Sample cap, hollow torsion interface shear triaxial apparatus and test method

Abstract

The present invention provides a sample cap, a hollow torsion interface shear triaxial instrument and a test method, wherein the sample cap comprises: a sample cap base and an annular plate fixedly connected to the sample cap base, wherein the annular plate is used to contact with a soil sample to form a soil-structure interface; the sample cap base is in a hollow cylindrical shape, a drainage pipeline is provided inside the cylinder wall of the sample cap base, a through hole is provided on the annular plate, an end of the drainage pipeline close to the annular plate corresponds to the through hole, and an end of the drainage pipeline away from the annular plate is used to connect an interface pore pressure volume change measurement controller. The present invention can accurately obtain the development law of interface pore water pressure, and more comprehensively explore the influence of parameters such as shear rate, structural roughness, cyclic load frequency, cyclic stress ratio, etc. on interface mechanical properties, especially pore water pressure properties.

Description

Technical Field

[0001] The invention relates to the technical field of civil engineering, and in particular to a sample cap, a hollow torsion interface shear triaxial apparatus and a testing method. Background Art

[0002] The mechanical behavior of the interface between saturated soil and structure is an important part of the study of soil-structure interaction. The constraint of the structure on the soil makes the mechanical properties of the interface area different from those of the soil in other areas, and the mechanical response of the interface will have an important impact on the stress and deformation of the structure. At present, the research mainly uses simple shear, direct shear and torsion shear test methods to explore the contact characteristics between cohesionless soil and steel, concrete, geosynthetics, and between clay and concrete and steel. However, the direct shear apparatus, simple shear apparatus and other devices used in these studies all use shear rate to approximate different drainage conditions, which have some obvious shortcomings: for example, it is impossible to accurately control the drainage state during the actual test process, and it is impossible to accurately reflect the influence of shear rate on the strength characteristics of the interface. Due to the lack of closing devices such as latex membranes, it is also impossible to accurately measure the changes in pore pressure during the shear process. In addition, the shear box has a strong constraint on the soil sample, which may lead to uneven interface stress and deformation.

[0003] After searching the prior art literature, it was found that:

[0004] Application number: 202110779192.0, invention name: An intelligent self-spinning hollow cylinder interface shear instrument and its test method, application publication number: CN 113640213 A, application publication date 2021.11.12, the method discloses an intelligent self-spinning hollow cylinder interface shear instrument and its test method, which is used to solve the shortcomings of the inability to test pore water pressure in direct shear tests and the inability to test interface friction under small displacement conditions, and the inability to test interface friction between different rock and soil bodies under complex stress conditions in ring shear instruments and the inability to use average shear stress and shear displacement. The core principle of this patent is to insert a solid cylinder into the hollow cylindrical soil sample and achieve interface shear by twisting the solid cylinder. Although this method introduces pore water pressure measurement, it measures the pore pressure at the bottom of the hollow cylindrical sample, rather than the pore pressure on the interface with the solid cylinder. For clay samples with low permeability coefficients, the pore pressure at the bottom is not completely consistent with the pore pressure development at the interface position, and the error is large. In addition, this test method can only perform static shear and cannot perform interface dynamic shear tests.

[0005] In summary, for the saturated soil-structure interface, the internal pore water pressure has an important influence on the mechanical properties of the interface. The existing test methods have not yet conducted a comprehensive study on the static and dynamic behavior of the soil-structure interface under the influence of pore water pressure, and cannot accurately control the drainage conditions of the soil samples. Directly applying the existing test results will cause misjudgment of the actual situation and bring safety risks. Therefore, it is necessary to introduce new test means and methods to conduct in-depth research on the static and dynamic characteristics of the soil-structure interface, accurately obtain the development law of the interface pore water pressure, and explore the influence of parameters such as shear rate, structural roughness, cyclic load frequency, and cyclic stress ratio on the mechanical properties of the interface, especially the pore water pressure characteristics, so as to better guide engineering practice. Summary of the invention

[0006] In view of the defects in the prior art, the object of the present invention is to provide a sample cap, a hollow torsion interface shear triaxial apparatus and a testing method.

[0007] The present invention is achieved by the following technical solutions:

[0008] According to a first aspect of the present invention, there is provided a sample cap for a hollow torsion interface shear triaxial apparatus, comprising: a sample cap base and an annular plate fixedly connected to the sample cap base, the annular plate being used to contact with a soil sample to form a soil-structure interface;

[0009] The sample cap base is in the shape of a hollow cylinder, a drainage pipe is provided inside the cylinder wall of the sample cap base, a through hole is opened on the annular plate, one end of the drainage pipe close to the annular plate corresponds to the through hole, and the end of the drainage pipe away from the annular plate is used to connect to the interface hole pressure volume change measurement controller.

[0010] Furthermore, the diameter of the drainage pipeline is the same as the aperture of the through hole; the through hole is filled with permeable stone, and the permeable stone is covered with filter paper.

[0011] Furthermore, the surface roughness of the annular plate is determined according to a simulated engineering structure.

[0012] Furthermore, the annular plate is fixedly connected to the sample cap base by bolts; and a sealing gasket is provided between the annular plate and the sample cap base.

[0013] Furthermore, the sample cap base is made of aluminum alloy.

[0014] According to a second aspect of the present invention, there is provided a hollow torsion interface shear triaxial apparatus, comprising:

[0015] A base for providing support;

[0016] A chamber is provided on the base, the chamber comprises an inner confining pressure chamber and an outer confining pressure chamber, a sample is installed between the inner confining pressure chamber and the outer confining pressure chamber, and the bottom of the sample is connected to a sample hole pressure volume change measurement controller;

[0017] The sample cap is covered on the sample and contacts the sample to form a soil-structure interface; the upper end of the sample cap is connected to an axial force torque sensor, a vertical servo loading system and a torsion servo loading system; one end of the drainage pipeline is connected to the sample, and the other end of the drainage pipeline is connected to an interface pore pressure volume change measurement controller;

[0018] A peripheral pressure measurement controller for measuring and controlling the peripheral pressure of the sample, wherein the peripheral pressure measurement controller is connected to the peripheral pressure chamber;

[0019] An internal confining pressure measurement controller for measuring and controlling the internal confining pressure of the sample, wherein the internal confining pressure measurement controller is connected to the internal confining pressure chamber;

[0020] Data acquisition module, used to collect interface pore pressure volume change data, sample pore pressure volume change data, peripheral pressure data and inner confining pressure data;

[0021] The control module is respectively connected with the data acquisition module, the axial force torque sensor, the vertical servo loading system and the torsion servo loading system.

[0022] Furthermore, both the vertical servo loading system and the torsion servo loading system use cylinders for servo control, and utilize electro-pneumatic converters to adjust cylinder pressure to achieve loading.

[0023] Furthermore, the torsion servo loading system realizes cyclic loading on the soil-structure interface by setting the waveform to any one of a sine wave, a triangle wave and a rectangular wave, and the changing frequency to 0.01-10 Hz.

[0024] According to a third aspect of the present invention, there is provided a method for testing interface mechanical properties using the above-mentioned hollow torsion interface shear triaxial apparatus, the method comprising:

[0025] Prepare a sample and install the sample in the chamber of a triaxial instrument, wherein the sample is in a hollow cylindrical shape and the inside and the outside of the sample are wrapped with a latex film, and install a sample cap on the sample, wherein the sample cap contacts the sample to form a soil-structure interface;

[0026] The sample is saturated, and then equal pressure is applied to the inner confining pressure chamber and the outer confining pressure chamber at the same time, and vertical pressure is applied through a vertical servo loading system to consolidate the sample;

[0027] The interface mechanical property shear test is carried out through the torsion servo loading system to obtain the interface mechanical property parameters.

[0028] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0029] 1. The present invention can study the dynamic and static mechanical properties of interfaces with drainage or non-drainage under different structural roughness conditions under normal stress conditions, only by replacing the annular plate of the sample cap. The test principle is simple, the operation is convenient, and it is easy to implement.

[0030] 2. The present invention utilizes the pore pressure volume change measurement controller of the hollow torsion triaxial instrument to measure the interface pore water pressure or volume change; the interface size remains unchanged during the shearing process, the sample is not constrained by the rigid shear box, the stress and deformation of the soil near the interface are more uniform, and it is more suitable for engineering and design needs; it can more comprehensively explore the influence of parameters such as shear rate, structural roughness, cyclic load frequency, cyclic stress ratio, etc. on the interface mechanical properties, especially the pore water pressure characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0032] Figure 1 A schematic diagram of the structure of a sample cap according to an embodiment of the present invention;

[0033] Figure 2 Schematic diagram of the structure of a hollow torsion interface shear triaxial apparatus according to an embodiment of the present invention.

[0034] In the figure: 1 is the vertical servo loading system, 2 is the torsional servo loading system, 3 is the axial force torque sensor, 4 is the sample cap base, 41 is the drainage pipeline, 5 is the annular plate, 51 is the through hole, 6 is the sample, 7 is the latex film, 8 is the base, 9 is the sample hole pressure volume change measurement controller, 10 is the interface hole pressure volume change measurement controller, 11 is the peripheral pressure measurement controller, 12 is the inner confining pressure measurement controller, 13 is the data acquisition module, 14 is the control module, 15 is the inner confining pressure chamber, and 16 is the peripheral pressure chamber. DETAILED DESCRIPTION

[0035] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention. In the description of the embodiments of the present invention, it should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein.

[0036] The sample cap for the hollow torsion interface shear triaxial instrument provided by one embodiment of the present invention is as follows: Figure 1 The sample cap includes: a sample cap base 4 and an annular plate 5 fixedly connected to the sample cap base 4, the annular plate 5 is used to contact with the sample (soil sample) 6 to form a soil-structure interface; the sample cap base 4 is in a hollow cylindrical shape, a drainage pipe 41 is provided inside the cylinder wall of the sample cap base 4, a through hole 51 is opened on the annular plate 5, an end of the drainage pipe 41 close to the annular plate 5 corresponds to the through hole 51, and an end of the drainage pipe 41 away from the annular plate 5 is used to connect the interface hole pressure volume change measurement controller 10.

[0037] The embodiment of the present invention adopts a modular design sample cap, which includes a sample cap base 4 and an annular plate 5 fixedly connected to the sample cap base 4. The upper part of the sample cap is used to connect with the axial force torque sensor 3, and can be connected to the vertical servo loading system 1 and the torsion servo loading system 2 through the loading rod. There is a drainage pipeline 41 inside the sample cap connected to the pressure volume controller. The lower part of the sample cap contacts the soil sample to form a soil-structure interface. It only needs to change the annular plate (loading plate) to achieve testing of different test conditions. The relevant test methods using the sample cap can more comprehensively explore the effects of parameters such as shear rate, structural roughness, cyclic load frequency, cyclic stress ratio, etc. on the interface mechanical properties, especially the pore water pressure characteristics.

[0038] In order to transmit the pore water pressure and volume change of the interface, in some preferred embodiments, the diameter of the drainage pipe 41 is the same as the aperture of the through hole 51. For example, the sample cap base 4 is drilled with a drainage pipe 41 with a diameter of 2 mm, and the annular plate 5 is drilled with a through hole 51 with a diameter of 2 mm. The position of the through hole 51 corresponds to the drainage pipe 41 of the sample cap base 4. Furthermore, in order to prevent soil particles from entering the drainage pipe 41, the through hole 51 is filled with permeable stone, and the permeable stone is covered with filter paper.

[0039] To facilitate processing and ensure the stability of surface properties, in some preferred embodiments, the annular plate 5 can be made of an annular steel plate. The surface roughness of the annular plate 5 is determined according to the simulated engineering structure. The annular plate 5 can be customized as needed to meet actual engineering requirements.

[0040] Furthermore, in order to adjust the surface roughness of the annular steel plate, the surface of the annular steel plate can be processed by milling, sandblasting and epoxy resin covering. Specifically, the surface of the annular steel plate is treated with epoxy resin to simulate the submarine pipeline after coating, and the roughness is generally 0.1-1μm; sandblasting can make the structure roughness 1-10μm, simulating the surface of the pipeline without coating and structures such as submarine anchors, pipe piles, and submerged foundations; milling can obtain an annular steel plate with a high roughness of more than 10μm.

[0041] In some other embodiments, the annular plate 5 may also be made of a concrete plate or an acrylic plate that meets the roughness requirements, or other types of plate materials may be selected according to actual needs, as long as the same functions as in the embodiment of the present invention can be achieved.

[0042] In order to ensure that the connection between the annular plate 5 and the sample cap base 4 is firm and reliable, in some preferred embodiments, corresponding bolt holes are provided on the annular plate 5 and the sample cap base 4, and the annular plate 5 is fixedly connected to the sample cap base 4 by bolts; a sealing gasket is provided between the annular plate 5 and the sample cap base 4 to prevent soil pore water from penetrating therein and affecting the accurate measurement of pore pressure.

[0043] In order to reduce the deadweight, in some preferred embodiments, the material of the sample cap base 4 is aluminum alloy, which can make the load application more accurate, especially for the sample 6 in a low stress state. Of course, in some other embodiments, the sample cap base 4 can also be made of other materials, as long as it can achieve the same function as in the embodiment of the present invention.

[0044] The embodiment of the present invention also provides a hollow torsion interface shear triaxial apparatus, referring to Figure 2The triaxial instrument comprises: a base 8 for providing support; a chamber arranged on the base 8, the chamber comprising an inner pressure chamber 15 and an outer pressure chamber 16, a sample 6 is installed between the inner pressure chamber 15 and the outer pressure chamber 16, and the bottom of the sample 6 is connected to a sample hole pressure volume change measurement controller 9; the sample cap in the above embodiment is covered on the top of the sample 6 and contacts with the sample 6 to form a soil-structure interface; the upper end of the sample cap is connected to an axial force torque sensor 3, a vertical servo loading system 1 and a torsion servo loading system 2, and the axial force and torque applied to the sample cap during the shearing process are measured by the axial force torque sensor 3, so that the normal stress and shear stress of the soil-annular plate interface can be obtained; drainage pipeline One end of 41 is connected to the sample 6, and the other end of the drainage pipe 41 is connected to the interface pore pressure volume change measurement controller 10; the peripheral pressure measurement controller 11 is used to measure and control the peripheral pressure of the sample, and the peripheral pressure measurement controller 11 is connected to the peripheral pressure chamber 16; the internal confining pressure measurement controller 12 is used to measure and control the internal confining pressure of the sample, and the internal confining pressure measurement controller 12 is connected to the internal confining pressure chamber 15; the data acquisition module 13 is used to collect the interface pore pressure volume change data, the sample pore pressure volume change data, the peripheral pressure data and the internal confining pressure data; the control module 14 is respectively connected to the data acquisition module 13, the axial force torque sensor 3, the vertical servo loading system 1 and the torsional servo loading system 2.

[0045] In some preferred embodiments, both the vertical servo loading system 1 and the torsion servo loading system are servo-controlled by a cylinder, and the cylinder pressure is adjusted by an electro-pneumatic converter to achieve loading. The vertical servo loading system 1 can automatically adjust the cylinder pressure according to the external load, so as to balance the deadweight of the instrument components on the upper part of the sample 6, such as the loading rod and the sample cap, and control the soil-structure interface normal stress to remain constant during the test, so as to achieve the interface constant normal stress boundary condition.

[0046] The torsion servo loading system loads the interface through displacement control or stress control. The torsion servo loading system can realize static loading under multiple strain rates, and can also realize cyclic loading of the interface. The torsion servo loading system realizes cyclic variation of torque (rotation angle) by setting two parameters, peak value and frequency. In some preferred embodiments, the torsion servo loading system realizes cyclic loading of the interface by setting the waveform to any one of sine wave, triangle wave and rectangular wave, and the variation frequency to 0.01-10Hz.

[0047] The embodiment of the present invention further provides a method for testing interface mechanical properties using the hollow torsion interface shear triaxial apparatus in the above embodiment, comprising:

[0048] S1. Prepare sample 6 and install it in the chamber of the triaxial instrument. The sample is in a hollow cylindrical shape, and the inside and outside of sample 6 are wrapped with latex film 7. Install the sample cap on top of sample 6, and the sample cap contacts sample 6 to form a soil-structure interface. Sample 6 is wrapped with latex film inside and outside. After closing the drainage valve, it can ensure a completely non-drained state, and the drainage conditions can be controlled more accurately.

[0049] A hollow torsion triaxial specimen (or soil sample) of clay or sand required for the test is prepared. The specimen is in the shape of a hollow cylinder, such as a hollow cylinder with a height of 100 mm, an outer diameter of 100 mm, and an inner diameter of 60 mm. The latex film 7 is wrapped inside and outside the specimen 6 to achieve the measurement of the interfacial pore water pressure or volume change. Step S1 specifically includes:

[0050] S11. Install the selected annular plate 5 with a certain roughness and the sealing gasket for waterproofing on the sample cap base 4. Note that the through hole 51 of the annular plate 5 corresponds to the drainage pipe 41 inside the sample cap base 4. The surface of the annular plate 5 is treated with epoxy resin to simulate the submarine pipeline after coating, and the roughness is generally 0.1-1μm; sandblasting can make the structure roughness 1-10μm, simulating the surface of the pipeline without coating and structures such as submarine anchors, pipe piles, and submerged foundations; through milling groove processing, an annular steel plate with a high roughness of more than 10μm can be obtained. In a preferred embodiment, the roughness of the steel plate is determined to be 1μm.

[0051] S12. Prepare and install hollow cylindrical specimens.

[0052] When the soil property is clay soil, the sample preparation method is:

[0053] (1) Take out the original or reshaped clay sample and cut it into hollow cylinders of the required size. When cutting, be sure to reduce the disturbance of the sample when cutting the inner hole;

[0054] (2) Put the inner latex film on the lower base 8, and then install the base 8 on the triaxial machine.

[0055] (3) Place the cut hollow cylindrical clay sample on the lower base 8, and extend the inner latex membrane from the hollow part of the cylinder.

[0056] (4) The outer latex film is installed on a negative pressure split film-bearing cylinder, and the film-bearing cylinder is evacuated to make the outer latex film close to the inner wall of the film-bearing cylinder, and the film-bearing cylinder is put on the sample 6.

[0057] (5) Install the sample cap onto the sample 6. At this time, care should be taken to prevent the sample cap from causing disturbance to the sample due to its own weight. Use rubber rings to clamp the upper parts of the inner and outer latex membranes onto the sample cap, and clamp the lower part of the outer latex membrane onto the base 8. The sample installation is now complete.

[0058] When the soil property is sandy soil, the sample preparation method is:

[0059] (1) Put the inner latex membrane on the lower base 8 and seal it with a rubber ring, and then install the base 8 into the confining pressure chamber.

[0060] (2) Straighten the inner latex membrane vertically, install two pairs of support plates into the inner membrane in turn, and fix the upper end of the inner membrane on the support plate to ensure that the inner membrane can be tightly attached to the support plate to facilitate the subsequent loading of sand samples.

[0061] (3) The outer latex film is put on the periphery of the circular base 8 and is tightly put on the outer film with two hoops; a negative pressure split mold is installed outside the outer latex film, and the upper part of the latex film is turned over and hooped on the end of the split mold.

[0062] (4) The split mold is evacuated to make the outer latex film close to the split mold, and a hollow cylindrical space is formed between the inner and outer latex films in the mold.

[0063] (5) Divide the dried sand sample into five equal parts and fill them into the mold layer by layer. During the sand filling process, the sand must be added slowly and evenly; and the strength and number of impacts should be controlled according to the relative density of the sand required for the test.

[0064] (6) Take out the assembled sample cap and slowly pass it through the cylinder composed of the support plate wrapped with the inner film until it is installed on the top of the sample. Then, flip the inner and outer latex films off the support plate and the split mold respectively, and clamp the upper parts of the inner and outer latex films on the sample cap with rubber rings respectively. The installation of sample 6 is completed.

[0065] S13. After installing the sample 6 and the sample cap, open the upper and lower drainage pipelines, i.e., the sample hole pressure volume change measurement controller 9 and the interface hole pressure volume change measurement controller 10, apply a certain negative pressure to the sample to make the sample as a whole have a certain strength, and then connect the sample cap to the upper loading device of the instrument, wherein the loading device includes an axial force torque sensor 3, a vertical servo loading system 1 and a torsional servo loading system 2.

[0066] S2. Saturate the sample, then apply equal pressure to the inner and outer pressure chambers 15 and 16 at the same time, and apply vertical pressure through the vertical servo loading system 1 to consolidate the sample. The installed sample is saturated by head saturation, back pressure saturation, etc. The sand sample also needs to be saturated with carbon dioxide, and the sample saturation must meet the B value greater than 95%. After the sample is saturated, equal pressure is applied to the inner and outer pressure chambers at the same time, and vertical pressure is applied through the vertical servo loading system 1. The sample can be isotropically consolidated or K0 consolidated according to the instrument program. After consolidation, the sample can be subjected to shear test.

[0067] Specifically, after the sample is installed, the inner and outer pressure chambers are filled with water according to the specification requirements, and the instrument loading rod is connected to the vertical servo loading system 1. At this time, the sample can be subjected to subsequent consolidation operations. The hollow cylindrical sample has two inner and outer pressure chambers, which can provide inner and outer pressures for the sample respectively. During consolidation, the inner and outer pressures should be applied in stages according to the selected consolidation pressure to reduce sample disturbance and avoid sample expansion and contraction caused by unbalanced internal and external pressures. The vertical servo loading system 1 can collect the stress conditions acting on the interface in real time according to the axial force torque sensor 3, and adjust the vertical stress to meet the isotropic consolidation or K0 consolidation requirements.

[0068] S3. Perform a shear test on the interface mechanical properties through a torsional servo loading system to obtain the interface mechanical property parameters.

[0069] When the interface is subjected to a torsion test, the inner and outer latex membranes will also deform with the relative rotation between the structure and the soil, which will affect the interface shear strength, pore pressure or volume change, so the influence of the latex membrane needs to be corrected. The correction method is: make a hollow cylindrical rubber specimen with a Teflon coating on the upper part of the rubber specimen and apply a drag-reducing lubricant; polish the prefabricated annular steel plate of the specimen cap, then paste the Teflon membrane and apply a drag-reducing lubricant. According to the clay specimen installation method, the rubber specimen and the specimen cap are installed in the instrument and a saturated consolidation process is carried out. Based on the correction experience, it can be assumed that the interface resistance during the torsion process is completely provided by the inner and outer latex membranes, and the pore pressure or volume change of the interface during the torsion process is also caused by the deformation of the inner and outer latex membranes during torsion. By conducting correction tests under different confining pressures, we can obtain the influence of the inner and outer latex films on the interface shear strength, pore pressure, and volume change, and fit and analyze the mathematical expressions between the subsequent shear strength, pore pressure, volume change and consolidation pressure, shear displacement (rotation), so as to correct the results of the central controlled torsional shear test on the interface of clay, sand and steel plate.

[0070] Through the torsion servo loading system 2, the interface between the soil and the annular plate is drained or undrained. The shear mode can be monotonically loaded or cyclically loaded. According to the mechanical properties of the interface, only different annular plates are needed to study the dynamic and static mechanical properties of the interface under different structural roughness conditions under constant normal stress. The test principle is simple, easy to operate and easy to implement. The interface size remains unchanged during the shearing process, the sample is not constrained by the rigid shear box, and the stress and deformation of the soil near the interface are more uniform, which is more suitable for engineering and design needs.

[0071] The volume change and pore pressure change can be directly measured according to the pressure volume controller in the instrument. The instrument can collect shear stress, shear displacement, and normal stress, and then the friction angle can be obtained according to the specification GB-T50123-2018.

[0072] Based on the loading system of the hollow torsion interface shear instrument, the loading rate of the interface static shear test, the load frequency of the cyclic shear and the cyclic stress ratio can be controlled. By changing the roughness of the annular plate, interface shear tests under different roughness can be performed. During the test, the change of the interface pore water pressure can be measured, so the influence of the above parameters on the interface pore water pressure can be explored.

[0073] Therefore, after correcting the influence of the latex film, through the testing method in the embodiment of the present invention, the interface friction angle between the soil and the annular plate under different roughness, the interface pore pressure development law or volume change law during the shear process, the shear stress-shear displacement relationship can be obtained, and the influence of factors such as cyclic stress ratio, load frequency, and shear rate on the interface mechanical properties can be analyzed.

[0074] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various modifications or variations within the scope of the claims, which does not affect the essence of the present invention. The above preferred features can be used in any combination without conflicting with each other.

Claims

1. A specimen cap for a hollow torsion interface shear triaxial apparatus, characterized in that: include: A sample cap base and an annular plate fixedly connected to the sample cap base, wherein the annular plate is used to contact the soil sample to form a soil-structure interface; The sample cap base is in the shape of a hollow cylinder, a drainage pipeline is arranged inside the cylinder wall of the sample cap base, a through hole is opened on the annular plate, one end of the drainage pipeline close to the annular plate corresponds to the through hole, and one end of the drainage pipeline away from the annular plate is used to connect to the interface hole pressure volume change measurement controller; The through hole is filled with permeable stone, and the permeable stone is covered with filter paper; The surface roughness of the annular plate is determined according to the simulated engineering structure; The upper part of the sample cap is used to connect with the axial force torque sensor, and can be connected to the vertical servo loading system and the torsion servo loading system through the loading rod. By changing the annular plate, testing under different test conditions can be achieved.

2. The sample cap for the hollow torsion interface shear triaxial apparatus according to claim 1, characterized in that: The diameter of the drainage pipeline is the same as the aperture of the through hole.

3. The sample cap for the hollow torsion interface shear triaxial apparatus according to claim 1, characterized in that: The annular plate is fixedly connected to the sample cap base through bolts; a sealing gasket is arranged between the annular plate and the sample cap base.

4. The sample cap for the hollow torsion interface shear triaxial apparatus according to claim 1, characterized in that: The material of the sample cap base is aluminum alloy.

5. A hollow torsion interface shear triaxial apparatus, characterized in that: include: A base for providing support; A chamber is provided on the base, the chamber comprises an inner confining pressure chamber and an outer confining pressure chamber, a sample is installed between the inner confining pressure chamber and the outer confining pressure chamber, and the bottom of the sample is connected to a sample hole pressure volume change measurement controller; The sample cap according to any one of claims 1 to 4 is covered on the top of the sample and contacts the sample to form a soil-structure interface; the upper end of the sample cap is connected to an axial force torque sensor, a vertical servo loading system and a torsion servo loading system; one end of the drainage pipeline is connected to the sample, and the other end of the drainage pipeline is connected to an interface pore pressure volume change measurement controller; A peripheral pressure measurement controller for measuring and controlling the peripheral pressure of the sample, wherein the peripheral pressure measurement controller is connected to the peripheral pressure chamber; An internal confining pressure measurement controller for measuring and controlling the internal confining pressure of the sample, wherein the internal confining pressure measurement controller is connected to the internal confining pressure chamber; Data acquisition module, used to collect interface pore pressure volume change data, sample pore pressure volume change data, peripheral pressure data and inner confining pressure data; The control module is respectively connected with the data acquisition module, the axial force torque sensor, the vertical servo loading system and the torsion servo loading system.

6. The hollow torsion interface shear triaxial apparatus according to claim 5, characterized in that: The vertical servo loading system and the torsion servo loading system both use cylinders for servo control, and utilize electro-pneumatic converters to adjust cylinder pressure to achieve loading.

7. The hollow torsion interface shear triaxial apparatus according to claim 5, characterized in that: The torsion servo loading system realizes cyclic loading on the soil-structure interface by setting the waveform to any one of a sine wave, a triangle wave and a rectangular wave and the changing frequency to 0.01-10 Hz.

8. A method for testing interface mechanical properties using the hollow torsion interface shear triaxial apparatus according to any one of claims 5 to 7, characterized in that: include: Prepare a sample and install the sample in the chamber of a triaxial instrument, wherein the sample is in a hollow cylindrical shape and the inside and the outside of the sample are wrapped with a latex film, and install a sample cap on the sample, wherein the sample cap contacts the sample to form a soil-structure interface; The sample is saturated, and then equal pressure is applied to the inner confining pressure chamber and the outer confining pressure chamber at the same time, and vertical pressure is applied through a vertical servo loading system to consolidate the sample; The interface mechanical property shear test is carried out through the torsion servo loading system to obtain the interface mechanical property parameters.

Images