An experimental method combining photoelastic test to study shear mechanical properties of rock structural surfaces

Abstract

The present invention provides a test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests, based on a photoelastic test platform and a direct shear instrument, the direct shear instrument comprising a base unit, a loading unit, a data monitoring and acquisition unit, a control unit and a shear box. The test method comprises the following steps: 1. Adjusting the direct shear instrument and installing the sample; 2. Adjusting the position of the shear box and preparing for the test; 3. Presetting target parameters and selecting a loading mode; 4. Applying a load and collecting test images and data; 5. Returning the direct shear instrument to its original position after the test and saving the data; 6. Image and data analysis. The test method can observe the changes in the stress field and strain field of the sample during the test in real time according to the collected stress optical images, loads, displacements and other test data, combined with preset target parameter values, draw corresponding load-displacement curves, and analyze the influence of different loading conditions on the shear mechanical properties and deformation characteristics of the rock structural surface.

Description

Technical Field

[0001] The invention relates to a test method for studying the shear mechanics characteristics of a rock structural surface in combination with a photoelastic test, and belongs to the technical field of rock mechanics engineering. Background Art

[0002] Under the long geological action, the rock mass is cut by joints, faults, fissures and other structural surfaces, showing extremely high discontinuity. The criss-crossing and complex structural surfaces control the mechanical behavior of the rock mass. In actual engineering practice, shear deformation of rock mass structural surfaces is a common failure mode in rock mass engineering. Shear deformation can lead to instability of rock mass structure, induce earthquakes, rock bursts and other geological disasters. Therefore, studying the shear mechanical properties of rock mass structural surfaces is conducive to revealing the instability mechanism and failure mechanism of fractured rock mass, which is of great significance to the entire process of design, construction, operation and maintenance of rock mass engineering.

[0003] At present, there are many technical means to observe the stress state of rock joints. Among them, the photoelastic test method can intuitively simulate the changes in the stress field inside the rock joints and observe the shear deformation characteristics of the rock structure surface in real time, which has a relatively strong advantage. The photoelastic test is usually carried out on a photoelastic test platform, which is composed of a complete set of devices, including lasers, polarizers (1 / 4 wave plates), loading devices, analyzers (1 / 4 wave plates) and cameras. However, when conducting photoelastic tests, due to the limitations of test devices or site conditions, the commonly used test methods are mostly carried out under constant force conditions, that is, under the conditions where the test device maintains a constant normal load and shear load, the shear mechanical properties of the rock structure surface are studied and observed, without considering the influence of loading rate and deformation rate. However, this method has strong limitations and is only suitable for simulating the destruction and deformation process of anchored rock slopes and deep engineering rock masses when the structure surface is subjected to static loads. For engineering rock masses in different environments, the stress environments they are in are different. Therefore, when the structural surface undergoes destruction and deformation, the normal loading conditions and shear loading conditions are varied. For example, for the surrounding rock mass of a deep chamber and the anchored rock slope, since there is an open surface in the rock mass after the chamber is excavated, the rock structural surface will undergo initial shear deformation under the action of ground stress, which will cause the shear and normal directions of the structural surface to be simultaneously subjected to dynamic loads and be in a dynamic change process. In this case, the use of dynamic normal and shear loading conditions is more in line with engineering practice.

[0004] According to the above situation, during the shear failure and deformation process of the rock mass structural surface, the normal and shear forces are not static, and the loading rate and deformation rate of the normal and shear loads are in dynamic change. At present, when the laboratory conducts experimental research on the shear mechanical properties of the rock mass structural surface, the loading conditions considered are relatively simple, and the test is not designed completely according to the actual engineering situation. Therefore, there are inevitably certain limitations in the application of the research results. Summary of the invention

[0005] The technical problem to be solved by the present invention is that the current common test methods cannot study and observe the dynamic failure deformation characteristics of rock structure surfaces, and provide a test method for studying the shear mechanical characteristics of rock structure surfaces in combination with photoelastic tests. This method can set different normal loading rates, normal deformation rates, shear loading rates and shear deformation rates through a self-developed and designed direct shear apparatus. According to the problem to be studied, the appropriate loading rate and deformation rate are selected to simulate the different stress environments of the engineering rock structure surface well, thereby providing an experimental basis for exploring the shear mechanical characteristics and deformation characteristics of the rock structure surface under static or dynamic loads.

[0006] The present invention adopts the following technical solutions to solve the above technical problems:

[0007] A test method for studying the shear mechanical properties of rock structure surfaces in combination with photoelastic tests is based on a photoelastic test platform and a direct shear apparatus. The direct shear apparatus includes a base unit, a loading unit, a data acquisition unit, a control unit, and a shear box:

[0008] The base unit is arranged at the bottom of the direct shear instrument, and is used to bear and support the weight of the entire direct shear instrument, and includes a bottom support plate and a first height adjustment mechanism connected between the bottom of the bottom support plate and the ground. A first linear guide movable pair is connected between the bottom of the bottom support plate and the photoelastic test platform. The position of the direct shear instrument on the photoelastic test platform is adjusted by the first linear guide movable pair, and the height of the direct shear instrument is adjusted by the first height adjustable mechanism, so that the optical paths can be aligned in sequence when performing the photoelastic test to form continuity;

[0009] The loading unit is arranged on the upper side of the base unit, and comprises a rigid frame and a normal loading device, a shear loading device and a supporting device arranged on the rigid frame, wherein the normal loading device and the shear loading device both adopt servo electric cylinders, the servo electric cylinder of the normal loading device is installed on the top of the rigid frame, and the servo electric cylinder of the shear loading device is installed on the left side of the rigid frame;

[0010] The support device is used to support the shear box during the test, and includes a first support device installed on the right side of the rigid frame and a second support device installed on the bottom of the rigid frame;

[0011] A vertical slide groove is provided on the right side of the rigid frame, and the first supporting device is fastened to the vertical slide groove by screws;

[0012] The second support device is in the same straight line as the normal loading device and is connected to the bottom of the rigid frame through a second height adjustment mechanism;

[0013] The data monitoring and acquisition unit is arranged inside the loading unit and is used to monitor and acquire test data during the test, including a normal pressure sensor, a tangential pressure sensor, a normal displacement sensor and a tangential displacement sensor;

[0014] The control unit has a signal input end connected to the data monitoring and acquisition unit, and a signal output end connected to the loading unit;

[0015] The shear box is used to place the test sample, and includes an upper shear box and a lower shear box of the same geometric size. There are no shields on the front and back of the shear box, so that the light source can pass through the sample to ensure the continuity of the light path. The inner walls of the upper shear box and the lower shear box are both provided with grooves that match the size of the sample. The sample is placed in the shear box along the grooves and is tightly fixed.

[0016] The following steps are involved:

[0017] Step 1: After plugging in the direct shear apparatus, adjust the working lengths of the normal servo electric cylinder and the shear servo electric cylinder to the shortest state, adjust the base unit to keep it flush with the bottom of the rigid frame, and adjust the direct shear apparatus to a suitable height and position, put the prepared photoelastic test specimen into the shear box and fix it, and then install the upper shear box and the lower shear box on the first top plate and the second top plate respectively;

[0018] Step 2: Adjust the position of the shear box and the top plate so that the center of the upper end face of the upper shear box and the center of the normal servo electric cylinder driving end are in the same straight line, and the center of the left side face of the lower shear box and the center of the shear servo electric cylinder driving end are in the same horizontal position, keeping the initial state of the joint surface consistent;

[0019] Step 3: Preset target parameters through the control unit to select different loading modes, the target parameters include: normal and shear target load values, loading rate and deformation rate, control the normal servo electric cylinder and the shear servo electric cylinder to preload respectively until the servo electric cylinder drive end is just completely in contact with the end face of the shear box, and keep the shear box stable. At this time, the upper shear box is fixed along the normal and shear directions without displacement, and the lower shear box is fixed along the normal direction of the joint surface and can only move freely along the shear direction, but displacement along the normal direction of the joint surface is not allowed;

[0020] Step 4: If it is a static loading mode, the normal electric cylinder and the shear electric cylinder are controlled to apply normal load and shear load to the sample at a constant loading rate and deformation rate respectively to the target value and then keep it static and constant; if it is a dynamic loading mode, after the normal load and shear load reach the target value, the normal electric cylinder or the shear electric cylinder is continued to be controlled to load the sample at a preset loading rate and deformation rate until the normal or shear displacement reaches a certain value to end the test, the control unit collects the data of the sensor during the test and processes it into a corresponding curve, and uses a high-speed camera to take real-time photos of the sample changes during the entire loading process;

[0021] Step 5: After loading, return the loading device to its original position, unload the shear direction load first, and keep the normal load unchanged to prevent sudden deformation in the shear direction when the normal load is unloaded. Unload the normal load after the shear loading device is no longer in contact with the shear box. Finally, remove the shear box, dismantle and clean the specimen, and then proceed to the next set of tests.

[0022] Step 6: After the test, based on the images and data collected during the test, the shear mechanical properties and deformation characteristics of the rock structure surface are simulated and analyzed according to the principle of photoelastic test.

[0023] The first height adjustment mechanism includes a foot cup and a support column, and the support column is installed on the foot cup through a first screw rod on the foot cup.

[0024] Reinforcement ribs are arranged inside and outside the rigid frame to prevent vibration and shaking of the direct shear instrument during loading of the photoelastic test, thereby ensuring the stability of the test platform.

[0025] A floating joint is connected to the driving end of the servo electric cylinder to ensure full contact with the shear box during loading, thereby completely transferring the load applied by the electric cylinder to the specimen.

[0026] The servo electric cylinder of the normal loading device and the servo electric cylinder of the shear loading device are both equipped with a reducer.

[0027] The first supporting device includes a screw, a first top rod and a first top plate; the first top rod is installed on the right side of the rigid frame by means of a screw, and the top end of the first top rod is connected to the first top plate;

[0028] The second supporting device comprises a second screw rod, a second top plate and a slide groove guide rail. The second top plate is mounted on the low-resistance slide groove guide rail. The low-resistance slide groove guide rail is fixed to the bottom of the rigid frame through four second screw rods with adjustable heights.

[0029] The right side of the upper shear box is provided with a first slide rail, the first top plate is provided with a first slide groove, and the upper shear box is installed on the first slide groove of the first top plate through the first slide rail;

[0030] The bottom surface of the lower shear box is provided with a second slide rail, and the second top plate is provided with a second slide groove. The lower shear box is installed on the second slide groove of the second top plate through the second slide rail.

[0031] The captured image refers to a stress optical image used for photoelastic test analysis, and the collected test data includes normal load, normal displacement, shear load, and shear displacement;

[0032] The static loading mode means that the normal and shear loads applied to the specimen remain unchanged after reaching the target value until the end of the test;

[0033] The dynamic loading modes are divided into three types: static normal-dynamic shear loading mode, dynamic normal-static shear loading mode and dynamic normal-dynamic shear loading mode.

[0034] According to the recorded stress optical images and the normal load, normal displacement, shear load and shear displacement data of the specimen structure surface, the stress field and strain field of the specimen are calculated according to the principle of photoelastic test, and the normal load-normal displacement curve, normal displacement-shear displacement curve and shear load-shear displacement curve are drawn. The shear mechanical properties and deformation characteristics of the rock structure surface are obtained through analysis.

[0035] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0036] First, this test method is based on the principle of photoelastic test. Based on the self-designed direct shear apparatus, it can accurately analyze the shear mechanical properties and deformation characteristics of rock structure surfaces under different loading conditions, ensuring the accuracy and stability of the photoelastic test.

[0037] Second, by using the control system of the direct shear apparatus, different loading rates and deformation rates can be set to realize shear tests of rock structure surfaces under different loading modes, such as static loading shear tests and dynamic loading shear tests.

[0038] Third, this test method controls the preset loading target parameters (normal and shear target load values, loading rate and deformation rate) of the supporting control software, and then considers the shear failure of the rock structure surface under different loading modes (static loading mode or dynamic loading mode). It can more realistically reproduce the shear failure process of engineering rock mass, and the test method is simple and easy to operate, which can provide an experimental basis for the study of shear mechanical properties and deformation characteristics of rock structure surfaces. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a flow chart of the test method;

[0040] Figure 2 This is the main view of the direct shear apparatus;

[0041] Figure 3 It is the overall schematic diagram of the photoelastic test platform;

[0042] Figure 4 This is a detailed view of the shear box of the direct shear apparatus;

[0043] Figure 5 This is the control principle block diagram of the direct shear apparatus;

[0044] Figure 6 This is the control software interface diagram of the direct shear instrument.

[0045] In the figure: 1 is the foot cup, 2 is the support column, 3 is the bottom support plate, 4 is the rigid frame, 5 is the screw, 6 is the first push rod, 7 is the first push plate, 8 is the normal pressure sensor, 9 is the normal floating joint, 10 is the normal servo electric cylinder, 11 is the normal displacement sensor, 12 is the shear displacement sensor, 13 is the shear servo electric cylinder, 14 is the shear floating joint, 15 is the shear pressure sensor, 16 is the triangle plate, 17 is the second screw rod, 18 is the second push plate, 19 is the low-resistance slide rail, 20 is the lower shear box, 21 is the upper shear box, 22 is the slider, 23 is the reinforcing rib, 24 is the computer, 25 is the amplifier circuit, 26 is the signal processing circuit, 27 is the control software, 28 is the display screen, 29 is the mouse and keyboard. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0047] like Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 As shown, the present invention provides a test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests, based on a photoelastic test platform, on which a direct shear instrument capable of studying the shear mechanical properties of rock joints in combination with photoelastic tests is installed, including a base unit, a loading unit, a data monitoring and acquisition unit, a control unit, and a shear box. The loading unit is located on the upper part of the base unit, the base unit supports the weight of the entire direct shear instrument, the data monitoring and acquisition unit is installed inside the loading unit, and the control unit controls the operation of the direct shear instrument.

[0048] The base unit includes a first height adjustment mechanism and a bottom support plate 3. The first height adjustment mechanism consists of four foot cups 1 and four support columns 2. The support column 2 is installed on the foot cup 1 through the first screw on the foot cup, and the bottom support plate 3 is installed on the four support columns 2 through bolts. The height of the base is adjusted by rotating the foot cup screw, thereby ensuring that the direct shear instrument can perform photoelastic tests under different height conditions, and also supporting and fixing the direct shear instrument on the ground. A first linear guide moving pair is connected between the bottom of the bottom support plate and the photoelastic test platform. The position of the direct shear instrument on the photoelastic test platform is adjusted by the first linear guide moving pair, and the height of the direct shear instrument is adjusted by the first height adjustable mechanism, so that the light path can be aligned in sequence during the photoelastic test to form continuity. The materials are all made of stainless steel, and the maximum load-bearing capacity can reach 200kg. Figure 2 , 3 shown.

[0049] The loading unit includes a normal loading device, a shear loading device and a supporting device. The loading rate and deformation rate of the loading unit can reach up to 5KN / s and 100mm / s respectively, the loading load can reach up to 10KN, and the test space can reach up to 100mm (normal) × 200mm (tangential). Both the normal loading device and the shear loading device are composed of a servo electric cylinder and a floating joint. A reducer is installed on the servo electric cylinder to ensure that the electric cylinder can achieve stable stepless speed regulation. The supporting device is divided into a first supporting device located on the right side of the rigid frame and a second supporting device located at the bottom of the rigid frame. The first supporting device is composed of a screw 5, a first push rod 6 and a first top plate 7 from right to left, and the second supporting device is composed of a second top plate 18, a slide guide rail 19 and four second screw rods 17 from top to bottom.

[0050] The rigid frame 4 is made of multi-layer stainless steel material, with a triangular plate 16 on the inside, and reinforcing ribs 23 on the inside and outside for reinforcement, to ensure that the rigid frame will not deform during the test loading process, and to prevent the vibration or shaking of the direct shear instrument from affecting the test results. The normal loading device and the shear loading device are respectively arranged on the top and left side of the rigid frame 4, and the floating joint is installed on the servo electric cylinder to ensure full contact with the shear box during loading, so as to completely transfer the load applied by the electric cylinder to the specimen. The top plate 7 of the first support device is installed on the first push rod 6, which is fixed to the right side of the rigid frame 4 by screws 5. The first push rod 6 is a telescopic rod.

[0051] The second supporting device is in the same straight line as the normal loading device. The second top plate 18 is mounted on a low-resistance slide rail 19 and is fixed to the bottom of the rigid frame 4 through four second screw rods 17 with adjustable heights. This not only enables the shear box to slide horizontally left and right in the tangential direction, but also avoids the influence of friction on the test to the greatest extent. The length and position of the first supporting device and the second supporting device can be adjusted to ensure that the light source can pass through the specimen completely, and to ensure the continuity of the optical path and the stability of the test. Slide grooves are provided on the first top plate 7 and the second top plate 18, which coincide with the slide rails on the right side of the upper shear box 21 and the bottom of the lower shear box 20, limiting the shear box to slide only in a specific direction during the test, such as Figure 2 , 3 shown.

[0052] The data monitoring and acquisition unit includes a normal pressure sensor 8, a normal displacement sensor 11, a shear pressure sensor 15, a shear displacement sensor 11 and a signal processing circuit 26 connected to a computer. The pressure sensor is arranged on the floating joint, and can monitor and collect the load applied to the sample in real time. The displacement sensors are arranged on the servo electric cylinders, and can monitor and collect the deformation displacement of the sample in real time. Figure 2 , 3 shown.

[0053] The control unit includes a computer 24, an amplifier circuit 25, a signal processing circuit 26, a control software 27 and a display screen 28. The data collected by the sensor is processed by the signal processing circuit 26 and then transmitted to the control software 27 through the amplifier circuit 25. One end of the computer 24 is connected to the control software 27, and the other end is connected to the loading unit. The display screen 28 will display the self-designed supporting control software interface 27. By setting the target parameters normal and shear target load values, loading rate and deformation rate in the test through the control software, different loading modes, static loading mode and dynamic loading mode can be achieved. The data and target parameters collected by the sensor are collected and stored in the computer 24 as output signals. After being processed by the computer 24, they are used as input signals of the servo loading mechanism to form a closed-loop control of the direct shear instrument. The display screen 28 will display parameters such as loading rate, deformation rate, displacement and load, as well as load-time curve and displacement-time curve in real time. The control software 27 can be upgraded later to meet new loading modes or parameter requirements, such as Figure 5 , 6 shown.

[0054] The shear box is used to place photoelastic samples, and includes an upper shear box 21 and a lower shear box 20 of the same geometric dimensions. There are no shields on the front and back of the shear box, so that a high-speed camera can be used to record the deformation and failure process of the joint sample. There are grooves on the inner walls of the upper and lower shear boxes. The sample is placed into the shear box along the groove and is tightly fixed to ensure that the sample will not shift or slip during the test. The right side of the upper shear box 21 and the bottom of the lower shear box 20 are provided with slide rails, which coincide with the slide grooves of the first top plate 7 and the second top plate 18 respectively. Ensure that the upper shear box 21 can move freely along the normal direction of the joint surface, but cannot be displaced along the shear direction; the lower shear box 20 can move freely along the shear direction, but cannot be displaced along the normal direction of the joint surface, to ensure that the test can be carried out stably, such as Figure 2 , 3 , as shown in Figure 4.

[0055] The embodiments of the present invention are as follows:

[0056] Example 1

[0057] This embodiment studies the test method of shear mechanical properties of rock mass structural surface under static loading mode, and the test method includes the following steps:

[0058] Step 1: After plugging in the direct shear apparatus, adjust the working lengths of the normal servo electric cylinder and the shear servo electric cylinder to the shortest state, adjust the base unit to keep it flush with the bottom of the rigid frame, and adjust the direct shear apparatus to a suitable height and position, put the prepared photoelastic test specimen into the shear box and fix it, and then install the upper shear box and the lower shear box on the first top plate and the second top plate respectively;

[0059] Step 2: Adjust the position of the shear box and the top plate so that the center of the upper end face of the upper shear box and the center of the normal servo electric cylinder driving end are in the same straight line, and the center of the left side face of the lower shear box and the center of the shear servo electric cylinder driving end are in the same horizontal position, keeping the initial state of the joint surface consistent;

[0060] Step 3: Preset target parameters through the control unit, the target parameters include: normal and shear target load values, loading rate and deformation rate, control the normal servo electric cylinder and the shear servo electric cylinder to preload respectively until the servo electric cylinder drive end is just completely in contact with the end face of the shear box, and keep the shear box stable. At this time, the upper shear box is fixed along the normal and shear directions without displacement, and the lower shear box is fixed along the normal direction of the joint surface and can only move freely along the shear direction, but displacement along the normal direction of the joint surface is not allowed;

[0061] Step 4: Control the normal electric cylinder and the shear electric cylinder to apply normal load and shear load to the sample at a constant loading rate and deformation rate respectively, and then keep them stationary and constant until the test is terminated when the predetermined time is reached. The control unit collects the data of the sensors during the test and processes them into corresponding curves. At the same time, a high-speed camera is used to take photos in real time to record the changes of the sample during the entire loading process;

[0062] Step 5: After loading, return the loading device to its original position, unload the shear direction load first, and keep the normal load unchanged to prevent sudden deformation in the shear direction when the normal load is unloaded. Unload the normal load after the shear loading device is no longer in contact with the shear box. Finally, remove the shear box, dismantle and clean the specimen, and then proceed to the next set of tests.

[0063] Step 6: After the test, based on the images and data collected during the test, the shear mechanical properties and deformation characteristics of the rock structure surface are simulated and analyzed according to the principle of photoelastic test.

[0064] Example 2

[0065] This embodiment studies the test method of shear mechanical properties of rock mass structural surface under dynamic normal-dynamic shear loading mode, and the test method includes the following steps:

[0066] Step 1: After plugging in the direct shear apparatus, adjust the working lengths of the normal servo electric cylinder and the shear servo electric cylinder to the shortest state, adjust the base unit to keep it flush with the bottom of the rigid frame, and adjust the direct shear apparatus to a suitable height and position, put the prepared photoelastic test specimen into the shear box and fix it, and then install the upper shear box and the lower shear box on the first top plate and the second top plate respectively;

[0067] Step 2: Adjust the position of the shear box and the top plate so that the center of the upper end face of the upper shear box and the center of the normal servo electric cylinder driving end are in the same straight line, and the center of the left side face of the lower shear box and the center of the shear servo electric cylinder driving end are in the same horizontal position, keeping the initial state of the joint surface consistent;

[0068] Step 3: Preset target parameters through the control unit, the target parameters include: normal and shear target load values, loading rate and deformation rate, control the normal servo electric cylinder and the shear servo electric cylinder to preload respectively until the servo electric cylinder drive end is just completely in contact with the end face of the shear box, and keep the shear box stable. At this time, the upper shear box is fixed along the normal and shear directions without displacement, and the lower shear box is fixed along the normal direction of the joint surface and can only move freely along the shear direction, but displacement along the normal direction of the joint surface is not allowed;

[0069] Step 4: After controlling the normal electric cylinder and the shear electric cylinder to apply normal load and shear load to the sample at a constant loading rate and deformation rate to the target value, the normal electric cylinder and the shear electric cylinder are continued to be controlled to load the sample at the preset loading rate and deformation rate until the normal and shear displacements reach a certain value, and the test is terminated. The control unit collects the data of the sensors during the test and processes them into corresponding curves, and uses a high-speed camera to take photos of the sample changes in real time during the entire loading process;

[0070] Step 5: After loading is completed, return the loading device to its original position, unload the shear direction load first, and keep the normal load unchanged to prevent sudden deformation in the shear direction when the normal load is unloaded. Wait until the shear loading device is no longer in contact with the shear box, then unload the normal load; finally, remove the shear box, dismantle and clean the specimen, and then proceed to the next set of tests.

[0071] Step 6: After the test, based on the images and data collected during the test, the shear mechanical properties and deformation characteristics of the rock structure surface are simulated and analyzed according to the principle of photoelastic test.

[0072] Example 3

[0073] This embodiment studies the test method of shear mechanical properties of rock mass structural surface under static normal-dynamic shear loading mode, and the test method includes the following steps:

[0074] Based on Example 2, in step four, after the normal load and shear load are applied to the sample at a constant loading rate and deformation rate respectively by the normal loading device and the shear loading device of the direct shear apparatus to reach the target value, the normal loading device keeps the load target value unchanged, and only the shear loading device needs to continue loading the sample according to the preset loading rate and deformation rate.

[0075] Example 4

[0076] This embodiment studies the test method of shear mechanical properties of rock mass structural surface under dynamic normal-static shear loading mode, and the test method includes the following steps:

[0077] Based on Example 2, in step four, after the normal load and shear load are applied to the sample at a constant loading rate and deformation rate respectively by the normal loading device and the shear loading device of the direct shear apparatus to reach the target value, the shear loading device keeps the load target value unchanged, and the normal loading device only needs to continue loading the sample according to the preset loading rate and deformation rate.

[0078] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0079] The above embodiments are only for explaining the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention shall fall within the protection scope of the present invention. The above embodiments of the present invention are described in detail, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A test method for studying the shear mechanical properties of rock structure surfaces in combination with photoelastic tests, based on a photoelastic test platform and a direct shear apparatus, the direct shear apparatus comprising: Base unit, loading unit, data acquisition unit, control unit and shear box: The base unit is arranged at the bottom of the direct shear instrument, and is used to bear and support the weight of the entire direct shear instrument, and includes a bottom support plate and a first height adjustment mechanism connected between the bottom of the bottom support plate and the ground. A first linear guide movable pair is connected between the bottom of the bottom support plate and the photoelastic test platform. The position of the direct shear instrument on the photoelastic test platform is adjusted by the first linear guide movable pair, and the height of the direct shear instrument is adjusted by the first height adjustable mechanism, so that the optical paths can be aligned in sequence when performing the photoelastic test to form continuity; The loading unit is arranged on the upper side of the base unit, and comprises a rigid frame and a normal loading device, a shear loading device and a supporting device arranged on the rigid frame, wherein the normal loading device and the shear loading device both adopt servo electric cylinders, the servo electric cylinder of the normal loading device is installed on the top of the rigid frame, and the servo electric cylinder of the shear loading device is installed on the left side of the rigid frame; The support device is used to support the shear box during the test, and includes a first support device installed on the right side of the rigid frame and a second support device installed on the bottom of the rigid frame; A vertical slide groove is provided on the right side of the rigid frame, and the first supporting device is fastened to the vertical slide groove by screws; The second support device is in the same straight line as the normal loading device and is connected to the bottom of the rigid frame through a second height adjustment mechanism; The data acquisition unit is arranged inside the loading unit and is used to monitor and collect test data during the test, including a normal pressure sensor, a tangential pressure sensor, a normal displacement sensor and a tangential displacement sensor; The control unit has a signal input end connected to the data acquisition unit and a signal output end connected to the loading unit; The shear box is used to place the test sample, and includes an upper shear box and a lower shear box of the same geometric size. There are no shields on the front and back of the shear box, so that the light source can pass through the sample to ensure the continuity of the light path. The inner walls of the upper shear box and the lower shear box are both provided with grooves that match the size of the sample. The sample is placed in the shear box along the grooves and is tightly fixed. It is characterized by comprising the following steps: Step 1: After plugging in the direct shear apparatus, adjust the working lengths of the normal servo electric cylinder and the shear servo electric cylinder to the shortest state, adjust the base unit to keep it flush with the bottom of the rigid frame, and adjust the direct shear apparatus to a suitable height and position, put the prepared photoelastic test specimen into the shear box and fix it, and then install the upper shear box and the lower shear box on the first top plate and the second top plate respectively; Step 2: Adjust the position of the shear box and the top plate so that the center of the upper end face of the upper shear box and the center of the normal servo electric cylinder driving end are in the same straight line, and the center of the left side face of the lower shear box and the center of the shear servo electric cylinder driving end are in the same horizontal position, keeping the initial state of the joint surface consistent; Step 3: Preset target parameters through the control unit to select different loading modes, the target parameters include: normal and shear target load values, loading rate and deformation rate, control the normal servo electric cylinder and the shear servo electric cylinder to preload respectively until the servo electric cylinder drive end is just completely in contact with the end face of the shear box, and keep the shear box stable. At this time, the upper shear box is fixed along the normal and shear directions without displacement, and the lower shear box is fixed along the normal direction of the joint surface and can only move freely along the shear direction, but displacement along the normal direction of the joint surface is not allowed; Step 4: If it is a static loading mode, the normal electric cylinder and the shear electric cylinder are controlled to apply normal load and shear load to the sample at a constant loading rate and deformation rate respectively to the target value and then keep it static and constant; if it is a dynamic loading mode, after the normal load and shear load reach the target value, the normal electric cylinder or the shear electric cylinder is continued to be controlled to load the sample at a preset loading rate and deformation rate until the normal or shear displacement reaches a certain value to end the test, the control unit collects the data of the sensor during the test and processes it into a corresponding curve, and uses a high-speed camera to take real-time photos of the sample changes during the entire loading process; Step 5: After loading is completed, return the loading device to its original position, unload the shear direction load first, and keep the normal load unchanged to prevent sudden deformation in the shear direction when the normal load is unloaded. Wait until the shear loading device is no longer in contact with the shear box, and then unload the normal load. Finally, remove the shear box, dismantle and clean the specimen, and then proceed to the next set of tests; Step 6: After the test, based on the images and data collected during the test, the shear mechanical properties and deformation characteristics of the rock structure surface are simulated and analyzed according to the principle of photoelastic test.

2. The test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests according to claim 1, characterized in that: The first height adjustment mechanism includes a foot cup and a support column, and the support column is installed on the foot cup through a first screw rod on the foot cup.

3. The test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests according to claim 1, characterized in that: Reinforcement ribs are arranged inside and outside the rigid frame to prevent vibration and shaking of the direct shear instrument during loading of the photoelastic test, thereby ensuring the stability of the test platform.

4. The test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests according to claim 1, characterized in that: A floating joint is connected to the driving end of the servo electric cylinder to ensure full contact with the shear box during loading, thereby completely transferring the load applied by the electric cylinder to the specimen.

5. The test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests according to claim 1, characterized in that: The servo electric cylinder of the normal loading device and the servo electric cylinder of the shear loading device are both equipped with a reducer.

6. The test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests according to claim 1, characterized in that: The first supporting device includes a screw, a first top rod and a first top plate; the first top rod is installed on the right side of the rigid frame by means of a screw, and the top end of the first top rod is connected to the first top plate; The second supporting device comprises a second screw rod, a second top plate and a slide groove guide rail. The second top plate is mounted on the low-resistance slide groove guide rail. The low-resistance slide groove guide rail is fixed to the bottom of the rigid frame through four second screw rods with adjustable heights.

7. The test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests according to claim 1, characterized in that: The right side of the upper shear box is provided with a first slide rail, the first top plate is provided with a first slide groove, and the upper shear box is installed on the first slide groove of the first top plate through the first slide rail; The bottom surface of the lower shear box is provided with a second slide rail, and the second top plate is provided with a second slide groove. The lower shear box is installed on the second slide groove of the second top plate through the second slide rail.

8. The test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests according to claim 5, characterized in that: The captured image refers to a stress optical image used for photoelastic test analysis, and the collected test data includes normal load, normal displacement, shear load, and shear displacement; The static loading mode means that the normal and shear loads applied to the specimen remain unchanged after reaching the target value until the end of the test; The dynamic loading modes are divided into three types: static normal-dynamic shear loading mode, dynamic normal-static shear loading mode and dynamic normal-dynamic shear loading mode.

9. The test method for studying the shear mechanical properties of rock structural surfaces in combination with photoelastic tests according to claim 1, characterized in that: According to the recorded stress optical images and the normal load, normal displacement, shear load and shear displacement data of the specimen structure surface, the stress field and strain field of the specimen are calculated according to the principle of photoelastic test, and the normal load-normal displacement curve, normal displacement-shear displacement curve and shear load-shear displacement curve are drawn. The shear mechanical properties and deformation characteristics of the rock structure surface are obtained through analysis.

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