Model construction method considering strain hardening and softening characteristics of rib-soil interface

Abstract

The invention discloses a model construction method considering the strain hardening and softening characteristics of a rib-soil interface, and the method comprises the steps: setting normal stress as a single variable, and obtaining a plurality of shear stress-shear displacement curves under different normal stress levels of a to-be-tested soil sample through a pull-out test; a model is established according to the influence rule of normal stress on the characteristics of the rib-soil interface and the change characteristics of the interface shear stress in the shearing process. According to the model considering the strain hardening and softening characteristics of the reinforcement-soil interface, the characteristics of the reinforcement-soil interface in different stress states can be predicted more accurately, the efficiency is high, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering and relates to a model construction method taking into account the strain hardening and softening characteristics of a reinforcement-soil interface. Background Art

[0002] The interaction between geosynthetics and soil is a common problem in roadbed engineering. However, due to the obvious stiffness difference between the reinforcement and soil, the mechanical properties of the contact interface between the two media are significantly different from those of the soil far away from the interface. In actual engineering, under the action of external forces, the contact interface between geogrid and soil will show characteristics such as strain hardening and strain softening.

[0003] For the constitutive model of the reinforcement-soil interface, the Mohr-Coulomb linear elastic constitutive model is commonly used. Although this model has certain practicality, the mechanical behavior of the actual reinforcement-soil interface usually shows nonlinear characteristics. In 1971, Clough and Duncan conducted a direct shear test on the sand-concrete slab interface and proposed the Clough-Duncan model, a hyperbolic relationship model between shear stress and relative displacement, based on the test results. This model is often used to describe the characteristic relationship between the reinforcement-soil interface, but it can only reflect the monotonically increasing characteristics of shear stress with the increase of shear strain. When the shear stress-strain curve of the reinforcement-soil interface softens, the Clough-Duncan hyperbolic model is no longer applicable for studying the shear stress-displacement relationship. A large number of test results show that strain softening will occur on the contact surface during the shear process. Even for the same set of shear tests, when the normal stress is large, the contact surface will show a hardening curve, and when the normal stress is small, the contact surface will show a softening curve. However, it is difficult to effectively reflect the influence of stress state on the reinforcement-soil interface characteristics in the current reinforcement-soil interface model, and there is no effective interface model analysis method that can simultaneously reflect both strain softening and strain hardening stress states. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a model construction method that takes into account the strain hardening and softening characteristics of the reinforcement-soil interface. The constructed model can more accurately predict the reinforcement-soil interface characteristics under different stress states with high efficiency and low cost.

[0005] The technical solution adopted by the present invention is a model construction method considering the strain hardening and softening characteristics of the reinforcement-soil interface, comprising the following steps: S1, setting the normal stress as a single variable, and obtaining shear stress-shear displacement curves at multiple different normal stress levels through a pull-out test on the soil sample to be tested; S2, according to the normal stress The influence of the reinforcement-soil interface characteristics and the change characteristics of the interface shear stress during shearing are established. ;in, represents the shear displacement, represents shear stress, a, b, c are model parameters; in, ; G represents the initial shear modulus, represents the peak shear displacement, represents the peak shear stress.

[0006] Furthermore, in S2, the method for determining the model parameter c is: Model , find the partial derivative: , initial shear modulus ,Right now .

[0007] Furthermore, in S2, the method for determining the model parameter a is: When the shear stress reaches its peak value, the corresponding peak shear displacement .

[0008] Furthermore, in S2, the method for determining the model parameter b is: When the shear stress reaches its peak, according to the model get: ,Will Bring in the model ,get ; is the peak shear stress; .

[0010] Furthermore, the initial shear modulus G and the normal stress The relationship between them is: ; Where Pa is atmospheric pressure, M and n are fitting parameters; Peak shear stress and normal stress The relationship between them is: , is the cohesion of the soil, is the internal friction angle; When shear displacement When the shear displacement increases, the shear stress gradually decreases after reaching the peak value. Where , the corresponding residual shear stress is taken as ; , k is a dimensionless parameter; the introduction of damage ratio Defining Residual Shear Stress and peak shear stress The relationship between: ; and then get: ; The c of the soil samples of the same soil type sg , φ, M, n, k and Pa, as well as different normal stresses Corresponding , bring in and , the initial shear modulus G and peak shear displacement are obtained and peak shear stress , and then determine the model parameters a, b, c.

[0011] Furthermore, the cohesion c sg And the method for determining the internal friction angle φ: The shear strength envelope of the reinforcement-soil interface is drawn according to the shear stress-shear displacement curve in S1. The horizontal coordinate of the shear strength envelope of the reinforcement-soil interface is the normal stress. , the ordinate is the peak shear stress ; Cohesion c sg is the ordinate intercept of the shear strength envelope of the reinforcement-soil interface, and tanφ is the slope of the shear strength envelope of the reinforcement-soil interface.

[0012] The beneficial effects of the present invention are: In the prior art, in order to obtain the shear stress-shear displacement curve of the same soil sample under different stress states, it is usually necessary to conduct a separate test for each stress state. This method has the problems of complicated steps, long test cycle, low operating efficiency, etc., especially in the scenario where a large amount of data is required for interface characteristic analysis, it significantly increases the manpower and time costs. The present invention can effectively solve the above problems by analyzing, summarizing and modeling the test results of the same soil sample under a finite stress state, thereby deriving the shear stress-shear displacement curve under other stress states, without the need to conduct separate tests for each stress state. This not only simplifies the test steps and improves the test efficiency, but also reduces the test cost and improves the overall efficiency and accuracy of interface characteristic research. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0014] Figure 1 It is a schematic diagram of the shear stress-shear displacement relationship of the model of the embodiment of the present invention.

[0015] Figure 21 is a shear stress-shear displacement relationship diagram under different normal stresses of an embodiment of the present invention.

[0016] Figure 3 It is the shear strength envelope of the interface between clay and geogrid in the embodiment of the present invention.

[0017] Figure 4 This is the model verification effect diagram. DETAILED DESCRIPTION

[0018] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0019] Embodiment, a model construction method considering the strain hardening and softening characteristics of the reinforcement-soil interface, comprising the following steps: S1, set the normal stress as a single variable, and obtain the shear stress-shear displacement at six levels of normal stress of 0 kPa, 10 kPa, 20 kPa, 40 kPa, 60 kPa and 80 kPa through the pull-out test. Curve, see Figure 2 ; S2, according to the normal stress The influence law of the reinforcement-soil interface characteristics and the change characteristics of the interface shear stress during shearing process. Specifically, according to the phenomenon in the pull-out test: the reinforcement-soil interface characteristics show strain softening characteristics when the normal stress is small, and strain hardening characteristics when the normal stress is large, a model is established ;in, represents the shear displacement, represents shear stress, and a, b, c are model parameters.

[0020] S21, cohesion c sg And the method for determining the internal friction angle φ: According to S1 Drawing the shear strength envelope of the reinforcement-soil interface based on the curve test results ,See Figure 3 , using the Mohr-Coulomb criterion: , fitting is obtained ; is the peak shear stress (kPa), is the normal stress (kPa). Cohesion c sg is the ordinate intercept of the shear strength envelope of the reinforcement-soil interface, and tanφ is the slope of the shear strength envelope of the reinforcement-soil interface.

[0021] S22, normal stress For example, through the corresponding Curve, determine the parameters M, n, k, R f ; (1) According to the experimental curve fitting parameter c=0.1299; represents the shear displacement, represents shear stress; the relationship between shear stress and shear displacement of the model is as follows Figure 1 shown.

[0022] (2) Model , find the partial derivative: , initial shear modulus ,Right now ; (3) For equation Take the logarithm of both sides: , Pa is atmospheric pressure, take = 101kPa, and get the fitting parameters M =0.107, n =0.147; is a whole, representing the normal stress; the "n" in the nth power is a dimensionless parameter; (4) When the shear stress reaches its peak value, the corresponding shear displacement for: ,but ;

[0023] (5) Bring in the model , ,Will Bring in get ;

[0024] (6) When shear displacement When the shear displacement increases, the shear stress gradually decreases after reaching the peak value. The corresponding residual shear stress is By introducing the damage ratio To define the residual shear stress and peak shear stress The relationship between: , In this embodiment, k=1.6, at this time R f is 0.925.

[0025] Where: G is the initial shear modulus; M and n are dimensionless parameters; is the normal stress (kPa); Pa is the atmospheric pressure (kPa); is the peak shear stress (kPa); csg is the cohesion (kPa); φ is the internal friction angle ( ° ); is the peak shear displacement (mm); is the residual shear displacement (mm); is the destruction ratio; k is a dimensionless parameter with a value range of (1, ∞).

[0026] The value of k is not fixed. It is related to the selected position. For the convenience of calculation, the k value is the same under different normal stresses. Method for determining: Determine c sg , φ, M, n, Pa parameters, a The value corresponds to a k value, which is greater than Select , through the normal stress Corresponding curve( Figure 2 ) to obtain the normal stress Corresponding ; According to the same method, the model parameters under different normal stresses are obtained, as shown in Table 1: Table 1 Model parameters under different normal stresses

[0027] when When it is large enough, it will no longer change with the increase of normal stress. As shown in Table 1, when When it is 0.985, it can be considered that when k is 1.6, No longer changes.

[0028] When the soil type and external conditions (water content, compaction degree, etc.) are the same, the parameters M, n, Pa,c sg The values ​​of , φ and k remain unchanged. It only changes with the normal stress. Assuming that a lot of soil is taken on site, and a part of the soil is taken for the pull-out test, the soil pile is suitable for the method of the embodiment of the present invention.

[0029] The parameters , substitute into the following formula to determine the parameters a, b, c, ; ; Then, the strain hardening and softening characteristics of the reinforcement-soil interface are considered through the model, and the model fitting effect is shown in Figure 4 , the fitting effects are all over 0.9.

[0030] Table 2 Different normal stresses The parameters a, b, c under

[0031] In Table 2, “8.1E-05” means 8×10 -5 .

[0032] Given the shear stress-shear displacement curve under 0-40 kPa, the parameters can be obtained through S2 c sg ,φ,M,n,k, , Pa, through the known parameters and normal stress , the model parameters a, b, c at 60 kPa and 80 Pa can be obtained, and the test curve can be derived. From the indoor test, the fitting effect of the actual curve and the predicted curve is very close, and the fitting effect exceeds 0.9.

[0033] The derivation process: (1) Will Substituting into formula (1), we get: (2) Will Substituting into formula (2), we get: (3) Will Substituting into formula (3), we get: (4) Solving formula (4) yields: .

[0034] The reinforcement-soil interface shear stress calculation formula disclosed in the Chinese patent with publication number CN 115976899 A cannot simultaneously characterize the strain softening and hardening characteristics of the reinforcement-soil interface; the reinforcement-soil interface shear displacement curve under different moisture content conditions is obtained through indoor interface shear test, and then the interface shear type is determined according to the evolution trend of the reinforcement-soil interface shear displacement curve, and then the reinforcement-soil interface parameters are obtained by fitting the test data with the calculation formula, that is, the interface parameters can only be obtained by fitting a set of parameters through a set of test data, and the parameter acquisition process is relatively difficult.

[0035] In the embodiment of the present invention, several groups of pull-out tests under different normal stresses are first performed on the unknown soil sample, and the shear strength envelope of the reinforcement-soil interface is drawn according to step S21. ,get , φ value; according to step S22, M, n, k, R f , Pa value; The value of the parameter changes with the change of the normal stress. By substituting the parameter into the calculation, the shear stress-shear displacement curve of the same soil sample under the unknown stress state can be obtained. nThe influence of the reinforcement-soil interface characteristics and the change characteristics of the interface shear stress during shearing were established. n The connection between It can simultaneously characterize the strain softening and hardening characteristics of the reinforcement-soil interface, and has a good fitting effect. It does not need to separately represent the shear hardening characteristics and softening characteristics, and the model parameters are few. And the normal stress is comprehensively considered. The influence of shear stress on the shear stress and the change characteristics of the interface shear stress during the shearing process can predict more test curves based on several sets of indoor test data under different normal stresses; it can not only accurately simulate the nonlinear behavior of the reinforcement-soil interface under different stress states, but also effectively reflect the stress-strain response in actual engineering. Respectively, the normal stress Establish a connection and determine the parameters M, n, Pa, k, , when the normal stress increases to a certain extent, It no longer changes, and there is no need to conduct experiments on this type of experimental soil. Based on these parameters, a, b, and c under different normal stresses can be calculated to predict the shear stress-shear displacement curve of the reinforced soil interface.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A model construction method considering the strain hardening and softening characteristics of the reinforcement-soil interface, characterized in that: The following steps are involved: S1, setting the normal stress as a single variable, and obtaining shear stress-shear displacement curves at multiple different normal stress levels through a pull-out test on the soil sample to be tested; S2, according to the normal stress The influence of the reinforcement-soil interface characteristics and the change characteristics of the interface shear stress during shearing are established. ;in, represents the shear displacement, represents shear stress, a, b, c are model parameters; in, ; G represents the initial shear modulus, represents the peak shear displacement, represents the peak shear stress.

2. A model construction method considering the strain hardening and softening characteristics of the reinforcement-soil interface according to claim 1, characterized in that: In S2, the method for determining the model parameter c is: Model , find the partial derivative: , initial shear modulus ,Right now .

3. A model construction method considering the strain hardening and softening characteristics of the reinforcement-soil interface according to claim 2, characterized in that: In S2, the method for determining the model parameter a is: When the shear stress reaches its peak value, the corresponding peak shear displacement .

4. A model construction method considering the strain hardening and softening characteristics of the reinforcement-soil interface according to claim 3, characterized in that: In S2, the method for determining the model parameter b is: When the shear stress reaches its peak, according to the model get: ,Will Bring in the model ,get ; is the peak shear stress; .

5. A model construction method considering the strain hardening and softening characteristics of the reinforcement-soil interface according to any one of claims 2 to 4, characterized in that: The initial shear modulus G and normal stress The relationship between them is: ; Where Pa is atmospheric pressure, M and n are fitting parameters; Peak shear stress and normal stress The relationship between them is: , is the cohesion of the soil, is the internal friction angle; When shear displacement When the shear displacement increases, the shear stress gradually decreases after reaching the peak value. Where , the corresponding residual shear stress is taken as ; , k is a dimensionless parameter; the introduction of damage ratio Defining Residual Shear Stress and peak shear stress The relationship between: ; and then get: ; The c of the soil samples of the same soil type sg , φ, M, n, k and Pa, as well as different normal stresses Corresponding , bring in and , the initial shear modulus G and peak shear displacement are obtained and peak shear stress , and then determine the model parameters a, b, c.

6. A model construction method considering the strain hardening and softening characteristics of the reinforcement-soil interface according to claim 5, characterized in that: The cohesion c sg And the method for determining the internal friction angle φ: The shear strength envelope of the reinforcement-soil interface is drawn according to the shear stress-shear displacement curve in S1. The horizontal coordinate of the shear strength envelope of the reinforcement-soil interface is the normal stress. , the ordinate is the peak shear stress ; Cohesion c sg is the ordinate intercept of the shear strength envelope of the reinforcement-soil interface, and tanφ is the slope of the shear strength envelope of the reinforcement-soil interface.

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