A numerical model construction method for soil plugging effect of open piles based on material point method

Abstract

The present invention discloses a method for constructing a numerical model of the soil plug effect of an open pile based on a material point method, comprising: conducting an indoor half-model tank test using standard sand to record data on the internal and external friction of the pile, soil stress, soil plug height, and displacement field during the pile sinking process; establishing a geometric model based on the indoor model test, using a two-dimensional axisymmetric material point method combined with a grid encryption strategy to perform numerical simulation to obtain data on the internal and external friction of the pile, soil stress field, soil plug height, and displacement field; comparing and analyzing the indoor test data with the numerical simulation results, and confirming the validity of the numerical model if the error meets predetermined requirements; and optimizing the numerical model if the comparison result does not meet the requirements. The present invention can effectively simulate the soil plug effect during the pile sinking process, conduct in-depth research on the stress field and displacement field response of the open pile to the surrounding soil, and provide a more accurate basis for the structural design and bearing capacity calculation of the open pile.

Description

Technical Field

[0001] The present invention relates to the field of pile foundation engineering, and in particular to a method for constructing a numerical model of soil plug effect of open piles based on a material point method. Background Art

[0002] Open piles, with their low installation resistance and high bearing capacity, are widely used in onshore and offshore structural foundation construction. During installation, the underlying soil is pushed into the pile, creating a so-called "soil plug." Depending on the relative displacement between the pile and the soil plug, open piles can be categorized as plugged, partially plugged, or unplugged. Different forms of soil plugging can significantly affect the installation resistance and bearing capacity of open piles, making it essential to understand soil plugging behavior during pile installation.

[0003] While field and laboratory experiments provide valuable information about open pile installation, the highly nonuniform stress and strain fields near the pile shaft are difficult to measure reliably. Numerical simulation offers great potential for obtaining more detailed information about these stress and strain fields. Traditional mesh-based numerical methods, such as the standard Lagrangian finite element method (FEM), encounter significant challenges in simulating pile driving due to the mesh distortions inevitably caused by large soil deformations. Discrete element methods are computationally expensive and may not currently provide a viable approach to solving practical pile installation problems. Summary of the Invention

[0004] The present invention aims to address the deficiencies of the prior art and propose a method for constructing a numerical model of the soil plug effect of open piles based on the material point method.

[0005] The object of the present invention is achieved through the following technical solution: a method for constructing a numerical model of the soil plug effect of an open pile based on the material point method, comprising the following steps:

[0006] S1. Obtain the mechanical parameters of sandy soil materials and conduct indoor model tank tests to obtain data on the internal and external friction of piles, soil stress, soil plug height, and displacement field.

[0007] S2. Simulation of open pile sinking process based on material point method:

[0008] Based on the indoor model slot test, the same two-dimensional axisymmetric geometric model was established, meshed, and layered mesh refinement was performed. The open pile model problem domain was discretized into material points, and the corresponding material parameters of the soil material points were assigned based on the mechanical parameters of the sand obtained in the test, thus obtaining the open pile material point method model.

[0009] Apply the same boundary conditions and loads as the model tank test and perform material point method simulation:

[0010] Map the information of each material point to the grid node through the basis function, solve the tentative momentum of the grid node without considering the contact, calculate the contact force and correct the tentative momentum, map the grid node information back to the material point through the basis function, update the material point information, and repeat the simulation steps until the simulation time ends;

[0011] Obtain the internal and external friction of the pile, soil stress, soil plug height and displacement field data within the simulation time;

[0012] S3. Compare and analyze the indoor test results with the numerical simulation results. If the error meets the requirements, the numerical model is confirmed to be reliable; if the comparison result does not meet the requirements, the numerical model is optimized and adjusted until the error meets the requirements.

[0013] Furthermore, the indoor model tank test includes:

[0014] Strain gauges were placed inside and outside the semi-molded aluminum sleeve open piles; the model test box was filled and soil pressure cells were buried at different soil depths and radial positions. A camera system was also placed on one side of the glass surface.

[0015] Static pressure construction was carried out according to the design conditions, and data from strain gauges, earth pressure cells, and high-speed cameras were recorded to obtain data on the internal and external friction of the pile, soil stress, soil plug height, and displacement field.

[0016] Furthermore, the data recorded from the strain gauge, earth pressure cell and high-speed camera to obtain the internal and external friction of the pile, soil stress, soil plug height and displacement field data specifically include:

[0017] The friction resistance is measured by strain gauges arranged on the half-mold aluminum sleeve open pile to obtain the inner friction resistance and the outer friction resistance of the pile;

[0018] The soil stress is measured by an earth pressure cell to measure the radial, circumferential and vertical stresses of the sand within a radial distance D-10D from the pile axis, where D is the pile diameter;

[0019] The displacement field data are obtained by processing and analyzing continuous deformation images of the soil around the pile during the pile sinking process using a high-speed camera using DIC technology.

[0020] Furthermore, establishing the same two-dimensional axisymmetric geometric model based on the indoor model slot test includes: establishing open pile models of the same size according to the model slot width, height, pile diameter, and pile wall thickness data.

[0021] Furthermore, the grid division and layered grid encryption include: determining a minimum grid size, determining the number of grid encryption layers; using regular rectangular units to divide the grid and perform layered grid encryption, and setting the number of material points in the units.

[0022] Furthermore, the material point method simulation specifically includes:

[0023] Read the open pile material point method model and initialize the model-related calculation parameters;

[0024] Based on the mesh node positions and material point positions of the open pile material point method model, the basis functions are used to calculate the node shape function values and shape function gradient values;

[0025] For each object, the shape function values of each object's material point information are mapped to the grid nodes through calculation;

[0026] The same displacement boundary conditions and stress boundary conditions as those in the model slot test are applied to the mesh nodes;

[0027] Use the constitutive model to update the stress and strain information of material points;

[0028] Solve the momentum equation without considering contact and calculate the tentative momenta of the mesh nodes;

[0029] Calculate contact force based on contact algorithm and correct the tentative momentum;

[0030] The information such as the velocity and position of the grid nodes is mapped back to the material points through the shape function values, and the information of the material points is updated; the above material point method simulation process is repeated until the simulation time ends.

[0031] Furthermore, the basis function is a truncated cubic B-spline basis function.

[0032] Furthermore, the boundary conditions are set as follows: the bottom is a fixed boundary, and the left and right sides are set as symmetrical boundary conditions.

[0033] Furthermore, the Mohr-Coulomb model is used as the constitutive model of the soil during the simulation of open pile sinking.

[0034] On the other hand, the specification also provides a numerical model construction device for open pile soil plug effect based on material point method, including a test model box, a memory and one or more processors, wherein the test model box is used to carry out indoor model tank tests and obtain data;

[0035] The memory stores executable code, and when the processor executes the executable code, it realizes the process of simulating the open pile sinking process based on the material point method and the process of comparing and analyzing the indoor test results with the numerical simulation results.

[0036] Beneficial effects of the present invention:

[0037] Calibration data obtained through half-model tank tests provided a reliable basis for the numerical model. The axisymmetric material point method, combined with a mesh refinement strategy, significantly reduced computational costs while ensuring accurate simulation of the pile sinking area and improving the accuracy of the results. The numerical model was calibrated based on laboratory test data to further optimize its construction.

[0038] Each material point can carry individual material information. After further exploration of geological information, numerical models of multi-layered soil and large-diameter open piles (D / t>20) can be constructed based on reliable numerical models, further optimizing pipe pile design and construction plans. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The geometric model of the numerical model of the embodiment of the present invention and the distribution diagram of the material points after discretization;

[0040] Figure 2 This is a cloud diagram of the accumulated vertical displacement field of the numerical model of the embodiment of the present invention after the pile has penetrated a certain depth;

[0041] Figure 3 Schematic diagram of a device for constructing a numerical model of the soil plug effect of an open pile based on the material point method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0042] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0043] Step 1: Conduct indoor model tank test

[0044] S11. Use standard sand materials and conduct conventional indoor tests such as triaxial compression tests and dry density tests to obtain sand mechanical parameters, including elastic modulus, Poisson's ratio, density, cohesion, and internal friction angle;

[0045] S12. Strain gauges are arranged on the inner and outer sides of the semi-molded aluminum sleeve open pile to monitor the inner and outer frictional resistance of the pile respectively;

[0046] S13. Fill the half-model trough test box and bury soil pressure cells at different soil depths and radial distances within the radial distance range of D-10D (D is the pile diameter) from the pile axis. Arrange a camera system on one side of the glass surface. The camera system consists of a CMOS high-pixel camera and an illumination system. Arrange a reaction frame and a small jack system above the model trough test box.

[0047] S14. Perform static pressure construction according to the design conditions, penetrate the pile into the designated location, record the data from the strain gauge, soil pressure cell, and high-speed camera, and analyze the internal and external friction of the pile, soil stress, soil plug height, and displacement field data.

[0048] Step 2: Simulate the open pile sinking process based on the material point method:

[0049] S21. Based on the indoor model tank test, establish the same two-dimensional axisymmetric geometric model. According to the model tank width, height, pile diameter, pile wall thickness and other data, establish the same size open pile model. Determine the minimum grid size (t / 4) and the number of grid encryption layers (4 layers). Use regular rectangular cells to divide the grid and perform layered grid encryption. Set the number of material points in the cell (4). Discretize the entire problem domain into material points, such as Figure 1 and Figure 2 As shown, through the above steps, a material point method model corresponding to the actual model size is obtained.

[0050] S22. Set constitutive model parameters for the open pile model. The Mohr-Coulomb model is used for soil material points. The main parameters include elastic modulus, Poisson's ratio, density, cohesion, and internal friction angle, which are consistent with the sand parameters in the solid model. The pile body is set as a rigid body.

[0051] S23. Apply the same boundary conditions as those in the model slot test to the open pile model, with the bottom set as a fixed boundary and the left and right sides set as symmetrical boundary conditions. In this embodiment, there is no additional load on the upper part of the model slot test soil, so the upper boundary of the numerical model is set as a free boundary.

[0052] S24. Key calculation parameters such as the pile-soil friction coefficient (between 0 and 1, 0.5 in this embodiment) and the pile penetration speed (5 m / s in this embodiment) are set for the open pile model.

[0053] S25. Set the material point method basis function for the open pile model and select the truncated cubic B-spline basis function.

[0054] S26. Perform material point method simulation on the open pile model: Set parameters related to simulation calculation of the open pile model based on the keywords specified in the material point method code. The specific keywords specified in the code include simulation time, time step, solution format, output setting, damping coefficient, etc. The open pile model generated in the above steps is solved and calculated. The specific calculation steps include:

[0055] (1) Read the open pile material point method model generated in step S21 and initialize the model-related calculation parameters;

[0056] (2) Based on the grid node positions and material point positions of the open pile material point method model, the node shape function values and shape function gradient values are calculated using the basis functions in S25;

[0057] surface Truncated cubic B-spline shape function and shape function gradient types

[0058] type Shape Function Shape function gradient 1 #timg# #timg# 2 #timg# #timg# 3 #timg# #timg# 4 #timg# #timg# 5 #timg# #timg# 6 #timg# #timg# 7 #timg# #timg# 8 #timg# #timg# 9 #timg# #timg#

[0059] (3) For each object, the material point information of each object is mapped to the grid node through the shape function value calculated in step (2);

[0060]

[0061]

[0062]

[0063]

[0064]

[0065] superscript Indicates the current time step, the superscript Indicates an object, represents the time step; represents the value of the shape function of node I at the material point p; represents the value of the shape function gradient of node I at the material point p; and They represent the mass of node I and material point p respectively; and denote the position and velocity of the material point p respectively; and denote the momentum of node I and material point p respectively; represents the nodal force, represents the external force at the node, represents the node internal force, represents the node traction force; represents the body force at the material point p.

[0066] (4) Apply the displacement boundary conditions and stress boundary conditions in S23 to the grid nodes;

[0067] If node I is fixed in direction i, then let:

[0068]

[0069] Stress boundaries are created by applying the traction force as a point force:

[0070]

[0071] represents the traction force on the material point p; represents the volume of the material point p; It represents the height of the material point perpendicular to the boundary surface (normal length).

[0072] (5) Use the constitutive model in S22 to update the stress and strain information of the material points;

[0073]

[0074] Represents the stress of material point p in the current time step; represents the stress at the material point p in the next time step; represents the stress increment at material point p.

[0075] (6) Solve the momentum equation without considering contact and calculate the tentative momentum of the mesh nodes;

[0076]

[0077] represents the tentative momentum of the forecast.

[0078] (7) Calculate the contact force based on the contact algorithm and correct the trial momentum;

[0079]

[0080] represents the nodal contact force; represents the node momentum at the next time step.

[0081] (8) Map the grid node velocity and position information back to the material point through the shape function value calculated in step (2), and update the velocity, position and other information of the material point;

[0082]

[0083]

[0084] (9) Repeat steps (2) to (8) until the simulation time ends.

[0085] S27. Obtain relevant data during the pile sinking process, including a graph of the internal and external frictional resistance of the pile versus penetration depth, a graph of the change in soil plug height, and data on the stress and displacement fields around the pile during the pile sinking process;

[0086] Step 3: Comparative analysis of indoor test data and numerical simulation results

[0087] S31. Compare and analyze the data on pile internal and external friction, soil stress, soil plug height, and displacement field recorded during the indoor model test with the numerical simulation results. Based on the error assessment criteria, if the error in the numerical simulation results meets the predetermined accuracy requirements, the numerical model is considered valid. If the error is significant, adjust the parameters in the numerical model to optimize key parameters such as the pile-soil friction coefficient and damping coefficient, and repeat the simulation until a reliable numerical model is obtained.

[0088] Corresponding to the aforementioned embodiment of a method for constructing a numerical model of the soil plug effect of an open pile based on a material point method, the present invention also provides an embodiment of an apparatus for constructing a numerical model of the soil plug effect of an open pile based on a material point method.

[0089] The test model box comprises a test model box, a memory and one or more processors, wherein the test model box is used to carry out indoor model tank tests and obtain data;

[0090] See also Figure 3 The memory stores executable code. When the processor executes the executable code, it realizes the process of simulating the open pile sinking process based on the material point method and the comparison and analysis process of indoor test results and numerical simulation results.

[0091] The embodiment of the numerical model construction device of the open pile soil plug effect based on the material point method provided by the present invention can be applied to any device with data processing capabilities, and the device with data processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented through software, or through hardware or a combination of software and hardware. Taking software implementation as an example, as a device in a logical sense, it is formed by the processor of any device with data processing capabilities in which it is located reading the corresponding computer program instructions in the non-volatile memory into the memory for execution. From the hardware level, if Figure 3 As shown in the figure, it is a hardware structure diagram of a numerical model construction device of soil plug effect of open pile based on material point method provided by the present invention, where any device with data processing capability is located. Figure 3 In addition to the processor, memory, network interface, and non-volatile memory shown, any device with data processing capabilities in which the apparatus in the embodiment is located may also include other hardware, generally based on the actual functions of the device with data processing capabilities, which will not be described in detail.

[0092] The implementation process of the functions and effects of each unit in the above-mentioned device is specifically described in the implementation process of the corresponding steps in the above-mentioned method, and will not be repeated here.

[0093] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the partial description of the method embodiments. The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present invention. A person of ordinary skill in the art can understand and implement the present invention without inventive work.

[0094] An embodiment of the present invention further provides a computer-readable storage medium having a program stored thereon. When the program is executed by a processor, the method for constructing a numerical model of the open pile soil plug effect based on the material point method in the above embodiment is implemented.

[0095] The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the aforementioned embodiments, such as a hard disk or memory. The computer-readable storage medium may also be an external storage device of any device with data processing capabilities, such as a plug-in hard disk, a smart media card (SMC), an SD card, a flash card, etc. equipped on the device. Furthermore, the computer-readable storage medium may also include both an internal storage unit and an external storage device of any device with data processing capabilities. The computer-readable storage medium is used to store the computer program and other programs and data required by any device with data processing capabilities, and may also be used to temporarily store data that has been output or is to be output.

[0096] Those skilled in the art will readily appreciate other embodiments of the present application after considering the specification and practicing the contents disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present application that follow the general principles of the present application and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered merely as exemplary, and the true scope and spirit of the present application are indicated by the claims.

[0097] It should be understood that the above general description and the detailed description that follows are exemplary and explanatory only and do not limit the present application. The present application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes may be made without departing from the scope of the present application. The scope of the present application is limited only by the appended claims.

Claims

1. A method for constructing a numerical model of soil plug effect of open piles based on the material point method, characterized in that: The steps include: S1. Conduct indoor model tank tests to obtain sand mechanical parameters, pile internal and external friction, soil stress, soil plug height, and displacement field data; S2. Simulation of open pile sinking process based on material point method: Based on the indoor model slot test, the same two-dimensional axisymmetric geometric model was established, meshed, and layered mesh refinement was performed. The open pile model problem domain was discretized into material points, and the corresponding material parameters of the soil material points were assigned based on the mechanical parameters of the sand obtained in the test, thus obtaining the open pile material point method model. Apply the same boundary conditions and loads as the model tank test and perform material point method simulation: Map the information of each material point to the grid node through the basis function, solve the tentative momentum of the grid node without considering the contact, calculate the contact force and correct the tentative momentum, map the grid node information back to the material point through the basis function, update the material point information, and repeat the simulation steps until the simulation time ends; Obtain the internal and external friction of the pile, soil stress, soil plug height and displacement field data within the simulation time; S3. Compare and analyze the indoor test results with the numerical simulation results. If the error meets the requirements, the numerical model is confirmed to be reliable; if the comparison result does not meet the requirements, the numerical model is optimized and adjusted until the error meets the requirements.

2. The method for constructing a numerical model of soil plug effect of open piles based on the material point method according to claim 1, characterized in that: The indoor model tank test includes: Strain gauges were placed inside and outside the semi-molded aluminum sleeve open piles; the model test box was filled and soil pressure cells were buried at different soil depths and radial positions. A camera system was also placed on one side of the glass surface. Static pressure construction was carried out according to the design conditions, and data from strain gauges, earth pressure cells, and high-speed cameras were recorded to obtain data on the internal and external friction of the pile, soil stress, soil plug height, and displacement field.

3. The method for constructing a numerical model of soil plug effect of open piles based on the material point method according to claim 2, characterized in that: The data recorded by the strain gauge, earth pressure cell and high-speed camera to obtain the internal and external friction of the pile, soil stress, soil plug height and displacement field data specifically include: The friction resistance is measured by strain gauges arranged on the half-mold aluminum sleeve open pile to obtain the inner friction resistance and the outer friction resistance of the pile; The soil stress is measured by an earth pressure cell to measure the radial, circumferential and vertical stresses of the sand within a radial distance D-10D from the pile axis, where D is the pile diameter; The displacement field data are obtained by processing and analyzing continuous deformation images of the soil around the pile during the pile sinking process using a high-speed camera using DIC technology.

4. The method for constructing a numerical model of soil plug effect of open piles based on the material point method according to claim 1, characterized in that: The establishing of the same two-dimensional axisymmetric geometric model based on the indoor model slot test includes: establishing an open pile model of the same size according to the model slot width, height, pile diameter, and pile wall thickness data.

5. The method for constructing a numerical model of soil plug effect of open piles based on the material point method according to claim 4 is characterized in that: The grid division and layered grid encryption include: determining the minimum grid size, determining the number of grid encryption layers; using regular rectangular units to divide the grid and perform layered grid encryption, and setting the number of material points in the units.

6. The method for constructing a numerical model of soil plug effect of open piles based on the material point method according to claim 1, characterized in that: The material point method simulation specifically includes: Read the open pile material point method model and initialize the model-related calculation parameters; Based on the mesh node positions and material point positions of the open pile material point method model, the basis functions are used to calculate the node shape function values and shape function gradient values; For each object, the shape function values of each object's material point information are mapped to the grid nodes through calculation; The same displacement boundary conditions and stress boundary conditions as those in the model slot test are applied to the mesh nodes; Use the constitutive model to update the stress and strain information of material points; Solve the momentum equation without considering contact and calculate the tentative momenta of the mesh nodes; Calculate contact force based on contact algorithm and correct the tentative momentum; The grid information is mapped back to the material point through the shape function value, and the information of the material point is updated; the above material point method simulation process is repeated until the simulation time ends.

7. The method for constructing a numerical model of soil plug effect of open piles based on the material point method according to claim 6, characterized in that: The basis function is a truncated cubic B-spline basis function.

8. The method for constructing a numerical model of soil plug effect of open piles based on the material point method according to claim 6, characterized in that: The boundary conditions are set as follows: the bottom is a fixed boundary, and the left and right sides are set as symmetrical boundary conditions.

9. The method for constructing a numerical model of soil plug effect of open piles based on the material point method according to claim 6, characterized in that: In the simulation of open pile sinking, the Mohr-Coulomb model is used as the soil constitutive model.

10. A device for implementing the method according to any one of claims 1 to 9, characterized in that: The test model box comprises a test model box, a memory and one or more processors, wherein the test model box is used to carry out indoor model tank tests and obtain data; The memory stores executable code, and when the processor executes the executable code, it realizes the process of simulating the open pile sinking process based on the material point method and the process of comparing and analyzing the indoor test results with the numerical simulation results.

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