A soil-rock interface direct shear-seepage test device and test method under constant normal stress conditions

Abstract

The present invention provides a soil-rock interface direct shear-seepage test device under constant normal stress conditions and a test method thereof. The test device includes a direct shear loading system, a seepage control system and a monitoring system. The direct shear loading system includes an upper shear box and a lower shear box. A rock specimen is arranged in the upper shear box, and a soil specimen is arranged in the lower shear box. A diversion channel is arranged in the rock specimen, one end of the diversion channel corresponds to a water inlet, and the other end is arranged at the interface. The lower shear box is provided with a water outlet and a water trough. A vertical jack is arranged on the top of the upper shear box, and a servo motor and a loading rod are arranged on one side of the lower shear box. The seepage control system includes a water pipe, and the water pipe is supplied with water through a water supply device. The monitoring system includes a normal load sensor, a shear load sensor, a shear displacement sensor and a flow measurement device that are connected to a data acquisition system for communication. The test device and method can apply constant normal stress conditions to soil-rock specimens and realize the direct shear-seepage process of the test object.

Description

Technical Field

[0001] The invention relates to the field of geotechnical engineering, and in particular to a soil-rock interface direct shear-seepage test device under constant normal stress conditions and a test method thereof. Background Art

[0002] Deposition slopes are usually composed of a soil-rock mixture or are located on bedrock, forming a natural soil-rock contact surface between the rock and the soil. The shear seepage mechanical properties of the soil-rock interface under hydrodynamic effects such as rainfall and reservoir water level changes are important factors affecting slope stability. Therefore, studying the direct shear-seepage coupling characteristics of the soil-rock interface can provide theoretical support for the evaluation of geotechnical engineering slope stability.

[0003] At present, there are few studies on the direct shear-seepage coupling characteristics of soil-rock interface by scholars at home and abroad. Many scholars have conducted experimental test systems on the direct shear-seepage coupling characteristics of single-fracture rock, including "A rock fracture shear seepage coupling test system under confining pressure" (CN 102253183 A) of Shandong University of Science and Technology, which proposed a rock fracture shear seepage coupling test system that can realize rock fracture permeability testing and analysis under complex stress states; "Rock fracture shear seepage coupling test box" (CN 202133661 U) of Shandong University of Science and Technology, which can ensure that during the shear process of rock joints, when the upper and lower joint surfaces produce relative displacement under the action of shear force, the water in the rock joints flows along the specified path, and no water leakage occurs on the boundary perpendicular to the water flow direction; "Rock joint shear-seepage coupling test system" (CN 201237591 Y), while loading, the change values ​​of joint opening, horizontal displacement, flow rate, etc. can be obtained; Wuhan University's "Shear box and test method suitable for rock joint shear seepage coupling test" (CN102944665A), mainly solves the technical problems of insufficient sealing means in the prior art and inability to achieve good water sealing effect, and provides a shear box and test method suitable for rock joint shear seepage coupling test that can form a good water sealing boundary around the specimen; Taiyuan University of Technology's "A single-crack rock specimen direct shear-seepage test device and test method under hydrostatic pressure conditions" (CN 107782628 A), can apply hydrostatic pressure conditions to single-crack specimens and realize the direct shear-seepage process of the test object. However, these existing rock shear seepage coupling test equipment cannot be used to test the shear seepage coupling characteristics of the soil-rock interface, and the following problems need to be solved: 1) The focus of the shear seepage coupling test is to solve the sealing problem in the direct shear seepage process, that is, to ensure that water only flows along the interface channel without side leakage during the shear displacement of the rock specimen, but the sealing operation of the test equipment is relatively cumbersome and the sealing effect is difficult to meet the test accuracy requirements; 2) The applied rock fracture shear displacement is small, mainly because the larger the shear displacement, the more difficult it is to ensure the sealing of the fractured rock. Considering that the above patents have low reliability and difficult operation for specimen sealing, and affect the application of shear displacement, the present invention proposes a new method for direct shear-seepage coupling test, which does not require strict sealing of the specimen, greatly reducing the difficulty of designing and operating the test device.

[0004] Therefore, in order to solve the defects and shortcomings of the above-mentioned test methods, an efficient, reliable and easy-to-operate direct shear-seepage test device for soil-rock interface was developed to obtain the evolution law of shear seepage characteristics of soil-rock interface under different stress states, which is of great significance for studying the shear seepage mechanical mechanism of slope instability of accumulation body slope under the action of hydrodynamic factors such as rainfall and reservoir water level changes. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a soil-rock interface direct shear-seepage test device and a test method under constant normal stress conditions, which can apply constant normal stress conditions to soil-rock specimens and realize the direct shear-seepage process of the test object.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a soil-rock interface direct shear-seepage test device under constant normal stress conditions, including a direct shear loading system, a seepage control system and a monitoring system. The direct shear loading system includes an upper shear box and a lower shear box. A rock specimen is arranged in the upper shear box, and a soil specimen is arranged in the lower shear box. A water inlet is arranged on the side wall of the upper shear box, and a diversion channel is arranged in the rock specimen. One end of the diversion channel corresponds to the water inlet, and the other end is arranged at the interface between the rock specimen and the soil specimen. A water outlet is arranged on the side wall of the lower shear box, and a water trough is arranged on the outer side of the lower shear box relative to the water outlet. The water trough is provided with a drain pipe, and a vertical jack is arranged on the top of the upper shear box. A servo motor is provided on one side of the lower shear box, and a loading rod for applying force to the lower shear box is provided at the output end of the servo motor; the seepage control system includes a water pipe connected to the water inlet, and the water pipe is supplied with water through a water supply device; the monitoring system includes a normal load sensor and a shear load sensor respectively arranged on the top and side wall of the upper shear box, and a shear displacement sensor arranged on one side of the lower shear box, the shear load sensor and the shear displacement sensor are installed on the head seat, and also includes a flow measuring device for measuring the flow of seepage water in the water tank, and the normal load sensor, the shear load sensor, the shear displacement sensor and the flow measuring device are communicatively connected with the data acquisition system.

[0007] In a preferred solution, the water supply device includes a water tank, the water tank is connected to the water inlet through a water pipe, and the water tank is connected to the air compressor through a pipeline.

[0008] In a preferred solution, the flow measurement device is an electronic balance, and a measuring cup is provided on the electronic balance.

[0009] In a preferred solution, a control valve and a water pressure sensor are provided on the water pipe, and the water pressure sensor is communicatively connected with a data acquisition system.

[0010] In a preferred solution, a roller is provided at the bottom of the lower shear box.

[0011] The present invention also provides a test method for a soil-rock interface direct shear-seepage test device under constant normal stress conditions, comprising the following steps:

[0012] Step 1: Prepare a rock specimen, drill a diversion channel in the rock specimen, and place the rock specimen in an upper shear box;

[0013] Step 2: Saturate the soil sample of the soil specimen, and then put it into the lower shear box, and close the upper shear box and the lower shear box;

[0014] Step 3: After installing the seepage control system and monitoring system, turn on the vertical jack to apply pressure, then turn on the servo motor to apply shear stress, turn on the seepage control system, and start the direct shear-seepage test;

[0015] Step 4: Data analysis.

[0016] In the preferred embodiment, in step 4, the applied pressure gradient is obtained by the pressure value measured by the water pressure sensor, and the change process of the permeability characteristics of the soil-rock interface from Darcy seepage to non-Darcy seepage can be obtained according to the relationship between the flow rate and the pressure gradient.

[0017]

[0018] Where p1 is the pressure value measured by the water pressure sensor, and d is the diameter of the soil-rock interface.

[0019] The present invention provides a soil-rock interface direct shear-seepage test device and test method under constant normal stress conditions, which can impose constant normal stress conditions on soil-rock specimens and realize the direct shear-seepage process of the test object, and obtain the evolution law of the shear seepage characteristics of the soil-rock interface under different stress states. It is of great significance to study the shear seepage mechanics mechanism of slope instability of an accumulation body under the action of hydrodynamic factors such as rainfall and reservoir water level changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below in conjunction with the accompanying drawings and implementation examples:

[0021] Figure 1 is a structural diagram of the test device of the present invention;

[0022] Figure 2 This is the shear stress-shear displacement relationship curve of soil-rock interface under 28.73kPa normal load;

[0023] Figure 3 This is the time history curve of water discharge under the normal load of 28.73kPa;

[0024] Figure 4 The pressure gradient-flow relationship curve under 28.73 kPa normal load

[0025] In the figure: upper shear box 1, lower shear box 2, rock specimen 3, soil specimen 4, water tank 5, vertical jack 6, servo motor 7, loading rod 8, water pipe 9, normal load sensor 10, shear load sensor 11, shear displacement sensor 12, head seat 13, flow measurement device 14, data acquisition system 15, water tank 16, air compressor 17, measuring cup 18, control valve 19, water pressure sensor 20, roller 21, water inlet 101, water outlet 201, diversion channel 301, drain pipe 501. DETAILED DESCRIPTION

[0026] like Figure 1 As shown, a soil-rock interface direct shear-seepage test device under constant normal stress conditions includes a direct shear loading system, a seepage control system and a monitoring system. The direct shear loading system includes an upper shear box 1 and a lower shear box 2. The upper and lower shear inner boxes are assembled with a diameter of 180 mm, a height of 180 mm and a thickness of 20 mm.

[0027] A rock specimen 3 is provided in the upper shear box 1, a soil specimen 4 is provided in the lower shear box 2, a water inlet 101 is provided on the side wall of the upper shear box 1, and a diversion channel 301 is provided in the rock specimen 3. In the present embodiment, the diversion channel 301 is an "L"-shaped structure, one end of the diversion channel 301 corresponds to the water inlet 101, and the other end is arranged at the interface between the rock specimen 3 and the soil specimen 4. By providing the diversion channel 301, water flows from the center of the rock specimen 3 through the soil-rock interface to the surrounding areas, thereby solving the problem of sealing the device under shear action.

[0028] A water outlet 201 is provided on the side wall of the lower shear box 2, and a water trough 5 is provided on the outer side of the lower shear box 2 opposite to the water outlet 201. The water trough 5 is a ring structure, which is arranged around the lower shear box 2 and is connected to the lower shear box 2 by bolts. The water trough 5 is provided with a drain pipe 501. A vertical jack 6 is provided on the top of the upper shear box 1, and a servo motor 7 is provided on one side of the lower shear box 2. A loading rod 8 for applying force to the lower shear box 2 is provided at the output end of the servo motor 7. The upper shear box 1 is relatively different and pushes the lower shear box 2 to generate a shear load. The control accuracy can reach 0.01kN / s or 0.001mm / s.

[0029] The seepage control system includes a water pipe 9 connected to the water inlet 101, and the water pipe 9 supplies water through a water supply device. The water flows from the water inlet 101 along the diversion channel 301 inside the rock and passes through the soil-rock interface. The water inlet 101, the diversion channel 301, the water outlet 201 and the soil-rock interface form a connected seepage channel. The water tank 5 is used to collect the water flow at the water outlet 201.

[0030] The monitoring system includes a normal load sensor 10 and a shear load sensor 11 respectively arranged on the top and side wall of the upper shear box 1, and a shear displacement sensor 12 arranged on one side of the lower shear box 2. The shear load sensor 11 and the shear displacement sensor 12 are installed on a head seat 13, and also includes a flow measuring device 14 for measuring the flow of seepage water in the water tank 5. The normal load sensor 10, the shear load sensor 11, the shear displacement sensor 12 and the flow measuring device 14 are communicatively connected to the data acquisition system 15.

[0031] In this embodiment, the water supply device includes a water tank 16 , which is connected to the water inlet 101 through a water pipe 9 , and the water tank 16 is connected to the air compressor 17 through a pipeline.

[0032] The air compressor 17 is the gas power source for all pneumatic loading in this test.

[0033] The flow measurement device 14 is an electronic balance, on which a measuring cup 18 is provided. The flow rate is calculated by testing the weight of the flowing water using the electronic balance.

[0034] The flow measurement device 14 may also be replaced by a flow meter.

[0035] Preferably, a control valve 19 and a water pressure sensor 20 are provided on the water pipe 9, and the water pressure sensor 20 is communicatively connected with the data acquisition system 15.

[0036] The control valve 19 can control a constant flow rate, and the water pressure sensor 20 can be used to monitor the pressure value of the fluid. At the same time, the change process of the permeability characteristics of the soil-rock interface from Darcy seepage to non-Darcy seepage can be obtained based on the relationship between the flow rate and the pressure gradient.

[0037] Preferably, a roller 21 is provided at the bottom of the lower shear box 2. By providing the roller 21, the movement of the lower shear box 2 is facilitated and the resistance is reduced.

[0038] A test method for a soil-rock interface direct shear-seepage test device under constant normal stress conditions, comprising the following steps: Step 1, preparing a rock specimen 3, using a Brazilian splitting device to split a cylindrical rock specimen with a diameter of 180 mm and a height of 360 mm into two halves, the diameter of the rock specimen 3 being 180 mm and the height being 180 mm, drilling a diversion channel 301 in the rock specimen 3, placing the rock specimen 3 in an upper shear box 1, the diversion channel 301 being connected to a water inlet 101, and using a rock interface data processing system to perform data processing on the rock interface.

[0039] Step 2: Saturate the soil sample of the soil specimen 4 to prevent water from entering the soil during seepage and affecting the test results. Then put it into the lower shear box 2. The soil contact surface is a circle with a diameter of 180 mm. Considering that the soil is subjected to the gravity of the rock and produces settlement displacement, the soil height is selected according to the weight of the rock, and the selection range is 180 to 230 mm. The upper shear box 1 and the lower shear box 2 are closed.

[0040] Step 3: After installing the seepage control system and monitoring system, turn on the vertical jack 6 to apply pressure. After a period of time, turn on the servo motor 7 to apply shear stress, turn on the seepage control system, apply shear stress and seepage pressure to the set value, and start the direct shear-seepage test.

[0041] Monitor all data changes throughout the process and change stress loading conditions according to the test plan. After the test, unload the pressure, turn off all monitoring equipment, and then disassemble the test equipment. Take the soil after the test out of the lower shear box 2, take the rock specimen 3 out of the upper shear box 1, and continue to scan the rock interface morphology characteristics after the test with a 3D morphology scanner, and compare them with the rock interface morphology characteristics before the test.

[0042] Step 4: Data analysis.

[0043] In step 4, the applied pressure gradient is obtained by the pressure value measured by the water pressure sensor 14. According to the relationship between the flow rate and the pressure gradient, the change process of the permeability characteristics of the soil-rock interface from Darcy seepage to non-Darcy seepage can be obtained.

[0044]

[0045] Where p1 is the pressure value measured by the water pressure sensor, and d is the diameter of the soil-rock interface.

[0046] In this embodiment, the normal load is measured to be 28.73 kPa. After the normal load is applied for a period of time, the servo motor 7 is started, and the shear stress is applied at a loading rate of 0.02 mm / s, and the changes in pressure and displacement are observed in real time. When the shear amount reaches 0.2 mm, the shear force loading is stopped, the control valve 19 is opened, and the air compressor 17 is turned on to inject the fluid at a certain rate, and the flow measurement device 14 is used to collect the liquid flow at the outlet. After the permeation is stable, the air compressor 17 is stopped. The servo motor 7 is enabled again to continue to apply the shear force at a rate of 0.02 mm / s, and this is repeated until the shear amount reaches 20 mm and the loading is stopped. After the test is over, the pressure of the injected fluid is first unloaded, and then all monitoring equipment is turned off after the shear force and normal force are unloaded, and then the shear box is disassembled.

[0047] The data recorded by the data acquisition system are sorted and analyzed, and the results are as follows Figures 2 to 4As shown. From the relationship curve obtained in the figure, it can be seen that under the action of high normal load, as the flow velocity increases, the pq curve gradually deviates from linearity and becomes concave. This is mainly because the increase in flow velocity causes the inertia effect of water flow to be non-negligible, which leads to the flow of water requiring more energy to overcome the head loss caused by the inertia force, thus causing nonlinear flow.

Claims

1. A test method for a soil-rock interface direct shear-seepage test device under constant normal stress conditions, characterized in that: A soil-rock interface direct shear-seepage test device under constant normal stress conditions is used for testing. The soil-rock interface direct shear-seepage test device under constant normal stress conditions comprises a direct shear loading system, a seepage control system and a monitoring system. The direct shear loading system comprises an upper shear box (1) and a lower shear box (2). A rock specimen (3) is arranged in the upper shear box (1), and a soil specimen (4) is arranged in the lower shear box (2). A water inlet (101) is arranged on the side wall of the upper shear box (1). A diversion channel (301) is arranged in the rock specimen (3). One end of the diversion channel (301) corresponds to the water inlet (101), and the other end is arranged at the interface between the rock specimen (3) and the soil specimen (4). A water outlet (201) is arranged on the side wall of the lower shear box (2). A water trough (5) is arranged on the outer side of the lower shear box (2) opposite to the water outlet (201). The water trough (5) is provided with a drainage pipe (501). A vertical jack (6) is arranged on the top of the upper shear box (1). A servo motor (7) is provided on one side of the lower shear box (2), and a loading rod (8) for applying force to the lower shear box (2) is provided at the output end of the servo motor (7); the seepage control system comprises a water pipe (9) connected to the water inlet (101), and the water pipe (9) supplies water through a water supply device; the monitoring system comprises a normal load sensor (10) and a shear load sensor (11) respectively arranged on the top and side wall of the upper shear box (1) and a shear displacement sensor (12) arranged on one side of the lower shear box (2), the shear load sensor (11) and the shear displacement sensor (12) being mounted on a head seat (13), and also comprises a flow measurement device (14) for measuring the flow of seepage water in the water tank (5), and the normal load sensor (10), the shear load sensor (11), the shear displacement sensor (12) and the flow measurement device (14) are communicatively connected to a data acquisition system (15); The steps include: Step 1: Prepare a rock specimen (3), drill a diversion channel (301) in the rock specimen (3), and place the rock specimen (3) in an upper shear box (1); Step 2: Saturate the soil sample of the soil specimen (4), and then place it into the lower shear box (2), and close the upper shear box (1) and the lower shear box (2); Step 3: After installing the seepage control system and the monitoring system, turn on the vertical jack (6) to apply pressure, then turn on the servo motor (7) to apply shear stress, turn on the seepage control system, and start the direct shear-seepage test; Step 4: Data analysis.

2. The test method of a soil-rock interface direct shear-seepage test device under constant normal stress conditions according to claim 1 is characterized in that: The water supply device comprises a water tank (16), the water tank (16) being connected to the water inlet (101) via a water pipe (9), and the water tank (16) being connected to the air compressor (17) via a pipeline.

3. The test method of a soil-rock interface direct shear-seepage test device under constant normal stress conditions according to claim 1 is characterized in that: The flow measurement device (14) is an electronic balance, and a measuring cup (18) is provided on the electronic balance.

4. The test method of a soil-rock interface direct shear-seepage test device under constant normal stress conditions according to claim 1 is characterized in that: The water pipe (9) is provided with a control valve (19) and a water pressure sensor (20), and the water pressure sensor (20) is communicatively connected with the data acquisition system (15).

5. The test method of a soil-rock interface direct shear-seepage test device under constant normal stress conditions according to claim 1, characterized in that: A roller (21) is provided at the bottom of the lower shear box (2).

6. The test method of a soil-rock interface direct shear-seepage test device under constant normal stress conditions according to claim 4 is characterized in that: In the fourth step, the applied pressure gradient is obtained by using the pressure value measured by the water pressure sensor (20), and the change process of the permeability characteristics of the soil-rock interface from Darcy seepage to non-Darcy seepage can be obtained based on the relationship between the flow rate and the pressure gradient; The pressure gradient is calculated as: ； In the formula, p 1 is the pressure value measured by the water pressure sensor, and d is the diameter of the soil-rock interface.

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