Method for analyzing uplift bearing capacity of PHC spiral pipe pile based on numerical simulation

Abstract

The invention discloses a method for analyzing the uplift bearing capacity of a PHC spiral pipe pile based on numerical simulation. The method comprises the following steps: vertically screwing a pile body into a designed elevation by adopting intelligent rotary excavating equipment provided with a special drill bit, and monitoring the press-in speed, the rotating speed, the torque and the perpendicularity in real time; recording a press-in resistance-depth curve, a torque-depth curve and pile body perpendicularity data; establishing a three-dimensional refined numerical model containing a real spiral blade, and calibrating soil key parameters through a parameter inversion algorithm to obtain a calibrated numerical model; an anti-pulling load is simulated on the calibrated numerical model, and the ultimate anti-pulling bearing capacity and the failure mode are analyzed; based on a multi-working-condition simulation result, a practical calculation formula of the ultimate uplift bearing capacity is obtained through regression analysis; and model inversion is driven through construction data, refined numerical simulation is combined, the uplift bearing capacity prediction precision is improved, and a reliable basis is provided for the uplift design of the PHC spiral pipe pile.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of geotechnical engineering pile foundation, and specifically discloses a PHC spiral pipe pile uplift bearing capacity analysis method based on numerical simulation. BACKGROUND

[0002] PHC (Prestressed High Strength Concrete) spiral pipe piles have been widely used in various types of building, bridge, wind power foundation and other engineering compression and uplift bearing due to their high pile strength, stable factory production quality, high construction efficiency and other advantages. The spiral blades on the outer wall of the pile can significantly increase the pile-soil contact area and effectively improve the uplift bearing capacity through the mechanical gripping effect with the surrounding soil. It is especially suitable for engineering scenarios that bear large uplift loads. However, the analysis and design of PHC spiral pipe pile uplift bearing capacity still face many challenges. The traditional analysis methods mainly rely on the following ways: Empirical formula method: based on classical soil mechanics theory or regional empirical formula for estimation. Although this method is simple, it often fails to consider the unique reinforcement and anchoring effect of spiral blades. The key parameters in the formula depend on the type and state of the soil, which has great dispersion and regional limitations. It is difficult to accurately reflect the real interaction mechanism between spiral blades and soil under complex geological conditions, resulting in generally low prediction accuracy and conservative or unsafe design.

[0003] Field static load test method: the ultimate bearing capacity is directly determined by conducting uplift static load test on site. The results are the most reliable, but this method is extremely costly, time-consuming, and has obvious point specificity, i.e. the test results only represent the soil conditions at the test point. For large-scale engineering or soil conditions with significant variations, it is difficult to represent the entire site with a limited number of tests, and the economic efficiency and universality are poor.

[0004] Conventional numerical simulation method: with the development of computer technology, numerical methods such as finite element are used to analyze pile bearing capacity. However, existing simulations often have significant simplifications, such as equivalent smooth straight wall pile or simplified equivalent model for spiral pipe pile, which cannot truly reflect the stirring and compaction effect of soil by spiral blades during uplift and the soil arching effect between blades. In addition, the soil constitutive model used in conventional simulation cannot accurately describe the nonlinear behavior of soil under complex stress paths, such as dilatancy and softening, leading to distortion of the simulation of pile-soil interaction and failure mode. More importantly, the soil parameters in the numerical model are usually directly taken from indoor soil test, without considering the significant influence of actual construction process on the stress state and mechanical properties of the soil around the pile, causing the model parameters to deviate from the actual soil conditions, and the calculation results to deviate greatly from the actual situation.

[0005] Therefore, it is necessary to provide a numerical simulation-based PHC spiral pipe pile uplift bearing capacity analysis method to solve the above problems. SUMMARY

[0006] In order to overcome the defects of the prior art, the present application provides a numerical simulation-based PHC spiral pipe pile uplift bearing capacity analysis method, which vertically rotates the pile body to the design elevation by using an intelligent rotary drilling device equipped with a special drill bit, and monitors the penetration speed, rotation speed, torque and verticality in real time; records the penetration resistance-depth curve, torque-depth curve and pile body verticality data; establishes a three-dimensional refined numerical model containing real spiral blades, calibrates the key soil parameters through a parameter inversion algorithm, and obtains a calibrated numerical model; simulates the uplift load on the calibrated numerical model, analyzes the uplift ultimate bearing capacity and failure mode; based on the simulation results of multiple working conditions, the practical calculation formula of the uplift ultimate bearing capacity is obtained through regression analysis, effectively solving the problems mentioned in the background art.

[0007] To achieve the above object, the present application provides the following technical scheme: a numerical simulation-based PHC spiral pipe pile uplift bearing capacity analysis method, specifically comprising the following steps: 1. A numerical simulation-based PHC spiral pipe pile uplift bearing capacity analysis method, characterized in that it specifically comprises the following steps: S1, construction control stage: using an intelligent rotary drilling device with a bidirectional communication interface to rotate the PHC spiral pipe pile; the device is equipped with a special drill bit suitable for the PHC spiral pipe pile, and the penetration speed, rotation speed and torque are monitored and controlled in real time during the construction process, to ensure that the pile body is vertically and uniformly rotated to the design elevation in a nearly synchronous drilling manner; S2, data acquisition and transmission stage: real-time acquisition and recording of the penetration resistance-depth curve, torque-depth curve and pile body verticality data formed in step S1; S3, model building and inversion stage: establishing a three-dimensional refined numerical model of the PHC spiral pipe pile and the surrounding soil containing real spiral blade geometry, and the soil adopts a high-level constitutive model reflecting shear dilation and softening characteristics; using the penetration resistance-depth curve and torque-depth curve obtained in S2 as the target, the key soil parameters in the three-dimensional refined numerical model are automatically calibrated through a parameter inversion algorithm, to obtain a calibrated numerical model consistent with the actual working conditions on site; S4, bearing capacity analysis stage: simulating the uplift load on the calibrated numerical model, extracting the load-displacement curve and soil stress-strain cloud chart, and analyzing the uplift ultimate bearing capacity and failure mode; S5, formula derivation and verification optimization stage: based on the simulation results of different working conditions obtained in S4, combined with the earth pressure balance theory, the practical calculation formula of the ultimate uplift bearing capacity of PHC spiral pipe pile is obtained by regression analysis; and its applicability and accuracy are verified.

[0008] Preferably, the special drill bit is a sleeve type drill bit with a guiding effect and can be reliably connected with the pile end of the PHC spiral pipe pile, and the approximate synchronous drilling refers to controlling the ratio of the penetration speed to the rotation speed, so that the footage of one rotation of the pile body matches the pitch of the spiral blade.

[0009] Preferably, the pile body verticality data includes: real-time measured pile body inclination angle, vertical deviation value and offset direction.

[0010] Preferably, the advanced constitutive model is a hardening soil model, and the key soil parameters include internal friction angle, cohesion and shear dilatancy angle.

[0011] Preferably, the analysis method of the ultimate uplift bearing capacity includes: extracting the ultimate load point from the load-displacement curve, and determining the ultimate uplift bearing capacity by using the inflection point method or the displacement control method.

[0012] Preferably, the analysis method of the failure mode is: identifying the failure modes such as soil shear failure, pile-soil interface slip or soil loosening between spiral blades through the soil stress-strain cloud diagram.

[0013] Preferably, the simulation results under different working conditions include: the pile body size parameters of different thread pitches, thread widths and thread angles, and the ultimate uplift bearing capacity values under different soil parameters such as cohesion, internal friction angle and Poisson's ratio.

[0014] Preferably, the practical calculation formula of the ultimate uplift bearing capacity of the PHC spiral pipe pile is: an empirical formula obtained by multiple regression analysis, taking the internal friction angle, cohesion and shear dilatancy angle of the soil as variables.

[0015] The technical effects and advantages of the present application are: 1. The intelligent construction equipment is used to collect the penetration resistance and torque curve data in real time, and the numerical model is calibrated inversely based on the data, so that the model can truly reflect the actual soil conditions and construction influence of a specific site, and the accuracy of the uplift bearing capacity prediction is greatly improved. 2. The advanced constitutive model reflecting the shear dilatancy and softening characteristics of the soil and the three-dimensional refined model containing the real spiral blade are used, so that the pile-soil interaction can be more accurately simulated, and the uplift failure mechanism can be clearly revealed. 3. The method forms a complete closed loop from "intelligent construction → data collection → model inversion → simulation analysis → formula derivation", and the practical calculation formula derived is rooted in actual engineering data, and has stronger universality.

[0016] 4. By emphasizing "approximate synchronous drilling" and verticality control, and considering their impact from an analytical perspective, it helps to solve the problem of reduced bearing capacity caused by improper construction from both technical and quality control perspectives. Attached Figure Description

[0017] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating the overall steps of the present invention.

[0019] Figure 2 This is a flowchart of the parameter inversion steps of the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides, for example Figure 1 The method shown is a numerical simulation-based analysis method for the pull-out bearing capacity of PHC helical pipe piles, such as... Figure 1 As shown, the specific steps include the following: S1. Construction Control Stage: Intelligent rotary drilling equipment with a two-way communication interface is used for the screwing-in construction of PHC spiral pipe piles. The equipment is equipped with a special drill bit suitable for PHC spiral pipe piles and monitors and controls the pressing speed, rotation speed and torque in real time during the construction process to ensure that the pile body is screwed in vertically and at a uniform speed to the design elevation in an almost synchronous drilling manner. Furthermore, in the above technical solution, the special drill bit is a sleeve-type drill bit that has a guiding function and can be reliably connected to the end of the PHC spiral pipe pile. The near-synchronous drilling refers to controlling the ratio of the pressing speed to the rotation speed so that the advance of the pile body in one revolution matches the pitch of the spiral blade.

[0022] In a preferred embodiment of the present invention, the specific implementation of the construction control phase is as follows: S101. Composition of Intelligent Rotary Drilling Equipment System: The host machine adopts a full-hydraulic rotary drilling rig with an electro-hydraulic proportional control system as the main equipment. The host machine should have strong torque and pressure-in force, and its hydraulic system can respond to precise electronic control instructions. The full-hydraulic rotary drilling rig is equipped with an integrated intelligent control platform, which includes: Programmable logic controller (PLC): as the control core, receiving sensor data and outputting control instructions; Human-machine interface (HMI): used to set construction parameters such as design depth, target rotation speed, and target pressure-in speed, display real-time data curves and equipment status; Bidirectional communication interface: using industrial Ethernet or CAN bus protocol to realize high-speed and reliable data exchange between PLC and sensors and actuators.

[0023] Sensor system: Torque sensor: installed at the power head of the drill rod, real-time monitoring of the torque value applied to the pile body.

[0024] Pressure sensor: installed in the hydraulic circuit of the main winch or pressure cylinder, real-time monitoring of the pressure resistance, converted to pressure-in force.

[0025] Displacement sensor: using a wire-drawing or GPS / Beidou positioning system, real-time monitoring of the sinking displacement of the drill rod or pile head, to calculate the pressure-in speed.

[0026] Rotation encoder: installed on the motor of the power head, real-time monitoring of the rotation speed of the drill rod.

[0027] Inclination sensor: a high-precision inclination sensor is directly installed on the drill rod near the power, real-time monitoring of the inclination angle of the pile body in two directions at 90 degrees to each other.

[0028] Actuator: the hydraulic pump and proportional valve of the host machine, receiving the instructions of the PLC, accurately adjusting the rotation speed of the power head and the pressure-in speed of the pressure system.

[0029] S102. Special drill bit connection and guidance: Drill bit design: using a sleeve type drill bit with a clamping groove or threaded interface on the inner wall matching the prestressed steel rod at the end of the PHC spiral pipe pile, to ensure reliable connection and synchronous rotation of the drill bit and the pile body.

[0030] Guiding function: the drill bit is designed with a guiding tip at the front end, which is slightly larger in diameter than the outer diameter of the pile body, which can first cut into the soil at the initial stage of rotation to form a guide hole, effectively restraining the initial deviation of the pile body.

[0031] S103. Implementation of approximate synchronous drilling control logic: Core parameter setting: preset a key process parameter "penetration-rotation ratio" on HMI, which is the ratio of penetration speed to rotation speed. The theoretical benchmark value of this ratio is: the penetration depth of pile body per 360° rotation should equal to the pitch of helical blade, i.e. penetration speed ≈ rotation speed × pitch.

[0032] Closed-loop control process: PLC acquires current penetration speed Va and rotation speed Na in real time through sensors.

[0033] PLC calculates actual ratio Ra=Va / Na and compares it with preset "penetration-rotation ratio".

[0034] Feedback regulation: If Ra>Rt, it indicates that the penetration is too fast, which may cause the soil between screw threads to be excessively extruded or sheared. PLC will fine-tune proportional valve to slightly reduce penetration speed or slightly increase rotation speed.

[0035] If Ra

[0036] Verticality compensation: the inclination sensor feeds the inclination data of pile body to PLC in real time. Once the inclination angle exceeds the preset inclination angle threshold, such as 0.5%, PLC will start the correction program. For example, if inclined to X direction, an opposite correction force will be applied in Y direction by controlling the fine-tuning oil cylinder of drilling machine base plate or mast, and the rotation or penetration parameters of the corresponding side will be temporarily adjusted to make the pile body return to vertical state.

[0037] S2, data acquisition and transmission stage: real-time acquisition and recording of penetration resistance-depth curve, torque-depth curve and pile body verticality data formed in step S1; Further, in the above technical solution, the pile body verticality data includes: real-time measured pile body inclination angle, vertical deviation value and offset direction.

[0038] Further, the core goal of this stage is to real-time acquisition and recording of key data formed in the construction process, including penetration resistance-depth curve, torque-depth curve and pile body verticality data, to provide real and reliable input for subsequent numerical model inversion calibration. The specific implementation is as follows: S201. Data acquisition content and sensor configuration: Penetration resistance-depth curve: Use the pressure sensor installed in the main winch or pressurized oil cylinder hydraulic circuit of intelligent rotary drilling equipment to monitor the penetration resistance in real time, which is converted into penetration force; Combined with displacement sensors such as wireline encoders or GPS / Beidou positioning systems, monitor the sinking displacement of the drill rod or pile head, and calculate the penetration speed; Correlate the penetration resistance with the depth information to form a continuous penetration resistance-depth curve.

[0039] Torque-depth curve: Use the torque sensor installed at the drill rod power head to monitor the torque value applied to the pile body in real time; Monitor the rotation speed of the drill rod through the rotary encoder and synchronize it with the depth data; Integrate torque and depth data to generate a torque-depth curve.

[0040] Pile body verticality data: Use a dual-axis tilt sensor directly installed on the drill rod near the power head to monitor the inclination angle of the pile body in two directions at right angles to each other in real time, calculate the vertical deviation value and offset direction, and form a verticality data set.

[0041] S202. Data transmission and processing: Sensor data is transmitted in real time to the PLC of the intelligent control platform through a bidirectional communication interface, and the PLC performs preliminary processing and quality inspection on the data to ensure data continuity and accuracy. The data is also uploaded to the HMI for real-time display of the penetration resistance, torque, and verticality curves in a graphical manner for operators to monitor; S203. Data recording and storage: Record the collected data, including time stamp, depth, penetration resistance, torque, and verticality data set, to a local or cloud storage database. The data is saved in a standard format, such as JSON format, for subsequent export for numerical model inversion.

[0042] S204. Data quality control: Implement real-time data verification, such as comparing the consistency of readings from multiple sensors to exclude outliers; Use key data to trigger an alarm mechanism to ensure that construction quality is controllable. For example, once the verticality data exceeds the preset inclination angle threshold, an early warning is triggered and a correction program is triggered.

[0043] S3, Model building and inversion phase: Establish a three-dimensional refined numerical model of PHC spiral pipe pile and surrounding soil containing real spiral blade geometry. The soil uses an advanced constitutive model that can reflect shear dilation and softening characteristics. Use the penetration resistance-depth curve and torque-depth curve obtained in S2 as the target, and automatically calibrate the key soil parameters in the three-dimensional refined numerical model through a parameter inversion algorithm to obtain a calibrated numerical model consistent with the actual field conditions. Further, in the technical scheme, the advanced constitutive model is a hardening soil model, and the key soil body parameters include an internal friction angle, a cohesion, and a shear dilation angle.

[0044] According to the technical scheme in the file, the core purpose of step S3 is to establish a high-precision pile-soil interaction model through a numerical simulation technology, and to perform parameter inversion calibration by using construction data collected on site, so as to ensure that the model is consistent with the actual working condition, and the specific implementation steps are as follows: S301. Three-dimensional refined numerical model construction: Geometric modeling: A professional finite element software such as ABAQUS is used to establish a three-dimensional model of the PHC spiral pipe pile and the surrounding soil body. The pile body model needs to accurately restore the geometric characteristics of the real spiral blade, including thread spacing, thread width, thread inclination angle and other parameters, to avoid simplification; the soil body model should cover the influence range of the pile body, usually taking 5-10 times of the pile diameter as the lateral boundary size, and taking 3-5 times of the pile length below the pile end as the vertical boundary size, so as to reduce the boundary effect.

[0045] Meshing: In the spiral blade and the pile-soil interface area, the structured mesh with a size of 1 / 20-1 / 10 of the pile diameter is used, such as 30-60 mm mesh corresponding to a 600 mm pile diameter, to ensure accurate capture of stress concentration and deformation behavior; The soil body area adopts a gradually changing mesh, which gradually thins away from the pile body, to balance the calculation efficiency and accuracy.

[0046] Constitutive model selection: The soil body adopts an advanced constitutive model, such as a hardening soil model Hardening Soil Model, which can effectively simulate the shear dilation, softening and stress path dependence of the soil body.

[0047] The pile body is regarded as a linear elastic material, and its elastic modulus, Poisson's ratio and other parameters are set according to the PHC pipe pile standard, such as C80 concrete, elastic modulus E p = 3.8 × 10 4 MPa, Poisson's ratio v p = 0.2.

[0048] S302. Initial parameter setting Soil body parameter initial value: According to the experience value and the site investigation report, the initial parameters of the soil body are set, including the internal friction angle φ, the cohesion c, the shear dilation angle ψ, the tangent elastic modulus E 50, Poisson's ratio v, etc. These parameters will be used as the starting point for the inversion calculation, for example, for cohesive soil, the initial values can be taken as c = 15 kPa, φ = 20°, ψ = 0°, v = 0.3; for sand, the initial values are taken as c = 0, φ = 30°, ψ = 10°, v = 0.25; the elastic modulus is set according to the type of soil, such as silty clay E 50 = 10-20 MPa, medium sand E 50 = 30-50 MPa.

[0049] Boundary conditions and contact definition: The bottom of the model is fixedly constrained, and the side is provided with a normal constraint to simulate a semi-infinite soil body.

[0050] The pile-soil interface adopts a face-face contact or friction contact model, the normal behavior is set as "hard contact", the tangential behavior adopts a Coulomb friction model, and the friction coefficient is initially set according to the type of soil, with a value range of [0.3, 0.5], which is adjusted according to the soil properties, with a large value for sand and a small value for cohesive soil.

[0051] S303. Parameter inversion calibration: As shown in Figure 2 , the parameter inversion process is as follows: The pressure resistance-depth curve and the torque-depth curve collected in the S2 stage are imported into the inversion platform as the calibration target, and the genetic algorithm is used to automatically adjust the soil parameters.

[0052] The inversion process is realized by iterative calculation to minimize the error between the pressure resistance curve and the torque curve obtained by numerical simulation and the field curve; Further, the iterative calculation process is as follows: The algorithm randomly generates a set of soil parameters, inputs a three-dimensional refined numerical model, and calculates the simulated pressure resistance-depth curve and torque-depth curve, and calculates the root mean square error RMSE between the simulated curve and the field curve: , in the formula, y si is the simulation value of the i-th data point, y fi is the field value of the i-th data point, and n is the number of data points. Take RMSE as the fitness function, and through the selection, crossover and mutation operations of the genetic algorithm, the parameters are iteratively optimized to reduce the error.

[0053] Further, the genetic algorithm parameters are set as follows: population size: 100; crossover rate: 0.8; mutation rate: 0.05; termination condition: maximum iteration number 100 times or RMSE < 5%.

[0054] Calibration verification: After each iteration, compare the fitting degree of the simulation curve with the field curve. When the error is lower than the preset fitting degree threshold, such as lower than 5%, stop the iteration, output the calibrated soil parameter set, and if the number of iterations exceeds the preset upper limit, such as 100 times, and still does not converge, adjust the parameter initial value or algorithm setting to re-invert.

[0055] S304. Output of calibrated numerical model Save the calibrated model file for subsequent uplift capacity analysis.

[0056] S4, bearing capacity analysis stage: simulate the uplift load on the calibrated numerical model, extract the load-displacement curve and soil stress-strain cloud map, and analyze the uplift ultimate bearing capacity and failure mode; Further, in the above technical solution, the analysis method of the uplift ultimate bearing capacity includes: extracting the limit load point from the load-displacement curve, and determining the uplift ultimate bearing capacity by using the inflection point method or the displacement control method.

[0057] Further, in the above technical solution, the analysis method of the failure mode is: identifying the soil shear failure, pile-soil interface slip or soil loosening between spiral blades from the soil stress-strain cloud map.

[0058] Further, this stage aims to simulate the response of PHC spiral pipe pile under uplift load by using the calibrated numerical model, accurately analyze the uplift ultimate bearing capacity and failure mode, and the specific implementation steps are as follows: S401. Uplift load simulation: On the calibrated numerical model, a monotonically increasing uplift load is applied. The load application method is usually displacement control to better capture the whole process of the load-displacement curve. The load application point is located at the top of the pile to simulate the actual uplift test conditions.

[0059] Further, the displacement control method specifically includes applying vertical displacement in stages: Elastic stage, i.e. estimated load is less than 70% of the limit value: 0.5 mm per displacement, 0.1 s after each loading to ensure that the soil stress is fully transmitted; Plastic stage, i.e. load exceeds 70% of the limit value: 0.2 mm per displacement, step size is reduced to accurately capture the load peak value.

[0060] S402. Data extraction and curve generation: During the simulation, the pile top load value and the corresponding pile top displacement value are extracted in real time to generate the load-displacement curve. At the same time, the stress field and strain field data of the soil region are extracted to generate the pile soil interface slip amount cloud map, the soil plastic strain cloud map and the pile soil interface slip amount cloud map for visual analysis of the response and failure mode of the soil.

[0061] S403. Ultimate uplift capacity analysis: Take the first derivative of the load-displacement curve, draw the slope-displacement curve, and the position where the curve changes from approximately linear to rapid decline is the inflection point. The uplift load corresponding to the inflection point is the ultimate uplift capacity.

[0062] If the load-displacement curve has no obvious inflection point, the curve shows gradual growth. Take the load corresponding to "pile top displacement = 4% pile diameter" as the ultimate uplift capacity. For example, when D = 600 mm, the load corresponding to a displacement of 24 mm; Further, the analysis needs to be combined with the convergence judgment of numerical simulation. If the calculation does not converge at a certain load, it usually indicates that the soil has failed. At this time, the load value of the previous load step can be considered as the ultimate uplift capacity.

[0063] S404. Failure mode analysis: Identify the failure mode through the stress-strain cloud of the soil. Focus on the following typical forms: Soil shear failure: The identification features include the appearance of "continuous high shear stress band" in the shear stress cloud, i.e., the shear stress value is close to the soil shear strength, and the formation of "plastic strain zone extending from the pile bottom to the ground surface" in the plastic strain cloud, with strain value > 2%; The occurrence scenario is mostly seen in dense sand and hard clay, as the soil around the pile is subjected to shear during uplift, forming a continuous shear plane.

[0064] Pile-soil interface slip failure: The identification features include the appearance of "local slip amount > 0.5 mm area" on the surface of the pile or spiral blade in the pile-soil interface slip amount cloud, and the expansion of the slip area with increasing load, as well as the sudden drop of the interface contact pressure; The occurrence scenario is mostly seen in soft clay and poor interface treatment, where the cohesion between the pile and the soil is insufficient, leading to interface failure before soil failure.

[0065] Loose soil failure between spiral blades: The identification features include the sudden decrease of soil principal stress on the upper and lower surfaces of the spiral blade, and the appearance of local voids between the soil and the blade, which is characterized by scattered plastic strain without continuous shear band; The occurrence scenario is mostly seen in pile types with excessively large thread spacing, where the soil between the blades cannot form effective engagement during uplift, resulting in loose disengagement.

[0066] S405. Output failure mode determination report: Identify the dominant failure mode, single mode or composite mode, mark the failure initiation position and development process, analyze the failure causes combined with soil parameters, and integrate the above information as the failure mode determination report output.

[0067] S5, formula derivation and verification optimization stage: based on the simulation results of different working conditions obtained in S4, combined with the earth pressure balance theory, the practical calculation formula of the ultimate uplift bearing capacity of PHC spiral pipe pile is obtained by regression analysis; and its applicability and accuracy are verified.

[0068] Further, in the above technical scheme, the simulation results under different working conditions include: the pile size parameters of different thread spacing, thread width and thread inclination angle, and the ultimate uplift bearing capacity values under different cohesion, internal friction angle and Poisson's ratio of soil body.

[0069] Further, in the above technical scheme, the practical calculation formula of the ultimate uplift bearing capacity of PHC spiral pipe pile is: the empirical formula with the internal friction angle, cohesion and dilatancy angle of soil body as variables obtained by multiple regression analysis.

[0070] Further, step S5 is based on the simulation results of S4, and the practical formula of the ultimate uplift bearing capacity is derived by combining the earth pressure balance theory, and the core implementation steps are as follows: S501. Foundation data system construction and pretreatment: Taking the calibrated numerical model output in S3 as the calculation tool, according to the corresponding relationship of "pile parameter-soil parameter-uplift bearing capacity", the data set covering the commonly used range of engineering is generated, and the parameter value range is shown in Table 1: Table 1 PHC spiral pipe pile ultimate uplift bearing capacity multi-condition simulation data collection parameter table Parameter type Specific parameter Value range Interval step Pile body thread parameter Thread spacing s 100-500mm 50mm Thread width b 50-200mm 25mm Thread angle a 10°～30° 5° Pile body basic parameter Pile diameter D 300-800mm 100mm Pile length L 5～30m 3m Soil core parameter Internal friction angle f 5°～40° 5° Cohesion c 0-100kPa 10kPa Shear dilatancy angle f 0～20° 4° Pullout bearing capacity parameter Pullout ultimate bearing capacity U Determined by S4 inflection point method / displacement control method Adopt 3σ criterion and engineering logic verification double screening, first eliminate abnormal U value exceeding mean value ± 3 times standard deviation, then exclude "thread spacing < 150mm but bearing capacity drops sharply", "internal friction angle > 30° but U grows slowly" and other data not conforming to engineering law; The dimensionless parameters (s, b, D, L, c, U) are normalized according to "parameter value / parameter maximum value", and the non-dimensional parameters (α, φ, ψ) retain the original angle value, which is converted to radian in calculation to eliminate the interference of dimension difference on regression analysis.

[0071] S502. Stress mechanism disassembly based on earth pressure balance theory: Combined with the earth pressure balance theory, the three core stress sources of PHC spiral pipe pile during uplift are determined, which lays the theoretical framework for formula construction: Spiral blade end resistance U1: the passive earth pressure generated by the soil under the blade, which is positively correlated with soil φ, ψ and blade projection area; Spiral blade side friction resistance U2: the sliding resistance between blade side and soil, which depends on b, α and pile-soil interface friction coefficient; U3: the side friction of the pile body, which is positively correlated with the pile diameter D, the pile length L and the soil lateral pressure coefficient.

[0072] Based on the force analysis, the theoretical expression of the ultimate uplift capacity is determined as follows: U=U1+U2+U3, wherein: ; ; ; S503. Derivation of the practical formula for the ultimate uplift capacity: The significance (P value) of the influence of each candidate variable on U is calculated by variance analysis of SPSS. The insignificant variables with P value>0.05 are removed, and the soil elastic modulus E and Poisson's ratio v have less influence on U and can be excluded. The core independent variables are finally retained: s, b, a, D, L, f, c and y; Since U has a nonlinear relationship with the independent variables, such as tan f, sin a and 1 / s, a multivariate nonlinear regression model is selected, and the model form is set based on the theoretical framework of S502: , wherein: k1-k8 are regression coefficients to be fitted; The regression coefficients are solved by "least squares method + iterative optimization" by substituting step S501 and the processed data set into the model; A set of regression coefficients with high significance is obtained by regression analysis of 256 groups of numerical simulation results covering the typical engineering parameter range: k1=12.5, k2=0.85, k3=1.8, k4=0.025, k5=2.2, k6=0.15, k7=8.0, and k8=-150; S504. Formula verification: Select 3-5 PHC spiral pipe pile engineering cases that have completed the uplift static load test, covering clay, silt and sand. Substitute s, b, a, D, L, f, c and y into the formula to calculate the theoretical value of U, and compare it with the field test value. If the determination coefficient R 2 ≥0.92 and the root mean square error is <5%, output the practical calculation formula; otherwise, re-solve the regression coefficients.

[0073] Further, the calculation formula of R 2 is , wherein S res is the residual sum of squares, and S tot is the total sum of squares. Further, the calculation formula of the residual sum of squares Sres is , and the calculation formula of the total sum of squares S tot is ; wherein U iaU is the ultimate uplift bearing capacity value obtained by numerical simulation under the i th group of working conditions, i.e., the actual value; ip U is the ultimate uplift bearing capacity prediction value calculated by substituting the pile-soil parameters of the i th group of working conditions into the regression formula; R is the average value of the actual values of the ultimate uplift bearing capacity obtained by numerical simulation under all n groups of working conditions; 2 The value range of R is [0, 1], and the closer the value is to 1, the stronger the regression formula's ability to explain the data, and the higher the degree of agreement between the prediction value and the actual value.

[0074] Finally, it should be pointed out that the above description is only for the preferred embodiments of the present application and is not intended to limit the present application. Although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments or make equivalent replacements to some technical features, as long as the modifications, equivalent replacements, improvements, etc. are within the spirit and principles of the present application, they should be included in the protection scope of the present application.

Claims

1. A numerical simulation-based analysis method for the uplift capacity of PHC spiral pipe piles, characterized in that, Specifically comprising the following steps: S1, construction control stage: using an intelligent rotary drilling equipment with a bidirectional communication interface to carry out the rotary construction of the PHC spiral pipe pile; the equipment is provided with a special drill bit suitable for the PHC spiral pipe pile, and the penetration speed, the rotary speed and the torque are monitored and controlled in real time during the construction process, so as to ensure that the pile body is vertically and uniformly rotated to the design elevation in a nearly synchronous drilling manner; S2, data acquisition and transmission stage: real-time acquisition and recording of the penetration resistance-depth curve, the torque-depth curve and the pile body verticality data formed in step S1; S3, model construction and inversion stage: a three-dimensional refined numerical model of the PHC spiral pipe pile and the surrounding soil containing the real spiral blade geometry is established, the soil is provided with a high-level constitutive model capable of reflecting the shear dilatancy and softening characteristics; the penetration resistance-depth curve and the torque-depth curve obtained in S2 are taken as the target, the key soil parameters in the three-dimensional refined numerical model are automatically calibrated through a parameter inversion algorithm, and a calibrated numerical model consistent with the actual working condition is obtained; S4, bearing property analysis stage: simulating the uplift load on the calibrated numerical model, extracting the load-displacement curve and the soil stress-strain nephogram, and analyzing the uplift ultimate bearing capacity and the failure mode; S5, formula derivation and verification and optimization stage: based on the simulation results under different working conditions obtained in S4, combining with the soil pressure balance theory, a practical calculation formula of the PHC spiral pipe pile uplift ultimate bearing capacity is obtained through regression analysis; and the applicability and accuracy are verified.

2. The numerical simulation-based analysis method for the uplift capacity of a PHC spiral pipe pile according to claim 1, characterized in that: The special drill bit is a sleeve type drill bit with a guiding function and capable of being reliably connected with the pile end of the PHC spiral pipe pile, and the nearly synchronous drilling refers to controlling the ratio of the penetration speed and the rotary speed, so that the footage of one rotation of the pile body matches the pitch of the spiral blade.

3. The numerical simulation based analysis method of the uplift capacity of the PHC spiral pipe pile according to claim 1, characterized in that: The pile body verticality data includes: the real-time measured pile body inclination angle, the vertical deviation value and the offset direction.

4. The numerical simulation based analysis method of the uplift capacity of a PHC spiral pipe pile according to claim 1, characterized in that: The high-level constitutive model is a hardening soil model, and the key soil parameters include the internal friction angle, the cohesion and the shear dilatancy angle.

5. The numerical simulation based analysis method of the uplift capacity of the PHC spiral pipe pile according to claim 1, characterized in that: The analysis method of the uplift ultimate bearing capacity includes: extracting the limit load point from the load-displacement curve, and determining the uplift ultimate bearing capacity by using the inflection point method or the displacement control method.

6. The numerical simulation based analysis method of the uplift capacity of a PHC spiral pipe pile according to claim 1, characterized in that: The analysis method of the failure mode is: identifying the failure modes such as soil shear failure, pile-soil interface slip or soil loosening between spiral blades through the soil stress-strain nephogram.

7. The numerical simulation based analysis method of the uplift capacity of a PHC spiral pipe pile according to claim 1, characterized in that: The simulation results under different working conditions include: the uplift ultimate bearing capacity values under different thread spacing, thread width, thread inclination angle of the pile body size parameters, and different cohesion, internal friction angle, Poisson's ratio of the soil parameters.

8. The numerical simulation based analysis method of the uplift capacity of a PHC spiral pipe pile according to claim 1, characterized in that: The practical calculation formula of the PHC spiral pipe pile uplift ultimate bearing capacity is: an empirical formula taking the soil internal friction angle, the cohesion and the shear dilatancy angle as variables obtained through multiple regression analysis.

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