A pile foundation length calculation method and system

Abstract

The application provides a pile foundation length calculation method and system, and relates to the technical field of pile foundation design. The specific steps include: calculating the maximum flow rate and the highest water level under a preset recurrence period to form an environmental characteristic parameter based on the method of moments estimation, so as to accurately quantify the extreme hydrological evolution trend; combining the water-blocking characteristic parameter to construct a maximum scour depth calculation formula to obtain a scour datum, thereby overcoming the defect of physical boundary failure; reconstructing the effective stress field of the underlying soil layer according to the scour datum and the stress release logic to truly restore the physical unloading effect; combining the nonlinear strength attenuation logic to calculate the side friction resistance at each depth, so as to accurately evaluate the degradation loss of the pile-soil bearing capacity; combining the preset limit end resistance of the pile end bearing layer, and outputting the optimal pile foundation length under the preset load safety threshold through a dynamic step iteration algorithm, so as to guarantee the bottom line of flood resistance mechanical safety while avoiding excessive structural design.

Description

Technical Field

[0001] This invention relates to the field of pile foundation design technology, specifically to a method and system for calculating pile foundation length. Background Technology

[0002] As transportation infrastructure extends into cross-river, cross-sea, and deep-water complex areas, bridge and culvert pile foundation engineering faces severe challenges from extreme hydrological disasters. In recent years, engineering-aided design software has been deeply integrated with geotechnical engineering, and automated calculation technology based on parameter extraction from three-dimensional vertical stratigraphic numerical models has gradually replaced traditional manual verification. However, most current computer-aided design systems only handle simple physical mapping between static geological strata and foundation mechanical parameters. When dealing with complex fluid-structure interaction hydrodynamic boundary evolution such as flood erosion, the underlying algorithms of existing software still have significant technical limitations.

[0003] In the prior art, CN111274633A discloses a method for calculating pile foundation length. This technique uses a target vertical stratum layered numerical model to load pile foundation bearing capacity parameters onto multiple soil layers, obtains pile foundation information, and calculates the intersection points of virtual pile foundation rays with each soil layer. This determines the pile length and bearing capacity of each virtual pile foundation. Finally, a piecewise function is constructed to inversely calculate the shortest pile length that satisfies the target bearing capacity. This scheme achieves automated calculation of the axial bearing capacity of a single pile based on the static geometric slice characteristics of pure underground soil and rock space.

[0004] The aforementioned existing technologies only perform static physical calculations on the isolated geometric parameters of a single pile, which has the following technical shortcomings: They fail to incorporate the coupled evolution of hydrological extreme parameters and the water-blocking characteristics of the pier, and neglect the problem of riverbed physical boundary incision caused by flood erosion. Furthermore, the existing technologies do not include the effective stress loss and nonlinear degradation mechanism of the underlying layer caused by the stripping and unloading of the overlying soil. This static and rigid algorithm results in a dangerously high output pile bearing capacity under severe hydrological disaster conditions, failing to provide a safe pile length that conforms to the actual physical failure limit.

[0005] The information disclosed in the background section is only intended to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for calculating pile foundation length, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for calculating the length of a pile foundation, comprising the following steps:

[0009] Step 1: Obtain the historical hydrological dataset of the water area for the bridge pier design parameters. Analyze the historical hydrological dataset using the method of moments to calculate the maximum flow velocity and the highest water level under the preset return period, thus forming environmental characteristic parameters.

[0010] Step 2: Based on the environmental characteristic parameters and the preset water-blocking characteristic parameters of the bridge piers, calculate the maximum scour depth of the riverbed soil under the continuous action of the flood with the preset return period, and use the maximum scour depth of the riverbed soil as the scour reference surface.

[0011] Step 3: Remove the scoured soil from the vertical strata layering numerical model based on the scour reference surface, and reconstruct the effective stress field of the underlying soil layer along the depth direction according to the stress release law.

[0012] Step 4: Based on the effective stress field, starting from the scour reference surface, fit the side friction of the underlying soil layer at different depths to obtain the side friction corresponding to each depth.

[0013] Step 5: Based on the preset initial pile foundation depth, obtain the comprehensive resistance of a single pile at the corresponding depth. Iterate the pile foundation depth according to the preset iteration step size, adjust the pile foundation depth one by one and recalculate the comprehensive resistance of a single pile. When the comprehensive resistance of a single pile is greater than or equal to the preset load safety threshold for the first time, and the bottom of the pile foundation extends below the maximum scour depth, stop the iteration and output the pile foundation depth of the current iteration as the optimal pile foundation length.

[0014] Furthermore, the pier design parameters include the ultimate end resistance of the pile bearing layer and the pile bottom radius;

[0015] The historical hydrological dataset consists of the maximum flow velocity sequence and the highest water level sequence for each year within a preset time period.

[0016] The distribution location parameters of the annual maximum flow velocity sequence are obtained by first-order moment estimation, and the distribution scale parameters of the annual maximum flow velocity sequence are obtained by second-order moment estimation.

[0017] Based on the location and scale parameters of the maximum flow velocity sequence over the years, and combined with the preset return period, the maximum flow velocity under the given return period is obtained using the Gumbel extreme value distribution theory formula.

[0018] Furthermore, the distribution location parameters of the historical highest water level sequence are obtained by performing first-order moment estimation on the historical highest water level sequence, and the distribution scale parameters of the historical highest water level sequence are obtained by performing second-order moment estimation on the historical highest water level sequence.

[0019] Based on the distribution location parameters and distribution scale parameters of the historical highest water level sequence, and combined with the preset return period, the highest water level under the given return period is obtained using the Gumbel extreme value distribution theory formula.

[0020] The environmental characteristic parameters are the maximum flow velocity and the highest water level under the preset return period.

[0021] Furthermore, the preset water-blocking characteristic parameters of the bridge pier include the comprehensive correction coefficient of the bridge pier, the width of the bridge pier, the constraint constant of the influence of water depth, the critical flow velocity for sediment initiation, and the flow velocity intensity decay index.

[0022] Based on environmental characteristic parameters and preset bridge pier water-blocking characteristic parameters, the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period is calculated using the following formula:

[0023]

[0024] in, This indicates the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period. This represents the preset comprehensive correction coefficient for the bridge piers. Indicates the width of the bridge pier. This represents the preset water depth influence constraint constant. This represents the preset flow rate intensity attenuation index. This indicates the preset critical velocity for sediment initiation. This indicates the maximum flow rate under the preset return period. This indicates the highest water level under the preset return period.

[0025] Furthermore, the specific logic of step 3 is as follows:

[0026] Using the scour reference surface as the geometric division reference, the soil medium within the depth range from 0 to the scour reference surface is removed in the preset vertical depth coordinate system. For the underlying soil layer below the scour reference surface, the effective unit weight of the soil is calculated vertically along the preset vertical depth coordinate system. The scour reference surface is used as the lower limit of integration, the preset vertical depth coordinate is used as the upper limit of integration, and the vertical depth is used as the integration variable. The preset first integrand is vertically integrated to calculate the effective stress at different vertical depth coordinates, thereby obtaining the effective stress field of the underlying soil layer corresponding to different vertical depth coordinates.

[0027] The first integrand is the effective unit weight of the soil at different vertical depths.

[0028] Furthermore, the side friction resistance at each depth is calculated using the following formula:

[0029]

[0030] in, Side friction at the vertical depth coordinate z, This represents the preset vertical depth coordinates, where the value of the vertical depth coordinate z is greater than the depth corresponding to the scour reference surface value. , This indicates the preset pile-soil lateral pressure coefficient. Represents the vertical depth coordinates Effective stress at the point, This indicates the preset pile-soil interface friction angle. Represents the base of the natural logarithm. This represents the preset unloading degradation sensitivity coefficient. This represents the preset stress recovery rate constant.

[0031] Furthermore, the preset axial load of the bridge and culvert structure design is multiplied by the structural importance safety factor, and the result is used as the preset load safety threshold.

[0032] Furthermore, based on the side friction resistance at different depths, the scour reference surface is used as the lower limit of integration, the depth of the pile bottom is used as the upper limit of integration, and the vertical depth coordinate is used as the integration variable. The preset second integrand is integrated to obtain the total bearing capacity of the side friction resistance. The preset ultimate end resistance of the pile end bearing layer is multiplied by the preset cross-sectional area of ​​the pile bottom to obtain the total bearing capacity of the pile end. The total bearing capacity of the side friction resistance is added to the total bearing capacity of the pile end to obtain the comprehensive resistance of a single pile.

[0033] The cross-sectional area of ​​the pile bottom is equal to the product of pi and the square of the pile bottom radius;

[0034] The pre-defined second integrand is the product of the pile section perimeter and the side friction at different depths;

[0035] The perimeter of the pile body is equal to the product of twice pi and the radius of the pile bottom.

[0036] To achieve the above objectives, the present invention also provides the following technical solution:

[0037] A pile foundation length calculation system, the system being used to execute the pile foundation length calculation method described in any one of the preceding claims, comprising:

[0038] Environment extraction module: Obtains historical hydrological datasets of the water area for bridge pier design parameters, analyzes the historical hydrological datasets using the method of moments, calculates the maximum flow velocity and highest water level under the preset return period, and forms environmental characteristic parameters;

[0039] Boundary definition module: Based on environmental characteristic parameters and preset bridge pier water-blocking characteristic parameters, calculate the maximum scour depth of the riverbed soil under the continuous action of floods with a preset return period, and use the maximum scour depth of the riverbed soil as the scour reference surface.

[0040] Stress field reconstruction module: Based on the scour reference plane, remove the scoured soil in the vertical strata layer numerical model, and reconstruct the effective stress field of the underlying soil layer along the depth direction according to the stress release law.

[0041] Resistance calculation module: Based on the effective stress field, starting from the scour reference surface, the side friction of the underlying soil layer at different depths is fitted to obtain the side friction corresponding to each depth;

[0042] Pile Length Optimization Module: Based on the preset initial pile foundation depth, obtain the comprehensive resistance of a single pile at the corresponding depth. Iteratively calculate the pile foundation depth according to the preset iteration step size, adjust the pile foundation depth one by one and recalculate the comprehensive resistance of a single pile. When the comprehensive resistance of a single pile is greater than or equal to the preset load safety threshold for the first time, and the bottom of the pile foundation extends below the maximum scour depth, stop the iteration and output the pile foundation depth of the current iteration as the optimal pile foundation length.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] This invention calculates the maximum flow velocity and highest water level within a preset return period based on historical hydrological datasets to form environmental characteristic parameters. These environmental characteristic parameters are then integrated with preset water-blocking characteristic parameters of bridge piers. Utilizing a nonlinear evolution model with energy dissipation constraints, the maximum scour depth of the riverbed soil under continuous flood action is accurately calculated and defined as the scour reference surface. This calculation mechanism overcomes the limitations of existing technologies that rely solely on static underground physical slices for calculation, and addresses the technical challenge of significant downcutting of the riverbed physical boundary caused by flood scour in flowing water. By integrating the water-blocking conditions of bridge piers with hydrodynamic evolution, it avoids the failure of the safety calculation reference due to neglecting the destructive effects of floods, thus providing a starting boundary that conforms to the actual hydrophysical limits for subsequent resistance calculations.

[0045] This invention also involves peeling away the scoured soil in a vertically layered numerical model based on a scour reference surface, reconstructing the effective stress field of the underlying soil layer below the scour reference surface according to stress release logic, and then calculating the side friction at different depths using pile-soil interface mechanics criteria and nonlinear strength attenuation logic. Under the constraint of satisfying a preset load safety threshold, a dynamic step-size iterative algorithm is used to obtain the optimal pile length that makes the comprehensive resistance of a single pile greater than or equal to the preset load safety threshold for the first time. This technical solution overcomes the computational deficiency of existing technologies that do not consider the stress release effect, quantifies the loss of effective stress in the underlying layer and the nonlinear degradation of side friction caused by the stripping and unloading of the overlying soil, and eliminates the hidden danger of the pile bearing capacity assessment being biased towards danger due to static rigid algorithms under severe disaster conditions by combining dynamic optimization, outputting the optimal pile length under the true physical failure limit. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the overall method flow of the present invention;

[0047] Figure 2 This is a schematic diagram of the overall system structure of the present invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0049] It should be noted that, unless otherwise defined, the technical or scientific terms used in this invention should have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0050] Example:

[0051] Please see Figure 1 The present invention provides a technical solution:

[0052] A method for calculating the length of a pile foundation, comprising the following steps:

[0053] Step 1: Obtain the historical hydrological dataset of the water area for the bridge pier design parameters. Analyze the historical hydrological dataset using the method of moments to calculate the maximum flow velocity and the highest water level under the preset return period, thus forming environmental characteristic parameters.

[0054] In this example, the pier design parameters include the ultimate end resistance of the pile bearing layer and the pile bottom radius;

[0055] The preset return period refers to the average probability period of hydrological extreme events pre-set according to relevant national bridge and culvert hydrological design specifications, combined with the importance level and design service life of the bridge and culvert structure. The ultimate end resistance of the pile bearing layer is obtained by combining the geological survey report during the detailed exploration stage of the construction site with standard penetration tests. It represents the maximum vertical support pressure that the deep stable bearing soil layer can provide to the pile end. The pile bottom radius is obtained by directly extracting and setting it according to the structural design drawings of the bridge and culvert foundation, and serves as the benchmark geometric parameter for subsequent calculation of the pile bottom cross-sectional area.

[0056] The historical hydrological dataset consists of the maximum flow velocity sequence and the highest water level sequence for each year within a preset time period.

[0057] The distribution location parameters of the annual maximum flow velocity sequence are obtained by first-order moment estimation, and the distribution scale parameters of the annual maximum flow velocity sequence are obtained by second-order moment estimation.

[0058] Based on the distribution location parameters and distribution scale parameters of the maximum flow velocity sequence over the years, and combined with the preset return period, the maximum flow velocity under the return period is obtained using the Gumbel extreme value distribution theory formula.

[0059] The distribution location parameters of the historical highest water level sequence are obtained by performing first-order moment estimation on the historical highest water level sequence, and the distribution scale parameters of the historical highest water level sequence are obtained by performing second-order moment estimation on the historical highest water level sequence.

[0060] Based on the distribution location parameters and distribution scale parameters of the historical highest water level sequence, and combined with the preset return period, the highest water level under the given return period is obtained using the Gumbel extreme value distribution theory formula.

[0061] The environmental characteristic parameters are the maximum flow velocity and the highest water level under the preset return period.

[0062] Building upon the above, it is important to note that to establish accurate initial input conditions for hydrodynamic calculations, it is essential to extract the historical maximum flow velocity and highest water level sequences generated over a predetermined period. Given that the service life of large infrastructure projects such as bridges and culverts typically extends to decades or even centuries, simply applying absolute maximum values ​​from historical records cannot effectively cover the low-probability flood conditions that may occur during the structure's future lifespan. Therefore, the collected time-series data must be transformed into maximum flow velocity and highest water level data within a predetermined return period. This calibrates the random, accidental historical events to a safety baseline that aligns with the project's importance level, thus endowing the hydrological input parameters with forward-looking probabilistic predictive value.

[0063] When performing this probability extrapolation transformation, the Gumbel extreme value distribution theory formula is chosen because annual extreme value data such as the maximum flow velocity and the highest water level naturally conform to the asymptotic characteristics of the extreme value type I distribution. The Gumbel extreme value distribution theory formula can deeply integrate the distribution location parameters and distribution scale parameters extracted by the method of moments, accurately capture the long-tail hazard probability of rare flood events, and thus scientifically quantify and deduce the maximum flow velocity and the highest water level under the preset return period using limited historical samples.

[0064] This data processing method eliminates the blindness of static value taking that relies on subjective amplification based on human experience in traditional engineering design. It constructs a high-fidelity dynamic environmental boundary for subsequent simulation of the maximum scour depth of the riverbed soil under the continuous action of floods, effectively preventing the hidden danger of overestimation of bearing capacity caused by distortion of initial hydrological parameters, and ensuring that the final output of the optimal pile foundation length can meet the flood control mechanical safety requirements under real working conditions.

[0065] Step 2: Based on the environmental characteristic parameters and the preset water-blocking characteristic parameters of the bridge piers, calculate the maximum scour depth of the riverbed soil under the continuous action of the flood with the preset return period, and use the maximum scour depth of the riverbed soil as the scour reference surface.

[0066] In this example, the preset water-blocking characteristic parameters of the bridge pier include the comprehensive correction coefficient of the bridge pier, the width of the bridge pier, the water depth influence constraint constant, the critical flow velocity for sediment initiation, and the flow velocity intensity decay index.

[0067] Based on environmental characteristic parameters and preset bridge pier water-blocking characteristic parameters, the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period is calculated using the following formula:

[0068]

[0069] in, This indicates the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period. This represents the preset comprehensive correction coefficient for the bridge pier, determined by referring to tables based on the actual geometry of the designed bridge pier and the angle of attack of the water flow, according to the current industry standard "Specifications for Hydrological Survey and Design of Highway Engineering". The width of the pier is determined based on the physical width of the pier's upstream face in the bridge and culvert foundation design drawings. If it is a pile foundation, the equivalent water-blocking width is calculated using a reduction factor according to the "Specifications for Hydrological Survey and Design of Highway Engineering" and is used as the calculated width of the pier. This represents a preset water depth influence constraint constant, obtained based on historical physical flume model experimental data or regional measured hydrological data of the target water area. It is used to control the convergence rate of scour depth with increasing water depth under shallow water conditions. Its physical nature is related to the angle of repose of the riverbed and the Froude number of the flow. A typical value is 1.0, but it can also be calibrated within the range of 0.8 to 1.5 based on physical flume model experimental data or regional measured hydrological data of the target water area. This represents the preset flow velocity intensity attenuation index, set according to the physical relationship between kinetic energy dissipation and head loss in fluid mechanics. Specifically, it is set to 0.5, characterizing the square root nonlinear attenuation law of the conversion of local scouring kinetic energy into mechanical energy in water flow. This represents the preset critical velocity for sediment initiation, taken from the median particle size of the surface sediment in the riverbed provided in the engineering site exploration report, and calculated by substituting it into the classical empirical formula for initiation velocity in sediment dynamics. This is the critical physical threshold for riverbed erosion resistance. This indicates the maximum flow rate under the preset return period. This indicates the highest water level under the preset return period.

[0070] Based on the above, it should be noted that in the design of bridge and culvert projects spanning waterways, the physical water-blocking surface of the bridge pier structure forces the flowing water to generate rapid kinetic energy conversion and downward vortices, thereby inducing severe stripping and erosion of the riverbed soil around the bridge pier. Therefore, calculating the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period is of significant engineering necessity. If the dynamic incision of the boundary caused by the above-mentioned hydrodynamic erosion effect is ignored, it will directly lead to the model overestimating the lateral wrapping support effect of the shallow soil on the pile foundation, thus severely amplifying the frictional bearing capacity of the pile foundation. Establishing the calculated maximum scour depth as the scour reference surface can effectively overcome the technical limitations of traditional geotechnical calculations that adhere to static underground geometric interfaces, truly quantify the degree of reshaping of the physical boundary of the soil layer by the destructive effect of water flow, and provide a starting boundary that conforms to the physical extreme values ​​of extreme hydrological disasters for subsequent effective stress reconstruction and lateral friction reduction, eliminating the hidden danger of the bearing capacity assessment being biased under rigid algorithms.

[0071] To accurately reflect this fluid-structure interaction evolution process, this scheme constructs a nonlinear calculation formula with an energy dissipation constraint mechanism. The maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period, which serves as the solution result of the formula, quantitatively characterizes the vertical spatial coordinates at the point where the potential energy of water erosion and the scour resistance of the riverbed soil reach final dynamic equilibrium under extreme catastrophic conditions with a set probability. Its core technical effect lies in establishing a stripping zero point that conforms to the actual physical loss state for the integral calculation of the comprehensive resistance of a single pile. The formation mechanism of this maximum scour depth is driven by the deep coupling of multiple hydrodynamic parameters and water-blocking parameters. Specifically, the maximum flow velocity under the preset return period represents the initial kinetic energy of flood impact erosion; the pier comprehensive correction coefficient and the pier width jointly determine the local vortex intensity and scour disturbance geometry generated after the water flow is blocked; and the highest water level under the preset return period constrains the downward transmission and dissipation of water kinetic energy in the deep water environment through a hyperbolic tangent function. Simultaneously, the preset critical velocity for sediment initiation acts as the natural mechanical defense threshold for the riverbed particles to resist water stripping.

[0072] At the level of numerical function constraint logic, the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period shows a significant positive correlation with the maximum flow velocity, the highest water level, the pier width, and the comprehensive correction coefficient of the pier under the preset return period. This means that the faster the flood flow, the higher the water level, and the wider the water-blocking section of the pier, the stronger the downward scouring and destructive force of the water flow, and the deeper the ultimate depth of the riverbed being eroded. Conversely, the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period shows a clear negative correlation constraint characteristic with the preset critical velocity for sediment initiation. That is, the higher the physical threshold of the surface sediment particles of the riverbed, the stronger the soil's ability to resist water erosion, and the shallower the physical depth of scour and incision.

[0073] Step 3: Remove the scoured soil from the vertical strata layering numerical model based on the scour reference surface, and reconstruct the effective stress field of the underlying soil layer along the depth direction according to the stress release law.

[0074] In this example, the specific logic of step 3 is as follows:

[0075] Using the scour reference surface as the geometric division reference, the soil medium within the depth range from 0 to the scour reference surface is removed in the preset vertical depth coordinate system. For the underlying soil layer below the scour reference surface, the effective unit weight of the soil is calculated vertically along the preset vertical depth coordinate system. The scour reference surface is used as the lower limit of integration, the preset vertical depth coordinate is used as the upper limit of integration, and the vertical depth is used as the integration variable. The preset first integrand is vertically integrated to calculate the effective stress at different vertical depth coordinates, thereby obtaining the effective stress field of the underlying soil layer corresponding to different vertical depth coordinates.

[0076] The first integrand is the effective unit weight of the soil at different vertical depths, and the vertical depth coordinates are obtained through the coordinate system of the preset vertical stratum numerical model.

[0077] Based on the above, it should be noted that after determining the scour reference surface, reconstructing the effective stress field of the underlying soil layer along the depth direction constitutes the necessary mechanical premise for accurately assessing the true bearing capacity of the foundation after extreme disasters. Since the flood erodes the surface soil around the bridge pier, the underlying soil layer will undergo a significant reduction in self-weight pressure and physical unloading process. If the initial static vertical stratification numerical model is continued to be used, the frictional normal stress of the bottom layer will be seriously overestimated. Therefore, by using the scour reference surface as the geometric division reference to completely remove the scoured soil and recalculate the stress, the dynamic evolution law of the stress state of the soil skeleton under disaster conditions can be truly restored, which has extremely rigorous geotechnical physical and mechanical rationality.

[0078] To accurately realize this stress reconstruction process, this method constructs a vertical depth integral calculation formula. The effective stress obtained at different vertical depth coordinates directly reflects the real vertical normal pressure remaining on the soil skeleton at any specific depth in the underlying soil layer after being unloaded by water flow. Its core technical effect lies in accurately eliminating the ineffective self-weight of the lost overlying soil, providing a bottom-level normal force benchmark for subsequent scientific deduction of the nonlinear degradation of pile side friction. The integral calculation logic of this effective stress is strictly controlled by multiple spatial depth and medium property parameters. Since the soil above the scour reference surface has been completely stripped away by water flow and has completely lost its compressive effect on the underlying strata, the calculation forces the scour reference surface as the lower limit starting point of the vertical depth integral calculation. At the same time, the vertical depth is used as the integration variable, and the first integrand representing the effective unit weight of the soil at different vertical depths is continuously accumulated spatially, thereby transforming the discretely distributed layered geological parameters into a continuously changing dynamic stress field.

[0079] Regarding the specific functional constraints, the effective stress at different vertical depth coordinates shows a significant positive correlation with both the preset vertical depth coordinate (which serves as the upper limit of integration) and the effective unit weight of the soil (representing material density). This means that the deeper the vertical depth of the target calculation point, the greater the thickness of the effective soil layer above it involved in the accumulation. Furthermore, the higher the effective unit weight of the corresponding stratum, the higher the effective stress accumulated along the depth direction. Conversely, this effective stress exhibits an absolute negative correlation with the scour reference surface's indentation elevation. This implies that the greater the depth of the scour reference surface caused by flooding, the more overlying soil is stripped and removed, resulting in a significant compression of the overall integration interval. Consequently, the overburden stress obtainable from the remaining soil layers at the same absolute ground elevation decreases.

[0080] Step 4: Based on the effective stress field, starting from the scour reference surface, fit the side friction of the underlying soil layer at different depths to obtain the side friction corresponding to each depth.

[0081] In this example, the formula used to calculate the side friction at each depth is:

[0082]

[0083] in, Side friction at the vertical depth coordinate z, This represents the preset vertical depth coordinates, where the vertical depth coordinates are... The value is greater than the depth corresponding to the scour reference surface value. , This represents the preset pile-soil lateral pressure coefficient, set through the pile-forming process, indicating the lateral pressure effect of pile foundation construction on the surrounding soil. This represents the effective stress at the vertical depth coordinate z. This represents the preset pile-soil interface friction angle, obtained from the indoor geotechnical direct shear test report. Represents the base of the natural logarithm. This represents the preset unloading degradation sensitivity coefficient. It is determined by extracting undisturbed soil samples at the corresponding elevation and conducting indoor triaxial stress path unloading tests to simulate the overlying self-weight stress of the in-situ soil. Subsequently, the axial confining pressure is reduced according to the unloading amount calculated in step three, and the attenuation rate of the soil's undrained shear strength is measured to calibrate this parameter. For highly sensitive soft soils, a typical value is 0.40 to 0.50; for general cohesive soils, a typical value is 0.20 to 0.30; for soils with special structures, a typical value is 0.35 to 0.45; for dense, non-cohesive soils, the value ranges from 0.10 to 0.20; and for hard rock and soil, a typical value is 0.05 to 0.10. The preset stress recovery rate constant is obtained by inversion fitting of the static load test curve after on-site preloading and unloading. The preset stress recovery rate constant value is closely related to the elastic resilient modulus and lateral pressure coefficient of the soil, and follows the stress diffusion and attenuation law of elastic half-space. For soft plastic soil layers, the typical value is 0.2 to 0.4; for medium stiff soil layers, the typical value is 0.4 to 0.6; for special structural soils, the typical value is 0.5 to 0.7; and for hard and stiff soil layers, the typical value is 0.6 to 1.0.

[0084] Based on the above, it should be noted that after reconstructing the effective stress field of the underlying soil layer, the in-depth calculation of the side friction at the vertical depth coordinate constitutes a necessary calculation step for accurately quantifying the degree of degradation of the foundation bearing capacity. This is because the vertical compressive strength of the bridge pier piles is highly dependent on the frictional support provided by the soil on the pile side. The loss of surface soil caused by floods not only weakens the normal overburden force of the underlying layer, but also causes nonlinear structural relaxation and strength reduction of the underlying soil skeleton due to the release of self-weight stress. If this unloading damage mechanism is ignored, the bearing capacity will be dangerously overestimated. Therefore, introducing nonlinear strength decay logic to calculate the frictional resistance layer by layer can truly depict the frictional mechanical damage state of the pile-soil interface under flood conditions, which has significant physical necessity and engineering disaster prevention value.

[0085] To reproduce this frictional degradation process, this method constructs a nonlinear calculation formula for side friction resistance starting from the scour reference surface. The side friction resistance at the vertical depth coordinate, as the dependent variable, quantifies the true ultimate frictional resistance provided by the pile-soil interface at a specific elevation after extreme scour unloading. Its core technical advantage lies in providing high-fidelity discrete mechanical parameters for the subsequent integral calculation of the overall resistance of a single pile. This side friction resistance value is controlled by the deep coupling of the interface foundation mechanical parameters and the nonlinear unloading factor. Specifically, the effective stress at the vertical depth coordinate z, combined with the preset pile-soil lateral pressure coefficient, jointly determines the normal stress base plate acting on the pile under the soil squeezing effect. The preset pile-soil interface friction angle determines the theoretical conversion rate of this normal stress into shear friction force. Simultaneously, the preset unloading degradation sensitivity coefficient characterizes the mechanical sensitivity of specific soils to relaxation and softening due to the disappearance of overlying loads. The preset stress recovery rate constant and the exponential decay term composed of the physical relative depth constrain the spatial diffusion law of this unloading damage gradually decaying and healing from shallow to deep.

[0086] In terms of specific functional constraints, the lateral friction resistance at the vertical depth coordinate exhibits an absolute positive correlation with the preset pile-soil lateral pressure coefficient, the effective stress at the vertical depth coordinate, and the preset pile-soil interface friction angle. This means that the stronger the lateral compression of the soil around the pile, the greater the residual effective overburden force, and the rougher the contact surface, the more sufficient the generated frictional resistance. Conversely, this lateral friction resistance shows a negative correlation with the preset unloading degradation sensitivity coefficient, implying that the more sensitive the soil is to unloading disturbances, the more severe the frictional strength reduction caused by the destruction of its internal microstructure. Furthermore, this lateral friction resistance exhibits a nonlinear positive correlation evolution characteristic with the vertical depth coordinate z. That is, the deeper the target calculation point is from the scour reference surface, the weaker the soil relaxation damage effect caused by unloading becomes as the exponential function converges, and the soil frictional strength gradually recovers to its initial state before disturbance, thus providing higher lateral frictional resistance for the pile.

[0087] Step 5: Based on the preset initial pile foundation depth, obtain the comprehensive resistance of a single pile at the corresponding depth. Iterate the pile foundation depth according to the preset iteration step size, adjust the pile foundation depth one by one and recalculate the comprehensive resistance of a single pile. When the comprehensive resistance of a single pile is greater than or equal to the preset load safety threshold for the first time and the bottom of the pile foundation extends below the maximum scour depth, stop the iteration and output the pile foundation depth of the current iteration as the optimal pile foundation length.

[0088] In this example, the preset axial load of the bridge and culvert structure design is multiplied by the preset structural importance safety factor, and the result is used as the preset load safety threshold.

[0089] Among them, the preset axial load of the bridge and culvert structure design is set according to the preset input value of the combination of dead load and live load of the bridge and culvert superstructure design, and the preset structural importance safety factor is set according to the national mandatory specifications.

[0090] Based on the side friction resistance at different depths, the scour reference surface is used as the lower limit of integration, the preset initial pile foundation depth is used as the upper limit of integration, and the vertical depth coordinate is used as the integration variable. The preset second integrand is integrated to obtain the total bearing capacity of the side friction resistance. The preset ultimate end resistance of the pile tip bearing layer is multiplied by the preset cross-sectional area of ​​the pile bottom to obtain the total bearing capacity of the pile tip. The total bearing capacity of the side friction resistance is added to the total bearing capacity of the pile tip to obtain the comprehensive resistance of a single pile.

[0091] The cross-sectional area of ​​the pile bottom is equal to the product of pi and the square of the pile bottom radius;

[0092] The pre-defined second integrand is the product of the pile section perimeter and the side friction at different depths;

[0093] Among them, the perimeter of the pile body section is equal to the product of twice pi and the radius of the pile bottom;

[0094] The preset second integrand is the product of the pile section perimeter and the side friction at different depths;

[0095] The formula used to calculate the comprehensive resistance of a single pile is as follows:

[0096]

[0097]

[0098]

[0099] in, This represents the overall resistance of a single pile at a preset initial pile depth. This indicates the total bearing capacity of the side friction resistance. Indicates the total bearing capacity at the pile tip. This indicates the preset initial pile foundation depth. This represents the ultimate end resistance of the pile bearing layer, based on the preset evaluation parameters given in the geological survey report for deep stable bearing soil layers. This represents the cross-sectional area at the pile base, determined according to the bridge and culvert foundation design drawings. This indicates the perimeter of the pile cross-section, which is set according to the bridge and culvert foundation design drawings.

[0100] Input the preset initial pile foundation depth into the calculation formula of single pile comprehensive resistance to obtain the single pile comprehensive resistance, and compare the single pile comprehensive resistance with the preset load safety threshold.

[0101] If the overall resistance of a single pile is less than the preset load safety threshold, the preset initial pile foundation depth is increased according to the preset iteration step size and recalculated and compared until the overall resistance of a single pile after iteration is greater than or equal to the preset load safety threshold for the first time. Then, the pile foundation depth after the last iteration is taken as the optimal pile foundation length.

[0102] The preset initial pile foundation depth is set by relevant personnel in the field based on preliminary estimates of architectural design requirements, and the preset iteration step size is set by relevant personnel in the field based on actual engineering accuracy requirements.

[0103] Based on the above, it should be noted that after obtaining the distribution of lateral friction at different depths, the optimal pile length that satisfies the safety constraints is determined by a dynamic step-size iterative algorithm, constituting the decision-making output of the entire calculation scheme. Since engineering practice must ensure that the compressive strength provided by the piles is sufficient to withstand the design load transmitted from the superstructure, and that there is still a sufficient safety reserve after complex hydrological disasters, calculating the comprehensive resistance of a single pile by continuously accumulating the lateral friction contribution of the pile body and superimposing the bearing layer support force at the pile tip can directly determine whether the optimal pile length has reached the critical requirement for mechanical stability, thus possessing significant computational necessity.

[0104] The core significance of finding the physical depth that ensures the comprehensive resistance of a single pile is at a safe critical state through a dynamic step-size iterative algorithm lies in transforming all the aforementioned hydrological environment vectors, effective stress fields, and interface friction degradation parameters into the final engineering design indicators. The output optimal pile foundation length quantitatively represents the physical limit depth that can both maintain the flood control safety baseline and avoid over-design under the dual effects of flood scouring and soil unloading damage. In terms of specific numerical synthesis logic, the comprehensive resistance of a single pile is composed of the total bearing capacity of the side friction along the pile foundation depth and the total bearing capacity of the pile tip. The total bearing capacity of the side friction depends on the side friction along the preset initial pile foundation depth, while the total bearing capacity of the pile tip is controlled by the ultimate end resistance of the bearing layer at the pile tip and the cross-sectional area of ​​the pile bottom.

[0105] At the level of dynamic optimization function constraints, the overall resistance of a single pile exhibits an absolute positive correlation with the preset initial pile depth. This means that as the pile extends deeper into stable strata, the accumulated lateral friction area along its path increases, thereby driving a continuous rise in the overall resistance value. When the overall resistance of a single pile increases with pile depth and first crosses the aforementioned load safety threshold, the locked optimal pile length possesses rigorous mechanical rationality. This is because, while ensuring that the bottom of the pile extends below the maximum scour depth, it accurately captures the minimum physical depth that meets safety requirements. This effectively solves the problem of resource waste caused by excessive design redundancy in flowing water environments, achieving a balance between mechanical safety and engineering economy.

[0106] Please see Figure 2The present invention also provides a pile foundation length calculation system, the system being used to execute the pile foundation length calculation method described in any of the above claims, comprising:

[0107] Environment extraction module: Obtains historical hydrological datasets of the water area for bridge pier design parameters, analyzes the historical hydrological datasets using the method of moments, calculates the maximum flow velocity and highest water level under the preset return period, and forms environmental characteristic parameters;

[0108] Boundary definition module: Based on environmental characteristic parameters and preset bridge pier water-blocking characteristic parameters, calculate the maximum scour depth of the riverbed soil under the continuous action of floods with a preset return period, and use the maximum scour depth of the riverbed soil as the scour reference surface.

[0109] Stress field reconstruction module: Based on the scour reference plane, remove the scoured soil in the vertical strata layer numerical model, and reconstruct the effective stress field of the underlying soil layer along the depth direction according to the stress release law.

[0110] Resistance calculation module: Based on the effective stress field, starting from the scour reference surface, the side friction of the underlying soil layer at different depths is fitted to obtain the side friction corresponding to each depth;

[0111] Pile Length Optimization Module: Based on the preset initial pile foundation depth, obtain the comprehensive resistance of a single pile at the corresponding depth. Iteratively calculate the pile foundation depth according to the preset iteration step size, adjust the pile foundation depth one by one and recalculate the comprehensive resistance of a single pile. When the comprehensive resistance of a single pile is greater than or equal to the preset load safety threshold for the first time, and the bottom of the pile foundation extends below the maximum scour depth, stop the iteration and output the pile foundation depth of the current iteration as the optimal pile foundation length.

[0112] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0113] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented in software, the above embodiments can be implemented, in whole or in part, as a computer program product. Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution.

[0114] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment, depending on actual needs.

[0115] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for calculating the length of a pile foundation, characterized in that, The specific steps include: Step 1: Obtain the historical hydrological dataset of the water area for the bridge pier design parameters. Analyze the historical hydrological dataset using the method of moments to calculate the maximum flow velocity and the highest water level under the preset return period, thus forming environmental characteristic parameters. Step 2: Based on the environmental characteristic parameters and the preset water-blocking characteristic parameters of the bridge piers, calculate the maximum scour depth of the riverbed soil under the continuous action of the flood with the preset return period, and use the maximum scour depth of the riverbed soil as the scour reference surface. Step 3: Remove the scoured soil from the vertical strata layering numerical model based on the scour reference surface, and reconstruct the effective stress field of the underlying soil layer along the depth direction according to the stress release law. Step 4: Based on the effective stress field, starting from the scour reference surface, fit the side friction of the underlying soil layer at different depths to obtain the side friction corresponding to each depth. Step 5: Based on the preset initial pile foundation depth, obtain the comprehensive resistance of a single pile at the corresponding depth. Iterate the pile foundation depth according to the preset iteration step size, adjust the pile foundation depth one by one and recalculate the comprehensive resistance of a single pile. When the comprehensive resistance of a single pile is greater than or equal to the preset load safety threshold for the first time, and the bottom of the pile foundation extends below the maximum scour depth, stop the iteration and output the pile foundation depth of the current iteration as the optimal pile foundation length.

2. The method for calculating the length of a pile foundation according to claim 1, characterized in that: The pier design parameters include the ultimate end resistance of the bearing stratum at the pile tip and the pile bottom radius; The historical hydrological dataset consists of the maximum flow velocity sequence and the highest water level sequence for each year within a preset time period. The distribution location parameters of the annual maximum flow velocity sequence are obtained by first-order moment estimation, and the distribution scale parameters of the annual maximum flow velocity sequence are obtained by second-order moment estimation. Based on the location and scale parameters of the maximum flow velocity sequence over the years, and combined with the preset return period, the maximum flow velocity under the given return period is obtained using the Gumbel extreme value distribution theory formula.

3. The method for calculating the length of a pile foundation according to claim 2, characterized in that: The distribution location parameters of the historical highest water level sequence are obtained by performing first-order moment estimation on the historical highest water level sequence, and the distribution scale parameters of the historical highest water level sequence are obtained by performing second-order moment estimation on the historical highest water level sequence. Based on the distribution location parameters and distribution scale parameters of the historical highest water level sequence, and combined with the preset return period, the highest water level under the given return period is obtained using the Gumbel extreme value distribution theory formula. The environmental characteristic parameters are the maximum flow velocity and the highest water level under the preset return period.

4. The method for calculating the length of a pile foundation according to claim 1, characterized in that: The preset water-blocking characteristic parameters of the bridge piers include the comprehensive correction coefficient of the bridge piers, the width of the bridge piers, the constraint constant of the influence of water depth, the critical velocity for sediment initiation, and the velocity intensity decay index. Based on environmental characteristic parameters and preset bridge pier water-blocking characteristic parameters, the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period is calculated using the following formula: in, This indicates the maximum scour depth of the riverbed soil under the continuous action of a flood with a preset return period. This represents the preset comprehensive correction coefficient for the bridge piers. Indicates the width of the bridge pier. This represents the preset water depth influence constraint constant. This represents the preset flow rate intensity attenuation index. This indicates the preset critical velocity for sediment initiation. This indicates the maximum flow rate under the preset return period. This indicates the highest water level under the preset return period.

5. The method for calculating the length of a pile foundation according to claim 1, characterized in that: The specific logic of step 3 is as follows: Using the scour reference surface as the geometric division reference, the soil medium within the depth range from 0 to the scour reference surface is removed in the preset vertical depth coordinate system. For the underlying soil layer below the scour reference surface, the effective unit weight of the soil is calculated vertically along the preset vertical depth coordinate system. The scour reference surface is used as the lower limit of integration, the preset vertical depth coordinate is used as the upper limit of integration, and the vertical depth is used as the integration variable. The preset first integrand is vertically integrated to calculate the effective stress at different vertical depth coordinates, thereby obtaining the effective stress field of the underlying soil layer corresponding to different vertical depth coordinates. The first integrand is the effective unit weight of the soil at different vertical depths.

6. The method for calculating the length of a pile foundation according to claim 5, characterized in that: The formula used to calculate the side friction at each depth is as follows: in, Side friction at the vertical depth coordinate z, This represents the preset vertical depth coordinates, where the value of the vertical depth coordinate z is greater than the depth corresponding to the scour reference surface value. , This indicates the preset pile-soil lateral pressure coefficient. Represents the vertical depth coordinates Effective stress at the point, This indicates the preset pile-soil interface friction angle. Represents the base of the natural logarithm. This represents the preset unloading degradation sensitivity coefficient. This represents the preset stress recovery rate constant.

7. The method for calculating the length of a pile foundation according to claim 1, characterized in that: The product of the preset axial load of the bridge and culvert structure design and the structural importance safety factor is used as the preset load safety threshold.

8. The method for calculating the length of a pile foundation according to claim 7, characterized in that: Based on the side friction resistance at different depths, the scour reference surface is used as the lower limit of integration, the depth of the pile bottom is used as the upper limit of integration, and the vertical depth coordinate is used as the integration variable. The preset second integrand is integrated to obtain the total bearing capacity of the side friction resistance. The preset ultimate end resistance of the pile tip bearing layer is multiplied by the preset cross-sectional area of ​​the pile bottom to obtain the total bearing capacity of the pile tip. The total bearing capacity of the side friction resistance is added to the total bearing capacity of the pile tip to obtain the comprehensive resistance of a single pile. The cross-sectional area of ​​the pile bottom is equal to the product of pi and the square of the pile bottom radius; The pre-defined second integrand is the product of the pile section perimeter and the side friction at different depths; The perimeter of the pile body is equal to the product of twice pi and the radius of the pile bottom.

9. A pile foundation length calculation system, characterized in that: The system is used to execute the pile foundation length calculation method according to any one of claims 1-8, including: Environment extraction module: Obtains historical hydrological datasets of the water area for bridge pier design parameters, analyzes the historical hydrological datasets using the method of moments, calculates the maximum flow velocity and highest water level under the preset return period, and forms environmental characteristic parameters; Boundary definition module: Based on environmental characteristic parameters and preset bridge pier water-blocking characteristic parameters, calculate the maximum scour depth of the riverbed soil under the continuous action of floods with a preset return period, and use the maximum scour depth of the riverbed soil as the scour reference surface. Stress field reconstruction module: Based on the scour reference plane, remove the scoured soil in the vertical strata layer numerical model, and reconstruct the effective stress field of the underlying soil layer along the depth direction according to the stress release law. Resistance calculation module: Based on the effective stress field, starting from the scour reference surface, the side friction of the underlying soil layer at different depths is fitted to obtain the side friction corresponding to each depth; Pile Length Optimization Module: Based on the preset initial pile foundation depth, obtain the comprehensive resistance of a single pile at the corresponding depth. Iteratively calculate the pile foundation depth according to the preset iteration step size, adjust the pile foundation depth one by one and recalculate the comprehensive resistance of a single pile. When the comprehensive resistance of a single pile is greater than or equal to the preset load safety threshold for the first time, and the bottom of the pile foundation extends below the maximum scour depth, stop the iteration and output the pile foundation depth of the current iteration as the optimal pile foundation length.

Images