Soil-rock interface shear statistical damage constitutive model construction method considering interface slippage dynamic change

Abstract

The invention belongs to the field of geotechnical engineering, and provides a soil-rock interface shear statistical damage constitutive model construction method considering interface slippage dynamic change, and the method comprises the following steps: S1, constructing a soil-rock interface shear test platform, preparing soil-rock interface samples under different normal stress, moisture content and shear rate conditions, carrying out a shear test under the hydraulic coupling effect to obtain an interface shear stress-shear displacement curve; step S2, based on a statistical damage theory and in combination with a traditional contact surface statistical damage constitutive model, deriving a thickness-free soil-rock interface statistical damage constitutive model considering residual strength so as to represent damage evolution characteristics of the interface in a shear slip process; and S3, based on the shear stress-shear displacement curve, performing parameter identification on the thickness-free soil-rock interface statistical damage constitutive model considering the residual strength, and determining mechanical parameters in the model. According to the method, the calculation stability is improved, optimization is performed in combination with test data, and the engineering applicability is improved.

Description

Technical Field

[0001] The present invention belongs to the field of geotechnical engineering, and particularly relates to a method for constructing a shear statistical damage constitutive model of soil-rock interface considering dynamic changes of interface sliding. Background Technique

[0002] In the field of geotechnical engineering, soil-rock interfaces widely exist in engineering practices such as foundation pit engineering, slope stability analysis, tunnel engineering, and foundation. Due to the significant differences in the mechanical properties of soil and rock, their interfaces exhibit complex shear-slip behaviors under external loads. Especially during the excavation of deep foundation pits, tunnel tunneling, and slope deformation, interface shear-slip may cause local instability or even overall failure, seriously affecting engineering safety.

[0003] Currently, the mechanical research on soil-rock interfaces mainly focuses on shear strength, shear stiffness, and shear-slip characteristics. However, traditional constitutive models are difficult to accurately describe interface damage evolution, shear stiffness attenuation, and residual strength characteristics, resulting in large errors and insufficient reliability in engineering calculations and being difficult to meet the requirements under complex engineering environments. Therefore, establishing a statistical damage constitutive model that can describe interface shear damage evolution is of great significance for improving engineering prediction accuracy and optimizing support design. Summary of the Invention

[0004] To solve the problems in the prior art, the present invention provides a method for constructing a shear statistical damage constitutive model of soil-rock interface considering dynamic changes of interface sliding, including the following steps: Step S1, build a shear test platform for soil-rock interface, prepare soil-rock interface specimens under different normal stresses, water contents, and shear rates, and conduct shear tests under hydro-mechanical coupling to obtain interface shear stress-shear displacement curves; Step S2, based on the statistical damage theory, combined with the traditional contact surface statistical damage constitutive model, derive a zero-thickness soil-rock interface statistical damage constitutive model considering residual strength to characterize the damage evolution characteristics of the interface during shear-slip; Step S3, based on the shear stress-shear displacement curve, identify the parameters of the zero-thickness soil-rock interface statistical damage constitutive model considering residual strength to determine the mechanical parameters in the model.

[0005] Further, in step S1, the shear test includes: Fix the prepared soil-rock interface specimens in the shear test device, apply different normal stresses to simulate different burial depths or load conditions; Set different shear rates and conduct shear tests at 0.1 mm / min, 1 mm / min, and 10 mm / min respectively; Apply different pore water pressures through the hydro-mechanical coupling system to adjust the water flow direction and the hydraulic head gradient; Record the shear stress-shear displacement curve and monitor the damage, slip, and failure modes of the soil-rock interface during shearing; Repeat the test to obtain test data under different conditions.

[0006] Furthermore, the statistical damage theory is specifically as follows: , where: is the statistical damage; is the stress in the undamaged state; is the residual stress after complete damage; is the damage variable, and its value range is .

[0007] Furthermore, for the soil-rock interface, convert the statistical damage theory into the shear stress form: , where: is the shear stress; is the shear stress in the undamaged state; is the interface residual shear strength; characterizes the interface damage degree.

[0008] Furthermore, in the small deformation stage, the statistical damage constitutive model of the thicknessless soil-rock interface considering the residual strength is: , where: represents the shear stiffness; represents the initial shear stiffness; represents the shear displacement; represents the small deformation shear displacement threshold.

[0009] Furthermore, in the large deformation stage, the statistical damage constitutive model of the thicknessless soil-rock interface considering the residual strength is: , where: is an empirical parameter, a dimensionless parameter that controls the shear stress evolution rate; is the shear modulus, a physical quantity describing the shear resistance of a material; is the damage evolution parameter, a parameter controlling the evolution rate of the damage variable 𝐷; is the damage evolution exponent, an exponent characterizing the damage evolution rate.

[0010] Furthermore, when performing parameter identification on the zero-thickness soil-rock interface statistical damage constitutive model considering residual strength, the input data includes: Shear stress-shear displacement curve ; Shear stiffness vs. displacement curve ; Normal stress and water content .

[0011] Furthermore, the mechanical parameters in the model include: Shear stiffness ; Damage evolution parameter ; Residual shear strength .

[0012] Furthermore, when performing parameter identification on the zero-thickness soil-rock interface statistical damage constitutive model considering residual strength, set the number of calculation steps

[0013] , and set the convergence criterion that if 𝑛 is an integer multiple of 500, then enter the stiffness update step. Calculate the fitting error between the current stress curve and the test data: , where: is the model calculation value; is the test measured value; N is the number of data points.

[0014] The method for constructing the soil-rock interface shear statistical damage constitutive model considering the dynamic change of interface sliding provided by the present invention has the following beneficial effects: Accurately describe the shear damage evolution of the interface: Based on the statistical damage theory, the shear damage variable is established, which can accurately characterize the shear stiffness attenuation and shear strength change during the sliding process of the interface, and improve the prediction accuracy of shear behavior.

[0015] Consider the residual shear strength and improve the calculation stability: Introduce the residual shear strength, optimize the calculation of shear stress in the large deformation stage, make the model more applicable in foundation pit, slope and tunnel engineering, and enhance the long-term stability prediction ability.

[0016] Combine experimental data for parameter optimization and improve engineering applicability: Invert key parameters through shear test data, and calibrate the model by combining numerical calculations, making the model more in line with the actual engineering situation, and improving the accuracy and reliability of foundation pit support, slope stability and formation deformation prediction. Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments 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.

[0018] Figure 1 It is a schematic diagram of the method of the present invention. Detailed Embodiments

[0019] The following will make a preferred description of the invention in combination with the drawings and specific embodiments.

[0020] This embodiment solves the above problems through the following steps: In one embodiment, referring to Figure 1 , the present invention provides a method for constructing a shear statistical damage constitutive model of the soil-rock interface considering the dynamic change of interface slip. Based on experimental research, theoretical analysis and numerical simulation, the stress-strain relationship and damage evolution law of the material are determined, and a mathematical model capable of describing its mechanical behavior is established.

[0021] In the present invention, the dynamic change of interface slip refers to the relative displacement phenomenon generated during the shear deformation of the soil-rock interface under external loads and its evolution over time. Due to the significant differences in the mechanical properties of the soil layer and the rock layer, the interface may experience multiple stages such as elastic deformation, plastic deformation and slip failure under the stress state, showing non-linear shear mechanical characteristics. This method studies the influence of interface slip on shear stiffness, shear strength and residual strength through experiments and numerical simulations, and establishes the dynamic evolution law of shear slip to improve the description accuracy of the mechanical properties of the interface.

[0022] The soil-rock interface refers to the structural plane formed by the contact of soils and rocks with different compositions and mechanical properties under geological genetic actions. This interface is affected by both the self-weight pressure of the overlying soil and external loads, as well as the groundwater seepage. Its mechanical behavior plays a key role in foundation pit excavation, tunnel construction, and slope stability assessment. Since the soil-rock interface usually exhibits discontinuity, anisotropy, and strength softening effects, studying its shear properties is crucial for engineering safety.

[0023] The shear statistical damage constitutive model is a mathematical description method based on the damage mechanics theory, aiming to characterize the deformation and strength evolution relationship of the soil-rock interface under shear stress. By introducing a statistical damage variable, this model takes into account the cumulative effect of internal damage in the micro-structure and quantifies the mechanical degradation process of the interface material.

[0024] Specifically, the method of this embodiment includes the following steps: Step S10, build a soil-rock interface shear test platform, prepare soil-rock interface specimens under different normal stresses, water contents, and shear rates, and conduct shear tests under hydro-mechanical coupling to obtain the shear stress-shear displacement curve of the interface.

[0025] The soil-rock interface shear test platform is an experimental device used to simulate the mechanical behavior of the soil-rock interface under shear loads. This platform consists of a shear loading system, a normal loading system, a specimen fixing device, a displacement measurement system, a stress sensing system, and a data acquisition and analysis system. The shear loading system is used to apply horizontal shear force to simulate the stress state of the soil-rock interface in actual engineering; the normal loading system is used to apply different magnitudes of vertical stress to simulate the constraint state of the soil-rock interface under different burial depths or overlying load conditions; the specimen fixing device is used to maintain the stability of the soil-rock specimen and prevent unexpected movement of the specimen during the test; the displacement measurement system and the stress sensing system are used to monitor the interface displacement and stress changes in real time during shear; the data acquisition and analysis system is used to record, store, and process the test data to obtain the interface shear mechanical response curve.

[0026] The hydro-mechanical coupling refers to the change in mechanical behavior of the soil-rock interface under the combined action of groundwater seepage and external shear loads. Due to the presence of groundwater, the pore water pressure at the interface may change dynamically during the shear test, resulting in non-linear evolution of the interface shear stiffness, shear strength, and slip characteristics. The hydro-mechanical coupling affects the shear failure mode of the soil-rock interface, which may lead to the expansion of micro-cracks, particle loss, and shear softening at the interface. Therefore, by controlling the seepage conditions during the test, studying the influence of hydro-mechanical coupling on the shear mechanical properties of the soil-rock interface provides data support for establishing a more accurate shear damage constitutive model.

[0027] The specific experimental steps include: Step S11. Test platform setup 1) Select a large direct shear testing machine or a rotational shear testing device that can precisely control the normal stress and shear rate, and equip it with high-precision displacement sensors, force sensors, seepage monitoring systems, and data acquisition systems.

[0028] 2) Establish a hydro-mechanical coupling shear loading system, including an adjustable seepage channel to control the pore water pressure at the soil-rock interface during the test.

[0029] 3) Debug the test platform to ensure the stable operation of the normal loading system, shear loading system, and sensing and monitoring systems, and conduct preloading tests.

[0030] Step S12. Specimen preparation 1) Select typical combinations of upper soil layers and lower rock layers, and sample according to the actual engineering situation to ensure the representativeness of the specimens.

[0031] 2) Control the moisture content of the soil part, and use indoor humidification, drying, or vacuum saturation methods to treat the specimens to achieve different moisture content conditions.

[0032] 3) Control the surface roughness of the rock part, and use sandpapers with different gradations or mechanical processing to treat the soil-rock interface to simulate interface topographies with different undulations.

[0033] 4) Bond the soil and the rock to form an interface with no thickness, and ensure that the interface is perpendicular to the shear direction to avoid deviation affecting the test results.

[0034] Step S13. Shear test implementation 1) Fix the prepared soil-rock interface specimen in the shear test device, and apply different normal stresses (σ_n) to simulate different burial depths or loading conditions.

[0035] 2) Set different shear rates (v_s), and conduct low-speed (0.1 mm / min), medium-speed (1 mm / min), and high-speed (10 mm / min) shear tests respectively to study the influence of the rate on the interface shear performance.

[0036] 3) Apply different pore water pressures (u_w) through the hydro-mechanical coupling system, adjust the water flow direction and head gradient, and study the shear deformation characteristics under the action of dynamic water heads.

[0037] 4) Record the shear stress (τ)-shear displacement (δ) curve, and monitor the damage, slip, and failure modes of the soil-rock interface during the shear process.

[0038] 5) Repeat the test to obtain test data under different conditions, providing data support for the subsequent constitutive model construction.

[0039] Step S20: Based on the statistical damage theory and combined with the traditional statistical damage constitutive model of the contact surface, a statistical damage constitutive model of the soil-rock interface without thickness considering the residual strength is derived to characterize the damage evolution characteristics of the interface during the shear slip process.

[0040] In this step, starting from the general damage constitutive equation and combining the statistical damage theory, a constitutive model suitable for describing the slip shear behavior of the soil-rock interface is established. The whole process includes the establishment of the general damage constitutive equation, the derivation of the damage evolution equation, and the derivation of the shear stress-shear displacement relationship.

[0041] Step S21: Establishment of the general damage constitutive equation In damage mechanics, the stress of a material can be expressed as the stress in the undamaged state and the stress of the damaged part in combination: , where: is the statistical damage; is the stress in the undamaged state; is the residual stress after complete damage; is the damage variable, with a value range

[0042] For the soil-rock interface, we transform this formula into the shear stress form: , where: is the shear stress; is the shear stress in the undamaged state; is the interface residual shear strength; characterizes the degree of interface damage.

[0043] When , that is, when there is no damage, the shear stress is ; When , that is, when it is completely damaged, the shear stress drops to the residual shear strength ; The larger the damage variable , the lower the interface bearing capacity.

[0044] Step 22: Derivation of the damage evolution equation The statistical damage theory assumes that there are a large number of micro-units inside the material, and the failure of each unit follows a certain statistical distribution, such as the Weibull distribution. Assuming that the shear strain exceeds a certain threshold and then damage begins to accumulate, the damage variable can be described by the statistical distribution: , where: is the initial shear strain of damage; is the control parameter of the damage evolution rate; is the damage evolution exponent.

[0045] Substitute the damage variable into the generalized damage constitutive equation: , For the damage evolution stage: , This equation shows that as the shear strain increases, the damage variable gradually increases, causing the shear stress to gradually transition from to ; where the exponential term controls the attenuation rate of the shear stress.

[0046] Step 23: Derivation of the shear stress-shear displacement relationship The relationship between the shear strain and the shear displacement is: , where: is the thickness of the shear plane (for the soil-rock interface without thickness, directly use the shear displacement d); Thus, the shear strain damage variable becomes: , In the small deformation stage (i.e., the shear displacement ), the interface shear stiffness remains approximately constant, and the shear stress and shear displacement show a linear relationship: , There is no damage here (i.e., ), and the shear stiffness remains constant, , so the shear stress is linearly related to the displacement.

[0047] In the large deformation stage, that is, when the shear displacement is reached, the interface enters the plastic slip stage, and the shear stress is affected by the damage variable 𝐷: , where: The exponential decay term directly evolves from the exponential expression of the damage variable 𝐷; The residual strength term reflects the characteristic that when the interface undergoes slip failure, its ultimate shear strength tends to .

[0048] Step S30, based on the shear stress-shear displacement curve, perform parameter identification on the statistical damage constitutive model of the thicknessless soil-rock interface considering residual strength to determine the mechanical parameters in the model.

[0049] The core objective of this step is to use the shear test data and combine numerical calculation methods to identify and optimize the key mechanical parameters in the shear statistical damage constitutive model of the soil-rock interface. This process mainly includes steps such as data input, parameter initialization, optimization calculation, stiffness update, and convergence judgment to ensure that the model can accurately describe the shear behavior of the soil-rock interface.

[0050] The specific implementation includes the following steps: Step S31, preprocessing stage Read the shear test data of the soil-rock interface, including: Shear stress-shear displacement curve ; Shear stiffness vs. displacement curve ; Test conditions (normal stress , water content , etc.).

[0051] In the numerical calculation model, identify the node numbers of the upper and lower layers of the soil-rock interface and establish: Upper contact surface node array id1(m); Lower contact surface node array id2(m); Read the upper and lower layer element numbers of the contact surface according to the coordinate information and store them in: Upper contact element array: id1d(m); Lower contact element array: id2d(m); Set the initial contact surface parameters; Set the initial shear stiffness ;

[0052] Set the damage evolution parameter ;

[0053] Set the residual shear strength ;

[0054] Set the shear stiffness update rule: (Initial state); (After slip damage); Among them, represents the shear stiffness; Step S32. Calculation process Iterative calculation control: Set the iteration step size ; Set the number of calculation steps ; Set the convergence criterion: If 𝑛 is an integer multiple of 500, then enter the stiffness update link.

[0055] Read the node displacement: Read the arrays id1(m) and id2(m) to obtain the displacement d(m) of each node along the interface direction; Calculate the displacement increment Δd.

[0056] According to the shear stiffness evolution law, calculate the shear stiffness of each node: , Use the newly calculated Replace the originally stored shear stiffness ; Use the updated shear stiffness to calculate the current shear stress: , Record the calculated shear stress-shear displacement data and store it in the result array.

[0057] Step S33 Result convergence judgment Calculate the fitting error between the current stress curve and the test data: , Among them: is the model calculation value; is the measured value of the test; N is the number of data points.

[0058] Set the error convergence threshold , if: , It is considered that the identification of model parameters is completed and the calculation ends.

[0059] If not converged, continue with the optimization calculation Adjust using parameter optimization algorithms (such as genetic algorithm, particle swarm optimization, least squares method): Shearing stiffness , Damage evolution parameter , Residual shearing strength , Update the model parameters and continue the iterative calculation until the convergence condition is met.

[0060] For the part of the module structure not specifically defined in the present invention, it shall be subject to the content recorded in the prior art. The prior art mentioned in the foregoing background art part and the specific embodiment part of the present invention can be used as a part of the present invention to understand the meaning of some technical features or parameters.

Claims

1. A method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip, characterized in that The method includes the following steps: Step S1: Build a shear test platform for the soil-rock interface, prepare soil-rock interface specimens under different normal stresses, water contents, and shear rates, and conduct shear tests under the action of hydraulic coupling to obtain the shear stress-shear displacement curve of the interface; Step S2: Based on the statistical damage theory, combined with the traditional constitutive model of statistical damage for the contact surface, deduce the statistical damage constitutive model of the thicknessless soil-rock interface considering the residual strength to characterize the damage evolution characteristics of the interface during the shear slip process; Step S3: Based on the shear stress-shear displacement curve, identify the parameters of the statistical damage constitutive model of the thicknessless soil-rock interface considering the residual strength to determine the mechanical parameters in the model.

2. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 1, characterized in that: In the step S1, the shear test includes: Fix the prepared soil-rock interface specimen in the shear test device, apply different normal stresses to simulate different burial depths or load conditions; Set different shear rates and conduct shear tests at 0.1 mm / min, 1 mm / min, and 10 mm / min respectively; Apply different pore water pressures through the hydraulic coupling system and adjust the water flow direction and head gradient; Record the shear stress-shear displacement curve and monitor the damage, slip, and failure modes of the soil-rock interface during the shear process; Repeat the test to obtain test data under different conditions.

3. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 1, characterized in that The specific statistical damage theory is as follows: ， Where: is the statistical damage; For statistical damage; is the stress in the non-damaged state; is the residual stress after complete damage; is the damage variable, and its value range is .

4. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 3, characterized in that In the step S2, for the soil-rock interface, convert the statistical damage theory into the shear stress form: ， Where: is the shear stress; is the shear stress in the non-damaged state; is the interfacial residual shear strength; Characterize the degree of interface damage.

5. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 4, characterized in that In the small deformation stage, the statistical damage constitutive model of the thicknessless soil-rock interface considering the residual strength is: ， Where: represents the initial shear stiffness; Indicates the shear displacement; Indicates the small deformation shear displacement threshold.

6. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 5, characterized in that In the large deformation stage, the statistical damage constitutive model of the thicknessless soil-rock interface considering the residual strength is: ， Where: is an empirical parameter, a dimensionless parameter that controls the shear stress evolution rate; is the shear modulus, a physical quantity that describes the shear resistance of a material; is the damage evolution parameter, the parameter that controls the evolution rate of the damage variable 𝐷; It is the damage evolution index, an index that characterizes the damage evolution rate.

7. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 6, characterized in that When identifying the parameters of the statistical damage constitutive model of the thicknessless soil-rock interface considering the residual strength, the input data includes: Shear stress-shear displacement curve ; Shearing stiffness vs. displacement curve , represents the shearing stiffness; Normal stress and moisture content .

8. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 7, characterized in that The mechanical parameters in the model include: Shearing stiffness ; Damage evolution parameter ; Residual shear strength .

9. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 8, characterized in that When performing parameter identification on the statistical damage constitutive model of the thicknessless soil-rock interface considering residual strength, set the number of calculation steps , and set the convergence criterion that if 𝑛 is an integer multiple of 500, then enter the stiffness update step.

10. The method for constructing a shear statistical damage constitutive model of soil-rock interface considering the dynamic change of interface slip according to claim 8, characterized in that When identifying the parameters of the statistical damage constitutive model of the thicknessless soil-rock interface considering the residual strength, Calculate the fitting error between the current stress curve and the test data: ， Where: is the model calculated value; is the measured value in the test; N is the number of data points.

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