Numerical model construction method of open pile soil plug effect based on material point method

Abstract

The invention discloses a material point method-based open pile soil plug effect numerical model construction method, which comprises the following steps: carrying out an indoor semi-model tank test by adopting standard sandy soil, and recording data of friction resistance of the inner side and the outer side of a pile, soil stress, soil plug height and a displacement field in a pile sinking process; a geometric model is established based on an indoor model test, numerical simulation is performed by adopting a two-dimensional axisymmetric substance point method in combination with a grid encryption strategy, and data of friction resistance of the inner side and the outer side of a pile, a soil stress field, the soil plug height and a displacement field are obtained; performing comparative analysis on the indoor test data and the numerical simulation result, and if an error meets a preset requirement, confirming the validity of the numerical model; and if the comparison result does not meet the requirement, optimizing the numerical model. The soil plug effect in the pile sinking process can be effectively simulated, the response of the open pile to a stress field and a displacement field of a surrounding soil body can be deeply researched, and a more accurate basis can be provided for 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 particularly to a method for constructing a numerical model of the soil plug effect of an open-ended pile based on the material point method. Background Art

[0002] Open-ended piles have the advantages of low installation resistance and high bearing capacity, and are widely used in the construction of onshore and offshore structure foundations. 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-ended piles can be classified as plugged, partially plugged, and unplugged penetrations. Different forms of soil plug behavior can seriously affect the installation resistance and bearing capacity of open-ended piles. Therefore, it is very necessary to understand the soil plug behavior during pile installation.

[0003] Although field and laboratory experiments provide important information about open-ended pile installation, it is difficult to reliably measure the highly non-uniform stress and strain fields near the pile shaft. Numerical simulation offers great potential for obtaining more detailed information about the stress and strain fields. Traditional grid-based numerical methods, such as the standard Lagrangian finite element method (FEM), encounter great difficulties in simulating pile driving processes due to inevitable mesh distortion caused by large soil deformations. The computational cost of the discrete element method is extremely high and may not currently provide a feasible approach for solving practical pile installation problems. Summary of the Invention

[0004] The purpose of the present invention is to propose a method for constructing a numerical model of the soil plug effect of an open-ended pile based on the material point method in view of the deficiencies of the prior art.

[0005] The purpose of the present invention is achieved through the following technical solutions: A method for constructing a numerical model of the soil plug effect of an open-ended 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 frictional resistance on the inner and outer sides of the pile, soil stress, soil plug height, and displacement field;

[0007] S2. Simulate the driving process of the open-ended pile based on the material point method:

[0008] Establish the same two-dimensional axisymmetric geometric model based on the indoor model tank test, divide the grid and perform hierarchical grid encryption; discretize the problem domain of the open-ended pile model into material points, and assign corresponding material parameters to the soil material points according to the mechanical parameters of the sandy soil obtained from the test to obtain the open-ended pile material point method model;

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

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

[0011] Obtain the data of the frictional resistance on the inner and outer sides of the pile, soil stress, soil plug height, and displacement field during the simulation time;

[0012] S3. Compare and analyze the indoor test results with the numerical simulation results. If the error meets the requirements, confirm that the numerical model is reliable; if the comparison result does not meet the requirements, optimize and adjust the numerical model until the error meets the requirements.

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

[0014] Arrange strain gauges on the inner and outer sides of the semi-model aluminum sleeve open-ended pile; fill the model test box, bury earth pressure cells at different soil depths and radial positions, and arrange a photographic system on one side of the glass surface;

[0015] Conduct static pressure construction according to the design conditions, record the data of the strain gauges, earth pressure cells, and high-speed cameras, and obtain the data of the frictional resistance on the inner and outer sides of the pile, soil stress, soil plug height, and displacement field.

[0016] Furthermore, the recording of the data of the strain gauges, earth pressure cells, and high-speed cameras to obtain the data of the frictional resistance on the inner and outer sides of the pile, soil stress, soil plug height, and displacement field specifically includes:

[0017] The frictional resistance is measured by the strain gauges arranged on the semi-model aluminum sleeve open-ended pile to obtain the inner frictional resistance and outer frictional resistance of the pile;

[0018] The soil stress is measured by the earth pressure cells for the radial, circumferential, and vertical stresses of the sand within a range of D - 10D from the pile axis in the radial direction, where D is the pile diameter;

[0019] The displacement field data is obtained by processing and analyzing the continuous deformation pictures of the soil around the pile during the pile driving process synchronously using the DIC technology by the high-speed camera.

[0020] Furthermore, the establishment of the same two-dimensional axisymmetric geometric model based on the indoor model tank test includes: establishing an open-ended pile model with the same dimensions according to the data of the model tank width, height, pile diameter, and pile wall thickness.

[0021] Furthermore, the division of the grid and the hierarchical grid encryption include: determining the minimum grid size, determining the number of grid encryption layers; dividing the grid using regular rectangular elements and performing hierarchical grid encryption, and setting the number of material points within the element.

[0022] Further, the specific steps of the material point method simulation include:

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

[0024] Based on the grid node positions and material point positions of the open-ended pile material point method model, calculate the nodal shape function values and shape function gradient values using basis functions;

[0025] Loop through each object, and map the material point information of each object to the grid nodes through the calculated shape function values;

[0026] Apply the same displacement boundary conditions and stress boundary conditions as in the model tank test to the grid nodes;

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

[0028] Solve the momentum equation without considering contact to calculate the trial momentum of the grid nodes;

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

[0030] Map the grid node velocity and position information back to the material points through the shape function values and update the material point information; repeat the above material point method simulation process until the simulation time ends.

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

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

[0033] Further, during the simulation of the open-ended pile driving process, the Mohr-Coulomb model is used as the constitutive model of the soil.

[0034] On the other hand, the specification also provides a numerical model construction device for the soil plug effect of open-ended piles based on the material point method, including a test model box, a memory, and one or more processors. The test model box is used to conduct 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-ended pile driving process based on the material point method and the process of comparing and analyzing the indoor test results and numerical simulation results.

[0036] Advantages of the present invention:

[0037] Obtaining calibration data through semi - model slot tests provides a reliable basis for numerical models. The axisymmetric material point method combined with the mesh encryption strategy significantly saves the computational cost, while ensuring the accurate simulation of the pile driving area and improving the accuracy of the results. Calibrating the numerical model based on indoor test data further optimizes the construction of the numerical model.

[0038] Each material point can carry individual material information. After further exploring the geological information, based on the reliable numerical model, the numerical models of multi - layer soil and large - diameter open - ended piles (D / t>20) can be constructed, further optimizing the design and construction plan of pipe piles. Brief Description of the Drawings

[0039] Figure 1 It is the geometric model of the numerical model and the distribution diagram of discrete material points in the embodiment of the present invention;

[0040] Figure 2 It is the contour map of the cumulative vertical displacement field of the numerical model in the embodiment of the present invention after the pile penetrates a certain depth;

[0041] Figure 3 It is the schematic diagram of the device for constructing the numerical model of the soil plug effect of open - ended piles based on the material point method provided by the embodiment of the present invention. Detailed Description of the Invention

[0042] The following further elaborates on the specific embodiments of the present invention with reference to the drawings.

[0043] Step 1: Conduct indoor model slot tests

[0044] S11: Select 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: Arrange strain gauges on the inner and outer sides of the open - ended pile in the semi - model aluminum sleeve to monitor the frictional resistance on the inner and outer sides of the pile respectively;

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

[0047] S14: Carry out static pressure construction according to the design conditions, drive the pile into the specified position, record the data of strain gauges, soil pressure cells and high - speed cameras, and analyze to obtain the frictional resistance on the inner and outer sides of the pile, soil stress, soil plug height and displacement field data.

[0048] Step 2: Simulate the jacked pile driving process based on the material point method:

[0049] S21. Establish the same two-dimensional axisymmetric geometric model based on the indoor model tank test. Establish an open-ended pile model with the same dimensions according to the data such as the width, height, pile diameter, and pile wall thickness of the model tank; determine the minimum grid size (t / 4), and determine the number of grid refinement layers (4 layers); divide the grid using regular rectangular elements and perform hierarchical grid refinement, and set the number of material points in the element (4); the entire problem domain is discretized into material points, as Figure 1 and Figure 2 shown. Through the above steps, a material point method model corresponding to the actual model size is obtained.

[0050] S22. Set the constitutive model parameters for the open-ended pile model. The Mohr-Coulomb model is adopted for the soil material points, and the main parameters include elastic modulus, Poisson's ratio, density, cohesion, and internal friction angle, which are the same as those of the sand 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 tank test to the open-ended pile model. The bottom is set as a fixed boundary, and the left and right sides are set as symmetric boundary conditions. In this embodiment, there is no additional load on the upper part of the soil in the model tank test, so the upper boundary of the numerical model is set as a free boundary.

[0052] S24. Set the key calculation parameters such as the pile-soil friction coefficient (ranging from 0 to 1, and taking 0.5 in this embodiment) and the pile penetration speed (5 m / s in this embodiment) for the open-ended pile model.

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

[0054] S26. Perform the material point method simulation on the open-ended pile model: Set the parameters related to the simulation calculation for the open-ended 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 settings, damping coefficient, etc. Solve and calculate the open-ended pile model generated in the above steps. The specific calculation steps include:

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

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

[0057] Table Types of Truncated Cubic B-Spline Shape Functions and Shape Function Gradients

[0058] Type Shape function Gradient of shape function 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) Loop over each object and map the material point information of each object to the grid nodes through the shape function values calculated in step (2);

[0060]

[0061]

[0062]

[0063]

[0064]

[0065] Superscript represents the current time step, and superscript represents the object, represents the time step size; represents the value of the shape function of node I at material point p; represents the value of the gradient of the shape function of node I at material point p; and represent the masses of node I and material point p respectively; and represent the position and velocity of material point p respectively; and represent the momenta of node I and material point p respectively; represents the nodal force, represents the external nodal force, represents the internal nodal force, represents the nodal traction; represents the body force of 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 the i direction, then let:

[0068]

[0069] The stress boundary is applied by taking the traction as the particle force:

[0070]

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

[0072] (5) Update the stress and strain information of the material points using the constitutive model in S22;

[0073]

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

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

[0076]

[0077] Denote the predicted trial momentum.

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

[0079]

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

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

[0082]

[0083]

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

[0085] S27. Obtain the relevant data during the pile driving process, including the curve graphs of the skin friction on the inner and outer sides of the pile with the penetration depth, the curve graph of the change in the soil plug height, and the data of the stress field and displacement field around the pile during the pile driving process;

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

[0087] S31. Compare and analyze the data of the frictional resistance on the inner and outer sides of the pile, soil stress, soil plug height, and displacement field recorded during the indoor model test with the numerical simulation results. According to the error evaluation criterion, if the error of the numerical simulation results meets the predetermined accuracy requirements, the numerical model is confirmed to be effective; if the error is large, adjust the parameters in the numerical model, optimize the key parameters such as the pile-soil friction coefficient and damping coefficient, and re-simulate until a reliable numerical model is obtained.

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

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

[0090] See Figure 3 , the memory stores executable code, and when the processor executes the executable code, it realizes the process of simulating the pile driving process of the open-ended pile based on the material point method and the process of comparing and analyzing the indoor test results and the numerical simulation results.

[0091] The embodiment of the device for constructing a numerical model of the soil plug effect of an open-ended pile based on the material point method provided by the present invention can be applied to any device with data processing capabilities. The device with data processing capabilities can be a device or apparatus such as a computer. The device embodiment can be implemented by software, or by hardware or a combination of software and hardware. Taking software implementation as an example, as a logically meaningful device, it is formed by the processor of any device with data processing capabilities reading the corresponding computer program instructions in the non-volatile memory into the memory for operation. From the hardware level, as Figure 3 shown, it is a hardware structure diagram of any device with data processing capabilities where the device for constructing a numerical model of the soil plug effect of an open-ended pile based on the material point method provided by the present invention is located. In addition to Figure 3 the shown processor, memory, network interface, and non-volatile memory, the device where the device embodiment is located in any device with data processing capabilities usually also includes other hardware according to the actual functions of the device with data processing capabilities, which will not be elaborated here.

[0092] The specific implementation processes of the functions and roles of each unit in the above device are specifically described in the implementation processes of the corresponding steps in the above method, which will not be elaborated here.

[0093] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can be referred to the descriptions in the method embodiments. The device embodiments described above are merely illustrative. 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 to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of the present invention. A person of ordinary skill in the art can understand and implement it without creative work.

[0094] An embodiment of the present invention also provides a computer-readable storage medium, on which a program is stored. When the program is executed by a processor, it implements a method for constructing a numerical model of the soil plug effect of an open-ended pile based on the material point method in the above embodiments.

[0095] The computer-readable storage medium may be an internal storage unit of any device with data processing capabilities described in any of the foregoing 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. Further, 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 can also be used to temporarily store the data that has been output or will be output.

[0096] After considering the specification and practicing the content disclosed herein, those skilled in the art will readily think of other embodiments of the present application. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of the present application are pointed out by the claims.

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

Claims

1. A method for constructing a numerical model of the soil plug effect of open-ended piles based on the material point method, characterized in that It includes the following steps: S1. Conduct indoor model tank tests to obtain the mechanical parameters of sandy soil materials, the frictional resistance on the inner and outer sides of the pile, the soil stress, the soil plug height, and the displacement field data; S2. Simulate the sinking process of the open-ended pile based on the material point method: Establish the same two-dimensional axisymmetric geometric model based on the indoor model tank test, divide the grid and perform hierarchical grid encryption; discretize the problem domain of the open-ended pile model into material points, and assign the corresponding material parameters to the soil material points according to the mechanical parameters of the sandy soil obtained from the test to obtain the material point method model of the open-ended pile; Apply the same boundary conditions and loads as in the model tank test and conduct material point method simulation: Map the information of each material point to the grid nodes through the basis function, solve the trial momentum of the grid nodes without considering contact, calculate the contact force and correct the trial momentum, map the grid node information back to the material points through the basis function, update the material point information, and repeat the simulation steps until the simulation time ends; Obtain the frictional resistance on the inner and outer sides of the pile, the soil stress, the soil plug height, and the displacement field data during the simulation time; S3. Compare and analyze the indoor test results with the numerical simulation results. If the error meets the requirements, confirm that the numerical model is reliable; if the comparison results do not meet the requirements, optimize and adjust the numerical model until the error meets the requirements.

2. A method for constructing a numerical model of the soil plug effect of open-ended piles based on the material point method, characterized in that, The indoor model tank test includes: Arrange strain gauges on the inner and outer sides of the open-ended pile in the semi-model aluminum sleeve; fill the model test box, bury soil pressure cells at different soil depths and radial positions, and arrange a photographic system on one side of the glass surface at the same time; Carry out static pressure construction according to the design conditions, record the data of the strain gauges, soil pressure cells, and high-speed cameras, and obtain the frictional resistance on the inner and outer sides of the pile, the soil stress, the soil plug height, and the displacement field data.

3. A method for constructing a numerical model of the soil plug effect of open-ended piles based on the material point method according to claim 2, characterized in that The recording of the data of the strain gauges, soil pressure cells, and high-speed cameras to obtain the frictional resistance on the inner and outer sides of the pile, the soil stress, the soil plug height, and the displacement field data specifically includes: The frictional resistance is measured by the strain gauges arranged on the open-ended pile in the semi-model aluminum sleeve to obtain the inner frictional resistance and outer frictional resistance of the pile; The soil stress is measured by the soil pressure cells to measure the radial, circumferential, and vertical stresses of the sandy soil within the range of the radial distance D - 10D from the pile axis, where D is the pile diameter; The displacement field data is obtained by processing and analyzing the continuous deformation pictures of the soil around the pile during the sinking process synchronously by the high-speed camera using the DIC technology.

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

5. A method for constructing a numerical model of the soil plug effect of open-ended piles based on the material point method, characterized in that, The division of the grid and the hierarchical grid encryption include; determining the minimum grid size, determining the number of grid encryption layers; dividing the grid using regular rectangular elements and performing hierarchical grid encryption, and setting the number of material points in the element.

6. The numerical model construction method for the soil plug effect of open-ended piles based on the material point method according to claim 1, characterized in that The conduct of the material point method simulation specifically includes: Read the material point method model of the open-ended pile and initialize the relevant calculation parameters of the model; Based on the grid node positions and material point positions of the material point method model of the open-ended pile, calculate the shape function values and shape function gradient values of the nodes using the basis function; Loop through each object and map the material point information of each object to the grid nodes through the calculated shape function values; Apply the same displacement boundary conditions and stress boundary conditions to the grid nodes as in the model tank test; Update the stress and strain information of the material points using the constitutive model; Solve the momentum equation without considering contact to calculate the trial momentum of the grid nodes; Calculate the contact force based on the contact algorithm and correct the trial momentum; Map the grid information back to the material points through the shape function values and update the information of the material points; Repeat the above material point method simulation process until the simulation time ends.

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

8. A method for constructing a numerical model of the soil plug effect of open-ended piles based on the material point method, 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 symmetric boundary conditions.

9. A method for constructing a numerical model of the soil plug effect of open-ended piles based on the material point method, characterized in that, During the simulation of the jacked pile driving process, the Mohr-Coulomb model is used as the constitutive model of the soil.

10. An apparatus for implementing the method according to any one of claims 1-9, characterized in that, It includes a test model box, a memory, and one or more processors. The test model box is used to conduct indoor model tank tests and obtain data; The memory stores executable code. When the processor executes the executable code, it realizes the process of simulating the jacked pile driving process based on the material point method and the process of comparative analysis of indoor test results and numerical simulation results.

Images