CN110514533B - Triaxial device suitable for testing mechanical properties of soil body under water circulation permeation effect and application method - Google Patents

Abstract

The invention discloses a triaxial device suitable for testing mechanical properties of soil under the action of water circulation permeation and a use method thereof, wherein the device comprises a triaxial pressure chamber, an upper cross beam, a level gauge, a base, a bottom controller and a threaded support rod; the upper cross beam is provided with a level gauge and is fixedly connected with the bottom controller through a threaded support rod; the upper cross beam can control balance and contact according to the level gauge by adjusting the threaded support rod; the bottom controller is provided with a base, and the bottom controller can control the lifting of the base; the triaxial pressure chamber comprises a test system and a water circulation system of a soil sample; the triaxial pressure chamber is wholly open and airtight, the device can carry out the hydrologic cycle to the soil sample that awaits measuring, then survey the mechanical properties of soil sample after the hydrologic cycle. The invention has simple structure, convenient operation and true and reliable test result.

Description

A three-axis device suitable for testing the mechanical properties of soil under the action of water circulation and penetration How to set up and use

Technical field

The invention belongs to the field of geotechnical engineering soil property testing devices, and specifically relates to an improved three-axis device suitable for testing the mechanical properties of soil under the action of water circulation penetration.

Background technique

Sea sand is beaten and retreated by waves, causing particles in the soil to migrate, causing changes in the internal structure of the soil, thus affecting the mechanical properties of the soil. Such erosion will cause some geological disasters, such as landslides and sinkholes. Therefore, for offshore structures, it is particularly important to study the erosion of soil under the action of water circulation and penetration.

The triaxial device is currently the mainstream device in the geotechnical engineering community for measuring the mechanical shear properties of various soils. However, the existing three-axis device is not suitable for simulating water circulation, and cannot integrate the soil sample being subjected to water circulation penetration and measuring the mechanical properties of the soil sample. Then there is an urgent need for an improved triaxial device to test the effect of water circulation on the strength and deformation characteristics of natural sand with different grades.

Contents of the invention

In view of this, the present invention aims to propose an improved triaxial device suitable for testing the mechanical properties of soil under the action of water circulation penetration, so as to solve the above technical problems.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A triaxial device suitable for testing the mechanical properties of soil under the action of water circulation penetration, including a triaxial pressure chamber, an upper beam, a level, a base, a bottom controller and a threaded support rod; the upper beam is provided with a level, The upper beam is fixedly connected to the bottom controller through a threaded support rod; the upper beam can control balance and contact by adjusting the threaded support rod according to a level; the bottom controller is provided with a base, and the bottom The controller can control the lifting and lowering of the base; the three-axis pressure chamber is composed of an outer pressure chamber with hollow openings at both ends, a bottom plate of the pressure chamber and a top cover of the pressure chamber. The top cover of the pressure chamber is provided with an exhaust port. , a liquid inlet is provided on the bottom plate of the pressure chamber; an upper sample cap and a lower sample cap are symmetrically arranged in the triaxial pressure chamber, and the upper sample cap and the lower sample cap form a A storage space for the soil sample to be tested; the upper sample cap is provided with a water inlet and a circulation channel, the lower sample cap is provided with a water inlet and a circulation channel, and the upper test cap is provided with a water inlet and a circulation channel. The opposite end surfaces of the sample cap and the lower sample cap are respectively provided with nozzle hole one and nozzle hole two; the nozzle hole one is connected to the water inlet one through the circulation channel one, and the water inlet one is connected to the water supply tank through an external water supply pipe Connected, the upper water tank is provided with a second liquid outlet at the bottom and a second exhaust port at the top; the second nozzle hole is connected to the second water inlet through the second circulation channel, and the second water inlet is connected to the water inlet through an external sewer pipe. The lower water tank is connected. A flow valve, a water pump and a flow meter are arranged between the lower water pipe and the lower water tank. The lower water tank is provided with a liquid inlet three and an exhaust port three. The exhaust port three is connected to an external air extraction pump; the upper sample tube is provided with a sample cover, a pressure sensor is provided between the upper beam and the upper sample tube, and the pressure sensor runs through the The top cover of the pressure chamber and the sample cover are in contact with the upper sample cap; a displacement sensor is provided between the upper beam and the pressure sensor, and one end of the displacement sensor is fixed on the upper beam The other end is fixedly connected to the pressure sensor; the entire triaxial pressure chamber is gas-tight.

Further, the bottom of the upper beam is fixed with pads and top beads in sequence from top to bottom, and the pressure sensor is in central contact with the top beads.

Further, a filter screen 1 is provided between the upper sample cap and the soil sample to be tested, and a filter screen 2 is provided between the lower sample cap and the soil sample to be tested. The pore diameter of filter one and filter two is smaller than the diameter of the soil sample to be tested.

The invention also provides a method for using a triaxial device suitable for testing the mechanical properties of soil under the action of water circulation penetration. The specific steps are as follows:

S1: Arrange filter 2, lower sample cap, soil sample to be tested wrapped in rubber film, filter 1 and upper sample cap in sequence from bottom to top in the triaxial pressure chamber, and ensure that the above The nozzle hole one of the upper sample cap is opposite to the nozzle hole two of the lower sample cap, and the upper sample membrane and the lower sample membrane are integrally sealed through the rubber membrane, and the tendons are tied; and then the entire three parts are installed. The shaft device ensures that the three-axis pressure chamber is airtight as a whole and is leveled by a level;

S2: Open the exhaust port three of the lower water tank, fill the lower water tank with water through the liquid inlet three, and then close the liquid inlet; close the liquid outlet two of the upper water tank, and open the exhaust port two;

S3: Turn on the water pump, adjust the flow valve to control the water flow to the required parameter value, the water flows from the lower part of the soil sample to the upper part of the soil sample through the lower sample cap and enters the upper water tank; after the water in the lower water tank is pumped out, close the water pump. Turn on the air pump, and the water flows out of the upper water tank through the upper sample cap and the lower sample cap and flows into the lower water tank until the water level in the lower water tank no longer increases, thus completing a water cycle of the soil sample to be tested;

S4: Repeat the operation of step S3 n times to complete n+1 cycles, then close all valves in the three-axis pressure chamber to ensure that the whole is airtight, then open the liquid inlet one, and pass water into the three chambers to the experiment The required confining pressure is then set by the controller to set the strain rate of the base. The base will move upward and apply a vertical load to the soil sample. When the force monitored by the pressure sensor meets the requirements, the manual pause is performed; finally, after the confining pressure and Under the action of vertical force, shear strain is generated. The computer can draw Mohr's circle and measure the cohesion and friction angle of the soil after water circulation. Then the strength of the soil can be obtained. Specifically: (1) Change different conditions through the computer. The confining pressure is measured, and the axial stress σ ₁ and axial strain ε of the unit body under the spatial stress state are measured, and the elastic modulus E can be obtained. The formula is as follows:

σ ₁ =Eε

Curve fitting of the elastic modulus under different confining pressures was obtained, and the axial elastic modulus of the soil was obtained.

(2) Under drainage conditions, the volume strain of the soil can be known through the amount of drainage, and thus whether the soil is expanding or shrinking.

(3) Through the measured stresses σ ₁ , σ ₂ , and σ ₃ of the unit body in three directions. Based on these three stresses, a Mohr stress circle can be drawn, with the radius of the circle being half of the difference between the maximum stress and the minimum stress among the three stresses. The maximum shear stress τ _max can be obtained. According to the Mohr stress circle drawn according to different confining pressures, a tangent line is drawn on the circle. The slope of the tangent line is the friction angle. The value that intersects the shear stress coordinate axis is the cohesion C.

Compared with the existing technology, the beneficial effects of the present invention are:

The invention has simple structure, convenient operation and real and reliable simulation. Combining the infiltration effect of water circulation with testing avoids the disturbance of secondary soil sample preparation, which is conducive to the authenticity and reliability of test results.

Description of drawings

Figure 1 is a schematic structural diagram of the present invention;

Figure 2 is a structural diagram of the lower water tank of the present invention;

Figure 3 is a structural diagram of the upper sample cap of the present invention.

Detailed ways

The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

As shown in Figures 1 to 3, in the figure, 1. Level, 2. Upper beam, 3. Pad, 4. Top bead, 5. Displacement sensor, 6. Fixing clip, 7. Pressure chamber top cover, 8. Pressure chamber outdoor Barrel, 9. Pressure chamber bottom plate, 10. Base, 11. Bottom controller, 12. Upper sample cap, 13. Nozzle hole one, 14. Filter one, 15. Filter two, 16. Nozzle hole two, 17 , lower the sample cap, 18. liquid inlet one, 19. exhaust port one, 20. water inlet one, 21. water inlet two, 22. upper water pipe, 23. lower water pipe, 24. upper water tank, 25. lower Water tank, 26. Liquid outlet two, 27. Air outlet two, 28. Liquid inlet three, 29. Exhaust port three, 30. Water pump, 31. Air pump, 32. Soil sample to be tested, 33. Sample Cover, 34. Pressure sensor, 35. Flow meter, 36. Flow valve, 37. Circulation channel one, 38. Circulation channel two, 39. Threaded support rod.

A triaxial device suitable for testing the mechanical properties of soil under the action of water circulation penetration, including a triaxial pressure chamber, an upper beam 2, a level 1, a base 10, a bottom controller 11 and a threaded support rod; the upper beam 2 There is a level 1 on the top, and the upper beam 2 is fixedly connected to the bottom controller 11 through a threaded support rod; the upper beam 2 can control balance and contact by adjusting the threaded support rod according to the level 1; the bottom control The device 11 is provided with a base 10, and the bottom controller 11 can control the lifting and lowering of the base 10; the three-axis pressure chamber consists of an outer pressure chamber 8 with hollow interior openings at both ends, a bottom plate 9 of the pressure chamber, and a top cover of the pressure chamber. Composed of 7, the top cover 7 of the pressure chamber is provided with an exhaust port 19, and the bottom plate 9 of the pressure chamber is provided with a liquid inlet 18; the three-axis pressure chamber is symmetrically arranged with an upper sample cap 12 and lower sample cap 17. The space between the upper sample cap 12 and the lower sample cap 17 constitutes the accommodation space for the soil sample 32 to be tested; the upper sample cap and the soil sample to be tested are A filter screen 14 is arranged between 32, and a filter screen 2 15 is arranged between the lower sample cap 17 and the soil sample to be tested 32. The apertures of the filter screen 14 and the filter screen 2 15 are Smaller than the diameter of the soil sample 32 to be tested; the upper sample cap 12 is provided with a water inlet 20 and a circulation channel 37, and the lower sample cap 17 is provided with a water inlet 21 and a circulation channel 38 , the opposite end surfaces of the upper sample cap 12 and the lower sample cap 17 are respectively provided with nozzle holes 13 and 16; the water inlet 20 is connected to the upper water tank 24 through the external water supply pipe 22, so The upper water tank 24 is provided with a second liquid outlet 26 at the bottom, and a second exhaust port 27 is provided at the top; the second nozzle hole 16 is connected to the second water inlet 21 through the second circulation channel 38, and the second water inlet 21 passes through The external sewer pipe 23 is connected with the sewer tank 25. A flow valve 36, a water pump 30 and a flow meter 35 are arranged between the sewer pipe 23 and the sewer tank 25. The sewer tank 25 is provided with an inlet. Liquid port three 28 and exhaust port three 29, the exhaust port three 29 is externally connected to the air pump 31; the upper sample tube is provided with a sample cover 33, the upper beam 2 and the upper A pressure sensor 34 is provided between the sample tubes. The bottom of the upper beam 2 is fixed with a pad 3 and a top bead 4 in sequence from top to bottom. The pressure sensor 34 is in central contact with the top bead 4. The pressure sensor 34 penetrates the pressure chamber top cover 7 and the sample cover 33 and contacts the upper sample cap 12; a displacement sensor 5 is fixed on the upper beam 2, and the other part of the displacement sensor 5 One end is fixedly connected to the pressure sensor 34 through a fixing clip 6; the entire triaxial pressure chamber is airtight.

The invention also provides a method for using a triaxial device suitable for testing the mechanical properties of soil under the action of water circulation penetration. The specific steps are as follows:

S1: In the triaxial pressure chamber, filter screen 2 15, lower sample cap 17, soil sample to be tested 32 wrapped in rubber membrane, filter screen 14 and upper sample cap 12 are arranged in sequence from bottom to top. , and ensure that the nozzle hole one 13 of the upper sample cap 12 is opposite to the nozzle hole two 16 of the lower sample cap 17, and the upper sample film and the lower sample film are integrally sealed through the rubber film and tied Good beef tendon; then install the entire three-axis device to ensure that the three-axis pressure chamber is airtight as a whole, and level it with the level 1;

S2: Open the exhaust port three of the lower water tank 25, fill the lower water tank 25 with water through the liquid inlet three 28, and then close the liquid inlet; then close the liquid outlet two 26 of the upper water tank 24, and open the exhaust port mouth two;

S3: Turn on the water pump 30, adjust the flow valve 36 to control the water flow to the required parameter value, the water flows from the lower part of the soil sample to the upper part of the soil sample through the lower sample cap 17 and enters the upper water tank 24; wait until the water in the lower water tank 25 is pumped out , close the water pump 30, open the air pump 31, the water flows out from the upper water tank 24 through the upper sample cap 12 and the lower sample cap 17 and flows into the lower water tank 25 until the water level of the lower water tank 25 no longer increases, that is, once is completed cycle;

S4: Repeat the operation of step S3 n times to complete n+1 cycles, then close all valves in the three-axis pressure chamber to ensure that the whole is airtight, then open the liquid inlet 18, and pass water into the three chambers to The confining pressure required by the experiment is then set by the bottom controller 11 to set the strain rate of the base 10. The base 10 will move upward and apply a vertical load to the soil sample. When the force monitored by the pressure sensor 34 meets the requirements, the manual pause is performed. ; Finally, under the action of confining pressure and vertical force, shear strain is generated, and the computer can draw a Mohr circle, and measure the cohesion and friction angle of the soil after water circulation, and then the strength of the soil can be obtained;

Specifically, ① change different confining pressures through the computer, measure the axial stress σ ₁ and axial strain ε of the unit body under the spatial stress state, and then obtain the elastic modulus E. The formula is as follows:

σ ₁ =Eε

Obtain curve fitting of the elastic modulus under different confining pressures, and obtain the axial elastic modulus of the soil;

② Under drainage conditions, the volumetric strain of the soil can be known through the drainage volume, and it can be known whether the soil is expanding or contracting;

③ Through the measured stress σ ₁ , σ ₂ , σ ₃ of the unit body in three directions. Based on these three stresses, a Mohr stress circle can be drawn, with the radius of the circle being half of the difference between the maximum stress and the minimum stress among the three stresses. The maximum shear stress τ _max can be obtained. According to the Mohr stress circle drawn according to different confining pressures, a tangent line is drawn on the circle. The slope of the tangent line is the friction angle. The value that intersects the shear stress coordinate axis is the cohesion C;

Claims (2)

1. A triaxial device suitable for testing the mechanical properties of soil under the action of water circulation penetration, including a triaxial pressure chamber, an upper beam (2), a level (1), a base (10), a bottom controller (11) and Threaded support rod (39); a level (1) is provided on the upper crossbeam (2), and the upper crossbeam (2) is fixedly connected to the bottom controller (11) through the threaded support rod (39); The upper beam (2) can control balance and contact by adjusting the threaded support rod (39) according to the level (1); the bottom controller (11) is provided with a base (10), and the bottom controller (11) is provided with a base (10). 11) The lifting and lowering of the base (10) can be controlled; it is characterized in that: the three-axis pressure chamber consists of an outer pressure chamber (8) with hollow openings at both ends, a bottom plate (9) of the pressure chamber and a top cover (7) of the pressure chamber. Composed, the top cover (7) of the pressure chamber is provided with an exhaust port (19), and the bottom plate (9) of the pressure chamber is provided with a liquid inlet (18); the three-axis pressure chamber An upper sample cap (12) and a lower sample cap (17) are symmetrically arranged, and the space between the upper sample cap (12) and the lower sample cap (17) constitutes the accommodation of the soil sample (32) to be tested. space; a filter screen (14) is arranged between the upper sample cap (12) and the soil sample to be tested (32), and the lower sample cap (17) and the soil sample to be tested are A second filter (15) is arranged between the soil samples (32), and the pore diameters of the first filter (14) and the second filter (15) are smaller than the diameter of the soil sample (32) to be tested; the upper test The sample cap (12) is provided with a water inlet (20) and a circulation channel (37), and the lower sample cap (17) is provided with a water inlet (21) and a circulation channel (38), so The opposite end surfaces of the upper sample cap (12) and the lower sample cap (17) are respectively provided with nozzle hole one (13) and nozzle hole two (16); the nozzle hole one (13) passes through the circulation channel (37) is connected to the water inlet one (20). The water inlet one (20) is connected to the water supply tank (24) through the external water supply pipe (22). The water supply tank (24) is provided with a liquid outlet at the bottom. Two (26), there is an exhaust port two (27) on the top; the second nozzle (16) is connected to the second water inlet (21) through the second circulation channel (38), and the second water inlet (21) The external sewer pipe (23) is connected to the sewer tank (25). A flow valve (36), a water pump (30) and a flow rate are arranged between the sewer pipe (23) and the sewer tank (25). The meter (35) is provided with three liquid inlets (28) at the bottom of the lower water tank (25), and three exhaust ports (29) are provided at the top of the lower water tank (25). The three exhaust ports are (29) External air pump (31); the upper sample cap (12) is provided with a sample cover (33), and the upper beam (2) and the upper sample cap (12) There is a pressure sensor (34) between them. The bottom of the upper beam (2) is fixed with a pad (3) and a top bead (4) in sequence from top to bottom. The pressure sensor (34) is connected to the top bead (4). 4) Centering contact, the pressure sensor (34) penetrates the pressure chamber top cover (7) and the sample cover (33) and contacts the upper sample cap (12); the upper beam (2) A displacement sensor (5) is provided between the pressure sensor (34) and the displacement sensor (5). One end of the displacement sensor (5) is fixed on the upper beam (2), and the other end is connected to the pressure sensor (34). The sensor (34) is fixedly connected; the three-axis pressure chamber is airtight as a whole. 2. The method of use of a triaxial device suitable for testing the mechanical properties of soil under the action of water circulation penetration as claimed in claim 1, characterized in that: the method of use is carried out according to the following steps: S1: In the triaxial pressure chamber, there are two filter screens (15), a lower sample cap (17), a soil sample to be tested wrapped in a rubber film (32), and a filter screen one ( 14) and the upper sample cap (12), and ensure that the nozzle hole one (13) of the upper sample cap (12) is opposite to the nozzle hole two (16) of the lower sample cap (17), and pass The rubber membrane seals the upper sample membrane and the lower sample membrane as a whole, and the tendons are tied; then the entire triaxial device is installed to ensure that the triaxial pressure chamber is airtight as a whole, and is leveled with a level (1); S2: Open the exhaust port three (29) of the lower water tank (25), fill the lower water tank (25) with water through the third liquid inlet (28), and then close the third liquid inlet (28); close Open the second liquid outlet (26) of the upper water tank (24) and open the second exhaust outlet (27); S3: Turn on the water pump (30), adjust the flow valve (36) to control the water flow to the required experimental parameter value, and the water flows from the lower part of the soil sample (32) to be tested through the lower sample cap (17) to the upper part of the soil sample and enters the upper part. in the water tank (24); after the water in the lower water tank (25) is exhausted, turn off the water pump (30), open the air pump (31), and the water flows out from the upper water tank (24) through the upper sample cap (12) and The lower sample cap (17) flows into the lower water tank (25) until the water level in the lower water tank (25) no longer increases, which completes one water cycle of the soil sample (32) to be tested; S4: Repeat the operation of step S3 n times to complete n+1 cycles, then close all valves in the triaxial pressure chamber to ensure that the whole is airtight, then open the liquid inlet one (18), and press the pressure to the triaxial pressure chamber. Pour water into the room to the confining pressure required by the experiment, and then set the strain rate of the base (10) through the bottom controller (11). The base (10) will move upward and apply a vertical load to the soil sample. When the pressure sensor ( 34) When the monitored force meets the requirements, manually pause; finally, under the action of confining pressure and vertical force, shear strain is generated, the computer draws the Mohr circle, and the cohesion and friction angle of the soil after water circulation are measured, and we get The strength of the soil; That is: ① Use the computer to change different confining pressures, measure the axial stress σ ₁ and axial strain ε of the unit body under the spatial stress state, and then the elastic modulus E can be obtained. The formula is as follows: σ ₁ =Eε Obtain curve fitting of the elastic modulus under different confining pressures, and obtain the axial elastic modulus of the soil; ② Under drainage conditions, the volume strain of the soil can be judged through the amount of drainage, thereby determining whether the soil is expanding or shrinking; ③ Based on the measured stresses σ ₁ , σ ₂ , and σ ₃ in the three directions of the unit body, a Mohr stress circle is drawn based on these three stresses. The radius of the circle is the difference between the maximum stress and the minimum stress among the three stresses. Half; the maximum shear stress τ _max can be obtained. According to the Mohr stress circle drawn according to different confining pressures, draw the tangent line on the circle. The slope of the tangent line is the friction angle φ. The value that intersects with the shear stress coordinate axis is the cohesion force. C; τ _max =C+σtanφ.