An analytical method for testing the bearing capacity of single and multiple PHC piles in soft soil foundation

Abstract

The present invention discloses an analysis method for detecting the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation, which relates to the technical field of bearing capacity analysis and includes the following steps: S1, numerical model construction and initial setting; S2, single pile bearing capacity analysis; S3, multiple pile bearing capacity analysis; S4, force and load sharing analysis; S5, parameter sensitivity analysis; S6, field test and verification. The main advantage of the present invention is that the bearing capacity characteristics of a single PHC pile and multiple piles in a soft soil foundation are comprehensively and systematically analyzed by combining numerical simulation with field tests, and multiple factors such as pile-soil interaction, loading history, and time effect are considered. The numerical simulation method used has the advantages of low cost, short cycle, and strong repeatability compared to field tests, which greatly reduces research costs and improves research efficiency, and also analyzes parameter sensitivity.

Description

Technical Field

[0001] The invention relates to the technical field of bearing capacity analysis, and in particular to an analysis method for detecting the bearing capacity of a PHC single pile and multiple piles in a soft soil foundation. Background Art

[0002] There are extensive soft soil layers under the foundations of highways in Hubei, Hunan and coastal provinces and cities in my country. If a new expressway is built on it and handled improperly, it may cause serious quality problems or even damage to the road, such as cracks or misalignment of the road surface, which seriously affects driving safety and driving speed and requires maintenance all year round. With the vigorous development of expressways, the problem of soft soil reinforcement has become the main factor restricting the project cycle, cost and quality. Therefore, further strengthening the research on the soft foundation reinforcement technology of expressways has important practical significance for highway construction.

[0003] Among the existing methods for testing the bearing capacity of soft soil foundations, they are usually carried out through on-site in-situ tests and indoor geotechnical tests. These methods are costly, have great limitations, and the results are highly discrete. They cannot take into account complex factors. Therefore, some scholars have proposed theoretical analysis and numerical simulation research, but there is still no method that can take into account both comprehensiveness and systematicity, and they are also relatively weak in parameter optimization and comparison.

[0004] The bearing capacity detection method in the above scheme is costly, has great limitations, and the results are also highly discrete. By taking advantage of the high bearing capacity of PHC pipe piles and the large allowable settlement of the roadbed, the cost of the composite foundation can be reduced while ensuring the settlement and stability requirements. It is of great significance to analyze the working properties of PHC pipe piles to reinforce the soft soil roadbed on the slope under the load of high embankment.

[0005] However, in the analysis method of PHC pile bearing capacity detection, the unevenness of steep slope sections in mountainous areas still leads to problems in solving and unbalanced initial geostress fields. Summary of the invention

[0006] The purpose of the present invention is to solve the shortcomings existing in the prior art and to propose an analytical method for detecting the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation, which solves the problems of high cost and great limitations of the existing bearing capacity detection methods.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] An analytical method for detecting the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation comprises the following steps:

[0009] S1. Construction and initial setting of numerical model: establishing a three-dimensional grid model and setting material properties and boundary conditions, and performing initial calculation of foundation horizontal resistance coefficient;

[0010] S2, single pile bearing capacity analysis, setting single pile model establishment and parameters and simulating plate load test;

[0011] S3, multi-pile bearing capacity analysis, arrange multi-pile model and pile group and conduct embankment load application and settlement analysis;

[0012] S4. Stress and load sharing analysis: analysis of the stress state of PHC piles and pile-soil load sharing characteristics;

[0013] S5, parameter sensitivity analysis, analyzing numerical simulation and results after selecting key design parameters;

[0014] S6. Field testing and verification: formulate a field test plan for implementation and collect data.

[0015] As a further improvement of the present invention, in step S1, the numerical model construction selects ANSYS numerical simulation software, and the ANSYS numerical simulation software is used to establish a three-dimensional grid model, and the three-dimensional grid model includes a soil layer, a PHC pipe pile, a cushion layer, and an embankment fill structure layer. The three-dimensional grid model sets boundary conditions, and the boundary conditions include fixed boundaries, free boundaries, and elastic boundaries. The ground stress balance calculation is calculated in FLAC3D, and the calculation adopts the method of first balancing the ground stress and then establishing the contact surface. Thus, the transition grid is guaranteed by the grid continuity between the cushion layer and the embankment fill, or the mapping grid division technology is adopted to ensure the rationality of the grid. The constraints in the actual project can be simulated by the fixed boundaries, free boundaries, and elastic boundaries, and the model reaches the initial equilibrium state by gradually applying gravity loads and iterative calculations.

[0016] As a further improvement of the present invention, in step S2, the pile diameter, pile length, pile body material parameters and contact surface parameters are set for the single pile model, a plate load is applied to the pile top to simulate an on-site plate load test, and a QS curve is obtained through the simulated load test, and the QS curve is used to determine the bearing capacity characteristics of the single pile. Thus, a suitable pile-soil contact surface model is selected according to the actual situation, and the corresponding contact surface parameters are set.

[0017] As a further improvement of the present invention, in step S3, multiple PHC pipe piles are added to the numerical model and a pile group arrangement scheme is selected according to the project, a uniformly distributed load is set on the embankment fill to simulate the load effect of the high-fill embankment, and the settlement deformation of the multi-pile composite foundation is calculated through the numerical simulation. Thus, the change law of settlement deformation with the increase of load and the influence of pile group arrangement on settlement deformation are analyzed through the settlement difference between the pile top and the piles.

[0018] As a further improvement of the present invention, in step S4, the numerical simulation obtains the stress state of the PHC pile, the stress state includes the pile shaft axial force, bending moment, and shear force, and analyzes the law of the stress state changing with the increase of load and pile depth, and evaluates the contribution of piles and soil in bearing through the pile-soil load sharing ratio, and the contribution is used to analyze the change law of the load sharing ratio with the increase of load and the arrangement of pile groups. In this way, the bearing capacity and stability of the pile body material are evaluated, ensuring that the pile body will not be damaged or unstable, and the pile-soil interaction mechanism is used as the basis for optimizing the arrangement of pile groups and improving the bearing capacity of composite foundations.

[0019] As a further improvement of the present invention, in step S5, the parameters of the sensitivity analysis include geogrid modulus, pile modulus, pile length, pile spacing and pile cap size, the parameters are used to clarify the range of variation and step length, the parameters are used to combine for numerical simulation, the numerical simulation is used to analyze the deformation of the composite foundation, the stress of the pipe pile and the pile-soil load sharing characteristics, and the analysis is used to draw relevant curves and charts. In this way, the range of variation and step length of each parameter are clarified to comprehensively evaluate its impact on the bearing capacity, and the impact of parameter changes on the bearing capacity can be intuitively displayed, and targeted optimization suggestions can be put forward based on the analysis results.

[0020] As a further improvement of the present invention, in step S6, the numerical simulation is used to formulate a detailed field test plan, which includes the test purpose, test content, test method, test equipment and test personnel. Field tests are carried out according to the test plan, and test data, including plate load test data, settlement deformation data and pile body force data, are recorded and collected, and the test data are sorted and analyzed to verify the accuracy and reliability of the numerical simulation results.

[0021] As a further improvement of the present invention, in steps S1-S6, the analysis method is used to study the relationship between the roadbed deformation distribution, PHC pile stress and pile-soil load sharing characteristics as a function of the grid modulus, pile body modulus, pile length, pile spacing and pile cap size design parameters.

[0022] As a further improvement of the present invention, the initial foundation horizontal resistance coefficient calculation in step S1 is calculated as m, and the specific calculation formula of m is:

[0023]

[0024] The v x is the horizontal displacement coefficient of the pile top, H is the horizontal force acting on the ground, b0 is the calculated width of the pile body, X0 is the horizontal displacement of the horizontal force action point, EI is the bending strength of the pile body, and X cr is the displacement distance corresponding to the horizontal critical load of a single pile, and the H cris the critical load value of the single pile level, and m can also be obtained by the basic flexural differential equation.

[0025] As a further improvement of the present invention, the basic flexural differential equation of the pile is:

[0026]

[0027] Where d is the diameter of the pile, Z is the depth into which the pile is driven, and X is the displacement coefficient of the pile.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The bearing capacity analysis method of PHC single pile and multiple piles in soft soil foundation proposed in the present invention comprehensively and systematically analyzes the bearing capacity characteristics of PHC single pile and multiple piles in soft soil foundation by combining numerical simulation and field test, and considers multiple factors such as pile-soil interaction, loading history and time effect. The numerical simulation method adopted has the advantages of low cost, short cycle and strong repeatability compared with field test, which greatly reduces the research cost and improves the research efficiency. In addition, through parameter sensitivity analysis, the influence of each design parameter of grid modulus, pile body modulus, pile length, pile spacing and pile cap size on bearing capacity is clarified, which provides a scientific basis for engineering design and construction, realizes scheme optimization, and finally verifies the accuracy and reliability of numerical simulation results in combination with field test, ensures the practicability and credibility of analysis results, and provides safety guarantee for engineering design and construction.

[0030] 2. The method proposed in the present invention combines the FLAC3D modeling method to balance the ground stress first and then establish the contact surface, which solves the problem that the contact surface affects the solution and balance of the initial ground stress field when the steep slope section of the mountainous area uses pipe piles to reinforce the roadbed. On the basis of understanding the distribution of ground stress, the arrangement and number of pipe piles can be determined more scientifically to achieve the best reinforcement effect. Moreover, the reasonable contact surface setting and the balance of the initial ground stress field can ensure that the effect of the pipe pile reinforcement roadbed is fully exerted and the overall stability of the project is improved. Through the accurate solution of the initial ground stress field and the setting of the contact surface, the settlement of the roadbed can be more effectively controlled, the flatness of the road surface can be improved, and the reasonable pipe pile reinforcement and ground stress balance treatment can extend the service life of the steep slope section of the mountainous area and reduce the cost of repair and maintenance.

[0031] 3. The present invention proposes a plate load test based on the K31+100~K32+150 section, and draws a single pile PS curve. The results show that the bearing capacity of the composite foundation meets the design requirements; and on this basis, a PHC single pile composite foundation model is established, and the appropriate pile-soil contact surface parameters are obtained through repeated trials, providing a basis for the selection of contact surface parameters. Through the plate load test, the settlement of the foundation soil under a specific load can be directly measured, thereby evaluating whether the bearing capacity of the foundation meets the design requirements. This step is the basis for ensuring the safety of the project. The single pile PS curve can intuitively reflect the settlement characteristics of the pile under load, and further verify whether the bearing capacity of the composite foundation is up to standard. The established PHC single pile composite foundation model obtains appropriate pile-soil contact surface parameters through repeated trials, which can more accurately simulate the foundation stress conditions in actual projects, so that the optimized model parameters can provide guidance for subsequent construction and ensure quality control and safety management during construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0033] Figure 1 It is a schematic diagram of the steps of the present invention. DETAILED DESCRIPTION

[0034] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0035] An analytical method for detecting the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation comprises the following steps:

[0036] S1. Construction and initial setting of numerical model: establish a three-dimensional grid model and set material properties and boundary conditions to calculate the initial horizontal resistance coefficient of foundation. ANSYS numerical simulation software is used to build the numerical model. ANSYS numerical simulation software is used to build a three-dimensional grid model. The three-dimensional grid model includes soil layer, PHC pile, cushion layer and embankment fill structure layer. The three-dimensional grid model sets boundary conditions, which include fixed boundary, free boundary and elastic boundary. The ground stress balance calculation is performed in FLAC3D. The calculation adopts the method of ground stress balance first and then establishing contact surface.

[0037] The initial foundation horizontal resistance coefficient calculation in step S1 is m, and the specific calculation formula of m is:

[0038]

[0039] v x is the horizontal displacement coefficient of the pile top, H is the horizontal force acting on the ground, b0 is the calculated width of the pile body, X0 is the horizontal displacement of the horizontal force action point, EI is the bending strength of the pile body, X cr is the displacement distance corresponding to the horizontal critical load of a single pile, H cr is the critical load value of the single pile horizontally, and m can also be obtained by the basic deflection differential equation. The basic deflection differential equation of the pile is:

[0040]

[0041] d is the diameter of the pile, Z is the depth to which the pile is driven, and X is the displacement coefficient of the pile.

[0042] S2-S5, single pile bearing capacity analysis, set up single pile model establishment and parameters and simulate plate load test; multi-pile bearing capacity analysis, arrange multi-pile model establishment and pile group and carry out embankment load application and settlement analysis; force and load sharing analysis, carry out PHC pipe pile force state and pile-soil load sharing characteristics analysis; parameter sensitivity analysis, select key design parameters and analyze numerical simulation and results. The single pile model sets the pile diameter, pile length, pile body material parameters and contact surface parameters, applies a plate load on the pile top to simulate the on-site plate load test, and obtains the QS curve through the simulated load test. The QS curve is used to judge the bearing capacity characteristics of a single pile; add multiple PHC pipe piles to the numerical model and select the pile group layout plan according to the project. Set a uniformly distributed load on the embankment fill to simulate the high fill embankment load effect, and calculate the settlement deformation of the multi-pile composite foundation through numerical simulation; numerical simulation obtains the force state of the PHC pipe pile, which includes the pile body axial force, bending moment, shear Force, analyze the law of stress state changing with the increase of load and pile depth, evaluate the contribution of piles and soil in bearing through pile-soil load sharing ratio, and the contribution is used to analyze the change law of load sharing ratio with the increase of load and pile group arrangement; the parameters of sensitivity analysis include geogrid modulus, pile modulus, pile length, pile spacing and pile cap size, the parameters are used to clarify the range of change and step size, the parameters are used to combine for numerical simulation, numerical simulation is used to analyze the deformation of composite foundation, the stress of pipe piles and the pile-soil load sharing characteristics, and the analysis is used to draw relevant curves and charts.

[0043] S6. Field test and verification, formulate a field test plan for implementation and collect data. Numerical simulation is used to formulate a detailed field test plan, which includes the test purpose, test content, test method, test equipment and test personnel. Analytical methods are used to study the relationship between the roadbed deformation distribution, PHC pile force and pile-soil load sharing characteristics with the grid modulus, pile body modulus, pile length, pile spacing and pile cap size design parameters.

[0044] Example 1

[0045] like Figure 1 As shown, in actual application, the above PHC single pile and multi-pile bearing capacity analysis method in soft soil foundation has the following specific implementation process:

[0046] Step 1: Project initialization and data preparation:

[0047] Preparation of survey tools and equipment: prepare drilling equipment required for geological survey, such as drilling rigs, drill rods, drill bits and samplers, ensure the accuracy and reliability of measuring equipment (such as water level gauges, earth pressure gauges, inclinometers, etc.), and prepare laboratory testing equipment, such as geotechnical testing instruments, triaxial shear instruments, etc., for subsequent soil sample testing;

[0048] On-site drilling and sampling: Plan the drilling locations according to the topography and soil distribution of the project area to ensure that all key areas are covered. Use a drilling rig to drill to the predetermined depth, record the soil layer changes and abnormal conditions during the drilling process, and take samples in different soil layers to ensure that at least 3-5 representative soil samples are obtained for each soil layer;

[0049] On-site in-situ testing: Conduct standard penetration test (SPT) or dynamic cone penetration test (DPT) to obtain preliminary mechanical parameters of the soil layer, conduct lateral pressure test or cross-plate shear test to obtain more accurate data on soil cohesion and internal friction angle, use water level gauge to measure groundwater level, and record water level changes;

[0050] Laboratory soil sample testing: The retrieved soil samples are sent to the laboratory for geotechnical tests, including basic physical property tests such as density, water content, and particle analysis; consolidation tests are conducted to obtain the compression modulus and Poisson's ratio of the soil layer; triaxial shear tests or direct shear tests are conducted to obtain the cohesion and internal friction angle of the soil layer;

[0051] Data collation and analysis: The data from on-site in-situ tests and laboratory soil sample tests are collated to form a complete soil layer parameter table. Statistical methods are used to analyze the data to ensure the accuracy and reliability of the data. Based on the soil layer parameters, the applicability and bearing capacity of PHC piles in soft soil foundations are preliminarily evaluated.

[0052] Step 2: Numerical model construction and initial settings:

[0053] Step 2-1, select ANSYS numerical simulation software:

[0054] Software selection confirmation: confirm the ANSYS software version to ensure that it contains the modules and functions required for geotechnical engineering, evaluate the ANSYS operating interface and user experience to ensure that team members can use it efficiently;

[0055] Software advantage assessment: Analyze the application cases of ANSYS in geotechnical engineering, confirm its advantages in dealing with complex geological conditions and structural analysis, and confirm that ANSYS can support 3D modeling and bearing capacity analysis of PHC piles and soft soil foundations;

[0056] Software preparation and installation: Install ANSYS software on the project computer, ensure the software runs stably and is compatible with the existing system, prepare necessary software licenses and updates to ensure uninterrupted analysis;

[0057] Training and Support: Organize ANSYS software training for team members to ensure they are familiar with software operation and analysis processes, and establish contact with the ANSYS technical support team to obtain help when needed.

[0058] Step 2-2: Create a 3D mesh model in ANSYS:

[0059] Model planning: According to project requirements and geological survey data, plan the scope and level of the 3D grid model, and determine the layout and size of key components such as soil layer, PHC piles, cushion layer, embankment fill structure layer, etc.

[0060] Meshing: Use ANSYS meshing tools to generate reasonable 3D meshes for each component, pay special attention to the mesh continuity between the cushion layer and the embankment fill, and use transition meshing or mapping meshing technology to ensure the rationality of the mesh;

[0061] Mesh optimization: Check the quality of the mesh to ensure that the shape, size and distribution of the mesh units meet the analysis requirements, and perform mesh encryption in key areas (such as the contact surface between the PHC pile and the soil layer) to improve the analysis accuracy;

[0062] Model verification: After the mesh division is completed, the model is verified to ensure that the mesh is consistent with the actual situation. A simple loading test is performed on the mesh to check the stability and responsiveness of the mesh.

[0063] Step 2-3: Assign material properties and set boundary conditions:

[0064] Material attribute assignment: According to geological survey data, assign accurate material attributes to each soil layer and structural layer, including density, elastic modulus and Poisson's ratio, input material parameters in ANSYS, and confirm the correctness of the parameters;

[0065] Boundary condition setting: according to the actual engineering situation, set the boundary conditions of the model, including fixed boundary, free boundary or elastic boundary, define the boundary conditions in ANSYS, and check the rationality and applicability of the boundary conditions;

[0066] Contact surface setting: Set reasonable contact conditions and friction parameters at the contact surfaces between PHC piles and soil layers, cushion layers and embankment fill, etc., to ensure that the contact surface settings can reflect the actual situation and help improve the analysis accuracy;

[0067] Model check: After assigning material properties and setting boundary conditions, the model is fully checked to confirm the correctness of the model components and parameters to ensure that the model can be used for subsequent bearing capacity analysis.

[0068] Step 2-4: Calculate the initial foundation horizontal resistance coefficient in FLAC3D:

[0069] Model import and preparation: Import the 3D mesh model created in ANSYS into FLAC3D, and set the initial conditions and calculation parameters of the model in FLAC3D;

[0070] Geostress balance calculation: Perform initial geostress balance calculation in FLAC3D to ensure that the stress state of the model when not subjected to external loads conforms to the actual situation. The method of first balancing the geostress and then establishing the contact surface is adopted. By gradually applying gravity loads and iterative calculations, the model reaches the initial equilibrium state.

[0071] Calculation result check: Check the results of the ground stress balance calculation to ensure that the stress distribution inside the model is reasonable and consistent with the actual situation. Visualize the calculation results to better understand and analyze the stress state of the model.

[0072] Preparation for subsequent analysis: After the ground stress balance calculation is completed, save the model status for subsequent bearing capacity analysis, prepare the necessary loading conditions and calculation parameters, and prepare for the subsequent bearing capacity analysis.

[0073] Step 3: Single pile bearing capacity analysis:

[0074] Step 3-1: Establish a single PHC pile in the numerical model:

[0075] Model preparation: Open ANSYS software, load the established 3D grid model of soft soil foundation, and determine the pile diameter, pile length, and pile body material parameters of a single PHC pile according to the design data;

[0076] Establishing the PHC pile model: In the numerical model, the ANSYS modeling tool is used to establish the 3D geometric model of a single PHC pile. According to the pile diameter and pile length, the outer contour of the pile is accurately drawn, and its position is ensured to be consistent with the actual situation.

[0077] Set pile material parameters: define the material properties of PHC piles in the ANSYS material library, including elastic modulus, Poisson's ratio, density, etc., and assign these material parameters to the pile model to ensure that the model can accurately reflect the mechanical properties of the pile body;

[0078] Select the pile-soil contact model: According to the characteristics of soft soil foundation and engineering experience, select the appropriate pile-soil contact model. Common pile-soil contact models include Coulomb friction model, nonlinear spring model, etc.

[0079] Set the contact surface parameters: Set the parameters of the pile-soil contact surface in ANSYS, such as friction coefficient, contact stiffness, etc. These parameters should be reasonably selected based on geological survey data and engineering experience to ensure the accuracy of the analysis;

[0080] Model verification and adjustment: After completing the establishment and parameter setting of the PHC pile model, the model is fully verified to check the correctness of the pile body material parameters, contact surface model and parameters to ensure that the model can accurately reflect the actual situation.

[0081] Step 3-2: Apply a flat plate load on the pile top to simulate the on-site flat plate load test:

[0082] Apply plate load: In the numerical model, use the ANSYS loading tool to apply a plate load on the pile top. The load size should be reasonably selected according to the actual engineering needs and test requirements, and applied step by step.

[0083] Record the settlement of the pile top: During the loading process, use the ANSYS displacement monitoring tool to record the settlement of the pile top to ensure the accuracy and continuity of the recorded data for subsequent analysis;

[0084] Obtain QS curve: Draw QS curve based on the pile top load and settlement data recorded during the loading process. The QS curve should be able to accurately reflect the relationship between pile top load and settlement;

[0085] Analyze the QS curve: judge the bearing capacity characteristics of a single pile based on the shape and characteristic points of the QS curve. The proportional limit point indicates the maximum load that the pile can withstand within the elastic range; the yield point indicates the load at which the pile begins to enter the plastic deformation stage; the ultimate bearing capacity point indicates the maximum load that the pile can withstand before failure;

[0086] Bearing capacity characteristics assessment: Based on the analysis results of the QS curve, the bearing capacity characteristics of a single pile are assessed, including the bearing capacity, deformation characteristics, stability, etc., to provide a basis for engineering design and construction;

[0087] Result verification and adjustment: Compare and verify the numerical analysis results with the actual situation to ensure the accuracy and reliability of the analysis results. If large differences are found, the model parameters, loading conditions, etc. should be adjusted and the analysis and calculation should be repeated.

[0088] Step 4: Multi-pile bearing capacity analysis:

[0089] Step 4-1: Add multiple PHC piles to the numerical model:

[0090] Determine the pile group layout plan: According to the actual project needs and geological survey data, determine the pile diameter, pile length, pile spacing and pile arrangement parameters, select the appropriate pile group layout plan, such as square layout, rectangular layout, plum blossom layout, etc., and consider the overall stability and bearing capacity distribution of the pile group;

[0091] Establish a multi-pile model: Use the modeling tool of ANSYS software to add multiple PHC pipe piles to the existing 3D grid model of soft soil foundation. According to the selected pile group layout plan, accurately draw the position and geometric dimensions of each pile to ensure that the material parameters, pile-soil contact surface model and parameters of each pile are consistent with those in the single pile analysis;

[0092] Verify the model: conduct a comprehensive verification of the multi-pile model, check the correctness of the pile body material parameters, pile-soil contact surface settings, pile group layout scheme, etc., to ensure that the multi-pile model can accurately reflect the actual situation and has the ability to perform bearing capacity analysis;

[0093] Adjustment and optimization: Make necessary adjustments and optimizations to the model based on the validation results to improve the accuracy and reliability of the analysis.

[0094] Step 4-2: Simulate the load of high embankment and analyze the settlement deformation:

[0095] Apply uniform load: In the numerical model, the loading tool of ANSYS software is used to apply uniform load on the embankment fill. The load size should be reasonably selected according to the load requirements of high embankment in actual engineering, and the step-by-step application process of the load should be considered;

[0096] Calculation of settlement and deformation: Calculate the settlement and deformation of the multi-pile composite foundation under load through numerical simulation, use the displacement monitoring tool of ANSYS software to record the settlement of the pile top and between piles, and analyze the spatial distribution of settlement and deformation;

[0097] Settlement deformation analysis: Analyze the settlement difference between the pile top and the piles, evaluate the influence of pile-soil interaction on settlement deformation, and study the change law of settlement deformation with the increase of load, including the change trend of settlement amount and the change of settlement rate, etc.

[0098] Analysis of the impact of pile group arrangement: Compare the settlement and deformation results under different pile group arrangement schemes, analyze the influence of pile spacing, pile arrangement method and other parameters on settlement and deformation, evaluate the bearing capacity and stability performance of pile groups under different arrangement schemes, and provide a basis for engineering design and construction;

[0099] Result verification and discussion: Compare and verify the numerical simulation results with the field test results or other reliable data to ensure the accuracy and reliability of the analysis results, discuss and explain the problems and uncertainties found in the analysis process, and put forward improvement suggestions and directions for further research.

[0100] Step 5: Force and load sharing analysis:

[0101] Step 5-1, stress state analysis:

[0102] Establish an analysis model: Use ABAQUS or ANSYS to establish a three-dimensional numerical model including PHC piles and soft soil foundation, and set the pile diameter, pile length, pile body material parameters and soil parameters of the soft soil foundation according to the actual engineering conditions;

[0103] Apply loads and boundary conditions: Apply gradually increasing loads on the pile top or embankment fill to simulate the loading process in actual engineering, and set reasonable boundary conditions, such as fixed constraints on the foundation base and side normal constraints, to ensure the accuracy of the analysis results;

[0104] Numerical simulation calculation: Run numerical simulation calculation to obtain the stress state data of PHC piles under different load levels, including pile axial force, bending moment, shear force, etc., analyze the law of these data changing with the increase of load and pile depth, and draw the corresponding stress curve diagram;

[0105] Stress state assessment: Evaluate the bearing capacity and stability of the pile material according to the stress curve diagram, check whether the pile shows signs of stress concentration, plastic deformation or damage during loading, and ensure the safety performance of the pile;

[0106] Optimization suggestions: If it is found that the stress state of the pile body does not meet the design requirements or there are safety hazards, put forward corresponding optimization suggestions, such as adjusting the pile diameter, pile length, pile spacing or strengthening the pile body structure.

[0107] Step 5-2: Pile-soil load sharing ratio analysis:

[0108] Definition of load sharing ratio: Load sharing ratio refers to the proportion of load shared by the pile and soil when they share the upper load. The load sharing between the pile and soil is usually determined by comparing the reaction force at the top of the pile and the friction resistance at the side of the pile.

[0109] Numerical simulation calculation: During the numerical simulation process, the data of the pile top reaction force and pile side friction resistance changing with the increase of load are recorded simultaneously, and the pile-soil load sharing ratio under different load levels is calculated based on these data;

[0110] Analyze the changing law of load sharing ratio: Analyze the changing law of pile-soil load sharing ratio with the increase of load and the arrangement of pile groups, explore the influence of factors such as pile spacing and pile arrangement on the load sharing ratio, and how these factors affect the overall bearing capacity of the composite foundation;

[0111] Study on the pile-soil interaction mechanism: Combine numerical simulation results with theoretical analysis to study the pile-soil interaction mechanism, analyze the influence of pile deformation, soil pressure distribution on the pile side and other factors on the load sharing ratio, and how these factors affect the interaction effect between pile and soil;

[0112] Suggestions for optimizing pile group layout: Based on the analysis results of the pile-soil load sharing ratio and the discussion of the pile-soil interaction mechanism, suggestions for optimizing the pile group layout are put forward. By adjusting the pile spacing, pile arrangement and other measures, the load sharing between piles and soil can be improved, thereby improving the bearing capacity and stability of the composite foundation.

[0113] Step 6: Parameter sensitivity analysis:

[0114] Step 6-1, select key design parameters and set the range of variation:

[0115] Determine key design parameters: Geogrid modulus, pile modulus, pile length, pile spacing and pile cap size are selected as key design parameters for sensitivity analysis;

[0116] Set the range and step size:

[0117] Geogrid modulus: ranges from 100MPa to 1000MPa, with a step size of 100MPa;

[0118] Pile modulus: range from 20 GPa to 40 GPa, with a step size of 2 GPa;

[0119] Pile length: ranging from 10m to 30m, with a step length of 5m;

[0120] Pile spacing: ranges from 2D to 6D, with a step size of 1D;

[0121] Pile cap size: range from 1.2D to 2.0D, with a step size of 0.2D;

[0122] Step 6-2: Numerical simulation and result analysis:

[0123] Establishing numerical model: Using finite element analysis software to establish a three-dimensional numerical model of the composite foundation including PHC piles, soft soil foundation and geogrid;

[0124] Parameter combination and simulation: Generate the combination of all key design parameters according to the set variation range and step size, perform numerical simulation on each parameter combination, and simulate the response of the composite foundation under different load conditions;

[0125] Deformation analysis: Analyze the influence of various parameter changes on the settlement deformation of composite foundation, especially the settlement difference between pile top and pile soil, draw a curve of settlement deformation versus parameter change, and intuitively display the influence of various parameters on settlement deformation;

[0126] Pipe pile stress analysis: extract the pile axial force, bending moment and shear force data from the numerical simulation results, analyze the impact of various parameter changes on the pile stress, evaluate the bearing capacity and stability of the pile material, and draw a graph of the pile axial force, bending moment and shear force as the parameters change;

[0127] Analysis of pile-soil load sharing characteristics: Calculate the pile-soil load sharing ratio under various parameter combinations, analyze the law of pile-soil load sharing ratio changing with parameters, explore the pile-soil interaction mechanism, and draw a graph of pile-soil load sharing ratio changing with parameters;

[0128] Optimization suggestions: Based on the simulation results and analysis, make targeted optimization suggestions, point out which parameters have a significant impact on bearing capacity and deformation, and how to improve the performance of the composite foundation by adjusting these parameters. For example, if it is found that increasing the pile length can significantly increase the bearing capacity but the increased cost is also high, it can be suggested to appropriately shorten the pile length while ensuring the bearing capacity, and combine the optimization of other parameters to achieve the best effect;

[0129] Verification and adjustment: If conditions permit, the numerical simulation results can be verified through field tests or small-scale model tests. According to the verification results, necessary adjustments and optimizations can be made to the numerical model to improve the accuracy and reliability of the simulation results.

[0130] Step 7: Field test and verification:

[0131] Step 7-1: Develop a detailed field test plan:

[0132] The purpose of the test is to determine the actual bearing capacity of single and multiple PHC piles in soft soil foundation and verify the accuracy and reliability of numerical simulation results;

[0133] Determine the test content: Conduct a flat plate load test, measure the bearing capacity of the foundation, monitor the settlement deformation of the composite foundation during loading, including the settlement difference between the pile top and the piles, and collect pile body stress data, such as axial force, bending moment and shear force;

[0134] Select the test method: Use the slow sustained load method (SLT) to carry out the plate load test to ensure the accuracy and stability of the test results, and use equipment such as settlement observation instruments and strain gauges to monitor the settlement deformation and pile stress;

[0135] Prepare test equipment: The test equipment includes flat plate load test device, settlement observation instrument, strain gauge, data acquisition system, etc. Ensure that all equipment is calibrated and meets the requirements of relevant standards and specifications;

[0136] Organize test personnel: set up a special test team, including test leaders, technicians, safety supervisors, etc., and train test personnel to ensure that they are familiar with the test process, operating specifications and safety requirements;

[0137] Prepare test plan: Prepare a detailed test plan, including the test purpose, test content, test method, test equipment, division of labor among test personnel, test process, safety measures, etc. The plan should be reviewed and approved by experts before it can be implemented.

[0138] Step 7-2: Conduct field tests according to the test plan:

[0139] Site preparation: clean the test site, ensure that the test area is flat and free of debris, and arrange the flat plate load test device, settlement observation instrument, strain gauge and other equipment according to the test plan;

[0140] Installation and commissioning: Install the flat plate load test device to ensure its stability and reliability, and commission equipment such as settlement observation instruments and strain gauges to ensure accurate data collection;

[0141] Loading and observation: Apply loads step by step according to the test plan, record the settlement deformation and pile force data under each load level, observe the changes in settlement deformation and pile force with the increase of load, and pay attention to record abnormal conditions;

[0142] Data collection and processing: Use the data collection system to record the settlement deformation and pile body stress data in real time, organize and analyze the collected data, and calculate indicators such as foundation bearing capacity, settlement deformation and pile body stress distribution;

[0143] Result verification and evaluation: Compare and analyze the field test results with the numerical simulation results to verify the accuracy and reliability of the numerical simulation, evaluate the actual bearing capacity of PHC single piles and multiple piles in soft soil foundations, and analyze the pile-soil interaction mechanism and load sharing characteristics;

[0144] Writing test reports: Write test reports based on test data and analysis results, including test purpose, test content, test methods, test equipment, test process, test results, conclusions and suggestions. The report should objectively and accurately reflect the test conditions and analysis results, and provide a reference for engineering design and construction.

[0145] Example 3

[0146] Based on the above method, the present invention also proposes the application of the bearing capacity analysis method of PHC single pile and multiple piles in soft soil foundation in studying the relationship between the deformation distribution of roadbed, the force of PHC pipe piles and the pile-soil load sharing characteristics with the grid modulus, pile body modulus, pile length, pile spacing and pile cap size design parameters. Through experimental research, the relationship between the deformation distribution of roadbed, the force of PHC pipe piles and the pile-soil load sharing characteristics with the grid modulus, pile body modulus, pile length, pile spacing and pile cap size design parameters is analyzed, and the accuracy and reliability of the numerical simulation results are verified, so as to provide a scientific basis for engineering design and construction. Therefore, the following experiment is designed:

[0147] 1. Experimental Content

[0148] Measure the bearing capacity of the foundation under different design parameters, monitor the settlement deformation of the composite foundation during loading, including the settlement difference between the pile top and the piles, collect the stress data of the pile body, such as axial force, bending moment and shear force, and analyze the pile-soil load sharing characteristics;

[0149] 2. Experimental Methods

[0150] The slow sustained load method was used to carry out the flat plate load test, and the settlement deformation and pile stress were monitored using equipment such as settlement observation instruments and strain gauges. Multiple groups of experimental comparisons were carried out by changing the design parameters such as the grid modulus, pile modulus, pile length, pile spacing and pile cap size.

[0151] 3. Experimental equipment and materials

[0152] Plate load test device, settlement observation instrument, strain gauge, data acquisition system, PHC piles and matching pile caps, soft soil foundation simulation materials and geogrids;

[0153] 4. Experimental Procedure

[0154] Experiment 1: Experiment on the influence of grid modulus on bearing capacity and deformation

[0155] Experimental parameters

[0156] Grid modulus: 100MPa, 200MPa, 300MPa, ..., 1000MPaOther parameters: pile modulus 30GPa, pile length 20m, pile spacing 4D, pile cap size 1.5D.

[0157] Experimental Procedure

[0158] a. Prepare the experimental site and arrange the plate load test device, settlement observation instrument and strain gauge;

[0159] b. Install PHC piles and pile caps, lay geogrids, and set the geogrid modulus;

[0160] c. Apply loads step by step and record the settlement deformation and pile stress data;

[0161] d. After reaching the predetermined load or the settlement is stable, stop loading and analyze the data, see Table 1:

[0162] Table 1 Experimental data of the influence of grid modulus on bearing capacity and deformation

[0163]

[0164]

[0165] Therefore, it is concluded that:

[0166] 1) With the increase of grid modulus, the settlement under the same load level tends to decrease, indicating that the increase of grid modulus helps to enhance the stiffness of the foundation, thereby reducing settlement;

[0167] 2) Under the same load level, as the modulus of the grid increases, the force on the pile body may increase slightly, and the load is more effectively transferred to the pile body;

[0168] 3) The increase in grid modulus leads to an increase in failure load, because a stronger foundation can withstand a greater load without failure;

[0169] 4) When the failure load is reached, the total settlement decreases with the increase of the grid modulus, indicating that increasing the grid modulus helps to reduce the total settlement of the foundation when it is destroyed, thereby improving the stability of the foundation;

[0170] Experiment 2: Effect of pile modulus on bearing capacity and deformation

[0171] Experimental Procedure

[0172] e. Preparation stage: Select the experimental site, ensure the geological conditions are consistent, design test piles with different pile moduli, and keep other parameters such as pile length, pile diameter, and pile spacing unchanged;

[0173] f. Installation stage: Install test piles according to design parameters to ensure that the construction quality of each pile meets the specifications;

[0174] g. Loading test: Use a static load test machine to load each pile step by step, and record the settlement and deformation data under each level of load;

[0175] h. Data recording: record the settlement under each load level and the total settlement when the failure load is reached in detail, see Table 2:

[0176] Table 2 Experimental data of the influence of pile modulus on bearing capacity and deformation

[0177] Pile No. Pile modulus (GPa) Loading level (kN) Settlement (mm) 1 20 100 1.2 1 20 200 2.4 1 20 Destruction load Total sedimentation 2 25 100 1.0 2 25 200 1.8 3 30 100 0.9 3 30 200 1.5

[0178] Therefore, it is concluded that:

[0179] 1) With the increase of pile modulus, the bearing capacity of the pile is significantly improved. When the modulus increases from 20 GPa to 30 GPa, the total settlement under the failure load decreases, indicating that the pile stiffness is enhanced and the ability to resist deformation is improved;

[0180] 2) The pile modulus is negatively correlated with the settlement deformation, that is, the larger the modulus, the smaller the settlement under the same load, which verifies the important role of the pile modulus in controlling the deformation of the composite foundation;

[0181] Experiment 3: Effect of pile length on bearing capacity and deformation

[0182] Experimental Procedure

[0183] i. Preparation stage: Design test piles of different lengths, keeping the pile diameter, pile modulus, pile spacing and other parameters consistent;

[0184] j. Installation and loading: Install the test piles and conduct step-by-step loading tests, and record the settlement and deformation data under each level of load;

[0185] k. Data recording: record the settlement under each load level and the total settlement when the failure load is reached in detail, see Table 3:

[0186] Table 3 Experimental data of the influence of pile length on bearing capacity and deformation

[0187]

[0188]

[0189] Therefore, it is concluded that:

[0190] 1) As the pile length increases, the bearing capacity of the pile increases significantly, especially when the pile length increases from 10m to 15m, the bearing capacity increases significantly, but the increase slows down beyond a certain length;

[0191] 2) There is a negative correlation between pile length and settlement deformation, that is, the longer the pile length, the smaller the settlement under the same load. However, when the pile length exceeds a certain value, the reduction in settlement is no longer significant.

[0192] Experiment 4: Effect of pile spacing on bearing capacity and deformation

[0193] Experimental Procedure

[0194] 1. Preparation stage: Design test pile groups with different pile spacings, keeping the pile length, pile diameter, pile modulus and other parameters consistent;

[0195] m. Installation and loading: Install the test pile group and conduct overall loading test, and record the settlement and deformation data of the group under various levels of load;

[0196] n. Data recording: record the group settlement and soil deformation between piles under each load level in detail, see Table 4:

[0197] Table 4 Experimental data of the effect of pile spacing on bearing capacity and deformation

[0198]

[0199]

[0200] Therefore, it is concluded that:

[0201] 1) Pile spacing has a significant impact on bearing capacity. Too large a pile spacing leads to a decrease in bearing capacity, while too small a pile spacing leads to poor economic efficiency. Reasonable control of pile spacing can optimize the bearing performance of the composite foundation.

[0202] 2) The pile spacing is positively correlated with the settlement deformation. As the pile spacing increases, the settlement under the same load increases, and the soil deformation between piles intensifies. Therefore, by comparing and analyzing the group settlement and soil deformation between piles under different pile spacings, the importance of pile spacing on the deformation control of composite foundation and the reasonable range of pile spacing can be obtained;

[0203] Experiment 5: Effect of pile cap size on bearing capacity and deformation

[0204] Experimental Procedure

[0205] o. Preparation stage: design pile caps of different sizes and install them on the top of the test piles, keeping the pile length, pile diameter, pile modulus, pile spacing and other parameters consistent;

[0206] p. Installation and loading: Install the test piles with pile caps and conduct loading tests step by step, and record the settlement and deformation data under each level of load;

[0207] q. Data recording: Detailed records of the settlement under each load level and the deformation of the soil between piles under the pile cap, see Table 5:

[0208] Table 5 Effect of pile cap size on bearing capacity and deformation

[0209]

[0210] Therefore, it is concluded that:

[0211] 1) The size of the pile cap has a positive impact on the bearing capacity. The increase in the pile cap can increase the proportion of load shared by the pile body and enhance the overall bearing performance of the composite foundation;

[0212] 2) The size of the pile cap is negatively correlated with the amount of settlement deformation. Increasing the size of the pile cap can significantly reduce the amount of settlement and reduce the differential settlement between the pile top and the soil between the piles.

[0213] In summary, the bearing capacity analysis method of PHC single pile and multiple piles in soft soil foundation proposed in the present invention overcomes the limitations of traditional methods by comprehensively using numerical simulation and field test technology. It has the advantages of comprehensiveness, economy, efficiency and safety, and provides strong technical support for engineering practice.

[0214] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. An analytical method for detecting the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation, comprising the following steps: S1. Construction and initial setting of numerical model: establishing a three-dimensional grid model and setting material properties and boundary conditions, and performing initial calculation of foundation horizontal resistance coefficient; S2, single pile bearing capacity analysis, setting single pile model establishment and parameters and simulating plate load test; S3, multi-pile bearing capacity analysis, arrange multi-pile model and pile group and conduct embankment load application and settlement analysis; S4. Stress and load sharing analysis: analysis of the stress state of PHC piles and pile-soil load sharing characteristics; S5, parameter sensitivity analysis, analyzing numerical simulation and results after selecting key design parameters; S6. Field testing and verification: formulate a field test plan for implementation and collect data.

2. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation according to claim 1, characterized in that: In step S1, the numerical model construction selects ANSYS numerical simulation software, and the ANSYS numerical simulation software is used to establish a three-dimensional grid model. The three-dimensional grid model includes a soil layer, a PHC pipe pile, a cushion layer and an embankment fill structure layer. The three-dimensional grid model sets boundary conditions, and the boundary conditions include a fixed boundary, a free boundary and an elastic boundary. The ground stress balance calculation is performed in FLAC3D, and the calculation adopts a method of first balancing the ground stress and then establishing the contact surface.

3. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation according to claim 2, characterized in that: In step S2, the pile diameter, pile length, pile body material parameters and contact surface parameters are set for the single pile model, a flat plate load is applied to the pile top to simulate an on-site flat plate load test, and a QS curve is obtained through the simulated load test. The QS curve is used to determine the bearing capacity characteristics of the single pile.

4. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation according to claim 3, characterized in that: In step S3, a plurality of PHC pipe piles are added to the numerical model and a pile group arrangement scheme is selected according to the project. A uniformly distributed load is set on the embankment fill to simulate the load effect of the high-fill embankment. The settlement deformation of the multi-pile composite foundation is calculated through the numerical simulation.

5. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation according to claim 4, characterized in that: In step S4, the numerical simulation obtains the stress state of the PHC pipe pile, and the stress state includes the axial force, bending moment and shear force of the pile body. The law of the stress state changing with the increase of load and the pile depth is analyzed. The contribution of the pile and soil in the bearing is evaluated through the pile-soil load sharing ratio. The contribution is used to analyze the change law of the load sharing ratio with the increase of load and the arrangement of pile groups.

6. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation according to claim 5, characterized in that: In step S5, the parameters of the sensitivity analysis include geogrid modulus, pile modulus, pile length, pile spacing and pile cap size, and the parameters are used to clarify the range of variation and step size. The parameters are used to combine for numerical simulation, and the numerical simulation is used to analyze the deformation of the composite foundation, the stress of the pipe piles and the pile-soil load sharing characteristics. The analysis is used to draw relevant curves and charts.

7. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation according to claim 6, characterized in that: In step S6, the numerical simulation is used to formulate a detailed on-site test plan, which includes test objectives, test content, test methods, test equipment and test personnel.

8. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation according to claims 1 to 7, characterized in that: The analytical method is used to study the relationship between the roadbed deformation distribution, PHC pile stress and pile-soil load sharing characteristics as a function of the grid modulus, pile body modulus, pile length, pile spacing and pile cap size design parameters.

9. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation as claimed in claim 1, characterized in that: The initial foundation horizontal resistance coefficient calculation in step S1 is calculated as m, and the specific calculation formula of m is: The v x is the horizontal displacement coefficient of the pile top, H is the horizontal force acting on the ground, b0 is the calculated width of the pile body, X0 is the horizontal displacement of the horizontal force action point, EI is the bending strength of the pile body, and X cr is the displacement distance corresponding to the horizontal critical load of a single pile, and the H cr is the critical load value of the single pile level, and m can also be obtained by the basic flexural differential equation.

10. The method for analyzing the bearing capacity of a single PHC pile and multiple piles in a soft soil foundation as claimed in claim 9, characterized in that: The basic flexural differential equation of the pile is Where d is the diameter of the pile, Z is the depth into which the pile is driven, and X is the displacement coefficient of the pile.

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