Non-saturated soil test device of stress-moisture-freezing coupling

Abstract

The present application relates to stress-dry-wet-freeze coupling effect of unsaturated soil testing device, including pressure chamber, the bottom is equipped with in pressure chamber, the bottom is equipped with vertical loading mechanism above to realize to the sample load, still include for placing in the sample cap of sample top surface, the sample cap and the bottom are used for the surface for the experiment is equipped with liquid tank to cover with semi-permeable membrane, the liquid tank of sample cap and the bottom is connected in dry-wet circulation system to realize the dry-wet circulation of sample, the internal space of pressure chamber is connected in freeze-thaw circulation system to realize the freeze-thaw circulation of sample, the present application realizes the test under stress-dry-wet-freeze coupling effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of indoor geotechnical test, in particular to a non-saturated soil test device for stress-dry-wet-freeze coupling. BACKGROUND

[0002] The statements herein are provided only to enhance understanding of the present application and are not necessarily intended to constitute the prior art.

[0003] Non-saturated soil widely exists in nature, especially in arid and semi-arid areas, the internal pores of which are filled with water and air, and the non-saturated soil is extremely sensitive to temperature and moisture in the environment. The periodic changes of temperature and moisture with the seasons make the non-saturated soil experience periodic dry-wet and freeze-thaw actions, which correspondingly affect the mechanical properties of the non-saturated soil and endanger the long-term safety and stability of engineering structures. However, at present, there are few reports on the research on the deformation, water retention and strength of expansive soil under stress-dry-wet-freeze coupling conditions considering the periodic changes of climate and the actual stress state of soil.

[0004] At present, the laboratory soil true triaxial test system is mainly used for measuring the deformation, strength and other indicators of non-saturated soil under different stress paths. In order to study the influence of temperature, humidity and stress, on the one hand, the non-saturated soil true triaxial test system is upgraded by adding a temperature control box, so that it has the function of measuring the mechanical properties of the sample under stress-freeze coupling, but the influence of dry-wet on the mechanical properties is not considered. On the other hand, most non-saturated soil true triaxial tests consider the influence of stress-dry-wet-freeze multi-factors, and pre-dry-wet and freeze-thaw tests are carried out, and then the true triaxial mechanical property test of the sample is carried out. Obviously, this path cannot truly realize the coupling of stress-dry-wet-freeze, and the measurement results still have a gap with the actual stress state of the soil sample. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a non-saturated soil test device for stress-dry-wet-freeze coupling, which realizes the measurement of the strength and other indicator parameters of non-saturated soil under stress-dry-wet-freeze coupling.

[0006] In order to achieve the above purpose, the present application is realized by the following technical scheme:

[0007] The embodiment of the present application provides a non-saturated soil test device for stress-dry-wet-freeze coupling, which comprises a pressure chamber, a base is arranged in the pressure chamber, a vertical loading mechanism is arranged above the base to apply load to the sample, a sample cap is arranged on the top surface of the sample, the sample cap and the base are provided with a liquid tank on the surface facing the test, and are covered with a semi-permeable membrane, the liquid tank of the sample cap and the base is connected to a dry-wet circulation system to realize the dry-wet circulation of the sample, and the internal space of the pressure chamber is connected to a freeze-thaw circulation system to realize the freeze-thaw circulation of the sample.

[0008] Optionally, the dry-wet cycle system comprises a liquid storage tank, the liquid storage tank is placed on the weighing element and supported by the weighing element, the liquid storage tank and the liquid tank of the sample cap are connected to the first circulation pipeline, and the first circulation pipeline is provided with a driving pump to drive the liquid stored in the liquid storage tank to flow.

[0009] Optionally, the freeze-thaw cycle system comprises a hydraulic oil source, the hydraulic oil source and the internal space of the pressure chamber are connected to the second circulation pipeline, and the second circulation pipeline is provided with a switch valve and a heat exchange element.

[0010] Optionally, the hydraulic oil source is provided with a pressure regulating valve to regulate the liquid pressure output.

[0011] Optionally, the sample cap and the base are provided with a screen between the surface of the sample and the semi-permeable membrane.

[0012] Optionally, the pressure chamber is provided with a pressure detection element to detect the pressure of the liquid in the pressure chamber.

[0013] Optionally, the top of the pressure chamber is further provided with an exhaust pipe, and an exhaust valve is installed on the exhaust pipe.

[0014] Optionally, the top wall of the pressure chamber is provided with a vertical loading mechanism to apply a vertical load to the sample, and the two opposite side walls of the pressure chamber are provided with a horizontal loading mechanism to apply a horizontal load to the sample.

[0015] Optionally, the top surface of the base is provided with a first protrusion, the loading part of the vertical loading mechanism is provided with a first groove matched with the first protrusion, the first protrusion is embedded in the first groove, the bottom surface of the base is provided with a second protrusion coaxial with the first protrusion, the second protrusion is embedded in the second groove of the support frame, the base is fixed with the support frame, and the support frame is fixed in the pressure chamber to support the base.

[0016] Optionally, a plurality of liquid tanks are arranged on the base and the sample cap, the liquid tanks adopt a spiral shape, and the plurality of liquid tanks are arranged concentrically.

[0017] The beneficial effects of the present application are as follows:

[0018] 1. The test device of the present application has a vertical loading mechanism, which can apply load to the test sample to apply stress to the test sample, and the base and the test sample cap are provided with a liquid tank, which is connected to a dry-wet cycle system, the dry-wet cycle system can use a semi-permeable membrane to exchange water between the circulating liquid and the test sample, realize water absorption or drainage of the test sample, realize dry-wet cycle, and the pressure chamber and the freeze-thaw cycle system can freeze-thaw cycle the test sample, thereby realizing the test of the test sample under the stress-dry-wet-freeze-thaw coupling effect, measuring the strength index parameters of the unsaturated soil sample under the stress-dry-wet-freeze-thaw complex path, and solving the problem that the existing test instrument cannot realize the stress test of unsaturated soil under the stress-dry-wet-freeze-thaw coupling complex loading condition, which is more in line with the actual stress state of the soil body.

[0019] 2. The test device of the present application, two side chamber walls of the pressure chamber are provided with a transverse loading mechanism, so that the whole test can be carried out as uniaxial test or triaxial test, and the applicability of the whole test device is improved.

[0020] 3. The test device of the present application, the liquid storage tank in the dry-wet cycle system is placed on a weighing element, and the reading of the weighing element can determine whether the dry-wet cycle liquid reaches the suction balance with the test sample, which is convenient to use. BRIEF DESCRIPTION OF DRAWINGS

[0021] The drawings accompanying the specification of this application form a part thereof, serve to provide further understanding of the application, and together with the description of the exemplary embodiments of the application, explain the application, and do not constitute an improper limitation of the application.

[0022] Fig. 1 is a schematic diagram of the whole structure of embodiment 1 of the present application;

[0023] Fig. 2 is a schematic diagram of the dry-wet cycle system of embodiment 1 of the present application;

[0024] Among them, 1. pressure chamber, 2. bottom cavity wall, 3. base, 4. vertical loading mechanism, 5. test sample cap, 6. liquid tank, 7. screen, 8. semi-permeable membrane, 9. liquid storage tank, 10. first circulation pipeline, 11. drive pump, 12. electronic scale, 13. high molecular solution, 14. hydraulic oil source, 15. second circulation pipeline, 16. pressure regulating valve, 17. pipeline heat exchanger, 18. temperature sensor, 19. temperature digital display module, 20. first on-off valve, 21. second on-off valve, 22. control system, 23. pressure sensor, 24. hydraulic digital display module, 25. transverse loading mechanism, 26. exhaust valve, 27. test sample, 28. rubber membrane, 29. displacement digital display module, 30. pressure digital display module. DETAILED DESCRIPTION

[0025] For the convenience of description, if the words of "upper" and "lower" appear in the present application, they only mean the same direction as the upper and lower directions of the drawing itself, and do not limit the structure, but only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0026] Embodiment 1

[0027] The present embodiment provides a non-saturated soil test device for stress-moisture-freezing coupling, as shown in the figure, comprising a pressure chamber 1, the pressure chamber 1 adopts a cavity structure, and has an internal cavity for placing a non-saturated soil sample, and one side of the cavity wall of the pressure chamber 1 is detachable, which facilitates the placement of the sample into the interior of the pressure chamber. Figs. 1-2

[0028] The upper surface of the bottom cavity wall 2 of the pressure chamber 1 is provided with a support frame, the bottom end of the support frame is fixed with the bottom cavity wall, and the top end is provided with a base 3, which is used for supporting the sample.

[0029] The vertical loading mechanism 4 is arranged vertically above the base 3, and the vertical loading mechanism 4 is used for applying vertical load to the sample.

[0030] In the present embodiment, the bottom end of the loading part of the vertical loading mechanism 4 applies load to the sample through the sample cap 5, and the sample cap is used for placing on the top surface of the sample.

[0031] In order to center the installation positions of the base 3 and the sample cap 5, the top end of the sample cap 5 is provided with a first protrusion, and correspondingly, the bottom end of the loading part of the vertical loading mechanism 4 is provided with a first groove matched with the first protrusion, the first protrusion can be embedded in the first groove, and the positioning of the sample cap 5 and the loading part is realized.

[0032] The bottom surface of the base 3 is provided with a second protrusion coaxial with the first protrusion, and correspondingly, the top of the support frame is provided with a second groove matched with the second protrusion, the second protrusion is embedded in the second groove, and the positioning of the base 3 and the support frame is realized, and since the first protrusion and the second protrusion are coaxially arranged, the positions of the sample cap 5 and the base 3 can be guaranteed to be centered.

[0033] The top end of the sample cap 5 is used for cooperating with the loading part of the vertical loading mechanism 4, which is used for matching the surface of the sample, i.e. the bottom surface, with the sample to be tested.

[0034] The bottom surface of the sample cap 5 is provided with a liquid groove 6, in the present embodiment, the bottom surface of the sample cap 5 is provided with two liquid grooves 6, the liquid grooves 6 are distributed along the spiral, the two liquid grooves are coaxially arranged, and the sample cap 5 is provided with a channel communicating with the liquid grooves 6.

[0035] ​The base 3 is used for being close to the surface of the sample, that is, the top surface of the base is also provided with a liquid groove 6, the liquid groove 6 is provided in the same way as the liquid groove 6 of the sample cap 5, two liquid grooves 6 are provided, the liquid grooves 6 are distributed along the spiral, the two liquid grooves 6 are concentrically arranged, and the base 3 is provided with a channel communicating with the liquid grooves 6.

[0036] The bottom surface of the sample cap 5 is covered and fixed with a screen 7, and the screen 7 is covered with a semi-permeable membrane 8 below. Correspondingly, the top surface of the base 3 is covered and fixed with a screen 7, and the screen 7 is covered with a semi-permeable membrane 8 above.

[0037] In the embodiment, the semi-permeable membrane 8 is made of water-permeable stone material.

[0038] The liquid grooves 6 of the sample cap 5 and the base 3 are connected to a dry-wet circulation system to realize dry-wet circulation of the sample.

[0039] The dry-wet circulation system comprises a liquid storage tank 9, a weighing element, a first circulation pipeline 10 and a driving pump 11.

[0040] The liquid storage tank 9 is used for containing a high molecular solution 13. Preferably, the high molecular solution is an ethylene glycol solution, which has good fluidity at low temperature, meets the environmental requirements of freeze-thaw, and the ethylene glycol cannot permeate the semi-permeable membrane. The weighing element is an electronic scale 12, and the liquid storage tank is placed on the electronic scale. The electronic scale is used for measuring the mass change of the high molecular solution. The reading of the electronic scale 12 can determine whether the liquid for dry-wet circulation reaches the suction balance with the sample, and the use is convenient.

[0041] The liquid inlet end of the first circulation pipeline 10 extends to the bottom of the liquid storage tank 9. The first circulation pipeline 10 extends to the top of the liquid storage tank 9 after passing through the liquid grooves 6 of the base 3 and the liquid grooves 6 of the sample cap 5 in turn.

[0042] The driving pump 11 is installed on the pipe section between the liquid inlet end of the first circulation pipeline 10 and the liquid groove 6 of the base 3. The driving pump 11 can drive the high molecular solution 13 to flow out of the liquid storage tank 6, pass through the liquid grooves 6 of the base 3 and the liquid grooves 6 of the sample cap 5 in turn, and then flow back to the liquid storage tank 9.

[0043] In the embodiment, the first circulation pipeline 10 communicates with the liquid grooves 6 of the sample cap 5 through the channel of the sample cap 5, and communicates with the liquid grooves 6 of the base 3 through the channel of the base 3.

[0044] The internal space of the pressure chamber 1 is connected to a freeze-thaw circulation system.

[0045] The freeze-thaw circulation system comprises a hydraulic oil source 14, a second circulation pipeline 15, a heat exchange element and a switch valve.

[0046] The hydraulic oil source 14 adopts a hydraulic station, which is provided with a pressure regulating valve 16 to regulate the output hydraulic oil pressure.

[0047] The second circulating pipeline 15 includes a first pipeline and a second pipeline, wherein the liquid inlet end of the first pipeline is connected with the output end of the hydraulic oil source 14, the liquid outlet end of the first pipeline is communicated with the internal space of the pressure chamber 1, the liquid inlet end of the second pipeline is communicated with the internal space of the pressure chamber 1, and the liquid outlet end of the second pipeline is connected with the liquid inlet end of the hydraulic oil source 14.

[0048] The heat exchange element mounted on the first pipeline adopts a pipeline heat exchanger 17, and a temperature sensor 18 is mounted downstream of the pipeline heat exchanger 17 to detect the temperature of the heat-exchanged hydraulic oil. The temperature sensor 18 is connected with the control system 22 to transmit the collected temperature information to the control system 22, and the control system 22 is connected with a temperature digital display module 19 to display the temperature.

[0049] The pipeline heat exchanger 17 can be obtained by using existing equipment, which will not be described in detail. A first on-off valve 20 is arranged on the first pipeline section between the pipeline heat exchanger 17 and the pressure chamber 1 to control the conduction and disconnection of the first pipeline. A second on-off valve 21 is mounted on the second pipeline to control the conduction and disconnection of the second pipeline.

[0050] A pressure detection element is mounted inside the pressure chamber, which adopts a pressure sensor 23 to detect the pressure of the hydraulic oil in the pressure chamber.

[0051] The pressure sensor 23 is connected with the control system 22 to transmit the detected pressure information to the control system 22, and the control system 22 is connected with a hydraulic digital display module 24 to display the detected hydraulic oil pressure information.

[0052] The pressure chamber 1 is provided with a transverse loading mechanism 25 on each of the two opposite side walls to apply a horizontal load to the sample. This makes the entire test device capable of performing uniaxial test and triaxial test, thereby improving the applicability of the entire test device.

[0053] The transverse loading mechanism 25 has the same structure as the vertical loading mechanism 4, and both adopt an existing loading hydraulic cylinder provided with an oil pressure sensor and a piston rod displacement sensor. The end of the piston rod of the transverse loading mechanism is connected with a rigid cap to apply a transverse load to the sample through the rigid cap. The oil pressure sensor is connected with the control system 22 to transmit the detected oil pressure information in the loading hydraulic cylinder to the control system and display it on a pressure digital display module 30. The piston rod displacement sensor is connected with the control system 22 to transmit the detected piston rod displacement information of the loading hydraulic cylinder to the control system and display it on a displacement digital display module 29.

[0054] The top cavity wall of the pressure chamber 1 is provided with an exhaust pipe, and an exhaust valve 26 is installed on the exhaust pipe to exhaust the gas in the pressure chamber 1, facilitating the injection of hydraulic oil into the pressure chamber of the freeze-thaw cycle system.

[0055] The working method of the test device of the embodiment is as follows:

[0056] Step 1: The surface of the base 3 provided with the liquid tank is upward, then the semi-permeable membrane 8 is laid on the upper surface of the base, the unsaturated soil sample is prepared according to the test method of the national standard “GBT50123-1999”, the rubber membrane 28 is sleeved on the side of the sample 27, then the sample 27 is placed on the base 3, and the bottom end of the rubber membrane 28 is sleeved on the outer periphery of the base 3 and is fixed and sealed. The sample cap 5 is placed on the top surface of the sample 27, and the semi-permeable membrane 8 on the bottom surface of the sample cap 5 contacts the top surface of the sample 27. The assembled base 3, sample cap 5 and sample 27 are placed into the pressure chamber 1, and the base 3 is matched with the support frame of the bottom cavity wall of the pressure chamber 1 through the second protrusion and the second groove. The loading part of the vertical loading mechanism 4 is lowered, the first groove of the loading part is matched with the first protrusion of the sample cap 5, the horizontal loading mechanism 25 is worked, the loading part of the horizontal loading mechanism 25 contacts the rubber membrane 28 on the side of the sample, the pipeline connecting the freeze-thaw cycle system and the wetting and drying cycle system is installed, and after the installation is completed, the pressure chamber 1 is closed.

[0057] Step 2: The hydraulic station and the first switch valve 20 are opened, the exhaust valve 26 at the top of the pressure chamber is opened, and the injection of hydraulic oil into the pressure chamber 1 is started, but without pressurization.

[0058] Step 3: When the air in the pressure chamber 1 is exhausted and the hydraulic oil is filled, the exhaust valve 26 is closed, the pipeline heat exchanger 17 and the second switch valve 21 are opened, the hydraulic oil reaches the initial temperature set in the test through the pipeline heat exchanger 17, and whether the hydraulic oil reaches the set initial temperature can be judged according to the temperature data collected by the temperature sensor 18.

[0059] Step 4: When the hydraulic oil reaches the set initial temperature, the driving pump 11 is opened, and the air in the first circulation pipeline 10 is exhausted.

[0060] Step 5: After the test preparation work is completed, the vertical loading mechanism 4 and the horizontal loading mechanism 25 are started through the control system, and the hydraulic station starts pressurization, and the stress loading is carried out according to the stress loading path set in the test scheme.

[0061] Step 6: During the test, the temperature of the hydraulic oil in the pressure chamber 1 is adjusted by the pipe heat exchanger 17 to control the temperature of the sample 27, and the freeze-thaw cycle is carried out. The driving pump 11 is started, the high molecular solution flows in the liquid tank 6 of the sample cap 5 and the base 3, and the high molecular solution and the sample 27 are separated by the semi-permeable membrane 8. Because of the concentration difference between the two sides of the semi-permeable membrane 8, the sample 27 and the high molecular solution exchange water, the sample absorbs or discharges water, and the dry-wet cycle is realized.

[0062] The electronic scale 12 measures the mass change of the high molecular solution, and when the reading of the electronic scale 12 is stable, the high molecular solution and the unsaturated soil sample reach the suction balance; the suction of the sample 27 can be controlled by controlling the concentration of the high molecular solution, and the suction of the sample 27 can be calculated by the reading of the electronic scale 12.

[0063] Step 7: Read the data of the displacement digital display module 29 and the pressure digital display module 30 to obtain the related physical and mechanical parameters, and the measurement is completed.

[0064] The device of the embodiment realizes the test of the sample under the stress-dry-wet-freeze-thaw coupling effect, measures the strength index and other parameters of the unsaturated soil sample under the stress-dry-wet-freeze-thaw complex path, and solves the problem that the existing test instrument cannot realize the stress-dry-wet-freeze-thaw coupling complex loading condition of the unsaturated soil stress test, which is more in line with the actual stress state of the soil body.

[0065] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A test apparatus for unsaturated soil under stress-wet-freeze-thaw coupling, characterized in that, It includes a pressure chamber, a base inside the pressure chamber, a vertical loading mechanism above the base to apply load to the sample, a sample cap for placing on the top surface of the sample, a liquid tank for the sample cap and the base facing the test surface and covered with a semi-permeable membrane, the liquid tank of the sample cap and the base is connected to a wet-dry cycle system to realize wet-dry cycle of the sample, and the internal space of the pressure chamber is connected to a freeze-thaw cycle system to realize freeze-thaw cycle of the sample. The dry-wet circulation system includes a liquid storage tank. The liquid storage tank, the base, and the liquid tank of the sample cap are all connected to the first circulation pipeline. The liquid storage tank is used to hold the polymer solution. The first circulation pipeline is connected to the liquid tank of the sample cap through the channel of the sample cap and to the liquid tank of the base through the channel of the base. The freeze-thaw cycle system includes a hydraulic oil source. The hydraulic oil source and the internal space of the pressure chamber are both connected to the second circulation pipeline. The second circulation pipeline includes a first pipe and a second pipe. The inlet end of the first pipe is connected to the output end of the hydraulic oil source, and the outlet end of the first pipe is connected to the internal space of the pressure chamber. The inlet end of the second pipe is connected to the internal space of the pressure chamber, and the outlet end of the second pipe is connected to the inlet end of the hydraulic oil source.

2. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 1, characterized in that, The liquid storage tank is placed on a weighing element for support, and the first circulation pipeline is equipped with a drive pump to drive the flow of the liquid stored in the storage tank.

3. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 1, characterized in that, The second circulation pipeline is equipped with a switching valve and heat exchange elements.

4. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 3, characterized in that, The hydraulic oil source is equipped with a pressure regulating valve to adjust the output liquid pressure.

5. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 1, characterized in that, The sample cap and base are used to place a sieve between the sample-facing surface and the semi-permeable membrane.

6. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 1, characterized in that, The pressure chamber is equipped with a pressure detection element to detect the pressure of the liquid introduced into the pressure chamber by the freeze-thaw cycle system.

7. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 1, characterized in that, The pressure chamber is also equipped with an exhaust pipe at the top, and an exhaust valve is installed on the exhaust pipe.

8. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 1, characterized in that, The top wall of the pressure chamber is equipped with a vertical loading mechanism to apply a vertical load to the sample, and the two opposite side walls of the pressure chamber are equipped with a transverse loading mechanism to apply a horizontal load to the sample.

9. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 1, characterized in that, The top surface of the base is provided with a first protrusion, and the loading part of the vertical loading mechanism is provided with a first groove that cooperates with the first protrusion. The first protrusion is embedded in the first groove. The bottom surface of the base is provided with a second protrusion that is coaxial with the first protrusion. The second protrusion is embedded in the second groove of the support frame. The base and the support frame are fixed together. The support frame is fixed inside the pressure chamber to support the base.

10. The unsaturated soil testing apparatus for stress-wet-freeze-thaw coupling as described in claim 1, characterized in that, The base and sample cap have multiple liquid tanks, which are spiral-shaped and concentrically arranged.

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