Simulation analysis method for pore pressure static sounding in normal consolidated soil and over-consolidated soil

Abstract

The invention relates to the technical field of geotechnical engineering, in particular to a simulation analysis method for piezocone penetration in normal consolidated soil and over-consolidated soil, which comprises the following steps: S1, establishing a two-dimensional piezocone penetration numerical calculation model: establishing the two-dimensional numerical calculation model by using finite element analysis software, and adopting a two-dimensional axisymmetric deformable body as a soil body, the pore pressure static sounding adopts a two-dimensional axisymmetric discrete rigid body, soil material attributes, load conditions and boundary conditions are set, and changes of pore water pressure are simulated through numerical analysis; s2, the penetration speed is determined, wherein a dimensionless speed coefficient is calculated, and the drainage state of the soil body is determined; and S3, applying a load to the surface layer of the soil body, wherein no load is applied to the normal consolidated soil, and a time-varying load is applied to the surface layer of the soil body to the over-consolidated soil. According to the method, the modeling method of the pore pressure static sounding in the normally consolidated and over-consolidated soil and the implementation means of the over-consolidated ratio are realized, the calculation is convenient, and the result is accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of geotechnical engineering, and particularly relates to a simulation analysis method for piezocone penetration test in normally consolidated soil and overconsolidated soil. Background Art

[0002] In recent years, with the continuous development of survey means and data acquisition technologies, in-situ testing technologies in the ocean have gradually emerged and have been widely applied to the testing of ocean geotechnical engineering parameters, foundation evaluation, and engineering design. The piezocone penetration test (CPTU) is a new type of in-situ testing technology. Its penetration process is similar to the penetration mechanism of driven piles. It can continuously measure the cone tip resistance, sidewall friction resistance, and pore water pressure under the in-situ natural stress state. This technology does not require sampling, is simple, fast, and reliable in operation, so it is widely used in various tests of geotechnical engineering. With the improvement of in-situ testing technologies and data acquisition means, the method for determining the vertical bearing capacity of pile foundations based on the piezocone penetration test has been applied more and more.

[0003] The piezocone penetration test is usually carried out near the designed pile position, which helps to accurately restore the soil parameters in the actual project, thereby improving the accuracy of the calculation of pile foundation bearing capacity. However, the test results of the piezocone penetration test are often affected by on-site construction factors, such as the non-standard operation of technicians, resulting in inaccurate test results, especially in the measurement of pore water pressure. These problems limit the wide application of the piezocone penetration test technology under complex soil conditions. Especially when the consolidation state of the soil changes greatly, the reliability and accuracy of the test results may be greatly reduced. Summary of the Invention

[0004] The present invention provides a simulation analysis method for piezocone penetration test in normally consolidated soil and overconsolidated soil. By establishing a numerical calculation model, the test results of the piezocone penetration test can be predicted according to the actual parameters of the soil, thereby improving the accuracy of test parameters such as pore water pressure. By accurately simulating the behavior of the soil under different consolidation states, the on-site test conditions can be better restored, the reliability of the test results of the piezocone penetration test can be improved, and more accurate data support can be provided for the evaluation of pile foundation bearing capacity.

[0005] A simulation analysis method for piezocone penetration test in normally consolidated soil and overconsolidated soil includes the following steps: S1, establishing a two-dimensional numerical calculation model for piezocone penetration test: using finite element analysis software to establish a two-dimensional numerical calculation model. The soil is a two-dimensional axisymmetric deformable body, and the piezocone penetration is a two-dimensional axisymmetric discrete rigid body. Set the material properties, load conditions, and boundary conditions of the soil, and simulate the change of pore water pressure through numerical analysis; S2, determining the penetration speed: calculating the dimensionless speed coefficient to determine the drainage state of the soil; S3, Application of surface load on soil mass: For normally consolidated soil, no load is applied. For overconsolidated soil, a time-varying load is applied on the soil surface to keep the overconsolidation ratio of the soil mass unchanged during the penetration process.

[0006] Optionally, the establishment of the two-dimensional piezocone penetration numerical calculation model in S1 includes: S11, Modeling using finite element analysis software: Use finite element analysis software (Abaqus) to establish a piezocone penetration model. Construct components according to the dimensions of the piezocone penetration and the soil mass parameters. The piezocone penetration adopts two-dimensional axisymmetric discrete rigid bodies, and the soil mass adopts two-dimensional axisymmetric deformable bodies. During the construction of the piezocone penetration model, set the distance between the left edge of the soil mass and the axis of symmetry to 0.05r, where r is the radius of the piezocone penetration; S12, Defining soil material properties: Use the modified Cam clay model in the numerical analysis software Abaqus to define the material properties of the soil mass; S13, Model assembly: Assemble the piezocone penetration and the soil mass, and adjust the position of the piezocone tip; S14, Defining analysis steps: Create a geostatic equilibrium analysis step and a penetration analysis step, enable the large deformation calculation option, and determine the time of the penetration analysis step according to the penetration speed and depth; S15, Setting the contact conditions between the piezocone penetration test and the soil mass: Set the outer side of the probe and the outer side of the probe rod of the piezocone penetration as the master surface, and set the symmetry plane of the soil mass as the slave surface. Establish the surface-to-surface contact between the piezocone penetration and the soil mass, and use the hard contact algorithm to process the normal contact and the smooth contact algorithm to process the tangential contact; S16, Defining soil load, initial conditions and boundary conditions: Set soil load, initial conditions and boundary conditions, including applying soil gravity, time-varying vertical load, initial void ratio, radial stress distribution, and applying displacement constraints to the boundary, where the vertical load on the surface of normally consolidated soil is zero; S17, Mesh setting: The soil mesh adopts CAX8P elements to simulate the pore water pressure during the penetration process.

[0007] Optionally, the defining of soil load, initial conditions and boundary conditions in S16 includes: S161, Setting soil gravity: Apply the gravity of the soil mass through body force and simulate the excess pore water pressure; S162, The vertical load on the surface of normally consolidated soil is zero; When it is the surface of overconsolidated soil, apply a time-varying vertical pressure load: Apply a time-varying vertical pressure load on the soil surface, and the load distribution function is associated with the overconsolidation ratio and the penetration time; S163. Set the initial conditions of the soil mass: Set the initial void ratio of the soil mass and distribute the radial stress on the symmetry plane of the soil mass to simulate the influence of the surrounding soil pressure on the soil mass; S164. Set the boundary conditions: Constrain the horizontal displacement U1 and the vertical displacement U2 on the outer side and the bottom surface of the soil mass respectively.

[0008] Optionally, the dimensionless velocity coefficient is expressed as: ; Wherein, is the dimensionless velocity coefficient, is the diameter of the piezocone penetration test rod, is the absolute loading speed, is the consolidation coefficient of the soil mass.

[0009] Optionally, the drainage state of the soil mass includes: When the dimensionless velocity coefficient , the soil mass is in a fully drained state; When the dimensionless velocity coefficient , the soil mass is in a partially drained state; When the dimensionless velocity coefficient , the soil mass is in a fully undrained state; When the dimensionless velocity coefficient , the rate effect exists in the response of the soil mass.

[0010] Optionally, applying the time-varying load on the surface layer of the overconsolidated soil mass includes: Determine the total time of the penetration process: Determine the total time of the penetration process according to the penetration depth and speed ; Calculate the load applied to the surface layer: Set that when the total penetration depth is , the effective overburden stress at this depth is , the homogeneous overconsolidation ratio of the soil layer is , and calculate the load applied to the surface layer; Set the function of the load varying with time: Set the way of the load varying with time through the Amp linear function to realize the time variation of the load in the numerical calculation.

[0011] Optionally, the load applied to the surface layer is expressed as .

[0012] Advantages of the present invention: In the present invention, by establishing a two-dimensional numerical calculation model of piezocone penetration and applying finite element analysis software, combining the modified Cam clay model and the corresponding load application method, the change of pore water pressure during the penetration process can be effectively predicted, so as to provide a reliable basis for soil parameter testing and pile foundation bearing capacity calculation.

[0013] In the present invention, by reasonably setting the penetration speed, the load application method, and the adjustment means of the overconsolidation ratio, the accurate simulation of the load changing with time in overconsolidated soil is ensured, so that the overconsolidation ratio of the soil mass remains unchanged during the penetration process, avoiding the possible errors in the traditional method. It is not only simple in calculation and accurate in results, but also can obtain consistent and high-precision simulation results under different soil conditions, which has important practical application value for optimizing soil parameter testing and engineering design. Brief Description of the Drawings

[0014] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings described below are only those of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0015] Figure 1 Schematic diagram of the piezocone penetration test calculation model for the embodiment of the present invention; Figure 2 Schematic diagram of the function of the load changing with time for the embodiment of the present invention; Figure 3 Schematic diagram of the analysis method flow for the embodiment of the present invention. Detailed Embodiments

[0016] The present invention will be described in detail below in conjunction with the drawings and specific embodiments. At the same time, it should be noted here that in order to make the embodiments more detailed, the following embodiments are the best and preferred embodiments. For some well-known technologies, those skilled in the art can also adopt other alternative methods for implementation; moreover, the drawings are only for more specific description of the embodiments and are not intended to specifically limit the present invention.

[0017] It should be pointed out that in the specification, references to "an embodiment", "embodiments", "exemplary embodiments", "some embodiments", etc. indicate that the described embodiments may include specific features, structures, or characteristics, but not necessarily every embodiment includes such specific features, structures, or characteristics. Additionally, when combining embodiments to describe specific features, structures, or characteristics, implementing such features, structures, or characteristics in combination with other embodiments (whether explicitly described or not) should be within the knowledge of those skilled in the relevant art.

[0018] Generally, terms can be understood at least in part from their use in context. For example, depending at least in part on the context, the term "one or more" as used herein can be used to describe any feature, structure, or property in the singular sense, or can be used to describe a combination of features, structures, or properties in the plural sense. Additionally, the term "based on" can be understood as not necessarily intended to convey a set of exclusive factors, but rather can alternatively, depending at least in part on the context, allow for the existence of other factors that are not necessarily explicitly described.

[0019] As Figures 1 - 3 shown, a method for simulating and analyzing piezocone penetration tests in normally consolidated soil and overconsolidated soil includes the following steps: 1. Two-dimensional numerical calculation model for piezocone penetration tests: The process of establishing a two-dimensional piezocone penetration test model mainly includes the following steps: (1) Use finite element analysis software (such as Abaqus, etc.) for modeling. Establish components according to the dimensions of the piezocone penetration test and the soil body dimensions. The piezocone penetration test uses a two-dimensional axisymmetric discrete rigid body, and the soil body uses a two-dimensional axisymmetric deformable body. In order to avoid severe mesh distortion of the soil body during the penetration process, according to the research results in the literature, set the distance between the left edge of the soil body and the axis of symmetry to 0.05 r ( r is the radius of the piezocone penetration test), as Figure 1 shown.

[0020] (2) Define the material properties of the soil body. In order to simulate the evolution law of pore water pressure during the penetration process, the modified Cambridge model in the numerical analysis software Abaqus is used.

[0021] (3) Model assembly. Assemble the piezocone penetration test CPTU and the soil body together, adjust the position of the tip of the piezocone penetration test to ensure its embedding in the soil body and good contact. After the assembly is completed, as Figure 1 shown.

[0022] (4) Define the analysis steps. Create a geostatic equilibrium analysis step and a penetration analysis step, turn on the large deformation calculation option, and determine the time of the penetration analysis step according to the penetration speed and depth.

[0023] (5) Set the contact between the piezocone penetration test and the soil body. Set the outer side of the probe and the outer side of the rod as the master surface, and set the symmetric plane of the soil body as the slave surface to establish the surface-to-surface contact between the piezocone penetration test and the soil body. The normal direction uses a hard contact algorithm, and the tangential direction uses a smooth contact algorithm.

[0024] (6) Define the soil load, initial conditions, and boundary conditions. The soil gravity is applied through body force, and the pore water pressure simulated at this time is the excess pore water pressure; a time-varying vertical pressure load is applied on the surface, and the load distribution function has a functional relationship with the overconsolidation ratio and the penetration time. The determination method will be given in the following text. The initial conditions of the soil need to set the initial void ratio. The distribution of the radial stress along the depth is set on the soil symmetry plane to simulate the pressure of the surrounding soil on the soil in the radial direction; the horizontal displacement U1 and the vertical displacement U2 are respectively constrained on the outer side and the bottom surface of the soil.

[0025] (7) Mesh setting. The soil mesh uses CAX8P elements to simulate the pore water pressure during the penetration process.

[0026] 2. Determination of the penetration speed: When the dimensionless velocity coefficient V < 0.01, the soil is in a fully drained state; when V is in the range of 0.01 - 30, the soil is in a partially drained state; when V > 30, the soil is in a fully undrained state; when V > 300, the rate effect exists in the soil response.

[0027] (1) In the formula: V is the dimensionless velocity coefficient; D is the diameter of the piezocone penetrometer rod; v is the absolute loading speed; c v is the consolidation coefficient of the soil.

[0028] The penetration speed in the numerical calculation is determined by the actual penetration speed, and the drainage conditions of the soil during the penetration process are judged through formula (1).

[0029] 3. Method for applying the soil surface load: (1) During the piezocone penetration test in normally consolidated soil, no load is applied on the soil surface; (2) During the piezocone penetration test in homogeneous overconsolidated soil, a time-varying load needs to be applied on the soil surface to ensure that the overconsolidation ratio at any depth during the penetration process is maintained as constant as possible. The specific method is as follows: a) Determine the total time of the penetration process according to the penetration depth and speed ; b) Assume that when the total penetration depth is , the effective overburden stress at this depth is , the homogeneous overconsolidation ratio of the soil layer is , then the load that needs to be applied on the surface is ; c) Set the function of the load varying with time, that is, the variation of the load with time is realized through the Amp linear function in the numerical calculation, such as Figure 2As shown in the figure, 0 and 34 in Time / Frequency respectively correspond to the initial penetration time and the total time.

[0030] The present invention encompasses any alternatives, modifications, equivalent methods, and solutions made to the essence and scope of the present invention. For the public to have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, and those skilled in the art can fully understand the present invention without the description of these details. Additionally, well-known methods, processes, procedures, components, and circuits, etc. are not described in detail to avoid unnecessary confusion to the essence of the present invention.

[0031] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for simulating and analyzing piezocone penetration tests in normally consolidated soils and overconsolidated soils, characterized in that, It includes the following steps: S1. Establish a two-dimensional piezocone penetration numerical calculation model: Use finite element analysis software to establish a two-dimensional numerical calculation model. The soil body is a two-dimensional axisymmetric deformable body, and the piezocone penetration is a two-dimensional axisymmetric discrete rigid body. Set the soil material properties, load conditions, and boundary conditions, and simulate the change of pore water pressure through numerical analysis; S2. Determine the penetration speed: Calculate the dimensionless speed coefficient to determine the drainage state of the soil body; S3. Apply the surface load of the soil body: Do not apply load to the normally consolidated soil, and apply a time-varying load to the overconsolidated soil on the soil surface to keep the overconsolidation ratio of the soil body unchanged during the penetration process.

2. The method for simulating and analyzing piezocone penetration tests in normally consolidated soils and overconsolidated soils according to claim 1, characterized in that, The establishment of the two-dimensional piezocone penetration numerical calculation model in S1 includes: S11. Model building using finite element analysis software: Use finite element analysis software to establish a piezocone penetration model. Construct components according to the size of the piezocone penetration and the size parameters of the soil body. The piezocone penetration is a two-dimensional axisymmetric discrete rigid body, and the soil body is a two-dimensional axisymmetric deformable body. During the construction of the piezocone penetration model, set that the piezocone penetration does not directly contact the surrounding soil body. The distance between the piezocone penetration and the left edge of the soil body can be set to 0.05r, where r is the radius of the piezocone penetration; S12. Define the soil material properties: Use the modified Cam clay model in the numerical analysis software Abaqus to define the soil material properties; S13. Model assembly: Assemble the piezocone penetration and the soil body, and adjust the position of the piezocone tip; S14. Define the analysis steps: Create a geostatic equilibrium analysis step and a penetration analysis step, enable the large deformation calculation option, and determine the time of the penetration analysis step according to the penetration speed and depth; S15. Set the contact conditions between the piezocone penetration and the soil body: Set the outer side of the probe and the outer side of the probe rod of the piezocone penetration as the master surface, and set the symmetry plane of the soil body as the slave surface. Establish the surface-to-surface contact between the piezocone penetration and the soil body, and use the hard contact algorithm to process the normal contact and the smooth contact algorithm to process the tangential contact; S16. Define the soil load, initial conditions, and boundary conditions: Set the soil load, initial conditions, and boundary conditions, including applying the soil gravity, the time-varying vertical load, the initial void ratio, the radial stress distribution, and applying displacement constraints to the boundary. The vertical load on the surface of the normally consolidated soil is zero; S17. Mesh setting: The soil mesh uses CAX8P elements to simulate the pore water pressure during the penetration process.

3. The method for simulating and analyzing piezocone penetration tests in normally consolidated soils and overconsolidated soils according to claim 2, characterized in that, The definition of the soil load, initial conditions, and boundary conditions in S16 includes: S161. Set the soil gravity: Apply the gravity of the soil body through body force and simulate the excess pore water pressure; S162. The vertical load on the surface of the normally consolidated soil is zero; When it is the surface of the overconsolidated soil, apply a time-varying vertical pressure load: Apply a time-varying vertical pressure load on the soil surface, and the load distribution function is associated with the overconsolidation ratio and the penetration time; S163. Set the initial conditions of the soil body: Set the initial void ratio of the soil body and distribute the radial stress on the symmetry plane of the soil body to simulate the influence of the surrounding soil pressure on the soil body; S164. Set boundary conditions: Horizontally displacements U1 and vertically displacements U2 are constrained on the outer side and the bottom surface of the soil mass respectively.

4. The method for simulating and analyzing piezocone penetration tests in normally consolidated soils and overconsolidated soils according to claim 3, characterized in that, The dimensionless velocity coefficient is expressed as: ； Among them, is a dimensionless velocity coefficient, is the diameter of the piezocone sounding rod, is the absolute loading velocity, is the consolidation coefficient of the soil mass.

5. The method for simulating and analyzing piezocone penetration tests in normally consolidated soils and overconsolidated soils according to claim 4, characterized in that, The drainage state of the soil mass includes: When the dimensionless velocity coefficient the soil mass is in a fully drained state; When the dimensionless velocity coefficient the soil mass is in a state of partial drainage; When the dimensionless velocity coefficient the soil mass is in a completely undrained state; When the dimensionless velocity coefficient the rate effect exists in the response of soil mass.

6. The method for simulating and analyzing piezocone penetration tests in normally consolidated soils and overconsolidated soils according to claim 5, characterized in that, Applying a time-varying load on the surface layer of the overconsolidated soil mass includes: Determine the total time of the penetration process: Determine the total time of the penetration process based on the penetration depth and speed ; Calculate the surface applied load: Set that when the total penetration depth is , the effective overburden stress at this depth is , the soil layer homogeneity overconsolidation ratio is , and calculate the surface applied load; Set the function of the load varying with time: Set the way of the load varying with time through the Amp linear function to realize the time variation of the load in numerical calculation.

7. A method for simulating and analyzing piezocone penetration tests in normally consolidated soil and overconsolidated soil according to claim 6, characterized in that The surface applied load is expressed as .

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