Soil permeability test device and method under variable stress conditions

Abstract

The invention discloses a soil permeability test device and method under variable stress conditions, including a base, a soil sample, a sample chamber, a water inlet device, a water outlet device, an electronic displacement meter, a lateral loading hydraulic cylinder, a vertical loading hydraulic cylinder, and a computer are arranged on the base. The soil sample is in the shape of a square column and is arranged in the central compartment of the sample chamber. The water inlet device is used to provide permeation water pressure to the soil sample. The water storage device is used to collect test wastewater and monitor the seepage during the test. The lateral loading hydraulic cylinder applies a horizontal load to the side of the soil sample through a side pressure plate, and the vertical loading hydraulic cylinder applies a vertical load to the top surface of the soil sample through a water inlet trough. The computer is respectively connected to the lateral loading hydraulic cylinder and the vertical loading hydraulic cylinder to control the size of the output load. The invention can simulate the actual stress state of the sample during the test, and can change the stress state of one or more surfaces of the sample as needed, and accurately obtain the variation law of the permeability coefficient of the soil during the stress increase and decrease process.

Description

Technical Field

[0001] The invention relates to the field of geotechnical engineering, and in particular to a soil permeability test device and method under variable stress conditions. Background Art

[0002] In saturated soil, water flows through pores under pressure to form a permeability phenomenon. Permeability is an important characteristic of soil. Seepage can cause soil deformation and directly affect engineering safety. Studying soil permeability and seepage law is of great significance to engineering practice. The permeability characteristics of soil can be obtained in two ways: on-site or indoor. Most of the on-site methods use pumping or water injection, while indoors, permeability test devices are used, such as Darcy permeability test devices. However, when conducting permeability tests on soil, existing permeability test devices and methods use soil samples under a constant stress state, and most of them ignore the stress state of the soil and its change process, which is obviously inconsistent with the actual situation. For example, during tunnel excavation, the surrounding rock in front of the face is originally in a six-sided stress state. As the tunnel is excavated, the ground stress on one side close to the face will gradually release, resulting in a change in the state of the surrounding rock, which in turn affects the permeability characteristics; during the high embankment filling process, as the upper soil is filled, the stress of the lower soil gradually increases, and the permeability characteristics of the soil will also change. Therefore, the existing permeability test device cannot accurately simulate the permeability characteristics of soil under variable stress conditions. Summary of the invention

[0003] The purpose of the present invention is to provide a soil permeability test device and method under variable stress conditions.

[0004] To achieve the above object, the technical solution of the present invention is: a soil permeability test device under variable stress conditions, comprising a base, the base is provided with

[0005] The soil sample is in the shape of a square cylinder and is covered with a protective film;

[0006] The sample chamber for holding soil samples comprises side pressure plates arranged along the sides of the square, and side limit plates arranged along the extending directions of the two ends of the side pressure plates, the adjacent side limit plates are connected in pairs and arranged in a well grid shape with the side pressure plates, and the soil samples are placed in the central grid surrounded by the side pressure plates;

[0007] A water inlet device for providing osmotic water pressure to the soil sample comprises a water inlet pipe, one end of the water inlet pipe is connected to a water supply tank, the water inlet pipe is sequentially connected to a booster pump, a first water pressure gauge, and a first flow control valve in a direction away from the water supply tank, the end of the water inlet pipe is connected to a water inlet trough, the water inlet trough is square and is arranged on the upper end surface of the soil sample, and the lower end of the water inlet trough is connected to the protective membrane flange;

[0008] A water outlet device for collecting test wastewater, comprising a water outlet trough, the water outlet trough is square and is arranged at the bottom of the soil sample, the upper end of the water outlet trough is connected to the protective membrane flange, the lower end of the water outlet trough is connected to a water outlet pipe, and the water outlet pipe is sequentially connected to a second water pressure gauge, a flow meter, a second flow control valve and a water storage tank along a square away from the water outlet trough, and the second water pressure gauge and the flow meter are used to monitor the seepage during the test process;

[0009] Electronic displacement meters, respectively installed on the pressure plates on each side and the water inlet trough, are used to measure the lateral and vertical deformation of the soil sample;

[0010] The loading mechanism includes a lateral loading hydraulic cylinder corresponding to each side pressure plate, and a vertical loading hydraulic cylinder corresponding to the water inlet trough. The lateral loading hydraulic cylinders are respectively connected to the corresponding side pressure plates, and apply horizontal loads to the sides of the soil sample through the side pressure plates; the vertical loading hydraulic cylinder is connected to the water inlet trough, and applies vertical loads to the top surface of the soil sample through the water inlet trough;

[0011] The computer is connected to the lateral loading hydraulic cylinder and the vertical loading hydraulic cylinder to control the output load; the computer is also connected to the first flow control valve and the second flow control valve to control the start and stop of the water inlet device and the water outlet device.

[0012] Furthermore, the loading mechanism also includes a reaction frame, which includes columns and beams. The columns are arranged in a cross shape, and the beams are cross-shaped and their ends are respectively supported on the top of each column. The lateral loading hydraulic cylinders are respectively installed on each column, and the vertical loading hydraulic cylinders are installed on the beams.

[0013] Furthermore, the side limit plate is an L-shaped plate, and a linear slide groove is provided on the side of the L-shaped plate; the side pressure plate is a U-shaped plate, and a slider embedded in the linear slide groove is provided on the outer side of the leg of the U-shaped plate.

[0014] Furthermore, a filter layer is provided between the soil sample and the water inlet trough, and between the soil sample and the water outlet trough.

[0015] Furthermore, the protective film is a latex sleeve.

[0016] A soil permeability test method under variable stress conditions comprises the following steps:

[0017] S1. Use flange to fix the lower end of latex sleeve to the water outlet trough, set up filter layer above the square water outlet trough, install rectangular steel mold on the outside of latex sleeve, prepare samples in layers on the water outlet trough according to the requirements of Geotechnical Test Code SL237-1999, record the length L and height h of the bottom surface of the sample, place filter layer on the upper end of the sample, remove the rectangular steel mold, place the water inlet trough on the sample, and fix the upper end of latex sleeve to the water inlet trough with flange;

[0018] S2. Install each lateral loading hydraulic cylinder on the column of the reaction frame, and connect its output end to the corresponding lateral pressure plate; install the vertical loading hydraulic cylinder on the crossbeam of the reaction frame;

[0019] S3, control the lateral loading hydraulic cylinder and the vertical loading hydraulic cylinder by computer, so that each lateral pressure plate contacts the side of the sample, and connect the output end of the vertical loading hydraulic cylinder to the upper end surface of the water inlet tank;

[0020] S4, controlling the lateral loading hydraulic cylinder and the vertical loading hydraulic cylinder to output the specified load respectively through the computer;

[0021] S5, open the first flow control valve, wait until the first water pressure gauge and the second water pressure gauge have constant values, start the booster pump to apply water pressure, and control the flow through the flow control valve, and at the same time open the second flow control valve to start the penetration test;

[0022] S6. Use a computer to control the output load of the vertical loading hydraulic cylinder and the lateral loading hydraulic cylinder, change the stress state of one or more surfaces of the sample, simulate the stress change process of the soil, record the height deformation variable Δh, length deformation variable ΔL1, width deformation variable ΔL2, flow rate Q through the sample within time t, and the first water pressure gauge reading p1 and the second water pressure gauge reading p2 at the end of the time, then the permeability coefficient calculation formula is:

[0023]

[0024] S7. Repeat S6 to obtain the permeability characteristics of the sample under different stress states.

[0025] The beneficial effects of the present invention are as follows: the present invention can simulate the real stress state of the sample during the test, can change the stress state of one or more surfaces of the sample as needed, accurately obtain the variation law of the permeability coefficient of the soil during the stress increase and decrease process, and the test results are more in line with engineering practice. The present invention has a simple structure, is easy to operate, and is easy to promote and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the present invention;

[0027] Figure 2 It is the structural schematic diagram of the sample chamber;

[0028] Figure 3 This is a schematic diagram of the installation of soil samples;

[0029] In the figure, 1. base; 2. soil sample; 3. protective film; 4. side pressure plate; 5. side limit plate; 6. water inlet pipe; 7. water supply tank; 8. booster pump; 9. first water pressure gauge; 10. first flow control valve; 11. water inlet trough; 12. water outlet trough; 13. water outlet pipe; 14. second water pressure gauge; 15. flow meter; 16. second flow control valve; 17. water storage tank; 18. electronic displacement meter; 19. lateral loading hydraulic cylinder; 20. vertical loading hydraulic cylinder; 21. column; 22. beam. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings.

[0031] like Figure 1-3 As shown, a soil permeability test device under variable stress conditions includes a base 1, on which is provided

[0032] A square-cylindrical soil sample 2, the soil sample 2 is covered with a protective film 3; the protective film 3 is preferably a latex sleeve;

[0033] The sample chamber for holding the soil sample 2 includes side pressure plates 4 arranged along each side of the square, and side limit plates 5 arranged along the extending direction of both ends of the side pressure plates 4. Adjacent side limit plates 5 are connected in pairs and arranged in a well grid with the side pressure plates 4. The soil sample 2 is placed in the central grid surrounded by each side pressure plate 4; the side limit plates 5 are L-shaped plates, and the side surfaces of the L-shaped plates are provided with linear slide grooves; the side pressure plates 4 are U-shaped plates, and the outer side surfaces of the legs of the U-shaped plates are provided with sliders embedded in the linear slide grooves;

[0034] A water inlet device for providing osmotic water pressure to the soil sample 2, comprising a water inlet pipe 6, one end of the water inlet pipe 6 is connected to a water supply tank 7, the water inlet pipe 6 is sequentially connected to a booster pump 8, a first water pressure gauge 9, and a first flow control valve 10 in a direction away from the water supply tank 7, the end of the water inlet pipe 6 is connected to a water inlet trough 11, the water inlet trough 11 is square and is arranged on the upper end surface of the soil sample 2, and the lower end of the water inlet trough 11 is flange-connected to the protective membrane 3;

[0035] A water outlet device for collecting test wastewater, comprising a water outlet trough 12, the water outlet trough 12 is square and is arranged at the bottom of the soil sample 2, the upper end of the water outlet trough 12 is flange-connected to the protective membrane 3, the lower end of the water outlet trough 12 is connected to a water outlet pipe 13, and the water outlet pipe 13 is sequentially connected to a second water pressure gauge 14, a flow meter 15, a second flow control valve 16 and a water storage tank 17 along a square away from the water outlet trough 12, and the second water pressure gauge 14 and the flow meter 15 are used to monitor the seepage during the test process;

[0036] The electronic displacement meter 18 is respectively arranged on each side pressure plate 4 and the water inlet trough 11, and is used to measure the lateral and vertical deformation of the soil sample 2;

[0037] The loading mechanism includes a lateral loading hydraulic cylinder 19 corresponding to each side pressure plate 4, and a vertical loading hydraulic cylinder 20 corresponding to the water inlet trough 11. The lateral loading hydraulic cylinder 19 is respectively connected to the corresponding side pressure plate 4, and a horizontal load is applied to the side of the soil sample 2 through the side pressure plate 4; the vertical loading hydraulic cylinder 20 is connected to the water inlet trough 11, and a vertical load is applied to the top surface of the soil sample 2 through the water inlet trough 11; and also includes a reaction force frame, the reaction force frame includes columns 21 and beams 22, the columns 21 are arranged in a cross shape, the beams 22 are cross-shaped and the ends are respectively supported on the top of each column 21, the lateral loading hydraulic cylinder 19 is respectively installed on each column 21, and the vertical loading hydraulic cylinder 20 is installed on the beam 22;

[0038] The computer is connected to the lateral loading hydraulic cylinder 19 and the vertical loading hydraulic cylinder 20 respectively to control the size of the output load; the computer is also connected to the first flow control valve 10 and the second flow control valve 16 respectively to control the start and stop of the water inlet device and the water outlet device.

[0039] The computer is also connected to the electronic displacement meter 18, the flow meter 15, the first water pressure meter 9, and the second water pressure meter 14 respectively, collects test parameter information through a software program, and calculates and displays the deformation and permeability coefficient of the sample in real time.

[0040] The present invention can simulate the real stress state of the sample during the test, change the stress state of one or more surfaces of the sample as needed, accurately obtain the variation law of the permeability coefficient of the soil during the stress increase and decrease process, and the test result is more in line with engineering practice. The present invention has a simple structure, is easy to operate, and is easy to promote and use.

[0041] The above experimental device is used to carry out the soil permeability test under variable stress conditions, and the steps are as follows:

[0042] S1. Use a flange to fix the lower end of the latex sleeve to the water outlet trough 12, set a filter layer above the square water outlet trough 12, install a rectangular steel mold on the outside of the latex sleeve, prepare samples in layers on the water outlet trough 12 according to the requirements of the Geotechnical Test Code SL237-1999, record the side length L and height h of the bottom surface of the sample, place a filter layer on the upper end surface of the sample, remove the rectangular steel mold, place the water inlet trough 11 on the sample, and fix the upper end of the latex sleeve to the water inlet trough 11 with a flange;

[0043] S2, install each lateral loading hydraulic cylinder 19 on the column 21 of the reaction frame, and connect its output end to the corresponding lateral pressure plate; install the vertical loading hydraulic cylinder 20 on the crossbeam 22 of the reaction frame;

[0044] S3, control the lateral loading hydraulic cylinder 19 and the vertical loading hydraulic cylinder 20 by computer, so that each lateral pressure plate contacts the side of the sample, and connects the output end of the vertical loading hydraulic cylinder 20 to the upper end surface of the water inlet tank 11;

[0045] S4, controlling the lateral loading hydraulic cylinder 19 and the vertical loading hydraulic cylinder 20 through a computer to output designated loads respectively;

[0046] S5, open the first flow control valve 10, wait until the values ​​of the first water pressure gauge 9 and the second water pressure gauge 14 are constant, start the booster pump 8, apply water pressure, and control the flow through the flow control valve, and at the same time open the second flow control valve 16 to start the penetration test;

[0047] S6. Use a computer to control the output load of the vertical loading hydraulic cylinder 20 and the lateral loading hydraulic cylinder 19, change the stress state of one or more surfaces of the sample, simulate the stress change process of the soil, record the height deformation variable Δh, length deformation variable ΔL1, width deformation variable ΔL2, flow rate Q through the sample within time t, and the reading p1 of the first water pressure gauge 9 and the reading p2 of the second water pressure gauge 14 at the end of the time, then the permeability coefficient calculation formula is:

[0048]

[0049] S7. Repeat S6 to obtain the permeability characteristics of the sample under different stress states.

[0050] The described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of the present invention.

Claims

1. A soil permeability test method under variable stress conditions, characterized in that: A soil permeability test device under variable stress conditions is used, which includes a base, a square column-shaped soil sample is arranged on the base, and the soil sample is covered with a protective film; The sample chamber for holding soil samples comprises side pressure plates arranged along the sides of the square, and side limit plates arranged along the extending directions of the two ends of the side pressure plates, the adjacent side limit plates are connected in pairs and arranged in a well grid shape with the side pressure plates, and the soil samples are placed in the central grid surrounded by the side pressure plates; A water inlet device for providing osmotic water pressure to the soil sample comprises a water inlet pipe, one end of the water inlet pipe is connected to a water supply tank, the water inlet pipe is sequentially connected to a booster pump, a first water pressure gauge, and a first flow control valve in a direction away from the water supply tank, the end of the water inlet pipe is connected to a water inlet trough, the water inlet trough is square and is arranged on the upper end surface of the soil sample, and the lower end of the water inlet trough is connected to the protective membrane flange; A water outlet device for collecting test wastewater, comprising a water outlet trough, the water outlet trough is square and is arranged at the bottom of the soil sample, the upper end of the water outlet trough is connected to the protective membrane flange, the lower end of the water outlet trough is connected to a water outlet pipe, and the water outlet pipe is sequentially connected to a second water pressure gauge, a flow meter, a second flow control valve and a water storage tank along a square away from the water outlet trough, and the second water pressure gauge and the flow meter are used to monitor the seepage during the test process; Electronic displacement meters, respectively installed on the pressure plates on each side and the water inlet trough, are used to measure the lateral and vertical deformation of the soil sample; The loading mechanism includes a lateral loading hydraulic cylinder corresponding to each side pressure plate, and a vertical loading hydraulic cylinder corresponding to the water inlet trough. The lateral loading hydraulic cylinders are respectively connected to the corresponding side pressure plates, and apply horizontal loads to the sides of the soil sample through the side pressure plates; the vertical loading hydraulic cylinder is connected to the water inlet trough, and applies vertical loads to the top surface of the soil sample through the water inlet trough; A computer, the computer is connected to the lateral loading hydraulic cylinder and the vertical loading hydraulic cylinder respectively to control the size of the output load; the computer is also connected to the first flow control valve and the second flow control valve respectively to control the start and stop of the water inlet device and the water outlet device; The loading mechanism further comprises a reaction force frame, which comprises columns and beams, the columns are arranged in a cross shape, the beams are cross-shaped and their ends are respectively supported on the tops of the columns, the lateral loading hydraulic cylinders are respectively mounted on the columns, and the vertical loading hydraulic cylinders are mounted on the beams; The side limit plate is an L-shaped plate, and a linear slide groove is provided on the side of the L-shaped plate; the side pressure plate is a U-shaped plate, and a slider embedded in the linear slide groove is provided on the outer side of the leg of the U-shaped plate; A filter layer is provided between the soil sample and the water inlet trough, and between the soil sample and the water outlet trough; The protective film is a latex sleeve; The following steps are involved: S1. Use flange to fix the lower end of latex sleeve to the water outlet trough, set up filter layer above the square water outlet trough, install rectangular steel mold on the outside of latex sleeve, prepare samples in layers on the water outlet trough according to the requirements of Geotechnical Test Code SL237-1999, record the length L and height h of the bottom surface of the sample, place filter layer on the upper end of the sample, remove the rectangular steel mold, place the water inlet trough on the sample, and fix the upper end of latex sleeve to the water inlet trough with flange; S2. Install each lateral loading hydraulic cylinder on the column of the reaction frame, and connect its output end to the corresponding lateral pressure plate; install the vertical loading hydraulic cylinder on the crossbeam of the reaction frame; S3, control the lateral loading hydraulic cylinder and the vertical loading hydraulic cylinder by computer, so that each lateral pressure plate contacts the side of the sample, and connect the output end of the vertical loading hydraulic cylinder to the upper end surface of the water inlet tank; S4, controlling the lateral loading hydraulic cylinder and the vertical loading hydraulic cylinder to output the specified load respectively through the computer; S5, open the first flow control valve, wait until the first water pressure gauge and the second water pressure gauge have constant values, start the booster pump to apply water pressure, and control the flow through the flow control valve, and at the same time open the second flow control valve to start the penetration test; S6. Use a computer to control the output load of the vertical loading hydraulic cylinder and the lateral loading hydraulic cylinder to change the stress state of one or more surfaces of the sample, simulate the stress change process of the soil, record the height deformation variable Δh, length deformation variable ΔL1, width deformation variable ΔL2, flow rate Q through the sample within time t, and the first water pressure gauge reading p1 and the second water pressure gauge reading p2 at the end of the time, then the permeability coefficient calculation formula is: S7. Repeat S6 to obtain the permeability characteristics of the sample under different stress states.

Images