A centrifugal model test method for shear deformation law of contact clay in earth-rock dam

Abstract

A centrifugal model test method for shear deformation law of contact clay in earth-rock dams is applicable to the study of shear deformation of contact clay in earth-rock dams that cannot be simulated by conventional tests, and belongs to the field of soil mechanics test technology and application. The steps are as follows: (1) for the contact clay layer of the earth-rock dam, n local models are selected along the valley slope (slope is i), and centrifugal model tests are carried out under Ng conditions according to the geometric similarity scale 1 / N, where N≤30; (2) the model valley dam foundation is prepared with concrete; super-heavy materials are arranged on the upper boundary of the model so that the soil bears the self-weight stress of the prototype level under the super-gravity field; (3) the horizontal deformation increment and vertical deformation increment of the contact clay layer soil obtained in the test are decomposed and superimposed along the valley slope direction to calculate the shear deformation increment; (4) the relationship between the shear deformation increment and the self-weight stress is obtained by fitting analysis; (4) the overall shear deformation distribution law is obtained by integrating from bottom to top along the valley direction.

Description

Technical Field

[0001] The invention relates to a centrifugal model test method for shear deformation law of contact clay in earth-rock dams, belonging to the field of soil mechanics test technology and application. The test method can effectively study the shear deformation law of contact clay with very thin relative thickness in earth-rock dams. Background Art

[0002] A number of major water conservancy projects that have been built or are under construction in my country have adopted earth-rock dams, such as Xiaolangdi (160m), Nuozhadu (261.5m), Lianghekou (295m), Shuangjiangkou (314m), Changheba (240m), Maoergai (147m), Miaowei (139.8m), Quxue (164m), Dashimen (128.8m), Rumei (315m), etc. Earth-rock dams have the advantages of using local materials, adapting to complex terrain, and having sound construction machinery, but there is also a prominent technical difficulty: the coordination of contact clay with bank slope and core wall deformation, which is directly related to the safety performance of the dam.

[0003] As part of the core wall, contact clay is mainly set at the contact surface between the core wall and the dam foundation, the bedrock slopes on both sides, and the structure, which can improve the anti-splitting performance and deformation coordination ability of the above contact parts. The contact clay must have good plasticity, viscosity, anti-seepage deformation ability, and the construction quality must be guaranteed; even so, it is currently difficult to determine its shear deformation law under the long-term operation conditions of the dam, and it is difficult to predict its impact on the dam.

[0004] The research on the engineering properties of contact clay is mainly based on numerical analysis, shear test and permeability test. The difficulty of numerical analysis lies in the simulation of contact, and there is a lack of verification of measured data and model test data. Shear permeability test can only study the deformation-permeability-scour characteristics of soil units under ideal conditions, and does not actually involve contact problems. From the literature collected from home and abroad, no systematic model test research that includes contact parts, reflects contact problems, and targets the deformation characteristics of contact clay has been found.

[0005] Once an earth-rock dam fails, it will cause great losses to people's lives and property. The core-wall contact surface is a dangerous part where large deformation and cracks may occur, and it is a high-incidence area for earth-rock dam accidents. The complex stress and deformation conditions at the contact part, especially the sudden deformation that may be caused by earthquake disasters, will cause large deformation and cracks that affect the coordination of dam deformation, and then affect the seepage of the dam body, causing contact flow soil, contact scour, pipe burst and other damage, leading to the occurrence of earth-rock dam accidents. This key issue must be studied in depth. Therefore, conducting centrifugal model tests to study the shear deformation law of contact clay is related to whether the construction of the dam can be correctly and reasonably supported and the safety of the dam can be evaluated, which has important theoretical and practical significance.

[0006] However, since the contact clay layer is very thin relative to the entire dam body, usually with a horizontal thickness of only 2 to 4 meters, the current common geotechnical centrifuge model test technology is used to completely simulate the entire earth-rock dam. With the current common centrifuge model box with a maximum internal height of about 1 meter, the N in the geometric similarity scale 1 / N is often greater than 100. In this way, the horizontal thickness of the model contact clay layer will be only about 20 to 40 mm, and such a small soil sample cannot accurately observe its shear deformation. New test technology needs to be developed to use geotechnical centrifuge model test technology to carry out research on the shear deformation law of contact clay. Summary of the invention

[0007] The purpose of the present invention is to establish a new centrifuge model test method, by integrating a number of local centrifuge model test results, so as to obtain the shear deformation law of contact clay in earth-rock dam.

[0008] The technical solution to achieve the purpose of the present invention is a centrifugal model test method for shear deformation law of contact clay in earth-rock dams, comprising the following steps:

[0009] Step 1: For the earth-rock dam (height H) to be simulated and in contact with the clay layer (the slope of the valley dam foundation is i), select n local parts from bottom to top along the valley direction, and conduct centrifuge model tests under Ng conditions according to the geometric similarity scale 1 / N, where N should not be greater than 30;

[0010] Step 2: On one side of each local model, a boundary with a slope of i is prepared using concrete material according to the strength of the valley dam foundation; Vaseline is applied to the boundary on the other side; the bottom boundary is the bottom surface of the model box, even if the shear deformation of the bottom of the clay in contact is 0; the upper boundary surface is arranged with super-heavy substitute material, so that under the action of the centrifugal model super-gravity field, the self-weight stress borne by the upper boundary of the model is equal to the self-weight stress of the prototype;

[0011] Step 3: Through experiments, obtain the horizontal deformation increment Δs of the upper surface of the soil body of the jth local model contacting the clay layer xj (with the direction away from the valley dam foundation as positive) and the vertical deformation increment Δs yj (vertically downward is positive), then according to the formula Calculate the shear deformation increment Δs j ;

[0012] Step 4, by fitting analysis, the relationship between the shear deformation increment and the self-weight stress is obtained, Δs(y)=f[ρ*g*(Hy)], where y is the vertical height, which is the prototype value converted according to the similarity law of the centrifugal model;

[0013] Step 5: Integrate from bottom to top along the valley direction to obtain the overall shear deformation distribution law The h in the formula is the height from the current calculation point to the riverbed, which is the prototype value converted according to the similarity law of the centrifugal model, 0≤h≤H.

[0014] The beneficial effects of the present invention are as follows: the boundary conditions of the local model test can be accurately controlled; the relationship between the shear deformation increment and the deadweight stress of the contact clay can be obtained; and the overall shear deformation law of the contact clay layer of the earth-rock dam can be obtained by integration.

[0015] By adopting the method of the present invention, the geotechnical centrifuge model test technology can be used to effectively carry out experimental research on the shear deformation law of contact clay in earth-rock dams. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Taking a certain earth-rock dam as an example, the schematic diagram of the local model of 4 contact clay layers is selected;

[0017] Figure 2 It is the layout diagram of the local test model;

[0018] Figure 3 is the relationship curve between the contact clay shear deformation increment and the self-weight stress obtained from the experiment;

[0019] Figure 4 is the shear deformation law of the overall contact clay layer obtained by integration. DETAILED DESCRIPTION

[0020] Example 1

[0021] A high earth-rock dam with a maximum dam height of 100m is a core wall rockfill dam. It is necessary to study the shear deformation law of the contact clay (located between the core wall and the valley dam foundation). The horizontal thickness of the contact clay layer is 4m. If the usual geotechnical centrifuge model test method is used, in order to fully simulate the dam height of 100m, the current common centrifuge model box has a maximum internal height of about 1m, and the N in the geometric similarity scale 1 / N must be no less than 100. In this way, the horizontal thickness of the model contact clay layer will not exceed 40mm. With the current measurement technology in the centrifuge model test, it is difficult to accurately observe its shear deformation. Using "a centrifuge model test method for the shear deformation law of contact clay in earth-rock dams", 4 groups of local tests were carried out to integrate and obtain the overall shear deformation law of the contact clay layer, including the following steps:

[0022] Step 1: Collect core wall soil and contact clay materials from the project site, transport them to the laboratory, remove impurities, and prepare them for use according to the density, moisture content, gradation and other parameters of the project site;

[0023] Step 2, such as Figure 1, along the valley direction (in this case, the slope i = 1), four local areas were selected from bottom to top to carry out centrifugal model tests. The test conditions are shown in Table 1. The geometric scale of the local test in this case is 1 / 20, and the model layout is as follows Figure 2 As shown (unit: mm), the horizontal thickness of the contact clay layer is 200 mm, and the centrifugal acceleration is 20 g;

[0024] Table 1 Shear deformation test conditions of contact clay layer

[0025] serial number Height from upper surface to riverbed / m Overburden pressure / kPa M1 20 400 M2 40 800 M3 60 1200 M4 80 1600

[0026] Step 3: According to the results of the local test, the relationship curve between the contact clay shear deformation increment and the self-weight stress is fitted, as shown in Figure 3 ;

[0027] Step 4: Integrate from bottom to top along the valley direction to obtain the overall shear deformation law of the contact clay layer, such as Figure 4 .

Claims

1. A centrifugal model test method for shear deformation law of contact clay in earth-rock dams, comprising the following steps: Step 1: For the earth-rock dam contact clay layer to be simulated, select n local parts from bottom to top along the direction of the valley dam foundation, and conduct centrifuge model tests under Ng conditions; the height of the earth-rock dam is H, the slope of the valley dam foundation is i, the geometric similarity scale is 1 / N, and N is not greater than 30; Step 2: On one side of each local model, a boundary with a slope of i is prepared using concrete material according to the strength of the valley dam foundation; Vaseline is applied to the boundary on the other side; the bottom boundary is the bottom surface of the model box, even if the shear deformation of the bottom of the clay in contact is 0; the upper boundary surface is arranged with super-heavy substitute material, so that under the action of the centrifugal model super-gravity field, the self-weight stress borne by the upper boundary of the model is equal to the self-weight stress of the prototype; Step 3: Through experiments, obtain the horizontal deformation increment Δs of the upper surface of the soil body of the jth local model contacting the clay layer xj and the vertical deformation increment Δs yj Then, according to the formula Calculate the shear deformation increment Δs j ; Step 4, by fitting analysis, the relationship between the shear deformation increment and the self-weight stress is obtained, Δs(y)=f[ρ*g*(Hy)], where y is the vertical height, which is the prototype value converted according to the similarity law of the centrifugal model; Step 5: Integrate from bottom to top along the valley direction to obtain the overall shear deformation distribution law The h in the formula is the height from the current calculation point to the riverbed, which is the prototype value converted according to the similarity law of the centrifugal model, 0≤h≤H.

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