excessively enlarging the pile diameter due to ignoring the weakening of deep constraints.

[0067] In another scheme, the design optimization method for ultra-long piles in ultra-thick soft soil layers also includes a check for the additional lateral action of adjacent dike settlement. The specific steps for checking the additional lateral action of adjacent dike settlement are as follows: when the final settlement of the adjacent dike is not less than 0.2m, and the distance between the pile foundation and the dike side edge is less than twice the thickness of the soft soil layer, the additional lateral earth pressure generated by the dike consolidation is directly superimposed onto the outer boundary conditions of the three-dimensional pile-soil interaction model through mathematical vector decomposition; the additional bending moment generated after superposition is vector-superimposed with the original horizontal load bending moment; for the peak bending moment in the deep soft soil area 50m below the mud surface, a double-layer data threshold is set. When the superimposed bending moment exceeds the threshold, the excess additional bending moment value is converted into a value through bending moment- The force equivalent conversion formula is converted into an additional horizontal concentrated force, which is then applied to the pile-soil spring node at the corresponding depth in the overall pile-soil spring model of the wharf. For inclined piles or side piles near the dike, the negative bending moment distribution curve under superimposed load is extracted. The negative bending moment peak value appearing in the depth range directly below the dike edge is taken as the control condition, and the negative bending moment peak value is compared with the design allowable negative bending moment value. If it exceeds the allowable value, the pile diameter or wall thickness of the inclined pile or side pile is increased and adjusted, and the check of the additional lateral action on the settlement of the adjacent dike is re-executed. If the negative bending moment peak value of the inclined pile or side pile still exceeds the design allowable value after multiple rounds of adjustment, the current adjustment process is terminated, and isolation measures or measures to control the settlement of the dike during the construction stage are adopted.

[0068] When ultra-long steel pipe piles are subjected to stress in the wharf area near the embankment, they must not only bear the vertical and horizontal loads of the wharf itself, but also withstand the additional lateral earth pressure generated by the consolidation settlement of the adjacent embankment. In conventional design processes, the additional effect of embankment settlement on the pile foundation is often roughly estimated based on construction experience and is easily overlooked. This can lead to unpredictable peak bending moments near the mud surface and in deep soft soil areas during operation, causing structural safety hazards. Relying solely on conventional single pile bearing capacity and horizontal displacement checks cannot accurately assess the impact of this additional lateral force. A dedicated verification mechanism must be established to incorporate the long-term effects of embankment settlement into a unified calculation process.

[0069] Therefore, a complete verification process needs to be established for the additional lateral effects of adjacent embankments. When the final settlement of the adjacent embankment is not less than 0.2m, and the distance between the wharf pile foundation and the embankment wharf side edge is less than twice the thickness of the soft soil layer, it can be determined that the wharf is significantly affected by the embankment settlement. Once the above triggering conditions are met, the verification of the additional lateral effects of adjacent embankment settlement is immediately initiated. First, using mathematical vector decomposition, the additional lateral earth pressure generated during the embankment consolidation process is vector-decomposed and then directly superimposed onto the outer boundary conditions of the three-dimensional pile-soil interaction model to reflect the additional thrust exerted on the pile body by the embankment lateral displacement. Subsequently, the additional bending moment generated after superposition is vector-superimposed with the original horizontal load bending moment to obtain the true bending moment distribution of the pile body under the combined load.

[0070] After calculating the comprehensive bending moment distribution, it is crucial to focus on the bending moment variations within the deep soft soil zone at or below 50m below the mud surface. To effectively control the stress risk in this area, a dual-layer data threshold is set. When the superimposed bending moment exceeds this threshold, the excess bending moment value is converted into an additional horizontal concentrated force using the bending moment-force equivalent conversion formula. This additional horizontal concentrated force is then directly applied to the pile-soil spring node at the corresponding depth in the overall pile-soil spring model of the wharf. In this way, the local bending moment exceedance problem, which is difficult to handle directly in the three-dimensional pile-soil interaction model, is transformed into an equivalent concentrated force and fed back to the overall pile-soil spring model of the wharf, achieving a secondary verification of the model.

[0071] For inclined piles or edge piles close to the embankment, it is necessary to extract their negative bending moment distribution curves under comprehensive loads, and use the peak negative bending moment in the depth range directly below the embankment edge as the control point for this working condition. This peak negative bending moment should be rigorously compared with the design allowable negative bending moment value. If the peak negative bending moment exceeds the allowable value, the pile diameter or wall thickness of the inclined pile or edge pile needs to be increased, and the above-mentioned verification steps for the additional lateral effect of settlement of the adjacent embankment should be repeated. If, after multiple rounds of adjustments, the peak negative bending moment of the inclined pile or edge pile still exceeds the design allowable value, it indicates that simply increasing the structural dimensions is no longer sufficient. In this case, the current pure structural dimension adjustment process should be immediately terminated, and non-structural control measures such as setting up isolation measures or controlling settlement during embankment construction should be adopted to ensure the structural safety of the pile body.

[0072] Taking a wharf project near a water intake dike as an example, the final settlement of the dike was monitored to be approximately 0.47m. Furthermore, the distance between the inclined piles or side piles near the dike and the wharf side edge line was less than twice the thickness of the soft soil layer, meeting the triggering condition. Following the above method, the additional lateral earth pressure generated by the dike consolidation was directly superimposed onto the outer boundary conditions of the three-dimensional pile-soil interaction model through mathematical vector decomposition. The resulting additional bending moment was then vector-superimposed with the original horizontal load bending moment. For the peak bending moment in the deep soft soil zone at 50m below the mud surface, a dual-layer data threshold was set. When the superimposed bending moment exceeded this threshold, the excess additional bending moment was converted into an additional horizontal concentrated force using the moment-force equivalent conversion formula. This additional horizontal concentrated force was then applied to the pile-soil spring node at the corresponding depth in the overall pile-soil spring model of the wharf. For inclined piles or side piles near the embankment, the negative bending moment distribution curve under superimposed loads is extracted. The peak negative bending moment in the depth range directly below the embankment edge is taken as the control condition, and this peak negative bending moment is compared with the design allowable negative bending moment value. Under this combined load, the inclined piles or side piles exhibited a negative bending moment peak value exceeding the design allowable value near the embankment edge. To address this, the pile diameter and wall thickness were first increased multiple times, and the additional lateral effect of adjacent embankment settlement was re-checked. If, after multiple adjustments, the peak negative bending moment still could not be reduced below the design allowable value, the current adjustment process was terminated, and isolation measures or measures to control embankment settlement during construction were adopted, ultimately ensuring the structural safety of the inclined piles or side piles under this condition. By establishing this specialized verification mechanism, the additional effect of embankment settlement, which is easily overlooked in conventional design, is fully incorporated into the main design process, effectively avoiding structural risks to the pile body caused by continuous embankment settlement during the operational period.

[0073] In another approach, the optimization method for the design of ultra-long piles in ultra-thick soft soil wharves further includes a coupled verification of the long-term durability and buckling stability of the ultra-long steel pipe piles. An algorithm for the stiffness attenuation coefficient of the pile section is constructed based on the design service life of the steel pipe piles. In the three-dimensional pile-soil interaction model, a stiffness attenuation coefficient that evolves over time is applied to the section stiffness of the pile elements. When the stiffness attenuation coefficient decays to a preset warning threshold, both the overall pile-soil spring model and the three-dimensional pile-soil interaction model of the wharf simultaneously switch to the buckling stability master control verification mode. The buckling stability master control verification mode means that in subsequent design calculations, the pile buckling stability coefficient is used as the primary control indicator. By adjusting the pile diameter, wall thickness, number of piles, or pile position, the pile buckling stability coefficient is made to meet the design requirements. The required pile buckling stability coefficient is used as one of the verification bases for the final design scheme. Corrosion protection measures are designed for the steel pipe piles in the splash zone, water level fluctuation zone, underwater zone, and mud zone. The splash zone adopts heavy-duty anti-corrosion coating, the water level fluctuation zone and underwater zone adopt a combination of coating and sacrificial anode cathodic protection, and the mud zone is equipped with cathodic protection within 20-40m below the mud surface. The annual average corrosion rate of unprotected steel pipe piles is estimated to be 0.2-0.6mm / a, and the corrosion allowance is taken as 1-4mm. The effective wall thickness after corrosion is obtained by subtracting the corrosion allowance from the initial wall thickness of the steel pipe pile. The effective wall thickness after corrosion is used to replace the initial wall thickness in the buckling stability check to ensure that the maximum combined stress of the section does not exceed 0.85 times the design allowable value. The final design scheme also includes anti-corrosion measures.

[0074] When ultra-long steel pipe piles are used in wharf structures for extended periods, they must not only withstand the combined effects of vertical and horizontal loads but also cope with corrosion damage and structural instability risks in the marine environment. Conventional designs typically treat bearing capacity calculations and durability / corrosion protection design as two separate professional modules. Bearing capacity calculations often use the initial wall thickness as input, while corrosion allowance is merely added as a wall thickness reserve in the drawing requirements, lacking a direct mechanical coupling between the two. This separate design approach leads to a potential structural risk: throughout the wharf's design service life, as the steel pipe pile wall thickness gradually thins due to corrosion, the bending stiffness and buckling stability of the pile section will inevitably continue to degrade. When the wall thickness thins to a certain extent, even if the bearing capacity meets the requirements in the initial design stage, the pile may still experience buckling instability due to insufficient stiffness in the later stages of operation. Therefore, long-term durability and buckling stability must be comprehensively checked as a unified coupled problem. A stiffness degradation model that evolves over time should be established, and the effective wall thickness after corrosion should be directly used for verification in structural calculations to ensure that ultra-long steel pipe piles have sufficient safety redundancy throughout the entire design service life.

[0075] To address the aforementioned issues, this solution first constructs an algorithm for the stiffness attenuation coefficient of the pile section based on the design service life of ultra-long steel pipe piles. This algorithm takes time as input and the stiffness attenuation coefficient of the pile section as output, quantitatively describing the gradual decrease in the stiffness of the ultra-long steel pipe pile section with increasing service life. In the three-dimensional pile-soil interaction model, the stiffness attenuation coefficient is applied as a load step to the stiffness of the pile element section, causing the stiffness of the pile element in the model to gradually degrade with the advancement of the calculation time step, thus realistically simulating the mechanical performance degradation process of ultra-long steel pipe piles during long-term service.

[0076] When the cross-sectional stiffness attenuation coefficient decreases to the preset warning threshold due to wall thickness reduction, it indicates that the current pile cross-sectional stiffness has entered the risk range, and the original strength-based verification method is no longer sufficient to comprehensively assess structural safety. At this point, both the overall pile-soil spring model and the three-dimensional pile-soil interaction model of the wharf simultaneously switch to the pile buckling stability master control verification mode. The characteristic of the pile buckling stability master control verification mode is that, in subsequent design calculations, bearing capacity strength is no longer used as the sole control indicator, but rather the pile buckling stability coefficient is used as the primary control indicator. The pile buckling stability coefficient should not be less than the requirements of relevant design codes, preferably not less than 1.15-1.30. When adjusting pile diameter, wall thickness, number of piles, or pile location, priority is given to ensuring that the pile buckling stability coefficient meets the design requirements, and the pile buckling stability coefficient that meets the requirements is used as one of the verification bases for the final design scheme. The control focus is shifted from strength to buckling stability to ensure that the pile still has sufficient resistance to instability even when the cross-sectional stiffness degrades.

[0077] For durability and corrosion protection, the ultra-long steel pipe piles were divided into four different zones according to their environmental conditions. Each zone adopted corrosion protection measures matched to the corrosive environment. Specifically, the splash zone was protected with a heavy-duty anti-corrosion coating; the water level fluctuation zone and the underwater zone were protected with a combination of coating and sacrificial anode cathodic protection; and the submerged zone was protected with cathodic protection within 20-40m below the mud surface, preferably within 30m. For corrosion rate estimation, the annual average corrosion rate of unprotected ultra-long steel pipe piles was taken as 0.2-0.6 mm / a. Based on the above zoned corrosion protection measures, a corrosion allowance of 1-4 mm was determined according to the total corrosion within the design service life. The effective wall thickness after corrosion was obtained by subtracting the corrosion allowance from the initial wall thickness of the ultra-long steel pipe pile. The effective wall thickness after corrosion is substituted for the initial wall thickness in the pile buckling stability check to ensure that the maximum combined stress of the section does not exceed 0.85 times the design allowable value under the condition of effective wall thickness after corrosion. This establishes a direct coupling verification between long-term corrosion degradation and pile buckling stability, avoiding long-term operational risks caused by wall thickness reduction.

[0078] Taking a nuclear power plant's supporting heavy-duty wharf with a designed service life of 50 years as an example, the initial wall thickness of the ultra-long steel pipe piles is 20mm. Based on the corrosive environment, the average annual corrosion rate is taken as 0.3mm / a, the corrosion allowance is taken as 2mm, and the effective wall thickness after corrosion is 18mm. An algorithm for the stiffness attenuation coefficient of the pile section is constructed. In the three-dimensional pile-soil interaction model, the section stiffness attenuation coefficient is gradually applied to the pile elements according to the time step. When the calculation reaches the 40th year, the section stiffness attenuation coefficient attenuates to the preset warning threshold, and the overall pile-soil spring model and the three-dimensional pile-soil interaction model of the wharf switch to the pile buckling stability master control verification mode. Subsequent pile verification prioritized the pile buckling stability coefficient as the primary control indicator. By adjusting the pile diameter, wall thickness, number of piles, or pile location, the effective wall thickness after corrosion was increased to 18mm, and the wall thickness design was adjusted accordingly. After recalculation, the maximum combined stress of the section was controlled within 0.85 times the design allowable value. Simultaneously, the pile buckling stability coefficient met the design requirements. Anti-corrosion measures were designed for the splash zone, water level fluctuation zone, underwater zone, and mud zone. The final output pile type scheme simultaneously met the requirements for pile buckling stability and long-term durability. The final design scheme also included anti-corrosion measures. This scheme, by introducing corrosion degradation variables in real-time during structural calculations, ensures that the design scheme for ultra-long steel pipe piles maintains sufficient safety margin throughout the entire design service life, avoiding the long-term instability risk caused by the separation of durability and bearing capacity design, and achieving a harmonious balance between long-term service safety and material economy.

[0079] In another approach, the design optimization method for ultra-long piles at wharves in ultra-thick soft soil layers includes setting a convergence gradient threshold during the iterative process; and calculating the current equivalent constraint stiffness reduction factor after each iterative update of the soil spring stiffness in the overall pile-soil spring model of the wharf. d Compared with the previous round of equivalent constraint stiffness reduction factor d The normalized gradient is used to determine the equivalent constraint stiffness reduction factor when the normalized gradient is less than the convergence gradient threshold. d Under this condition, convergence has been achieved and the iteration has ended; when the normalized gradient is always greater than or equal to the convergence gradient threshold and the equivalent constraint stiffness reduction factor is applied... d Continuously deviating from the preset ideal range, i.e., determined by the degree of deviation. R The determined equivalent constraint stiffness reduction factor d When the value range is selected, it is determined that the deep soil constraint characteristics have high nonlinearity, triggering the recalibration of the deep soil constitutive parameters in the three-dimensional pile-soil interaction model based on field geological data, and restarting the repeated iteration process.

[0080] Horizontal stress analysis of ultra-long steel pipe piles in deep soft soil, using equivalent constraint stiffness reduction factor. dThe deep soil spring stiffness is iteratively corrected to approximate the calculated response of the overall pile-soil spring model of the wharf to a three-dimensional pile-soil interaction model. However, whether this dynamic correction process can converge effectively directly affects the reliability of the final design scheme. If the equivalent constraint stiffness reduction factor... d If significant fluctuations occur continuously throughout multiple iterations, or if the value remains consistently unstable near a fixed point, it indicates a fundamental flaw in the current correction logic. Simply adjusting the soil spring stiffness will not bring the calculation results from the two models in agreement. This situation typically signifies that the constraint effect of deep soil on the pile exhibits extremely strong nonlinear characteristics, and the existing soil constitutive parameters are no longer able to accurately describe the actual stress state. If this situation is not identified and addressed in a timely manner, the iterative process will fall into an infinite loop or output distorted results, leading to significant engineering risks in the final design. Therefore, a clear convergence determination mechanism must be established during the iterative correction process to ensure that each iteration has a clear exit criterion and to provide an effective response path when convergence is deemed impossible.

[0081] To address the aforementioned issues, this solution utilizes an equivalent constraint stiffness reduction factor. d A convergence gradient threshold is introduced during the dynamic correction process. The convergence gradient threshold is used to determine the equivalent constraint stiffness reduction factor. d Has the correction reached a stable state? The specific method for setting the convergence gradient threshold is based on the equivalent constraint stiffness reduction factor. d The final convergence criterion is a rate of change of less than 5%. The convergence gradient threshold is calculated based on 50%-80% of the final convergence criterion. When calculated based on 50% of the final convergence criterion, the corresponding value is 5% multiplied by 50%, i.e., 2.5%; when calculated based on 80% of the final convergence criterion, the corresponding value is 5% multiplied by 80%, i.e., 4%. Therefore, the corresponding value range for the convergence gradient threshold is 2.5%-4%. In the preliminary design stage, when higher computational efficiency is required, the upper limit of the convergence gradient threshold range, i.e., 4%, can be used. In the construction drawing refinement stage, when higher computational accuracy is required, the lower limit of the convergence gradient threshold range, i.e., 2.5%, can be used. After the soil spring stiffness in the overall pile-soil spring model of the wharf completes one iteration update, the system immediately calculates the equivalent constraint stiffness reduction factor for the current cycle. d The normalized gradient of the change between the value and the equivalent constraint stiffness reduction factor δ from the previous round. The normalized gradient reflects the equivalent constraint stiffness reduction factor. d The fluctuation amplitude between two adjacent iterations is a direct quantitative representation of the corrected stability. If the normalized change gradient is less than the set convergence gradient threshold, it indicates that the equivalent constraint stiffness reduction factor... d The value of has stabilized, and the correction amount generated by subsequent iterations is within a negligible range. At this point, the equivalent constraint stiffness reduction factor is determined. d The convergence state has been reached under the current operating conditions, so the iterative correction process ends, and the current equivalent constraint stiffness reduction factor is adjusted. d The value is used as the final value for subsequent design calculations.

[0082] When the normalized gradient is always greater than or equal to the convergence gradient threshold, and the equivalent constraint stiffness reduction factor is... d Continuous deviation is determined by the degree of deviation R The determined equivalent constraint stiffness reduction factor d If the value is within a certain range, it indicates that repeated stiffness adjustments cannot converge effectively. If the equivalent constraint stiffness reduction factor... d Continuous deviation is determined by the degree of deviation R The determined equivalent constraint stiffness reduction factor d The range of values ​​indicates that the constraint characteristics of the deep soil on the pile body are not a simple linear or weakly nonlinear response, but rather exhibit significant highly nonlinear behavior. This means that the soil resistance varies with deformation or depth and cannot be accurately described by the current linear or approximately nonlinear model. In this case, it should be determined that the constraint characteristics of the deep soil under the current working condition are highly nonlinear, and the original soil constitutive parameters are invalid. Continuing to adjust the soil spring stiffness based on the original parameters is meaningless. Based on this determination, the system triggers a recalibration of the deep soil constitutive parameters in the three-dimensional pile-soil interaction model based on field geological data. After recalibration, the updated constitutive parameters are substituted into the three-dimensional pile-soil interaction model, and the iterative correction process is restarted until the equivalent constraint stiffness reduction factor is reached. d The convergence condition is met.

[0083] Taking a certain isolated wharf project as an example, the deep soft soil area of ​​this project contains a large number of silt interlayers and disturbed soil layers. During the iterative correction process, the equivalent constraint stiffness reduction factor... d The problem continued to fluctuate after the 5th iteration, with the normalized gradient consistently exceeding the set convergence gradient threshold, and the equivalent constraint stiffness reduction factor... d The value has been consistently deviating from the deviation degree R The determined equivalent constraint stiffness reduction factor d The range of values ​​indicates difficulty in convergence. The normalized gradient is consistently greater than the convergence gradient threshold, and the equivalent constraint stiffness reduction factor... d The value continues to deviate due to the degree of deviation. R The determined range of values ​​for the equivalent constraint stiffness reduction factor δ indicates that the deep soil constraint characteristics under the current working condition are highly nonlinear. This triggers a recalibration of the deep soil constitutive parameters in the three-dimensional pile-soil interaction model based on field geological data, and restarts the iterative correction process. The recalibrated iteration reaches stable convergence on the third iteration, and the final output of the equivalent constraint stiffness reduction factor is... dThe value matches the calculation results of the three-dimensional pile-soil interaction model perfectly.

[0084] This scheme uses an equivalent constraint stiffness reduction factor. d In the dynamic iterative correction, a convergence gradient threshold is set, and a clear recalibration response path is set for cases where convergence fails, which effectively ensures the stability and computational efficiency of the ultra-long steel pipe pile design optimization method under different geological conditions.

[0085] In another approach, the optimization method for designing ultra-long piles for wharves in ultra-thick soft soil layers involves applying the equivalent constraint stiffness reduction factor. d In the coordinated optimization process involving pile diameter and pile length, a safety margin for the construction-deployable pile length is set. When the difference between the design pile length output under each candidate pile diameter scheme and the maximum pile length that can be driven by the piling vessel is less than the safety margin for the construction-deployable pile length, the equivalent constraint stiffness reduction factor is directly applied. d Substituting the convergence value into the long-term cross-sectional stiffness attenuation coefficient of the pile body under the current pile diameter scheme, the equivalent constraint stiffness reduction factor under long-term service conditions is calculated. d The degradation trajectory; when the pile buckling stability redundancy under the degradation trajectory is lower than the design standard, skip the current pile diameter scheme and directly lock the next larger pile diameter scheme; if the next larger pile diameter scheme still cannot meet the long-term stability requirements, the long-term stability requirements, i.e., the pile buckling stability redundancy under long-term service conditions, is not lower than the design standard, then return to the step of increasing the number of piles, and re-execute the process of adjusting the pile diameter, wall thickness, number of piles, or pile position; if the long-term stability requirements still cannot be met after multiple rounds of adjustment, then terminate the current adjustment process, and take local foundation treatment or set up isolation measures to meet the long-term stability requirements; at the same time, the hook capacity of the piling vessel is not less than the weight of a single pile. W p The maximum pile length is 1.10 times that of the design pile, and a safety margin of 3-8m is allowed relative to the equivalent length of the designed pile. Furthermore, the rated hammering energy of the pile hammer needs to be checked to ensure sufficient energy to drive the ultra-long steel pipe pile to the design elevation; the pile's durability needs to be verified to ensure no fatigue failure or local buckling occurs under repeated hammering; and the verticality deviation of the pile needs to be controlled to ensure the final pile displacement meets the allowable deviation value for construction acceptance. Through the joint verification of these various construction constraints, both construction feasibility and long-term stability are ensured to meet the constraints simultaneously. The final design scheme also includes pile driving control standards.

[0086] The optimization of pile diameter and length for ultra-long steel pipe piles in deep soft soil cannot solely rely on short-term bearing capacity as the only control indicator. The design phase must also consider the impact of corrosion-induced cross-sectional stiffness degradation on structural stability during long-term service, as well as the rigid constraints imposed by construction equipment capacity on pile length and weight. If the designed pile length is too close to the maximum pile length that the piling vessel can drive, risks related to pile frame height, hook capacity, or pile displacement during construction will significantly increase. If the combination of pile diameter and length results in insufficient buckling stability redundancy due to wall thinning after long-term service, the structure may become unstable within its design service life. Therefore, during the optimization of pile diameter and length, it is necessary to simultaneously incorporate the safety margin for the length of piles that can be driven, long-term stiffness degradation assessment, and a termination point after multiple rounds of adjustments to ensure that the final solution simultaneously meets the requirements of short-term construction feasibility and long-term service stability.

[0087] During implementation, the first step is to calculate the equivalent constraint stiffness reduction factor. d In the coordinated optimization phase involving pile diameter and pile length, a safety margin for the construction-capable pile length is established. The safety margin refers to the minimum difference between the designed pile length and the maximum pile length that the piling vessel can drive. This margin is used to address adverse factors during construction, such as pile frame positioning errors, hammer deviation, and tidal changes. Its value can be determined based on equipment performance, construction experience, and the project risk level, typically ranging from 3 to 8 meters. When the difference between the designed pile length and the maximum pile length that the piling vessel can drive under each candidate pile diameter scheme is less than the safety margin for the construction-capable pile length, it means that the pile length is already within the boundary of the equipment's capabilities, making construction difficult and risky. In this case, the scheme cannot be directly adopted, and further evaluation of its structural safety under long-term service conditions is required.

[0088] Specifically, the current scheme, after repeated iterations, satisfies the conditions of two adjacent calculations. d The final equivalent constraint stiffness reduction factor is determined after the convergence condition that the rate of change is less than 5% and the difference between the overall pile-soil spring model and the three-dimensional pile-soil interaction model at the maximum displacement and maximum bending moment is less than 5%. d Substituting the convergence value into the long-term cross-sectional stiffness attenuation coefficient of the pile body for this pile diameter scheme, the equivalent constraint stiffness reduction factor is calculated within the design service life of the wharf. dThe long-term degradation trajectory varies with wall thickness reduction and stiffness degradation. This trajectory reflects the changing trend of the reduction in spring stiffness of deep soil at future times and is an important basis for assessing long-term buckling stability. Based on the degradation trajectory, the pile buckling stability redundancy under combined vertical and horizontal loads at the end of service can be calculated. Pile buckling stability redundancy refers to the difference between the pile buckling stability coefficient and the design-required buckling stability coefficient. If this difference is negative, it indicates that the pile buckling stability coefficient does not meet the design requirements. When the pile buckling stability redundancy is lower than the design standard, it indicates that the scheme has a risk of buckling instability after long-term service. Therefore, the current pile diameter scheme must be skipped, and a scheme with a larger pile diameter must be directly selected to improve the cross-sectional stiffness and buckling stability by increasing the pile diameter.

[0089] If the next scheme with a larger pile diameter is subject to the equivalent constraint stiffness reduction factor d If, after convergence calculations and long-term degradation trajectory assessments, the long-term stability requirements still cannot be met—that is, the pile buckling stability coefficient must consistently be no less than the minimum value specified in relevant design codes throughout the wharf's design service life, and the maximum combined stress of the pile body must not exceed 0.85 times the design allowable value under the condition of effective wall thickness after corrosion—then the approach of simply increasing the pile diameter should be abandoned. Instead, the process of increasing the number of piles should be resumed, and multiple rounds of adjustments to pile diameter, wall thickness, number of piles, or pile location should be restarted. If, after multiple rounds of adjustments to pile diameter, number of piles, wall thickness, and pile location, the pile buckling stability redundancy under long-term service conditions still cannot meet the design standards, it indicates that purely structural-scale optimization is ineffective. In this case, the current adjustment process should be terminated, and non-structural engineering measures should be adopted, such as local foundation treatment or isolation measures, to improve pile-soil contact conditions or reduce additional effects, ultimately meeting the long-term stability requirements.

[0090] At the same time, regarding construction feasibility, it must be ensured that the hook capacity of the piling vessel is not less than the weight of a single pile. W p The maximum length of the pile driving vessel should be 1.10 times the design equivalent length of the pile to ensure the safety of the ultra-heavy steel pipe piles during lifting and driving. Simultaneously, a safety margin of 3-8 meters should be allowed relative to the maximum pile driving length of the design pile driving vessel to address uncertainties during the pile driving process. These two strict constraints jointly ensure that the design scheme not only meets long-term load-bearing requirements but also possesses practical construction feasibility. Furthermore, the design output should include pile driving control standards, including penetration control standards and final hammer test standards, as a basis for construction acceptance.

[0091] Taking a heavy equipment wharf as an example, the maximum pile length that a piling vessel can drive is 105m, while the design pile length under a certain candidate pile diameter scheme is 103m. The safety margin for the length of piles that can be driven during construction is set at 5m. The difference between the two is 2m, which is less than the safety margin for the length of piles that can be driven during construction, triggering a long-term degradation assessment. The equivalent constraint stiffness reduction factor is then applied. d Substituting the convergence value into the long-term cross-sectional stiffness attenuation coefficient of the pile body under the current pile diameter scheme, the equivalent constraint stiffness reduction factor under long-term service conditions is calculated. d The degradation trajectory is followed; when the pile buckling stability redundancy under this degradation trajectory is lower than the design standard, the current pile diameter scheme is skipped, and the next larger pile diameter scheme is directly locked. If, after long-term degradation trajectory evaluation, the pile buckling stability redundancy of the next larger pile diameter scheme is still lower than the design standard, the path of simply increasing the pile diameter is abandoned, and the step of increasing the number of piles is returned, and the process of adjusting the pile diameter, wall thickness, number of piles, or pile position is repeated. If the long-term stability requirements still cannot be met after multiple rounds of adjustment, the current adjustment process is terminated, and local foundation treatment or isolation measures are taken to meet the long-term stability requirements. At the same time, the hook capacity of the piling vessel is not less than the weight of a single pile. W p The pile length is 1.10 times that of the design pile, and the maximum pile driving length of the pile frame has a safety margin of 3-8m relative to the equivalent length of the designed pile. The final output is a pile type scheme that meets both construction feasibility and long-term stability constraints. The design scheme also includes pile driving control standards. This scheme integrates construction safety margin, long-term degradation assessment, multiple rounds of adjustment of the exit point, and construction capacity constraints into the pile diameter and pile length linkage optimization process. This ensures that the final output design scheme takes into account both construction feasibility and long-term service stability, effectively avoiding the hidden dangers of ignoring long-term risks and construction capacity due to the pursuit of economy alone.

[0092] In another approach, the design optimization method for ultra-long piles at wharves in ultra-thick soft soil layers involves applying a section stiffness attenuation coefficient to the pile element in a three-dimensional pile-soil interaction model, using the deviation degree... R Based on the deviation degree R The magnitude of the attenuation rate of the cross-sectional stiffness attenuation coefficient is modulated by partitioning; the attenuation rate includes a lower limit and an upper limit. Taking the lower limit means that the cross-sectional stiffness attenuation coefficient degrades according to the reference degradation rate, which is the ratio obtained by dividing the corrosion allowance by the design service life; taking the upper limit means that the cross-sectional stiffness attenuation coefficient degrades at a preset multiple of the reference degradation rate; when the deviation is... R When the coefficient of stiffness attenuation is greater than 2.8, the attenuation rate of the cross-sectional stiffness attenuation coefficient takes the lower limit value in the region above the hypothetical fixed point and the upper limit value in the deep soft soil region below the hypothetical fixed point; when the deviation... R When the value is ≤2.8, the attenuation rate of the cross-sectional stiffness attenuation coefficient is taken as the lower limit in both the region above the hypothetical fixed point and the deep soft soil region below the hypothetical fixed point.

[0093] During long-term service, ultra-long steel pipe piles not only suffer from cross-sectional stiffness degradation due to marine corrosion, but also from the risk of horizontal stress distortion caused by insufficient constraint of deep soft soil. In existing ultra-long pile design optimization methods, corrosion-induced cross-sectional stiffness reduction is usually treated as a variable uniformly applied across the entire pile, without considering the actual stress state at different depths and the constraint characteristics of the deep soil. However, the stress characteristics of ultra-long piles in deep soft soil exhibit significant zonal characteristics: in the shallow region above the hypothetical anchorage point and near the mud surface, the pile mainly bears bending moment and horizontal shear force, and its stress state is largely consistent with the assumption of the hypothetical anchorage point in the code; in the deep soft soil region below the hypothetical anchorage point, the pile is controlled by the lateral constraint of the deep soil, and the deviation between its actual horizontal displacement zero point and the hypothetical anchorage point in the code directly reflects the strength of the deep soil constraint. If the same rate of stiffness degradation is applied to both deep and shallow layers during the corrosion stiffness decay process, the coupled deterioration effect between insufficient deep soil constraint and cross-sectional stiffness degradation will be ignored, leading to an underestimation of the pile instability risk in deep soft soil areas. Therefore, a zoned modulation mechanism is needed to correlate the corrosion stiffness decay rate with the deep soil constraint state, enabling a synergistic determination of corrosion-induced stiffness degradation and insufficient deep soil constraint.

[0094] To address the aforementioned issues, this solution applies a section stiffness attenuation coefficient to the pile element in the three-dimensional pile-soil interaction model, using the deviation calculated under the current working conditions of the three-dimensional pile-soil interaction model. R Based on the deviation degree R The magnitude of the deviation modulates the attenuation rate of the cross-sectional stiffness attenuation coefficient in different zones. R A deviation R > 2.8 indicates weak deep constraints, while a deviation R ≤ 2.8 indicates normal or strong deep constraints. The core idea of ​​zoned modulation is that the corrosion stiffness attenuation rate in different depth regions of the pile should match the stress characteristics and constraint state of that region. When the deviation... R When the deviation is greater than 2.8, it indicates that the deep soil constraint is relatively weak, and the pile stress is closer to the deep soft soil control zone. At this time, the decay rate of the section stiffness attenuation coefficient takes the upper limit value in the deep soft soil zone below the hypothetical embedment point and the lower limit value in the region above the hypothetical embedment point; when the deviation... RWhen the coefficient of performance is ≤2.8, it indicates that the deep soil constraint is normal or relatively strong, and the pile stress is in good agreement with the specification assumptions. At this time, the attenuation rate of the cross-sectional stiffness attenuation coefficient is taken as the lower limit in both the deep soft soil region below the hypothetical embedment point and the region above the hypothetical embedment point. Taking the lower limit of the attenuation rate of the cross-sectional stiffness attenuation coefficient means that the stiffness degradation caused by corrosion proceeds according to the benchmark degradation rate. The benchmark degradation rate refers to the average annual degradation rate determined based on the corrosion margin and design service life of the steel pipe pile under the condition of no additional accelerating factors, that is, the quotient obtained by dividing the corrosion margin by the design service life. Taking the upper limit means that the stiffness degradation caused by corrosion is accelerated according to a preset multiple of the benchmark degradation rate. The preset multiple is greater than 1, and its specific value is determined comprehensively based on the severity of the insufficient deep soil constraint and the engineering design risk level. It is used to expose the structural weak parts under the superposition of long-term corrosion and insufficient deep soil constraint in the simulation calculation in advance. Through the above-mentioned zonal modulation, a synergistic deterioration judgment mechanism is formed between the stiffness degradation caused by corrosion and the insufficient deep soil constraint.

[0095] Taking a near-shore, isolated heavy cargo wharf project as an example, the site has ultra-long steel pipe piles approximately 90m in length, with a deep soft soil zone 60m below the mud surface. In the three-dimensional pile-soil interaction model calculation, the deviation under this condition is... R A value of 2.1 indicates that the deep constraints are at a moderate level, falling within the deviation range. R For values ​​≤2.8, the attenuation rate of the cross-sectional stiffness attenuation coefficient is modulated in zones based on 2.1. Due to deviation... R The attenuation rate of the cross-sectional stiffness attenuation coefficient is ≤2.8, with the lower limit value taken in both the region above the hypothetical embedment point and the deep soft soil region below the hypothetical embedment point. Simulation calculations over a 50-year design service life show that the maximum combined stress distribution of the pile body obtained by this zonal modulation method more accurately reflects the actual dangerous area distribution after long-term service than the uniform attenuation method, thus achieving the determination of the synergistic deterioration of stiffness degradation caused by corrosion and insufficient constraint of deep soil. This scheme effectively improves the accuracy of safety assessment for ultra-long steel pipe piles under long-term service conditions in deep soft soil by coupling cross-sectional stiffness attenuation with the constraint state of deep soil.

[0096] In another scheme, the design optimization method for ultra-long piles in ultra-thick soft soil wharfs involves implementing an active feedback suppression mechanism for additional bending moments after the additional lateral earth pressure generated by the consolidation of the dike is superimposed onto the boundary conditions of the three-dimensional model. The specific steps of this active feedback suppression mechanism are as follows: extracting the peak negative bending moment of inclined piles adjacent to the dike or edge piles near the dike in the three-dimensional pile-soil interaction model under superimposed loads; when the peak negative bending moment exceeds a preset proportion of the design allowable value, triggering a virtual unloading of the additional lateral earth pressure, generating an equivalent normal resistance force within a preset depth range below the mud surface of the three-dimensional pile-soil interaction model, with the force opposite in direction and proportional in magnitude to the additional earth pressure; and superimposing the equivalent normal resistance force onto the three-dimensional pile-soil interaction model. In this process, the actual stress state of the inclined piles or side piles after the superimposed calculation is dynamically evaluated, and the stress value or displacement value under the actual stress state after the superimposed calculation is compared with the design allowable value of the negative bending moment control condition. When the stress value or displacement value is greater than the design allowable value, it is determined that the current pile type parameters do not meet the requirements, and the process returns to the step of adjusting the pile diameter or wall thickness of the inclined piles or side piles, and the active feedback suppression mechanism for the additional bending moment is re-executed. When the stress value or displacement value is less than or equal to the design allowable value, it is determined that the current pile type parameters meet the requirements. If the stress value or displacement value is still greater than the design allowable value after multiple rounds of adjustment, the current adjustment process is terminated, and isolation measures or measures to control settlement during the construction stage of the embankment are adopted.

[0097] When ultra-long steel pipe piles are subjected to stress in areas adjacent to the embankment, they must bear not only the load of the wharf itself but also the additional lateral earth pressure generated by the consolidation settlement of the embankment. Existing methods, after superimposing the additional lateral earth pressure onto a three-dimensional pile-soil interaction model, typically perform only one overall internal force calculation and then address the excessive stress by conventional means such as increasing the pile diameter, wall thickness, or number of piles. However, the peak negative bending moment generated by inclined piles or edge piles near the embankment under superimposed loads often exhibits localized concentration characteristics. Simply relying on adjusting structural dimensions to passively address this may not accurately reflect the true stress state of the pile body after unloading or load redistribution, easily leading to over-design or omission of local risk points. Therefore, it is necessary to establish a suppression mechanism that can actively intervene and provide dynamic feedback, simulating the optimal stress state through virtual unloading when the negative bending moment exceeds the limit, and using this as a benchmark to evaluate the actual adjustment effect, ensuring the stress safety of inclined piles or edge piles near the embankment under complex load combinations.

[0098] The active feedback suppression mechanism for additional bending moment is activated after the additional lateral earth pressure generated by the consolidation of the embankment is superimposed onto the outer boundary conditions of the three-dimensional pile-soil interaction model. The specific execution steps of the active feedback suppression mechanism for additional bending moment include: firstly, extracting the peak negative bending moment of the inclined piles adjacent to the embankment or the edge piles near the embankment in the three-dimensional pile-soil interaction model under superimposed load. The peak negative bending moment refers to the maximum bending moment that occurs within a depth range directly below the embankment edge line, with a direction opposite to the conventional load bending moment. After extracting the peak negative bending moment, it is compared with the design allowable negative bending moment value, and a preset ratio is set as the trigger condition. When the peak negative bending moment exceeds the preset ratio, a virtual unloading operation on the additional lateral earth pressure is triggered. Virtual unloading does not actually change the embankment or foundation conditions, but rather generates an equivalent normal resistance force in the three-dimensional pile-soil interaction model within a preset depth range below the mud surface, with the opposite direction and proportional magnitude to the additional earth pressure. The magnitude of the equivalent normal resistance is determined proportionally according to the degree of exceeding the limit, and its direction is opposite to the additional lateral earth pressure. This is intended to offset some of the harmful effects, enabling the model to assess the true bearing potential of the structure under ultimate limit conditions without being constrained by excessive loads. Superimposing the equivalent normal resistance onto the three-dimensional pile-soil interaction model yields a new stress state, namely the true stress state of the inclined piles or side-row piles after superposition calculation.

[0099] Under actual stress conditions, the stress or displacement values ​​of the inclined piles or side piles are calculated and compared with the design allowable values ​​for the negative bending moment control condition. If the stress or displacement value is greater than the design allowable value, it indicates that the current pile parameters still do not meet the requirements. In this case, it is necessary to return to the step of adjusting the pile diameter or wall thickness of the inclined piles or side piles, and re-execute the complete process of the active feedback suppression mechanism for additional bending moment until the stress or displacement value meets the requirements. If the stress or displacement value is less than or equal to the design allowable value, it is determined that the current pile parameters meet the requirements, and no further adjustment is needed. Through this cyclic feedback mechanism, the stress state of the inclined piles or side piles gradually approaches the optimal control range, avoiding the waste caused by blindly increasing the size.

[0100] Taking a heavy-duty wharf supporting a nuclear power plant as an example, the wharf is located near a water intake dike. Calculations show the dike's final settlement is approximately 0.47m, and the distance between the wharf's pile foundation and the dike's side edge is less than twice the thickness of the soft soil layer, meeting the triggering conditions. After superimposing the additional lateral earth pressure generated by the dike consolidation onto the outer boundary conditions of the three-dimensional pile-soil interaction model, the peak negative bending moment of the inclined piles or the edge piles near the dike under the superimposed load is extracted. It is found that this peak moment exceeds the preset proportion of the design allowable value, triggering a virtual unloading of the additional lateral earth pressure. An equivalent normal resistance force, opposite in direction and proportional in magnitude to the additional earth pressure, is generated within a 30m depth below the mud surface in the three-dimensional pile-soil interaction model. This equivalent normal resistance force is superimposed onto the three-dimensional pile-soil interaction model. Recalculation reveals that the stress value still exceeds the design allowable value. Therefore, the process returns to adjusting the pile diameter of the inclined piles or edge piles, and the active feedback suppression mechanism for the additional bending moment is re-executed. After recalculation, the stress value drops below the design allowable value, ultimately determining the optimal edge pile diameter scheme.

[0101] This mechanism, through iterative optimization under virtual unloading conditions, ensures that inclined piles or side piles near the embankment undergo only the necessary minimum dimensional adjustments while meeting stress requirements, effectively reducing steel consumption and ensuring their long-term service safety.

[0102] In another approach, the design optimization method for ultra-long piles at wharves in ultra-thick soft soil layers involves reducing the equivalent constraint stiffness factor. d During the iterative correction process, a multi-parameter auxiliary judgment mechanism is set up. This mechanism simultaneously extracts the axial force normalization sequence, bending moment normalization sequence, and soil strength normalization sequence at various depths below the mud surface from the three-dimensional pile-soil interaction model; and calculates the equivalent constraint stiffness reduction factor. d First correlation index with the standardized sequence of pile axial forces, equivalent constraint stiffness reduction factor d The second correlation index with the standardized bending moment sequence, and the equivalent constraint stiffness reduction factor. d A third correlation index between the soil strength standardization sequence and the soil strength standardization sequence; when any one of the first, second, and third correlation indices shows a negative correlation, and the absolute value of the negative correlation exceeds a preset negative correlation threshold, the current equivalent constraint stiffness reduction factor is determined. d The effectiveness is questionable, and the equivalent constraint stiffness reduction factor is forcibly frozen. d The iterative update process involves: after freezing, comparing the actual distribution values ​​of axial force and bending moment extracted from the three-dimensional pile-soil interaction model at the freezing point with the calculated values ​​of axial force and bending moment obtained from the overall pile-soil spring model of the wharf, and then calculating a new equivalent constraint stiffness reduction factor that can eliminate this deviation. d Theoretical value, and the new equivalent constraint stiffness reduction factor. dThe theoretical value serves as the new equivalent constraint stiffness reduction factor. d Initial value; reduce the new equivalent constraint stiffness factor. d Theoretical values ​​are limited by deviation. R The corresponding equivalent constraint stiffness reduction factor d Within the value range, if the new equivalent constraint stiffness reduction factor d Theoretical value exceeds deviation R The corresponding equivalent constraint stiffness reduction factor d If the value range is specified, then the deviation must be taken. R The corresponding equivalent constraint stiffness reduction factor d The boundary limits of the range of values ​​are used as new equivalent constraint stiffness reduction factors. d Initial value, restart stiffness backoff correction closed loop; the specific steps of stiffness backoff correction closed loop are: reconstruct the equivalent constraint stiffness reduction factor d Initial values ​​are input into the overall pile-soil spring model of the wharf. The stiffness values ​​of the soil springs in the area 50m below the mud surface are recalculated and updated according to the multiplication correction formula. The calculation results of the updated overall pile-soil spring model of the wharf are then compared with the calculation results of the three-dimensional pile-soil interaction model. If the difference between the overall pile-soil spring model of the wharf and the three-dimensional pile-soil interaction model at the maximum displacement and maximum bending moment does not meet the requirement of less than 5%, the equivalent constraint stiffness reduction factor is adjusted repeatedly. d And recalculate the soil spring stiffness until the current step. d Compared to the previous round d When the rate of change is less than 5%, and the difference between the overall pile-soil spring model and the three-dimensional pile-soil interaction model at the maximum displacement and maximum bending moment is less than 5%, the convergence condition is deemed met. Simultaneously, the current multi-parameter auxiliary judgment results are stored as historical working condition markers in the working condition memory of the design optimization method, so that the equivalent constraint stiffness reduction factor can be directly retrieved during subsequent design of wharf pile foundations under similar geological conditions. d The initial value is obtained, thereby improving the versatility and iterative calculation efficiency of the ultra-long pile design optimization method under different geological profiles.

[0103] Horizontal stress analysis of ultra-long steel pipe piles in deep soft soil, using equivalent constraint stiffness reduction factor. d Iterative corrections were made to the deep soil spring stiffness to approximate the calculated response of the overall pile-soil spring model of the wharf to a three-dimensional pile-soil interaction model. However, d The convergence criterion mainly relies on two simple indicators: the rate of change between two adjacent iterations is less than 5%, and the difference between the maximum displacement and maximum bending moment of the two models is less than 5%. In actual engineering, when deep geological conditions are complex, soil strength distribution is uneven, or there is a coupling effect between pile stress and soil deformation, dThe corrected trajectory may be inconsistent with the actual axial force, bending moment, and soil strength distribution of the pile, leading to problems even if the above convergence conditions are met. d The value of still cannot truly reflect the constraint state of deep soil. At this point, if the iteration is forcibly terminated solely based on the numerical convergence index, it may output a value that is numerically stable but physically biased. d This value affects the accuracy of subsequent pile size determination and buckling stability verification. Therefore, a multi-parameter auxiliary judgment mechanism needs to be established during the iterative correction process to evaluate the pile's stress response and soil strength distribution from multiple dimensions. d Cross-validate the validity to ensure d The iterative process not only satisfies the numerical convergence condition, but also maintains intrinsic consistency with the actual stress characteristics of the pile body and the soil constraint state.

[0104] To address the aforementioned issues, this method uses an equivalent constraint stiffness reduction factor. d During the iterative correction process, a multi-parameter auxiliary judgment mechanism was established. The function of this mechanism is to simultaneously extract the standardized sequences of pile axial force, pile bending moment, and soil strength at various depths below the mud surface from the three-dimensional pile-soil interaction model after each iteration. The standardized sequence of pile axial force refers to the sequence obtained by dimensionlessly processing the measured or calculated values ​​of axial force at various depths of the pile, reflecting the distribution pattern of axial force along the pile. The standardized sequence of pile bending moment is the sequence obtained by dimensionlessly processing the measured or calculated values ​​of bending moment at various depths of the pile, reflecting the distribution law of bending moment along the pile. The standardized sequence of soil strength is the sequence obtained by normalizing the soil strength indices at various depths below the mud surface, characterizing the spatial variation of soil constraint capacity. These three sequences provide equivalent constraint stiffness reduction factors from the perspectives of pile stress response and foundation constraint conditions, respectively. d Information on closely related physical quantities.

[0105] Based on this, the equivalent constraint stiffness reduction factor is calculated. d The correlation index with the three standardized sequences. Specifically, the equivalent constraint stiffness reduction factor is calculated. d The first correlation index between the pile axial force and the standardized sequence reflects the equivalent constraint stiffness reduction factor. d The correlation between the value of and the axial force distribution pattern of the pile body; calculate the equivalent constraint stiffness reduction factor. d The second correlation index between the pile bending moment standardized sequence reflects the equivalent constraint stiffness reduction factor. d The degree of correlation with bending moment distribution; calculation of the equivalent constraint stiffness reduction factor. dThe third correlation index between the soil strength standardized sequence and the equivalent constraint stiffness reduction factor reflects the soil strength standardized sequence. d The degree of correlation with changes in deep soil strength. These three correlation indicators together constitute the reduction factor for equivalent constraint stiffness. d A multi-dimensional evaluation system for effectiveness. When any one of the correlation indicators shows a negative correlation, i.e., the equivalent constraint stiffness reduction factor... d When the increase or decrease of the negative correlation is opposite to the trend of the corresponding physical quantity, and the absolute value of the negative correlation exceeds the preset negative correlation threshold, then the current equivalent constraint stiffness reduction factor is determined. d The effectiveness of this study is questionable.

[0106] Once the equivalent constraint stiffness reduction factor is determined... d The effectiveness is questionable; the equivalent constraint stiffness reduction factor should be immediately and forcibly frozen. d Iterative updates to avoid ineffective equivalent constraint stiffness reduction factors. d The values ​​continue to affect subsequent calculations. After freezing, the actual distribution values ​​of axial force and bending moment extracted from the three-dimensional pile-soil interaction model at the freezing point are compared with the calculated values ​​of axial force and bending moment obtained from the overall pile-soil spring model of the wharf at the same time, and the deviations are back-calculated point by point. Specifically, the values ​​of the two at the same depth are compared, the absolute value of the difference is calculated, and then a new equivalent constraint stiffness reduction factor that minimizes the deviation is derived through least squares or similar fitting methods. d Theoretical value. The new equivalent constraint stiffness reduction factor. d Theoretical value and deviation R The corresponding equivalent constraint stiffness reduction factor d The value range is compared; if the new equivalent constraint stiffness reduction factor is... d The theoretical value is at a deviation. R The corresponding equivalent constraint stiffness reduction factor d Within the range of values, it is directly used as the new equivalent constraint stiffness reduction factor. d Initial value; if the new equivalent constraint stiffness reduction factor d Theoretical value exceeds deviation R The corresponding equivalent constraint stiffness reduction factor d If the range of values ​​is specified, then the equivalent constraint stiffness reduction factor corresponding to the deviation R is forcibly taken. d The boundary limits of the range of values ​​are used as new equivalent constraint stiffness reduction factors. d Initial value, restart stiffness backoff correction closed loop.

[0107] The specific steps of the stiffness reduction correction closed loop are as follows: The reconstructed equivalent constraint stiffness reduction factor... dInitial values ​​are input into the overall pile-soil spring model of the wharf. The stiffness values ​​of the soil springs in the area 50m below the mud surface are recalculated and updated according to the multiplication correction formula. Then, the calculation results of the updated overall pile-soil spring model are compared with those of the three-dimensional pile-soil interaction model. If the difference between the two models at the maximum displacement and maximum bending moment does not meet the requirement of less than 5%, the equivalent constraint stiffness reduction factor is adjusted iteratively. d And recalculate the soil spring stiffness until the current equivalent constraint stiffness reduction factor is reached. d Compared with the previous round of equivalent constraint stiffness reduction factor d The convergence condition is met when the rate of change is less than 5% and the difference between the two models at maximum displacement and maximum bending moment is less than 5%. This closed-loop mechanism ensures the equivalent constraint stiffness reduction factor. d After undergoing validity challenges, it was able to reconverge to a reasonable physical range.

[0108] Simultaneously, the current multi-parameter auxiliary judgment results are stored as historical working conditions in the working condition memory of the design optimization method. The working condition memory records the equivalent constraint stiffness reduction factor in each iteration. d The values, correlation indicators, deviation back-calculation results, and final convergence status form an empirical database. When designing wharf pile foundations with similar geological conditions in the future, the corresponding equivalent constraint stiffness reduction factor can be directly retrieved from the working condition memory database. d Initial values ​​are obtained, thereby reducing the number of iterations and improving the versatility and iterative calculation efficiency of the design optimization method for ultra-long steel pipe piles under different geological profiles.

[0109] Taking a near-shore, isolated heavy cargo wharf as an example, the site contains numerous silt interlayers in the deep soft soil zone, and the soil strength varies significantly with depth. In one iterative calculation, the equivalent constraint stiffness reduction factor... d The value was set to 0.7, but the standardized axial force sequence of the pile body extracted from the three-dimensional pile-soil interaction model showed that the axial force in the lower part of the pile body was significantly lower, while the standardized bending moment sequence of the pile body showed abnormal peak values ​​in the deeper layers. At the same time, the standardized soil strength sequences at various depths below the mud surface also reflected that the strength of the deep soil was highly discrete. The equivalent constraint stiffness reduction factor was calculated. d The first correlation index between the pile axial force and the standardized sequence is negatively correlated. If the absolute value of the negative correlation exceeds the preset negative correlation threshold, the equivalent constraint stiffness reduction factor is determined. d The effectiveness was questionable, so a forced freeze iteration was initiated. The actual distribution values ​​of axial force and bending moment at the freezing point were then extracted and compared with the calculated values ​​from the overall pile-soil spring model of the wharf. The deviation was then calculated to derive a new equivalent constraint stiffness reduction factor. d The theoretical value is 0.55. This new equivalent constraint stiffness reduction factor d The theoretical value is 0.55, which is lower than the deviation.R The corresponding equivalent constraint stiffness reduction factor d The lower limit of the value range is 0.6, therefore the deviation is forced to be taken. R The corresponding equivalent constraint stiffness reduction factor d The lower limit of the value range, 0.6, is used as the new equivalent constraint stiffness reduction factor. d Initial value. This is the new equivalent constraint stiffness reduction factor. d The initial value restarts the stiffness backoff correction closed loop; the specific steps of the stiffness backoff correction closed loop are: to apply the new equivalent constraint stiffness reduction factor. d Initial values ​​were input into the overall pile-soil spring model of the wharf. The stiffness values ​​of the soil springs in the area 50m below the mud surface were recalculated and updated according to the multiplication correction formula. The calculation results of the updated overall pile-soil spring model were then compared with the calculation results of the three-dimensional pile-soil interaction model. After several iterations, the maximum displacement difference between the two models decreased to within 3%, and the bending moment difference decreased to within 4%. d The rate of change stabilized at around 2%, satisfying the convergence condition. Simultaneously, the multi-parameter determination results of this iteration were stored in the working condition memory, allowing direct retrieval of the equivalent constraint stiffness reduction factor under subsequent similar geological conditions. d Using an initial value of 0.6 for iteration significantly reduces the number of iterations and improves design efficiency.

[0110] Figure 1 This is a flowchart illustrating the design optimization method for ultra-long piles at wharves in ultra-thick soft soil layers. Figure 1 This paper demonstrates the complete process of the design optimization method for ultra-thick soft soil layer wharf ultra-long piles proposed in this invention. The process consists of eight core steps, from basic data input to final scheme output, forming a complete closed-loop design system.

[0111] Step S1 involves basic data collection, which prepares the necessary data for subsequent modeling and calculation steps and serves as the starting point of the design process. Step S2 involves establishing a layered pile-soil model. Based on geological survey data, the soil below the mud surface is divided into different layers according to the actual geological strata, and the pile side friction and pile end resistance of each calculation layer are determined. A deep side friction correction coefficient is introduced to correct for deviations in the applicability of empirical values ​​in ultra-long piles. Step S3 involves establishing a hob-soil-spring model based on the m-method. This model simulates pile-soil interaction and calculates the internal forces and displacements of the hob-soil structure under load. Step S4 involves establishing a three-dimensional pile-soil interaction model. This model uses solid elements to simulate the soil, considering soil nonlinearity and pile-soil contact, and is used to identify three-dimensional stress characteristics such as the zero point of horizontal displacement, the maximum bending moment point, and the deep inflection point. Step S5 involves on-site testing and correction. Measured data from static load tests and high-strain tests are used to correct the parameters of the calculation model. When the deviation between the calculated bearing capacity and the tested bearing capacity exceeds 15%, the process returns to step S2 for parameter correction. Step S6 involves a comprehensive comparison of pile diameter, pile length, number of piles, wall thickness, and steel quantity. Multiple options are compared to find the optimal combination of pile parameters that meets the requirements for bearing capacity and stability. Step S7 involves multi-dimensional verification, including specific checks on the additional effects of settlement from adjacent embankments, buckling stability, construction feasibility, and durability. Step S8 outputs the final design scheme, providing complete design results including pile layout, pile diameter, pile length, number of piles, wall thickness, pile end elevation, pile side friction correction parameters, internal force displacement control points, pile driving control standards, and anti-corrosion measures.

[0112] This flowchart embodies the core idea of ​​the invention: to integrate standard calculations, three-dimensional numerical analysis, on-site testing, pile type comparison, embankment settlement, construction equipment, and durability requirements into the same design process, and to ensure that the final solution meets the comprehensive requirements of bearing capacity, displacement, stability, construction, and durability through a closed-loop backtracking mechanism.

[0113] Figure 2 This is a schematic diagram illustrating the pile-soil interaction and control depth of ultra-long piles in ultra-thick soft soil layers. Figure 2 This invention demonstrates the relationship between the stress characteristics of ultra-long steel pipe piles and the control depth in ultra-thick soft soil layers, providing a direct representation of the core technical means of this invention.

[0114] The ultra-long steel pipe piles shown in the figure have a pile length L of 60-130m, a pile diameter D of 1.0-2.0m, and a length-to-diameter ratio L / D of 40-110. The soil layers below the mud surface are divided into three main sections from top to bottom according to geological characteristics: 0-40m below the mud surface is silt or silty clay, which is a conventional soft soil section and the main area for horizontal loads; 40-70m below the mud surface is silty clay or sandy soil, which is the transition zone between the deep improved soil layer and the weak interlayer; 70-120m below the mud surface is a deep improved soil layer or relatively good soil layer, which is the main section for pile side friction resistance.

[0115] The diagram shows the depth of the hypothetical embedded point. h f Depth of horizontal displacement of the 3D model z 0. z 0 / h f The ratio is controlled within the range of 1.5-2.5. The hypothetical embedment depth is specified. h f It is an important reference point used in current design codes to calculate the horizontal displacement and bending moment of the pile body, and the three-dimensional model calculation... z 0 represents the position where the actual horizontal displacement of the pile is zero. The ratio of these two values ​​reflects the applicability of the code assumptions in the horizontal stress analysis of ultra-long piles. When z 0 / h f When the deviation from the control range of 1.5-2.5 indicates that the specification assumptions do not match the actual situation, and the soil spring parameters or pile size need to be adjusted.

[0116] Furthermore, it is required to forcibly output the axial force, shear force, bending moment, and displacement curves along the depth of the pile, with the vicinity of the mud surface, the imaginary embedment point, the zero point of horizontal displacement, and the location of abrupt changes in deep soil properties as the forced output points, to ensure that the stress state of ultra-long piles in deep soft soil is fully assessed. (Pile side skin friction contribution rate) or f It should be no less than 70%, preferably no less than 85%, to ensure that the side friction resistance is the main source of bearing capacity for ultra-long piles.

[0117] Figure 3 This is a sensitivity diagram of pile diameter, pile length, and steel consumption per pile. Figure 3 The paper demonstrates the linkage and optimization relationship between pile diameter, pile length, and the amount of steel in a single pile. This relationship is the core basis for pile size selection in step S6.

[0118] Under ultra-thick soft soil conditions, a typical foundation sensitivity relationship exists: for every 0.1m reduction in pile diameter, the pile length required to meet bearing capacity and stability increases by 2-5%, preferably 3-4%, or approximately 3-4m, while the amount of steel per pile decreases by 2-4%, preferably approximately 3%. Specifically, when the pile diameter decreases from 1.6m to 1.5m, 1.4m, and 1.3m, the longest pile length increases from approximately 96m to approximately 99m, 102m, and 106m respectively, while the amount of steel per pile decreases from approximately 86t to approximately 83t, 80t, and 78t respectively.

[0119] This sensitivity relationship reveals a nonlinear coupling effect between pile diameter and pile length: while reducing the pile diameter can decrease the amount of steel used in a single pile, it leads to a significant increase in pile length. In practical engineering, this increase in pile length may exceed the maximum pile length that the piling vessel can drive, rendering the design infeasible. Therefore, this sensitivity relationship cannot be used as the sole basis for pursuing smaller pile diameters; it must be inversely coupled with the capacity of the pile driving equipment. When the required pile length after reducing the pile diameter exceeds the construction limit, a larger pile diameter scheme should be prioritized, or the bearing capacity and stability requirements should be met by increasing the number of piles, adjusting pile positions, local foundation treatment, or increasing wall thickness.

[0120] Figure 4 This is a schematic diagram for verifying the additional lateral effect of adjacent dike settlement on ultra-long piles. Figure 4 The study demonstrates the additional lateral earth pressure exerted by the settlement of the adjacent dike on the ultra-long steel pipe piles of the wharf and its impact on the internal forces of the piles, as well as the corresponding verification methods.

[0121] When a wharf is located near adjacent dikes such as blasted silt-dissipating dikes, water intake dikes, riprap dikes, backfill areas, or construction access roads, the consolidation settlement of the dikes and lateral soil displacement will exert additional lateral earth pressure on the wharf's pile foundations, causing new peak bending moments near the mud surface and in deep soft soil areas. This additional lateral effect is a factor that is easily overlooked in conventional design, and if it is handled solely based on construction experience, its continuous effects during the operational period may be missed.

[0122] The verification method shown in the figure is as follows: the additional lateral earth pressure generated by the consolidation of the embankment is mathematically vector-decomposed and superimposed onto the outer boundary conditions of the three-dimensional pile-soil interaction model. Then, it is vector-superimposed with the original horizontal load bending moment to obtain the true bending moment distribution of the pile body. The figure highlights the bending moment peak control zone and displacement check depth: the maximum horizontal and vertical displacements caused by settlement are mainly checked in the range of 20-50m below the mud surface, preferably 30-40m; the bending moment peaks are mainly checked in the ranges of 0-8m, 30-35m, and 40-45m below the mud surface. For inclined piles or side piles close to the embankment, the negative bending moment near the edge of the embankment should be considered as one of the control conditions.

[0123] When additional lateral forces cause the pile stress, displacement, or stability coefficient to exceed the design limits, measures such as increasing the pile diameter, increasing the wall thickness, adjusting the pile position, setting up isolation measures, or controlling settlement during the construction of the embankment should be taken.

[0124] Figure 5 This is a schematic diagram of the durable zonal corrosion protection design for ultra-long steel pipe piles. Figure 5 This paper demonstrates a specific scheme for zoned corrosion protection design of ultra-long steel pipe piles according to different corrosive environments. The design divides the steel pipe pile into four zones along its depth, with each zone employing different corrosion protection measures.

[0125] The splash zone, located above the design high water level and affected by splashing, experiences frequent wet-dry cycles, resulting in the most severe corrosion. It is protected using heavy-duty anti-corrosion coatings or thermal metal spraying with a sealing coating. The water level fluctuation zone, located between the design high and low water levels, is affected by tides and water level changes, leading to faster corrosion. It is protected using a combination of coatings and sacrificial anodes or impressed current cathodic protection. The underwater zone, located below the design low water level and between the design low water level and the mud surface, is in a long-term underwater environment with a relatively stable corrosion rate. It is protected using a combination of coatings and sacrificial anodes or impressed current cathodic protection. The sub-mud zone, located below the mud surface, is less affected by direct seawater corrosion but faces risks of microbial and electrochemical corrosion. Cathodic protection is installed within 20-40m below the mud surface, preferably within 30m.

[0126] Regarding corrosion allowance, for a design service life of 50 years, the average annual corrosion rate of unprotected steel pipe piles is estimated at 0.2-0.6 mm / a, preferably 0.3-0.5 mm / a, with a corrosion allowance of 1-4 mm, preferably 2 mm. By combining the corrosion allowance with zoned anti-corrosion measures, the effective wall thickness after corrosion is finally obtained. Substituting this effective wall thickness into the buckling stability check ensures that the steel pipe piles maintain sufficient bearing capacity and stability throughout their design service life.

[0127] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A design optimization method for ultra-long piles in wharves with ultra-thick soft soil layers, wherein, The thickness of the soft soil layer in the wharf foundation is 20-80m, and the effective bearing layer depth is 50-120m; the length of the ultra-long steel pipe piles is 60-130m, the pile diameter is 1.0-2.0m, and the length-to-diameter ratio is 40-110; the method is characterized by the following steps: Preliminary determination of pile length, pile diameter, and number of piles; Based on geological survey data, a layered pile-soil model was established to obtain the standard values ​​of pile side friction resistance for each soil layer in the 0-50m range below the mud surface. qfik For areas 50m below the mud surface, sections are divided based on the physical and mechanical properties of the soil layers, and a correction factor for the side friction resistance of each layer is set. λ i Among them, for those with a natural water content greater than the liquid limit, a porosity greater than 1.0, and a compressibility coefficient greater than 0.5 MPa -1 And in conventional soft soil sections where the SPT blow count is less than 4, λ i Take a value of 0.8-1.1; for standard penetration tests (SPT) blow counts greater than 8 blows and compressibility coefficients less than 0.1 MPa. -1 Or deep improved soil layers with a compression modulus greater than 15 MPa, λ i Take 1.05-1.50; for soil layers with weak interlayers not less than 0.5-1.0m thick, or those affected by construction disturbance and soil displacement, λ i Take 0.6-1.0; according to the formula Calculate the ultimate vertical bearing capacity of a single pile Q uk ,in, qfik For the first i Standard value of side skin friction of piles u i For the first i Perimeter of pile layer, l i For the first i Effective length of pile side, a p This is the reduction factor for pile end resistance. q pk This is the standard value of pile end resistance. A p The area at the pile tip; and according to the formula Calculate the contribution rate of pile side friction η f ;when η f When the bearing capacity is less than 70%, the pile tip elevation is compared with the effective bearing layer depth. If the pile tip elevation is shallower than the effective bearing layer depth, the pile tip elevation is adjusted downwards to within the effective bearing layer, and the pile diameter or the number of piles is increased before recalculating the vertical ultimate bearing capacity of the single pile. Q uk and the contribution rate of pile side friction η f The steps continue until the desired result is achieved. η f Not less than 70%; Based on the soil layer division and pile-soil parameters provided by the layered pile-soil model, an overall pile-soil spring model of the wharf was established, and a three-dimensional pile-soil interaction model was also established; the depth of the hypothetical embedded point was obtained. h f The depth of the zero point of horizontal displacement calculated by the three-dimensional pile-soil interaction model. z 0 and the depth of the imaginary embedded point h f deviation R Deviation R The calculation formula is R = z 0 / h f ;when R When the value is <1.2 or >2.8, a review is performed. This review involves correcting the soil spring stiffness and soil layer boundary parameters in the overall pile-soil spring model of the wharf; extracting the maximum bending moment point based on the bending moment curve distributed along the depth of the pile; and addressing any deviations that cannot be corrected after the review. R It falls within the range of 1.5-2.5 and the point of maximum bending moment cannot be located in h f If the location is nearby, it is determined that the structure itself has insufficient stiffness; When the structure is determined to have insufficient rigidity, adjustments are made to the pile diameter, wall thickness, number of piles, or pile location, and the aforementioned verification steps are repeated until the deviation is correct. R The value falls within the range of 1.5-2.5 and the point of maximum bending moment is located at... h f Nearby; if the requirements still cannot be met after adjustment, then based on the degree of deviation. R Establish equivalent constraint stiffness reduction factor δ ;like R When the value is greater than 2.8, the equivalent constraint stiffness reduction factor is... δ Take 0.6-0.8; if R When <1.2, the equivalent constraint stiffness reduction factor δ Take 1.2-1.4; if R If the value is within the range of 1.2-2.8, the original calculation parameters of the overall pile-soil spring model of the wharf will be directly used as the basis for subsequent calculations; when the equivalent constraint stiffness reduction factor is used... δ At that time, the equivalent constraint stiffness reduction factor δ Used to determine the original stiffness of the soil springs in the area 50m below the mud surface in the integral pile-soil spring model of the wharf. K 原始 Perform multiplication correction; the formula for multiplication correction is as follows: K 修正 = δ × K 原始 The corrected soil spring stiffness is then re-substituted into the overall pile-soil spring model of the wharf for calculation, and the calculation is iterated repeatedly until the equivalent constraint stiffness reduction factor obtained from two adjacent calculations is obtained. δ If the rate of change is less than 5%, and the difference between the recalculated overall pile-soil spring model of the wharf and the three-dimensional pile-soil interaction model at the maximum displacement and the maximum bending moment is less than 5%, then convergence is determined. The measured bearing capacity obtained from static load tests or high strain tests is compared with the ultimate vertical bearing capacity of a single pile. Q uk Comparison, when the vertical ultimate bearing capacity of a single pile Q uk When the deviation from the measured bearing capacity exceeds 15%, a proportional correction is applied; the proportional correction includes correction for the corresponding coefficients of the source of deviation at the pile tip or pile side; when the deviation mainly originates from the pile tip, the pile tip resistance reduction factor is applied. a p According to the formula Make corrections. a p,old and a p,new These are the reduction factors for pile end resistance before and after the correction, respectively, and the correction factor is used as the reference. a p,new As the reduction factor for pile end resistance in subsequent calculations, and the corrected a p,new The value is limited to the range of 0.6-1.0; when the deviation mainly originates from the pile side, the correction factor for side skin friction is... λ i According to the formula Make corrections. λ i,old and λ i,new These are the correction factors for side friction resistance before and after the correction, respectively, and the correction factor after the correction is... λ i,new The values ​​are limited to the range of values ​​for the corresponding section; repeat the above calculation until the deviation between the calculated bearing capacity and the measured bearing capacity does not exceed 15%; Output the final design scheme, which includes pile diameter, pile length, number of piles, wall thickness, and pile end elevation.

2. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 1, characterized in that, The specific method for determining whether the deviation mainly originates from the pile tip or pile side is as follows: Extract the calculated value of the pile axial force distribution along the depth output from the overall pile-soil spring model or the three-dimensional pile-soil interaction model of the wharf, as well as the measured value of the pile axial force distribution along the depth obtained by actual measurement. Calculate the absolute value of the difference between the calculated value and the measured value of the axial force at each depth, and calculate the sum of the absolute values ​​of the axial force differences at all depths. When the absolute value of the difference at the pile tip accounts for 60% or more of the sum of the absolute values ​​of the differences, it is determined that the deviation mainly originates from the pile tip. When the absolute value of the difference at the pile tip accounts for less than 60% of the sum of the absolute values ​​of the differences, it is determined that the deviation mainly originates from the pile side.

3. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 1, characterized in that, When making adjustments to the pile diameter, wall thickness, number of piles, or pile location, the equivalent constraint stiffness reduction factor is used. δ The linkage optimization relationship between pile diameter, pile length, and single pile steel quantity is controlled; multiple pile diameter schemes are established under the same pier, the same load combination, and the same geological profile, and the foundation sensitivity relationship between pile diameter, pile length, and single pile steel quantity is set. The foundation sensitivity relationship is defined as the increase rate of pile length required to meet bearing capacity and stability when the pile diameter is reduced by 0.1m, and the steel weight of a single steel pipe pile is reduced by 2-4%; when the equivalent constraint stiffness reduction factor... δ A low value of 0.6-0.8 is selected to indicate weak deep confinement, and the pile length increase rate is forcibly set to the upper limit of 5%; when the equivalent confinement stiffness reduction factor... δ When the pile length is within the range of 1.2-1.4, the lower limit of 2% is selected as the pile length increase rate. The maximum pile driving length of the piling vessel is used as a hard constraint. When the adjusted pile length exceeds the maximum pile driving length of the piling vessel, the next scheme with a larger pile diameter is locked and the subsequent calculations are re-executed. If the next scheme with a larger pile diameter still cannot meet the bearing capacity and stability requirements, the step of increasing the number of piles is returned, and the process of adjusting the pile diameter, wall thickness, number of piles, or pile position is re-executed. If, after multiple rounds of the above-mentioned adjustments, the current design scheme still cannot meet the bearing capacity and stability requirements, the current adjustment process is terminated, and local foundation treatment or isolation measures are taken to meet the design requirements.

4. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 1, characterized in that, The method also includes verification of the additional lateral force of adjacent dike settlement. The specific steps for verifying the additional lateral force of adjacent dike settlement are as follows: when the final settlement of the adjacent dike is not less than 0.2m, and the distance between the wharf pile foundation and the wharf side edge is less than twice the thickness of the soft soil layer, the additional lateral earth pressure generated by the consolidation of the dike is directly superimposed onto the outer boundary conditions of the three-dimensional pile-soil interaction model through mathematical vector decomposition; the additional bending moment generated after superposition is vector superimposed with the original horizontal load bending moment; for the peak bending moment in the deep soft soil area at 50m below the mud surface, a double-layer data threshold is set. When the superimposed bending moment exceeds the threshold, the excess additional bending moment value is converted into additional horizontal load value through the bending moment-force equivalent conversion formula. Concentrate the force and apply the additional horizontal concentrated force to the pile-soil spring node at the corresponding depth position in the overall pile-soil spring model of the wharf; for inclined piles or side piles near the dike, extract their negative bending moment distribution curves under superimposed loads, take the negative bending moment peak value appearing in the depth range directly below the dike edge as the control condition, and compare the negative bending moment peak value with the design allowable negative bending moment value; if it exceeds the allowable value, increase the pile diameter or wall thickness of the inclined pile or side pile, and re-perform the check of the additional lateral action on the settlement of the adjacent dike; if the negative bending moment peak value of the inclined pile or side pile still exceeds the design allowable value after multiple rounds of adjustment, terminate the current adjustment process, and adopt isolation measures or treatment measures to control the settlement of the dike during the construction stage.

5. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 1, characterized in that, This method also includes a coupled verification of the long-term durability and buckling stability of ultra-long steel pipe piles; an algorithm for the stiffness attenuation coefficient of the pile section is constructed based on the design service life of the steel pipe piles, and a stiffness attenuation coefficient that evolves with time is applied to the section stiffness of the pile element in the three-dimensional pile-soil interaction model; when the stiffness attenuation coefficient decays to a preset warning threshold, the overall pile-soil spring model of the wharf and the three-dimensional pile-soil interaction model simultaneously switch to the buckling stability master control verification mode; the buckling stability master control verification mode means that in subsequent design calculations, the pile buckling stability coefficient is used as the primary control index, and the pile diameter, wall thickness, number of piles or pile position are adjusted to make the pile buckling stability coefficient meet the design requirements, and the pile buckling stability coefficient that meets the requirements is used as the primary control index. This serves as one of the verification bases for the final design scheme. Corrosion protection measures are designed for the steel pipe piles in the splash zone, water level fluctuation zone, underwater zone, and mud zone. The splash zone uses a heavy-duty anti-corrosion coating; the water level fluctuation zone and underwater zone use a combination of coating and sacrificial anode cathodic protection; and the mud zone has cathodic protection installed within 20-40m below the mud surface. The average annual corrosion rate of unprotected steel pipe piles is estimated at 0.2-0.6mm / a, with a corrosion allowance of 1-4mm. The effective wall thickness after corrosion is obtained by subtracting the corrosion allowance from the initial wall thickness of the steel pipe pile. This effective wall thickness is then used to replace the initial wall thickness in the buckling stability check, ensuring that the maximum combined stress of the section does not exceed 0.85 times the design allowable value. The final design scheme also includes corrosion protection measures.

6. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 1, characterized in that, During the iterative process, a convergence gradient threshold is set; after each iteration update of the soil spring stiffness in the overall pile-soil spring model of the wharf, the current equivalent constraint stiffness reduction factor is calculated. δ Compared with the previous round of equivalent constraint stiffness reduction factor δ The normalized gradient is used to determine the equivalent constraint stiffness reduction factor when the normalized gradient is less than the convergence gradient threshold. δ Under this condition, convergence has been achieved and the iteration has ended; when the normalized gradient is always greater than or equal to the convergence gradient threshold and the equivalent constraint stiffness reduction factor is applied... δ Continuous deviation is determined by the degree of deviation R The determined equivalent constraint stiffness reduction factor δ When the value range is selected, it is determined that the deep soil constraint characteristics have high nonlinearity, triggering the recalibration of the deep soil constitutive parameters in the three-dimensional pile-soil interaction model based on field geological data, and restarting the repeated iteration process.

7. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 3, characterized in that, When performing the equivalent constraint stiffness reduction factor δ In the coordinated optimization process involving pile diameter and pile length, a safety margin for the construction-deployable pile length is set. When the difference between the design pile length output under each candidate pile diameter scheme and the maximum pile length that can be driven by the piling vessel is less than the safety margin for the construction-deployable pile length, the equivalent constraint stiffness reduction factor is directly applied. δ Substituting the convergence value into the long-term cross-sectional stiffness attenuation coefficient of the pile body under the current pile diameter scheme, the equivalent constraint stiffness reduction factor under long-term service conditions is calculated. δ The degradation trajectory; when the pile buckling stability redundancy is lower than the design standard under the degradation trajectory, skip the current pile diameter scheme and directly lock the next larger pile diameter scheme; if the next larger pile diameter scheme still cannot meet the long-term stability requirements, return to the step of increasing the number of piles, and re-execute the process of adjusting the pile diameter, wall thickness, number of piles, or pile position; if the long-term stability requirements still cannot be met after multiple rounds of adjustment, terminate the current adjustment process, and take local foundation treatment or set up isolation measures to meet the long-term stability requirements; at the same time, the hook capacity of the piling vessel is not less than the weight of a single pile. W p The maximum pile length is 1.10 times that of the design pile, and the maximum pile driving length of the pile frame is 3-8m with a safety margin relative to the equivalent length of the designed pile, so as to ensure that the construction feasibility and long-term stability meet the constraints at the same time; the final design scheme also includes pile driving control standards.

8. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 1, characterized in that, When applying a section stiffness attenuation coefficient to the pile element in a three-dimensional pile-soil interaction model, the deviation is used as the basis for the calculation. R Based on the deviation degree R The magnitude of the attenuation rate of the cross-sectional stiffness attenuation coefficient is modulated by partitioning; the attenuation rate includes a lower limit and an upper limit. Taking the lower limit means that the cross-sectional stiffness attenuation coefficient degrades according to the reference degradation rate, which is the ratio obtained by dividing the corrosion allowance by the design service life; taking the upper limit means that the cross-sectional stiffness attenuation coefficient degrades at a preset multiple of the reference degradation rate; when the deviation is... R When the coefficient of stiffness attenuation is greater than 2.8, the attenuation rate of the cross-sectional stiffness attenuation coefficient takes the lower limit value in the region above the hypothetical fixed point and the upper limit value in the deep soft soil region below the hypothetical fixed point; when the deviation... R When the value is ≤2.8, the attenuation rate of the cross-sectional stiffness attenuation coefficient is taken as the lower limit in both the region above the hypothetical fixed point and the deep soft soil region below the hypothetical fixed point.

9. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 4, characterized in that, After the additional lateral earth pressure generated by the consolidation of the embankment is superimposed onto the outer boundary conditions of the three-dimensional model, an active feedback suppression mechanism for the additional bending moment is executed. The specific execution steps of the active feedback suppression mechanism for the additional bending moment are as follows: extracting the peak negative bending moment of the inclined piles adjacent to the embankment or the side piles close to the embankment in the three-dimensional pile-soil interaction model under superimposed load; when the peak negative bending moment exceeds a preset proportion of the design allowable value, a virtual unloading of the additional lateral earth pressure is triggered, generating an equivalent normal resistance force in the opposite direction and proportional in magnitude to the additional earth pressure within a preset depth range below the mud surface of the three-dimensional pile-soil interaction model; superimposing the equivalent normal resistance force into the three-dimensional pile-soil interaction model to dynamically evaluate the inclined piles or side piles under the load. The actual stress state after superposition calculation is calculated, and the stress or displacement value under this actual stress state is compared with the design allowable value of the negative bending moment control condition. When the stress or displacement value is greater than the design allowable value, it is determined that the current pile type parameters do not meet the requirements, and the process returns to adjust the pile diameter or wall thickness of the inclined pile or side pile, and the active feedback suppression mechanism for the additional bending moment is re-executed. When the stress or displacement value is less than or equal to the design allowable value, it is determined that the current pile type parameters meet the requirements. If the stress or displacement value is still greater than the design allowable value after multiple rounds of adjustment, the current adjustment process is terminated, and isolation measures or measures to control settlement during the construction stage of the embankment are adopted.

10. The design optimization method for ultra-long piles in ultra-thick soft soil layer wharves as described in claim 1, characterized in that, In the equivalent constraint stiffness reduction factor δ During the iterative correction process, a multi-parameter auxiliary judgment mechanism was set up. This mechanism simultaneously extracts the axial force standardized sequence, bending moment standardized sequence, and soil strength standardized sequence at various depths below the mud surface from the three-dimensional pile-soil interaction model; and calculates the equivalent constraint stiffness reduction factor. δ First correlation index with the standardized sequence of pile axial forces, equivalent constraint stiffness reduction factor δ The second correlation index with the standardized bending moment sequence, and the equivalent constraint stiffness reduction factor. δ A third correlation index between the soil strength standardized sequence and the soil strength; when any one of the first, second, and third correlation indices shows a negative correlation, and the absolute value of the negative correlation exceeds a preset negative correlation threshold, the current equivalent constraint stiffness reduction factor is determined. δ The effectiveness is questionable, and the equivalent constraint stiffness reduction factor is forcibly frozen. δ The iterative update process involves: after freezing, comparing the actual distribution values ​​of axial force and bending moment extracted from the three-dimensional pile-soil interaction model at the freezing point with the calculated values ​​of axial force and bending moment obtained from the overall pile-soil spring model of the wharf, and then calculating a new equivalent constraint stiffness reduction factor that can eliminate this deviation. δ Theoretical value, and the new equivalent constraint stiffness reduction factor. δ The theoretical value serves as the new equivalent constraint stiffness reduction factor. δ Initial value; reduce the new equivalent constraint stiffness factor. δ Theoretical values ​​are limited by deviation. R The corresponding equivalent constraint stiffness reduction factor δ Within the value range, if the new equivalent constraint stiffness reduction factor δ Theoretical value exceeds deviation R The corresponding equivalent constraint stiffness reduction factor δ If the value range is specified, then the deviation must be taken. R The corresponding equivalent constraint stiffness reduction factor δ The boundary limits of the range of values ​​are used as new equivalent constraint stiffness reduction factors. δ Initial value, restart stiffness backoff correction closed loop; the specific steps of stiffness backoff correction closed loop are: reconstruct the equivalent constraint stiffness reduction factor δ Initial values ​​are input into the overall pile-soil spring model of the wharf. The stiffness values ​​of the soil springs in the area 50m below the mud surface are recalculated and updated according to the multiplication correction formula. The calculation results of the updated overall pile-soil spring model of the wharf are then compared with the calculation results of the three-dimensional pile-soil interaction model. If the difference between the overall pile-soil spring model of the wharf and the three-dimensional pile-soil interaction model at the maximum displacement and maximum bending moment does not meet the requirement of less than 5%, the equivalent constraint stiffness reduction factor is adjusted repeatedly. δ And recalculate the soil spring stiffness until the current step. δ Compared to the previous round δ When the rate of change is less than 5%, and the difference between the overall pile-soil spring model and the three-dimensional pile-soil interaction model at the maximum displacement and the maximum bending moment is less than 5%, the convergence condition is satisfied. Simultaneously, the current multi-parameter auxiliary judgment results are stored as historical working conditions in the working condition memory of the design optimization method, so that the equivalent constraint stiffness reduction factor can be directly retrieved when designing wharf pile foundations under similar geological conditions in the future. δ The initial value is obtained, thereby improving the versatility and iterative calculation efficiency of the ultra-long pile design optimization method under different geological profiles.

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