Testing device for rapidly determining hydraulic characteristics of unsaturated soil

Abstract

The utility model relates to the technical field of geotechnical engineering, in particular to a testing device for rapidly measuring hydraulic characteristics of unsaturated soil, which comprises an air compressor, the air compressor is connected with a pressure chamber system through an air delivery pipe, the pressure chamber system comprises a sample chamber, the top of the sample chamber is in lap joint with a cover plate, and the bottom of the sample chamber is in lap joint with a base. A communicating pipe is arranged on the side wall of the sample chamber, a measuring tube is arranged on the other side of the sample chamber, the cover plate is connected with the base after being matched with a nut through a screw rod, the gas conveying pipe is connected with a gas inlet hole in the cover plate, and a water outlet hole in the base is connected with a data acquisition system through a water drainage pipe. The beneficial effects of the utility model are that: 1, the data acquisition system can monitor the data change in each time period in the measurement process in real time, and the test precision is improved; 2, the test device can be used for simultaneously measuring the soil-water characteristic curve and the unsaturated permeability coefficient of the soil sample, and the problem that the soil-water characteristic curve and the unsaturated permeability coefficient of the soil sample cannot be simultaneously measured is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of geotechnical engineering, and particularly relates to a test device for quickly measuring the hydraulic characteristics of unsaturated soil. Background Technique

[0002] Unsaturated soil is a heterogeneous porous medium composed of solid, liquid and gas phases, and is commonly found in landfills, earth-rock dams, soil slopes and subgrade fills. Some common engineering problems, such as slope instability, foundation swelling, dam breach, etc., are all closely related to the hydraulic characteristics of unsaturated soil. Therefore, the change of the hydraulic characteristics of unsaturated soil has always been the focus of people's attention. Specifically, the hydraulic characteristics of unsaturated soil include the soil-water characteristic curve and the permeability function. Among them, the soil-water characteristic curve describes the relationship between the matric suction and the degree of saturation, and reflects the water-holding capacity of the soil mass. The permeability function describes the relationship between the unsaturated permeability coefficient and the water content, and reveals the permeability performance of the soil mass.

[0003] There are many methods for measuring the soil-water characteristic curve or the unsaturated permeability coefficient, which can generally be divided into direct test methods and indirect prediction methods. The results obtained by the direct test method are highly accurate, but generally take a long time and are costly; the indirect prediction method relatively reduces the test time, but its basis is generally an empirical formula, and the accuracy of the prediction results is greatly reduced. Most of the current test devices only measure one of the soil-water characteristic curve and the unsaturated permeability coefficient. In order to save the test time, there is an urgent need for a test device that can simultaneously measure the soil-water characteristic curve and the unsaturated permeability coefficient.

[0004] Currently, the commonly used test method for obtaining the soil-water characteristic curve in China is the pressure plate apparatus. This method uses a high-air-entry ceramic plate to separate the pore water pressure and pore air pressure in the soil sample, and the control of the matric suction can be achieved by adjusting the air pressure. After applying a certain air pressure, by observing and recording the change of the liquid level of the drainage pipe connected to the lower part of the ceramic plate, it can be determined whether the moisture in the specimen reaches the equilibrium state at this level of suction.

[0005] The existing pressure plate apparatus has the following disadvantages: the air pressure is adjusted by using a pressure gauge, and the control accuracy is not high; during the test process, the liquid level readings in the drainage pipe need to be recorded multiple times, which is prone to human error; it is only suitable for measuring the soil-water characteristic curve and cannot measure the unsaturated permeability coefficient. Summary of the Invention

[0006] In view of the above-mentioned disadvantages in the prior art, the present utility model provides a test device for quickly measuring the hydraulic characteristics of unsaturated soil, and its technical solution is as follows: It includes an air compressor, which is connected to a pressure chamber system through an air delivery pipe. The pressure chamber system includes a specimen chamber. The top of the specimen chamber is lapped with a cover plate, and the bottom is lapped with a base. A connecting pipe is provided on the side wall of the specimen chamber, and a measuring tube is provided on the other side. The cover plate and the base are connected by a screw rod and a nut in cooperation. The air delivery pipe is connected to the air inlet hole on the cover plate, and the water outlet hole of the base is connected to a data acquisition system through a drain pipe.

[0007] In a preferred embodiment, the data acquisition system includes an electronic balance, a water collecting bottle, and a PC. The drain pipe is connected to the top water inlet hole of the water collecting bottle. The water collecting bottle is placed on the electronic balance, and the electronic balance is electrically connected to the PC.

[0008] In a preferred embodiment, the base is snap-connected to a clay plate.

[0009] In a preferred embodiment, a pressure controller is provided on the air delivery pipe, and the pressure controller is controlled by the data acquisition system.

[0010] In a preferred embodiment, one end of the connecting pipe is connected to the upper part of the specimen chamber, and the other end is connected to the lower part of the specimen chamber.

[0011] In a preferred embodiment, the measuring tube is connected to the lower part of the specimen chamber, and the surface of the measuring tube is provided with uniform scales.

[0012] The beneficial effects of the present utility model are as follows:

[0013] 1. The data acquisition system can monitor the data changes in each time period during the measurement process in real time, improving the test accuracy.

[0014] 2. This test device can simultaneously measure the soil-water characteristic curve and the unsaturated permeability coefficient of the soil sample, solving the problem that the soil-water characteristic curve and the unsaturated permeability coefficient of the soil sample cannot be measured simultaneously. Description of the Drawings

[0015] Figure 1 It is a schematic diagram of the overall structure of the present utility model.

[0016] Figure 2 It is a schematic diagram of the structure of the pressure chamber system in the present utility model.

[0017] In the figure: 1. Specimen chamber; 2. Clay plate; 3. Connecting pipe; 4. Measuring tube; 5. Cover plate; 6. Base; 7. Screw rod; 8. Nut; 9. Drain pipe; 10. Electronic balance; 11. Water collecting bottle; 12. PC; 13. Pressure controller; 14. Air delivery pipe; 15. Air compressor. Detailed Embodiments

[0018] The present utility model will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Embodiment 1

[0020] As Figure 1-2 shown, a test device for quickly measuring the hydraulic properties of unsaturated soil includes an air compressor 15. The air compressor 15 is connected to a pressure chamber system through an air delivery pipe 14. The pressure chamber system includes a specimen chamber 1. The top of the specimen chamber 1 is lapped with a cover plate 5, and the bottom is lapped with a base 6. A connecting pipe 3 is provided on the side wall of the specimen chamber 1, and a measuring tube 4 is provided on the other side. The cover plate 5 and the base 6 are connected by matching a screw rod 7 with a nut 8. The air delivery pipe 14 is connected to an air inlet hole on the cover plate 5. The water outlet hole of the base 6 is connected to a data acquisition system through a drain pipe 9.

[0021] The data acquisition system includes an electronic balance 10, a water collecting bottle 11, and a PC 12. The drain pipe 9 is connected to the top water inlet hole of the water collecting bottle 11. The water collecting bottle 11 is placed on the electronic balance 10. The electronic balance 10 is electrically connected to the PC 12. The precision of the electronic balance is higher than or equal to 0.001 g.

[0022] The base 6 is snap-connected to a clay plate 2. The clay plate 2 can be quickly disassembled and assembled by snap connection, which is convenient for maintaining the clay plate 2. The sample to be tested is placed on the clay plate 2.

[0023] A pressure controller 13 is provided on the air delivery pipe 14. The pressure controller 13 is controlled by the data acquisition system. The pressure of the device can be directly controlled through the PC 12, which is convenient for operation.

[0024] One end of the connecting pipe 3 is connected to the upper part of the specimen chamber 1, and the other end is connected to the lower part of the specimen chamber 1 to keep the internal air pressure of the specimen chamber 1 balanced.

[0025] The measuring tube 4 is connected to the lower part of the specimen chamber 1, and the surface of the measuring tube 4 is provided with uniform scales for recording the water level change in the specimen chamber 1.

[0026] Using the above device, its usage method is as follows:

[0027] Before the test, first check the connection of each pipeline, saturate the clay plate 2 and the specimen to be tested, place the saturated specimen on the clay plate 2, and tighten the nut 8 to seal the specimen chamber 1.

[0028] During the test, an appropriate amount of degassed water is injected into the vector tube 4 to maintain the specimen at a stable water head height. The air compressor 15 is turned on, and the first-stage air pressure is applied using the pressure controller 13. The gas is transmitted through the gas pipeline 14 to the pressure chamber system. The specimen undergoes a seepage process under the combined action of water pressure and air pressure. The water passes through the clay plate 2 and flows into the water collection bottle 11 through the drain pipe 9. The high-precision electronic balance 10 can display the mass change of the water collection bottle in real time and transmit its value to the PC 12. The readings of the burette 4 and the electronic balance 10 are taken at regular intervals. When the water outflow and inflow are equal, while keeping the initial water pressure the same, the second-stage air pressure is applied. Repeat the above process. When the applied air pressure reaches a certain value, the water outflow and inflow are always equal, that is, the specimen no longer drains. At this time, the air compressor 15 is turned off, and the specimen is taken out of the specimen chamber 1, and the mass and water content of the specimen are recorded.

[0029] Based on the mass and water content of the specimen to be tested after the test and the water outflow at the equilibrium state under each stage of air pressure, a series of matrix suction and water content characteristic points can be obtained, and the soil-water characteristic curve is plotted from these points. Using Darcy's law \(K\) s =QL s / A s tH s , where \(K\) s is the unsaturated hydraulic conductivity, with the unit of cm / s; \(L\) s is the height of the specimen, with the unit of cm; \(A\) s is the seepage area of the specimen to be tested, with the unit of cm 2 ; \(t\) is the time required from the start of pressurization to stable seepage, with the unit of s; \(Q\) is the water seepage volume of the specimen to be tested within time \(t\), with the unit of cm 3 ; \(H\) s is the water head difference between the top and bottom of the specimen, with the unit of cm; the unsaturated hydraulic conductivity of the specimen to be tested under each stage of matrix suction can be calculated.

Claims

1. A test device for rapidly measuring the hydraulic properties of unsaturated soil, comprising an air compressor (15), the air compressor (15) being connected to a pressure chamber system via an air pipe (14), characterized in that: The pressure chamber system comprises a sample chamber (1), the top of the sample chamber (1) is overlapped with a cover plate (5), and the bottom is overlapped with a base (6). A connecting pipe (3) is provided on the side wall of the sample chamber (1), and a measuring tube (4) is provided on the other side. The cover plate (5) and the base (6) are connected by means of a screw (7) and a nut (8). The air supply pipe (14) is connected to the air inlet on the cover plate (5), and the water outlet of the base (6) is connected to the data acquisition system via a drain pipe (9).

2. A test device for rapidly determining the hydraulic properties of unsaturated soil according to claim 1, characterized in that: The data acquisition system comprises an electronic balance (10), a water collection bottle (11) and a PC (12); the drainage pipe (9) is connected to the water inlet hole at the top of the water collection bottle (11); the water collection bottle (11) is placed on the electronic balance (10); and the electronic balance (10) is electrically connected to the PC (12).

3. A test device for rapidly determining the hydraulic properties of unsaturated soil according to claim 1, characterized in that: The base (6) is snap-connected to the clay plate (2).

4. A test device for rapidly determining the hydraulic properties of unsaturated soil according to claim 1, characterized in that: The gas delivery pipe (14) is provided with a pressure controller (13), and the pressure controller (13) is controlled by a data acquisition system.

5. A test device for rapidly determining the hydraulic properties of unsaturated soil according to claim 1, characterized in that: One end of the connecting tube (3) is connected to the upper part of the sample chamber (1), and the other end is connected to the lower part of the sample chamber (1).

6. A test device for rapidly determining the hydraulic properties of unsaturated soil according to claim 1, characterized in that: The measuring tube (4) is connected to the lower part of the sample chamber (1), and the surface of the measuring tube (4) is provided with uniform scales.

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