A model test method for simulating progressive weakening of slope strength

Abstract

The application provides a model test method for simulating progressive weakening of slope strength, and relates to the technical field of geomechanical model test, which comprises the following steps: curing base material to obtain a sample, wherein the sample is a cylinder; selecting a weakening solution by trial method according to a preset model slope evolution time length; performing a weakening test on the model slope by immersing the model slope in the weakening solution; obtaining evolution process information of the model slope, and determining a critical time corresponding to the occurrence of a sliding surface of the model slope; performing a weakening test on the sample by using the weakening solution, and performing an unconfined compression test on the sample when the test time reaches the critical time, so as to obtain the cohesion of the sample; and calculating the critical cohesion of a prototype slope from the cohesion of the sample. In the case that the shear strength of the slope body is insufficient, the strength parameter of the slope body is gradually reduced, and the whole process of the slope body instability evolution is studied.

Description

[0001] This application is a divisional application. The original application has the application number CN202211646346.X and the application date is December 21, 2022. The invention title is "A model slope fabrication and model test method for simulating the progressive weakening of slope strength". Technical Field

[0002] This invention relates to the field of geomechanical model testing technology, and more specifically, to a model testing method for simulating the gradual weakening of slope strength. Background Technology

[0003] Geomechanical model testing is an important tool for slope safety and stability research and mechanism analysis. Model tests scale down the slope object according to certain similarity criteria, using appropriate similar materials to create a model similar to the prototype, simulating the working state and mechanical behavior of the prototype slope. To study the slope instability mechanism and evolution process, model tests first need to simulate slope instability. For example, centrifugal model tests achieve slope instability by applying centrifugal force, and bottom friction model tests achieve slope instability by applying frictional force at the bottom of the model slope, and so on. All of these model tests apply external factors to achieve slope instability. However, even without external triggering factors, insufficient shear strength or reduced strength of the slope itself is the intrinsic cause of slope instability. Summary of the Invention

[0004] The purpose of this invention is to provide a model slope fabrication and model test method for simulating the gradual weakening of slope strength, thereby improving the aforementioned problems. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0005] This application provides a model test method for simulating the gradual weakening of slope strength, including:

[0006] A sample is obtained by curing the matrix material, and the sample is a cylinder;

[0007] Based on the preset model slope evolution time, the weakening solution was selected using a trial mixing method;

[0008] Weakening tests were conducted by immersing the model slope in the weakening solution.

[0009] Obtain information on the evolution process of the model slope and determine the critical time when the model slope exhibits a slip surface;

[0010] The sample is subjected to a weakening test using the weakening solution, and an unconfined compression test is performed on the sample when the test time reaches the critical time to obtain the cohesive force of the sample.

[0011] The critical cohesion of the prototype slope was calculated from the cohesion of the sample.

[0012] The beneficial effects of this invention are as follows:

[0013] This invention utilizes a high-precision model slope for testing. By selecting a suitable weakening solution, the entire evolution process of the model slope is controlled within a reasonable timeframe. This ensures that the test results, such as stress field, strain field, displacement field, and time-dependent strength parameters, are recorded in detail during each evolution process of the model slope. This allows for accurate determination of the moment when the model slope exhibits a slip surface. Furthermore, the cohesion of the model slope exhibiting a slip surface is obtained through reverse testing using test specimens. Simultaneously, by gradually reducing the slope strength parameters, the entire process of slope instability evolution can be studied, providing a methodological basis for the following four important slope engineering problems: (1) the mechanical behavior of slope instability due to internal strength reduction; (2) revealing the potential instability characteristics of slopes; (3) predicting the entire process of future slope instability evolution; and (4) verifying the correctness of the numerical simulation strength reduction method.

[0014] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing embodiments of the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of a method for creating a model slope according to the present invention;

[0017] Figure 2 This is a flowchart of a model test method for simulating the gradual weakening of slope strength according to the present invention;

[0018] Figure 3 The curve showing the change in cohesive strength of the matrix material sample of the present invention with weakening time;

[0019] Figure 4 This is a schematic diagram of the model box of the present invention.

[0020] Marked in the image:

[0021] 1. Internal structural template; 2. Front glass; 3. Back glass; 4. Steel frame; 5. Side door; 6. Support frame. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0023] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0024] Example 1:

[0025] This embodiment provides a model test method for simulating the gradual weakening of slope strength.

[0026] like Figure 1 As shown, this embodiment provides a method for creating a model slope, including the following steps:

[0027] S1. Conduct an on-site survey of the prototype slope to obtain its morphology, geometric parameters, and mechanical parameters. The geometric parameters of the prototype slope include the slope height and the width at the base. The mechanical parameters include at least the unit weight γ of the slope soil. p Initial cohesion C p and internal friction angle Specifically, the geometric and mechanical parameters of the prototype slope are shown in Table 1:

[0028] Table 1

[0029]

[0030] Based on the above embodiments, this method further includes:

[0031] S2. Determine the mass ratio of adhesive and aggregate in the matrix material using the geometric parameters and the mechanical parameters;

[0032] Specifically, step S2 includes:

[0033] S21. The limiting cohesion is calculated based on the unit weight, initial cohesion, and internal friction angle of the slope soil.

[0034] Specifically, step S21 includes:

[0035] S211. Based on the internal friction angle, conduct an angle of repose test on the aggregate to select the type and particle size of the aggregate;

[0036] Preferably, the angle of repose test for cohesion-free soils in the "Standard for Geotechnical Testing Methods" (GB / T50123-2019) was conducted on aggregates of different types and sizes, and 3mm stainless steel balls were finally selected as the aggregate. The internal friction angle of this steel ball accumulation was 21°, which deviated from the internal friction angle of the prototype slope by less than 10%. In this embodiment, by using stainless steel balls as the matrix material, the uniform distribution of internal voids can be ensured, and the uniform weakening of strength over the entire area can be achieved better.

[0037] S212. Determine the buoyancy γ of aggregate in water. m According to the buoyancy γ m and the unit weight γ of the slope soil p Determine the high similarity ratio R γ =γ m γ p ;

[0038] In this embodiment, the buoyancy of the steel ball pile in water is 42.05 kg / m³. 3 The similarity ratio R was calculated. γ =γ m γ p =1:0.48.

[0039] S213. Determine the geometric similarity ratio R based on the geometric parameters and the preset geometric parameters of the model slope. L ;

[0040] In this embodiment, the preset geometric parameters of the model slope are a slope height of 59cm and a slope base width of 82cm, from which the geometric similarity ratio R can be obtained. L =Geometric parameters of the model slope:Preset geometric parameters of the model slope = 1:20.74.

[0041] As shown in Table 2, Table 2 presents a comparison of the geometric or mechanical parameters of the prototype slope and the model slope.

[0042] Table 2

[0043]

[0044] S214. Using the geometric similarity ratio and the density similarity ratio, determine the intensity similarity ratio based on the similarity criterion;

[0045] Specifically, based on the high similarity ratio R γ =1:0.48, geometric similarity ratio R L =1:20.74 and the Buckingham similarity criterion were used to determine the intensity similarity ratio R of the model test. σ =R γ ×R L =1:10;

[0046] S215. The limiting cohesion C is obtained from the strength similarity ratio and the initial cohesion. m :

[0047] C m =R σ ×C p = 4.6 kPa; (1)

[0048] S22. Select multiple samples and immerse each sample in a variety of different solutions, wherein the ratio of weakening agent and harmonizing agent is different in each solution;

[0049] S23. Triaxial compression tests are performed on multiple cured matrix samples respectively, and a target cured matrix sample is selected by trial mixing method. The cohesive force of the target matrix material sample is not less than the specified cohesive force.

[0050] Specifically, triaxial compression tests were performed on the multiple solidified matrix samples according to the "Standard for Geotechnical Testing Methods" (GB / T50123-2019), with confining pressures of 100 kPa, 200 kPa, 300 kPa and 400 kPa respectively, to obtain the target solidified matrix sample. The cohesion of the target solidified matrix sample was 49.81 kPa and the internal friction angle was 21.86°.

[0051] By conducting an unconfined compression test on the target cured matrix sample, the curve of cohesion changing with weakening time can be obtained, as follows: Figure 3 As shown in the figure, it can be seen that the cohesion of the target solidified matrix sample decreases with the increase of weakening time, which means that the matrix material made from the mass ratio of the target solidified matrix sample can simulate the strength aging weakening characteristics of soil.

[0052] S24. The mass ratio of aggregate and adhesive in the target matrix material sample is taken as the mass ratio of the matrix material: PVAc adhesive: aggregate = 5:1846.

[0053] Based on the above embodiments, this method further includes:

[0054] S3. Weigh the aggregate and adhesive according to the mass ratio, and mix them to obtain the matrix material;

[0055] Specifically, weigh the steel ball assembly and adhesive according to the mass ratio of 5:1846, put the weighed steel ball assembly into a mixer, and then evenly add the adhesive into the steel ball assembly and mix thoroughly to obtain the matrix material.

[0056] Based on the above embodiments, this method further includes:

[0057] S4. Create a model box based on the shape and geometric parameters of the prototype slope;

[0058] Specifically, step S4 includes:

[0059] S41. Create a model box and internal configuration template based on the shape and geometric parameters of the prototype slope;

[0060] like Figure 4 As shown, the model box includes a steel frame 4 and a support 6. The steel frame 4 is a cuboid, and the support 6 is fixed to the four bottom corners of the steel frame 4. The front and back of the steel frame 4 are respectively a front glass 2 and a back glass 3. One side of the steel frame 4 is set as an openable side door 5.

[0061] Preferably, the front glass and the back glass are both 1.6cm thick and are two pieces of transparent laminated tempered glass. The side of the front glass 2 and the back glass 3 located inside the model box is coated with an anti-stick material to reduce the sidewall effect.

[0062] S42. The internal configuration template is placed into the model box to form a spatial model, wherein the spatial model is the shape of the model slope.

[0063] The internal configuration template 1 is placed inside the steel frame 4 and closely attached to the side door 5, forming a spatial model inside the steel frame 4 that has the same shape as the model slope.

[0064] In this embodiment, the internal configuration template 1 is trapezoidal in shape, and the spatial model is a trapezoidal model slope.

[0065] Based on the above embodiments, this method further includes:

[0066] S5. The matrix material is placed in layers into the model box, and after curing, the model slope is obtained;

[0067] Specifically, step S5 includes:

[0068] S51. The matrix material is poured into the model box in layers, and each layer is tamped to make it dense. When the matrix material reaches the preset height, the surface of the matrix material is repaired to achieve the shape of the model slope.

[0069] S52. The matrix material is cured at a first preset temperature and under windless conditions for a first preset time, and then cured at a second preset temperature under ventilated conditions for a second preset time. After the matrix material is cured, the model slope is obtained.

[0070] Specifically, the substrate material is cured for 1 day under windless conditions at 30±2℃, and then cured for 5 days under ventilated conditions at 30±2℃ to obtain a cured substrate material.

[0071] S53. Remove the internal configuration template from the model box, which contains only the model slope.

[0072] Example 2

[0073] Please see Figure 2 The present invention also provides a model test method for simulating the gradual weakening of slope strength, comprising the following steps:

[0074] S6. The matrix material is cured to obtain a sample, wherein the sample is a cylinder;

[0075] Preferably, the diameter of the sample is 61.8 mm and the height is 125 mm.

[0076] Based on the above embodiments, this method further includes:

[0077] S7. Based on the preset model slope evolution time, select the weakening solution using the trial mixing method;

[0078] Specifically, step S7 includes:

[0079] S71. Obtain the preset model slope evolution time;

[0080] In this embodiment, the preset model slope evolution time is 15 minutes, which represents the total time required for the slope to evolve from its current state to the point where a slip surface appears.

[0081] S72. Select multiple samples and immerse each sample in a variety of different solutions, wherein the ratios of weakening agent and harmonizing agent in the various solutions are different;

[0082] S73. A weakening solution is selected from a variety of solutions by trial mixing, wherein the weakening solution makes the weakening rate of the sample not less than the preset weakening rate of the matrix material.

[0083] In this embodiment, the final selected mass ratio of the weakening solution is weakening agent: harmonizer = 1: 0.9. In the weakening test under this ratio, the evolution time of the sample is 54 min 51 s.

[0084] Based on the above embodiments, this method further includes:

[0085] S8. The model slope is immersed in the weakening solution to conduct a weakening test;

[0086] Specifically, step S8 includes:

[0087] S81. Install a high-speed camera to capture the evolution process of the model slope;

[0088] S82. Pour the weakening solution into the model box until the weakening solution submerges the top surface of the model slope;

[0089] Preferably, a water pipe is placed inside the model box, with the outlet of the water pipe located at the bottom of the model box and kept at a distance from the model slope. A weakening solution is injected into the model box through the water pipe, and the liquid level rises continuously. When the weakening solution completely submerges the model slope, the injection is stopped, the water pipe is removed, and the model slope submerged in the weakening solution immediately exhibits strength weakening characteristics.

[0090] S83. The camera captures images of the model slope evolution process. Specifically, during the weakening process of the model slope, the camera is taken in a space surrounded by a black curtain, with three incandescent lamps providing the light source. A white background board is laid on the back of the model box to obtain better photographic results.

[0091] Based on the above embodiments, this method further includes:

[0092] S9. Obtain information on the evolution process of the model slope and determine the critical time when the model slope exhibits a slip surface;

[0093] Specifically, step S9 includes:

[0094] S91. Obtain images of the slope evolution process of the model;

[0095] S92. Analyze the image of the model slope evolution process using digital image technology to interpret the strain field and displacement field of the model slope, i.e., the internal deformation and external relative deformation of the model slope;

[0096] S93. Determine whether a slip surface appears on the model slope by analyzing the strain field and displacement field of the model slope, and record the critical time corresponding to the appearance of the slip surface;

[0097] Specifically, the strength of the model slope gradually decreases as the weakening time increases. In this embodiment, when the weakening time lasts for 42 minutes and 11 seconds, a slip surface appears due to insufficient slope strength. After the slip surface appears, the sliding body slides down rapidly, indicating that the slope is destroyed at this moment. The 42 minutes and 11 seconds is the critical time corresponding to the appearance of the slip surface.

[0098] Based on the above embodiments, this method further includes:

[0099] S10. The sample is subjected to a weakening test using the weakening solution, and an unconfined compression test is performed on the sample when the test time reaches the critical time to obtain the cohesive force of the sample.

[0100] Specifically, step S10 includes:

[0101] S101. The sample is placed in a weakening solution for a weakening test;

[0102] S102. When the weakening test reaches the critical time, the sample is subjected to an unconfined compression test.

[0103] S103. The cohesive force of the specimen is calculated using the stress peak value from the stress-strain curve of the unconfined compression test according to the Mohr-Coulomb strength criterion:

[0104] As strain increases, the stress-strain curve of the unconfined compression test shows a pattern of first rising and then falling. The stress peak value is recorded. In this embodiment, the stress peak value is 7.604 kPa.

[0105] According to the Mohr-Coulomb strength criterion, the cohesive force can be derived using the aforementioned stress peak value, as shown in the following formula:

[0106]

[0107] In the formula, c is the cohesive force of the sample, σ1 is the peak stress, The internal friction angle of the sample;

[0108] Based on the above embodiments, this method further includes:

[0109] S11. The critical cohesion of the prototype slope is calculated from the cohesion of the sample:

[0110] Specifically, based on the model test strength similarity ratio of 1:10, the critical cohesion of the prototype slope can be calculated to be 26.13 kPa, indicating that when the critical cohesion of the prototype slope reaches 26.13 kPa, the prototype slope will exhibit a slip surface.

[0111] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A model test method for simulating the gradual weakening of slope strength, characterized in that: A sample is obtained by curing the matrix material, and the sample is a cylinder; Based on the preset model slope evolution time, the weakening solution was selected using a trial mixing method; Weakening tests were conducted by immersing the model slope in the weakening solution. Obtain information on the evolution process of the model slope and determine the critical time when the model slope exhibits a slip surface; The sample is subjected to a weakening test using the weakening solution, and an unconfined compression test is performed on the sample when the test time reaches the critical time to obtain the cohesive force of the sample. The critical cohesion of the prototype slope was calculated from the cohesion of the sample.

2. The model test method for simulating the gradual weakening of slope strength according to claim 1, characterized in that, The preset model slope evolution time is determined by selecting the weakening solution using a trial-and-error method, including: Obtain the preset model slope evolution time; Multiple samples are selected and immersed in various different solutions, with different ratios of weakening agent and harmonizing agent in each solution; A weakening solution is selected from a variety of solutions using a trial-and-error method. The weakening solution ensures that the weakening rate of the sample is not less than the predetermined weakening rate of the matrix material.

3. The model test method for simulating the gradual weakening of slope strength according to claim 2, characterized in that, The weakening test involves immersing the model slope in the weakening solution, including: Install cameras to film the evolution process of the model slope; The weakening solution is injected into the model box until it submerges the top surface of the model slope. The camera captured images of the model slope evolution process.

4. The model test method for simulating the gradual weakening of slope strength according to claim 3, characterized in that: The process of acquiring information on the evolution of the model slope and determining the critical time corresponding to the appearance of a slip surface on the model slope includes: Acquire images of the slope evolution process of the model; By analyzing images of the model slope evolution process using digital image technology, the strain field and displacement field of the model slope can be determined. The model slope is tested for slip surface by measuring the strain and displacement fields, and the critical time corresponding to the appearance of slip surface is recorded.

5. The model test method for simulating the gradual weakening of slope strength according to claim 1 or 4, characterized in that: The sample is subjected to a weakening test using the weakening solution, and an unconfined compression test is performed on the sample when the test time reaches the critical time to obtain the cohesion of the sample, including: The sample was placed in a weakening solution for a weakening test; When the weakening test reaches the critical time, the specimen is subjected to an unconfined compression test. According to the Mohr-Coulomb strength criterion, the cohesive force of the specimen is calculated using the stress peak value of the stress-strain curve of the unconfined compression test.

6. The model test method for simulating the gradual weakening of slope strength according to claim 1, characterized in that... The critical cohesion of the prototype slope is calculated from the cohesion of the sample, including: The strength similarity ratio of the model test is obtained. The ratio of the cohesion of the specimen to that of the prototype slope is equal to the strength similarity ratio. The strength similarity ratio of the model test is the product of the geometric similarity ratio and the specific gravity similarity ratio.

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