A testing method for the monotonic and cyclic shear interface friction characteristics of state-related sand-structure

Abstract

The present invention discloses a test method for the monotonic and cyclic shear interface friction characteristics of state-related sand-structure, including: obtaining a state-related sand-structure contact body specimen, pre-applying confining pressure to the state-related sand-structure contact body specimen, and using a sensor to obtain the monitoring results of the pre-applied confining pressure; based on the monitoring results, obtaining the corrected relative density of sand; conducting a first displacement monotonic shear test to obtain a first variation law; conducting a second displacement cyclic shear test to obtain a second variation law; based on the first variation law and the second variation law, respectively establishing a state-related initial shear modulus prediction model, a state-related friction coefficient prediction model for monotonic shear test, and a state-related friction coefficient evolution model for cyclic shear, and obtaining the friction coefficient and initial shear modulus for monotonic and cyclic shear. The present invention can ensure the construction and operation safety of the project.

Description

Technical Field

[0001] The present invention belongs to the field of indoor tests on soil-structure interaction in geotechnical engineering, and particularly relates to a test method for monotonic and cyclic shear interface friction characteristics of state-dependent sand-structure, which is applicable to the test method for monotonic and cyclic shear interface friction characteristics of state-dependent sand-structure. Background Art

[0002] The friction characteristics of the sand-structure interface are important research objects in the fields of civil engineering and water conservancy projects. The interface friction parameters are important parameters for the design of pile foundations, tunnels, slopes, and foundation pit retaining structures. Reasonably testing the friction characteristics of the sand-structure interface is a prerequisite for ensuring the safety of engineering construction and is related to the well-being of human interests.

[0003] Sand has obvious state-dependent characteristics, that is, sands with different relative densities have significant differences in strength and deformation characteristics, resulting in significant state-dependent characteristics of the friction characteristics of the sand-structure interface. The existing friction characteristics of the sand-structure interface are often tested and studied through indoor shear tests. However, due to the limitations of the sample preparation method and current sample preparation equipment, it is difficult to prepare sand-structure interface specimens with too low or too high relative densities, and the uniformity of the specimens is difficult to guarantee. Moreover, during the shear test of the sand-structure interface with too low or too high relative densities, there is a risk of sand sample extrusion or sand leakage, especially for large-scale interface shear testers, and such risks are more prominent, resulting in the difficulty of ensuring the scientific nature of the test results.

[0004] In addition, in the existing shear tests on the sand-structure interface, the evolution law of the test relative density caused by the application of the normal stress during the specimen preloading stage is ignored, resulting in a certain reduction in the accuracy of the test results.

[0005] Therefore, there is an urgent need for a test method for monotonic and cyclic shear interface friction characteristics of state-dependent sand-structure. Summary of the Invention

[0006] To solve the above technical problems, the present invention proposes a test method for monotonic and cyclic shear interface friction characteristics of state-dependent sand-structure, which can realize the test and analysis of the monotonic and cyclic shear interface friction characteristics of sand-structure interfaces with different relative densities, solve the problem that it is difficult to accurately obtain the shear characteristics of sand-structure interfaces with too low or too high relative densities, and ensure the construction and operation safety of the project.

[0007] To achieve the above object, the present invention provides a test method for monotonic and cyclic shear interface friction characteristics of state-dependent sand-structure, including:

[0008] Obtain a state-dependent sand-structure contact body specimen, pre-apply confining pressure to the state-dependent sand-structure contact body specimen, and obtain the monitoring results of the pre-application of confining pressure;

[0009] Based on the monitoring results, obtain the confining pressure - volume relationship curve. Based on the confining pressure - volume relationship curve, correct the relative density of sand, and obtain the corrected relative density of sand.

[0010] Conduct the first displacement monotonic shear test to obtain the first variation law of the shear stress - shear displacement monotonic curve under different corrected relative densities of sand and different normal stresses.

[0011] Conduct the second displacement cyclic shear test to obtain the second variation law of the shear stress - shear displacement hysteresis curve under different corrected relative densities of sand and different normal stresses.

[0012] Based on the first variation law and the second variation law, establish a friction characteristic prediction model, and obtain the monotonic shear friction coefficient and the cyclic shear friction coefficient.

[0013] Optionally, based on the confining pressure - volume relationship curve, correcting the relative density of sand to obtain the corrected relative density of sand includes:

[0014] Based on the confining pressure - volume relationship curve and the total mass of sand, obtain the confining pressure - dry density relationship.

[0015] Based on the confining pressure - dry density relationship, correct the relative density of sand to obtain the corrected relative density of sand.

[0016] Optionally, the first displacement monotonic shear test is: require the displacement at the end of the test to be the shear displacement corresponding to the critical state of the test.

[0017] Optionally, the second displacement cyclic shear test is: the amplitude of the cyclic shear displacement performed shall not exceed the shear displacement corresponding to the peak shear strength of the first displacement monotonic shear test.

[0018] Optionally, obtaining the monotonic shear friction coefficient and the cyclic shear friction coefficient includes: based on the friction characteristic prediction model, obtain the initial shear modulus, the monotonic shear friction coefficient, and the cyclic shear friction coefficient.

[0019] Optionally, the initial shear modulus is:

[0020] K 1 = A 1 + A 2 Dr

[0021] lg(K si / γ w ) = lgK 1 + nlg(σ n / P a )

[0022] Among them, K 1 is a dimensionless stiffness coefficient, n is the stiffness index, γ w is the unit weight of water, with a value of 9.8 kN / m 3 , P a is the standard atmospheric pressure, with a value of 101 kPa, σ n is the normal stress, A 1 is the dimensionless stiffness coefficient of the sand - structure in the ideal loosest state, A 2 is the dimensionless stiffness coefficient K 1 is the growth rate with respect to the relative density D r .

[0023] Optionally, the method for obtaining the monotonic shear friction coefficient is as follows:

[0024] μ p = A 3 + A 4 Dr

[0025] Among them, μ p is the monotonic shear friction coefficient, A 3 is the friction coefficient of the sand - steel interface in the ideal loosest state, A 4 is the rate at which the initial friction coefficient of the interface increases with the increase in relative density.

[0026] Optionally, the method for obtaining the cyclic shear friction coefficient is as follows:

[0027] A 5 = B 1 + B 2 Dr

[0028]

[0029] Among them, μ 1 is the cyclic shear friction coefficient, D r is the modified relative density of sand, A 5 is the model parameter that controls the evolution rate of the friction coefficient μ 1 with the number of cyclic shears N, μ r is the critical state friction coefficient, B 1 and B 2 are model parameters.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] The state-related sand-structure monotonic and cyclic shear interface friction characteristic test method provided by the present invention, compared with the traditional test analysis method, fully considers the change in relative density during the test preloading process and the influence of relative density on the monotonic and cyclic shear interface friction characteristics; based on the state-related theory, the present invention proposes an interface shear test that only needs to be carried out under a small number of relative densities to obtain complete relative density sand-structure interface friction parameters. The method steps of the present invention are simple, the selected evolution model conforms to the actual situation, corrects the defects of the traditional test method, the prediction result is more accurate, and it is convenient to promote, and can better serve the fields of civil engineering, water conservancy engineering design, construction and monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments of this application and their descriptions are used to explain this application and do not constitute an improper limitation to this application. In the drawings:

[0033] Figure 1 is a flowchart of a test method for state-related sand-structure monotonic and cyclic shear interface friction characteristics according to an embodiment of the present invention;

[0034] Figure 2 is a typical result curve graph of the first displacement monotonic shear according to an embodiment of the present invention;

[0035] Figure 3 is a typical result curve graph of the second displacement cyclic shear according to an embodiment of the present invention;

[0036] Figure 4 is a relationship curve graph of the dimensionless stiffness coefficient and relative density according to an embodiment of the present invention;

[0037] Figure 5 is a relationship curve graph of the monotonic shear friction coefficient and relative density according to an embodiment of the present invention;

[0038] Figure 6 is μ of an embodiment of the present invention 1 and the relationship curve graph of the number of cycles. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine the embodiments to detail this application.

[0040] It should be noted that the steps shown in the flowchart of the drawings can be executed in a computer system such as a set of computer-executable instructions, and although the logical order is shown in the flowchart, in some cases, the steps shown or described can be executed in a different order than here.

[0041] The present invention proposes a test method for the monotonic and cyclic shear interface friction characteristics of state-related sand-structure, as Figure 1 shown, which specifically includes the following steps:

[0042] Obtain a state-related sand-structure contact body specimen, pre-apply confining pressure to the state-related sand-structure contact body specimen, and obtain the monitoring results of the pre-application of confining pressure;

[0043] Based on the monitoring results, obtain the confining pressure-volume relationship curve, and based on the confining pressure-volume relationship curve, correct the relative density of the sand to obtain the corrected relative density of the sand;

[0044] Conduct the first displacement monotonic shear test to obtain the first variation law of the shear stress-shear displacement monotonic curve under different corrected relative densities of the sand and different normal stresses;

[0045] Conduct the second displacement cyclic shear test to obtain the second variation law of the shear stress-shear displacement hysteresis curve under different corrected relative densities of the sand and different normal stresses;

[0046] Based on the first variation law and the second variation law, establish a friction characteristic prediction model to obtain the monotonic shear friction coefficient and the cyclic shear friction coefficient.

[0047] Furthermore, correcting the relative density of the sand based on the confining pressure-volume relationship curve to obtain the corrected relative density of the sand includes:

[0048] Based on the confining pressure-volume relationship curve and the total mass of the sand, obtain the confining pressure-dry density relationship;

[0049] Based on the confining pressure-dry density relationship, correct the relative density of the sand to obtain the corrected relative density of the sand.

[0050] Specifically, the relative density (D r ):

[0051]

[0052] where D r is the relative density, ρ d is the dry density, ρ dmax is the maximum dry density, and ρ dmin is the minimum dry density.

[0053] Furthermore, the large displacement monotonic shear test, i.e., the first displacement monotonic shear test, is: the displacement at the critical state is the monitored test conducted.

[0054] Specifically, the large displacement in the large displacement monotonic shear test means that the displacement at the end of the shear test can bring the test to the critical state or close to the critical state.

[0055] Further, the small displacement cyclic shear test, i.e., the second displacement cyclic shear test, is such that the amplitude of the cyclic shear displacement shall not exceed the shear displacement corresponding to the peak shear strength in the large displacement monotonic shear test.

[0056] Specifically, the small displacement in the small displacement cyclic shear test means that the amplitude of the cyclic shear displacement shall not exceed the shear displacement corresponding to the peak shear strength in the large displacement monotonic shear test. In addition, the number of cyclic shears shall be ensured to bring the test to the critical state before the end of the shear test.

[0057] Further, obtaining the monotonic shear friction coefficient and the cyclic shear friction coefficient includes: obtaining the initial shear modulus based on the friction characteristic prediction model;

[0058] Obtaining the monotonic shear friction coefficient and the cyclic shear friction coefficient based on the initial shear modulus.

[0059] Specifically, based on the state - related theory, an initial shear modulus (K r ) prediction model considering the effect of relative density (D si ) is established; the initial shear modulus (K si ) prediction model calculates the influence of relative density (D r ) on the dimensionless stiffness coefficient (K 1 ) by analyzing the monotonic shear stress - shear displacement curve, and fits and calculates the dimensionless stiffness coefficient of the sand - structure in the ideal loosest state (denoted as A 1 ) and the growth rate (A 1 ) of the dimensionless stiffness coefficient (K r ) with relative density (D 2 ) as shown in Figure 4 ; the calculation process includes:

[0060] lg(K si / γ w ) = lgK 1 + nlg(σ n / P a )

[0061] In the formula, K 1 is the dimensionless stiffness coefficient; n is the stiffness index; γ w is the unit weight of water, with a value of 9.8 kN / m 3 ; P a is the standard atmospheric pressure, with a value of 101 kPa.

[0062] K 1= A 1 + A 2 Dr

[0063] In the formula, A 1 is the dimensionless stiffness coefficient of sand - structure in the ideal loosest state, and A 2 is the growth rate of the dimensionless stiffness coefficient (K 1 ) with respect to the relative density (D r ). Both are calculated by back - calculation based on the test results.

[0064] Furthermore, the calculation process of the prediction model of the friction coefficient (μ r ) considering the effect of relative density (D p ) in the monotonic shear test includes:

[0065] 1) According to the test results, calculate the ratio of the peak shear stress to the confining pressure, and plot the relationship curve between this ratio and the relative density (D r );

[0066] 2) According to the above - mentioned curve, calculate the friction coefficient A 3 (the intercept of the curve on the vertical axis) of the sand - steel interface in the ideal loosest state and the rate A 4 (the slope of the curve on the vertical axis) at which the initial friction coefficient of the interface increases with the increase of relative density;

[0067] 3) Obtain the prediction model, which can be used to calculate the interface friction coefficient (μ r ) under any relative density (D p ), and the formula is as follows:

[0068] μ p = A 3 + A 4 Dr

[0069] where μ p is the monotonic shear friction coefficient, A 3 is the friction coefficient of the sand - steel interface in the ideal loosest state, and A 4 is the rate at which the initial friction coefficient of the interface increases with the increase of relative density.

[0070] Furthermore, the calculation process of the evolution model of the cyclic shear friction coefficient (μ r ) considering the effect of relative density (D 1 ) with respect to the number of cyclic shears includes:

[0071] 1) According to the test results, calculate the ratio of the peak shear stress to the confining pressure within each number of cyclic shears, plot the relationship curve between this ratio and the number of cyclic shears (N), and construct the relationship model between the friction coefficient (μ 1 ) and the number of cyclic shears (N), and the formula is:

[0072]

[0073] In the formula, μ r is the friction coefficient at the critical state, which is the ratio of the residual shear stress to the confining pressure in the large-displacement monotonic shear test or the small-displacement cyclic shear test; A 5 is the model parameter that controls the evolution rate of the friction coefficient (μ 1 ) with the number of cyclic shear times (N), and is inverted from the test results.

[0074] 2) According to the test results, calculate the functional relationship between the relative density (D r ) and A 5 . The formula is:

[0075] A 5 = B 1 + B 2 Dr

[0076] In the formula, B 1 and B 2 are model parameters.

[0077] 3) By synthesizing the above two formulas, the evolution model of the cyclic shear friction coefficient considering the effect of the relative density (D r ) with the number of cyclic shear times (μ 1 ) can be obtained.

[0078] Example

[0079] I. Prepare sand-structure contact body specimens related to the state, pre-apply the confining pressure, and monitor the normal deformation of the specimens through sensors

[0080] After installing the test structure, weigh the required sand samples and use the rain-fall method to prepare the samples. The total number of samples is 24, 12 for large-displacement monotonic shear and 12 for small-displacement cyclic shear; the relative densities after the rain-fall method are 0.5 (8), 0.6 (8), and 0.7 (8) respectively; apply confining pressures of 50, 100, 150, and 200 kPa respectively, and monitor the normal deformation (i.e., the sand shrinkage) of the specimens during the application of the confining pressure;

[0081] II. According to the monitoring results in the stage of pre-applying the confining pressure, obtain the confining pressure-volume relationship curve and correct the relative density (Dr) of the sand before the formal interface friction;

[0082] Based on the normal deformation of the specimen (i.e., the shrinkage of sand), combined with the size of the specimen, calculate the confining pressure - volume relationship curve. Then, combined with the weight of the specimen, calculate the evolution law of the dry density of the test with the confining pressure. Then, calculate the corrected relative density (Dr) of the sand according to the dry density; the true relative densities before the shear test after correction are 0.490 (8 specimens), 0.586 (8 specimens), and 0.687 (8 specimens) respectively.

[0083] III. Conduct large - displacement monotonic shear tests, i.e., the first displacement monotonic shear test, to obtain the variation laws of the shear stress - shear displacement monotonic curves at different relative densities (Dr) and different normal stresses (σ n ); the shear rate is set to 0.02 mm / s, and the shear displacement is taken as 60 mm. The typical test result curves are as shown in Figure 2 Figure.

[0084] IV. Conduct small - displacement cyclic shear tests to obtain the variation laws of the shear stress - shear displacement hysteresis curves at different relative densities (Dr) and different normal stresses (σ n ); the cyclic shear displacement is set to 5 mm, and the number of shear cycles is taken as 100 times. The typical test result curves are as shown in Figure 3 Figure.

[0085] V. Based on the state - related theory, establish a prediction model for the initial shear modulus (K r ) considering the effect of relative density (D si ); the prediction model of the initial shear modulus (K si ) calculates the influence of relative density (D r ) on the dimensionless stiffness coefficient (K 1 ) by analyzing the shear stress - shear displacement monotonic curve or the first shear stress - shear displacement experimental curve in cyclic shear, and fits and calculates the dimensionless stiffness coefficient of the sand - structure in the ideal loosest state (denoted as A 1 ) and the growth rate (A 1 ) of the dimensionless stiffness coefficient (K r ) with relative density (D 2 ); the calculation process includes:

[0086] lg(K si / γ w ) = lgK 1 + nlg(σ n / P a )

[0087] In the formula, K 1 is the dimensionless stiffness coefficient; n is the stiffness index; γ w is the unit weight of water, with a value of 9.8 kN / m 3 ; P ais the standard atmospheric pressure, with a value of 101 kPa.

[0088] K 1 = A 1 + A 2 Dr

[0089] In the formula, A 1 is the dimensionless stiffness coefficient of the sand - structure in the ideal loosest state, and A 2 is the growth rate of the dimensionless stiffness coefficient (K 1 ) with respect to the relative density (D r ). Both are back - calculated based on the test results. In this embodiment, A 1 = 24225 and A 2 = 9360. The relationship curve between the relative density and K 1 is shown in Figure 3.

[0090] VI. Based on the state - related theory, according to the results of monotonic shear tests and cyclic shear tests, a friction coefficient prediction model considering the effect of relative density (D r ) is established, including the friction coefficient prediction model (μ p ) for monotonic shear tests and the evolution model of the friction coefficient with the number of cyclic shears (μ 1 ) for cyclic shear.

[0091] The calculation process of the friction coefficient prediction model (μ r ) for monotonic shear tests considering the effect of relative density (D p ) includes:

[0092] 1) According to the test results, calculate the ratio of the peak shear stress to the confining pressure, and plot the relationship curve between this ratio and the relative density (D r );

[0093] 2) According to the above curve, calculate the friction coefficient A 3 of the sand - steel interface in the ideal loosest state (the intercept of the curve on the vertical axis, in this embodiment A 3 = 0.2468) and the rate A 4 at which the initial friction coefficient of the interface increases with the increase of relative density (the slope of the curve on the vertical axis, in this embodiment A 4 = 0.3175);

[0094] 3) Obtain the prediction model, which can be used to calculate the interface friction coefficient (μ r ) under any relative density (D p ). The formula is as follows:

[0095] μ p = A 3 + A 4 Dr

[0096] μ p The relationship curve with the relative density is shown in Figure 5 the figure below.

[0097] Considering the effect of relative density (D r ), the evolution model of the cyclic shear friction coefficient with the number of cyclic shears (μ 1 ) calculation process includes:

[0098] 1) According to the test results, calculate the ratio of the peak shear stress to the confining pressure within each number of cycles, plot the relationship curve of this ratio with the number of cyclic shears (N), and construct the relationship model between the friction coefficient (μ 1 ) and the number of cyclic shears (N). The formula is:

[0099]

[0100] where μ r is the critical state friction coefficient, which is the ratio of the residual shear stress to the confining pressure in the large-displacement monotonic shear test or the small-displacement cyclic shear test; A 5 is the model parameter that controls the evolution rate of the friction coefficient (μ 1 ) with the number of cyclic shears (N), and is inverted from the test results.

[0101] 2) According to the test results, calculate the functional relationship between the relative density (D r ) and A 5 . The formula is:

[0102] A 5 = B 1 + B 2 Dr

[0103] where B 1 and B 2 are model parameters. In this embodiment, B 1 = 4.07, B 2 = 10.3.

[0104] 3) Combining the above two formulas, the evolution model of the cyclic shear friction coefficient considering the effect of relative density (D r ) with the number of cyclic shears (μ 1 ) can be obtained. Figure 6 This is the relationship curve of μ 1 with the number of cycles.

[0105] The above are only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for testing friction characteristics of state-dependent sand-structure monotonic and cyclic shear interfaces, characterized in that: include: Acquire a state-related sand-soil-structure contact body sample, pre-apply confining pressure to the state-related sand-soil-structure contact body sample, and acquire a monitoring result of the pre-applying confining pressure; Based on the monitoring results, a confining pressure-volume relationship curve is obtained, and based on the confining pressure-volume relationship curve, the relative density of the sand is corrected to obtain the corrected relative density of the sand; Conduct the first displacement monotonic shear test to obtain the first variation law of the shear stress-shear displacement monotonic curve at different relative densities of modified sand and different normal stresses; The second displacement cyclic shear test was carried out to obtain the second variation law of the shear stress-shear displacement hysteresis curve under different relative densities of modified sand and different normal stresses; Based on the first and second change laws, a friction characteristic prediction model is established to obtain a monotonic shear friction coefficient and a cyclic shear friction coefficient; Acquiring the monotonic shear friction coefficient and the cyclic shear friction coefficient comprises: acquiring an initial shear modulus, the monotonic shear friction coefficient and the cyclic shear friction coefficient based on the friction characteristic prediction model; The initial shear modulus is: K1=A1+A2Dr lg(K si / c w )=lg K1+n lg(σ n / P a ) Among them, K1 is the dimensionless stiffness coefficient, n is the stiffness index, γ w is the bulk density of water, which is 9.8 kN / m 3 , P a is the standard atmospheric pressure, with a value of 101 kPa, σ n is the normal stress, A1 is the dimensionless stiffness coefficient of the ideal loose sand-structure, A2 is the dimensionless stiffness coefficient K1 with the modified sand relative density D r growth rate; The method for obtaining the monotonic shear friction coefficient is: m p =A3+A4Dr Among them, μ p is the monotonic shear friction coefficient, A3 is the friction coefficient of the sand-steel interface in the ideal loosest state, and A4 is the rate at which the initial friction coefficient of the interface increases with the increase of relative density; The method for obtaining the cyclic shear friction coefficient is: A5=B1+B2Dr Where μ1 is the cyclic shear friction coefficient, D r is used to correct the relative density of sand, A5 is the model parameter that controls the evolution rate of the friction coefficient μ1 with the number of cyclic shearing cycles N, and μ r is the critical friction coefficient, B1 and B2 are model parameters.

2. A method for testing friction characteristics of state-dependent sand-structure monotonic and cyclic shear interfaces according to claim 1, characterized in that: Based on the confining pressure-volume relationship curve, the relative density of the sand is corrected, and obtaining the corrected relative density of the sand includes: Based on the confining pressure-volume relationship curve and the total mass of sand, a confining pressure-dry density relationship is obtained; Based on the confining pressure-dry density relationship, the relative density of the sand is corrected to obtain the corrected relative density of the sand.

3. A method for testing friction characteristics of state-dependent sand-structure monotonic and cyclic shear interfaces according to claim 1, characterized in that: The first displacement monotonic shear test requires that the displacement at the time of test termination be the shear displacement corresponding to the critical state of the test.

4. A method for testing friction characteristics of state-dependent sand-structure monotonic and cyclic shear interfaces according to claim 1, characterized in that: The second displacement cyclic shear test is as follows: the amplitude of the cyclic shear displacement performed shall not exceed the shear displacement corresponding to the peak shear strength of the first displacement monotonic shear test.

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