A test device and method for testing the air permeability of unsaturated soil

Abstract

The present invention discloses a test device and method for testing the air permeability of unsaturated soil, and belongs to the field of civil engineering technology. The test device includes an air pressure control sub-device, a test sub-device, a high and low temperature test box, an air flow measurement sub-device, and a sample making device; the air pressure control sub-device is connected to the test sub-device, the high and low temperature test box provides the ambient temperature for the test sub-device, the air flow measurement sub-device is respectively connected to the high and low temperature test box and the test sub-device, the air flow measurement sub-device provides airflow measurement for the test sub-device, and the sample making device makes a sample for the test sub-device. The present invention solves the problems existing in the prior art and equipment, such as inaccurate measurement of the air permeability characteristics of unsaturated soil, difficulty in measuring soil with a low permeability coefficient, unreasonable traditional method of preparing samples, and failure to consider variable temperature conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering, and in particular relates to a test device and method for testing the air permeability of unsaturated soil. Background Art

[0002] In China's arid and semi-arid regions in northwest China, such as Gansu and Inner Mongolia, many highway and airport road projects have experienced some special phenomena, namely, a moisture accumulation layer has appeared between the top of the roadbed and the semi-rigid base. The accumulation of moisture has greatly reduced the strength of the semi-rigid base and roadbed materials, resulting in subsidence, uneven deformation and other diseases, which in turn reflected on the road surface and caused road cracking, subsidence and other diseases, which has had a significant impact on road projects and brought huge social and economic losses.

[0003] Analysis of the source of accumulated moisture found that rainfall in this area is rare, but evaporation is strong, and the evaporation is much greater than rainfall. The hydrological and hydrogeological conditions are that the groundwater system is relatively developed, but the surface water system is not developed. At the same time, the semi-rigid base is a commonly used road structure in this area because of its high structural strength, good integrity, and impermeable and airtight characteristics. The semi-rigid base is like an impermeable and airtight "lid" that prevents the invasion of water above the ground. Therefore, the moisture accumulation layer between the semi-rigid base and the top of the roadbed cannot come from the water above the surface, but from the migration of underground water vapor. In the arid and semi-arid areas of the northwest, the temperature difference between day and night is large. Studies have shown that moisture will migrate upward in the form of vapor water under the action of temperature gradient, but due to the impermeability of the semi-rigid base, the water vapor that migrates upward will gather at the bottom of the semi-rigid base, causing moisture to gather between the semi-rigid base and the top of the roadbed. Among them, exploring the permeability characteristics of unsaturated soil is crucial to explaining and solving the problem of water vapor migration.

[0004] At present, the test equipment for soil permeability is mainly tested by a modified unsaturated soil triaxial instrument. First, a rubber membrane is put on the triaxial specimen, and then it is placed on the triaxial instrument to apply confining pressure. After the confining pressure is stable, air pressure is introduced into one end of the specimen. After the airflow of the triaxial specimen is stable, the water output of the water tank installed on the exhaust pipe is used to equivalently replace the volume of air flowing through the triaxial specimen, thereby characterizing the permeability of the soil. From the above, it can be seen that although the traditional device meets the requirements of testing the permeability of soil to a certain extent, it is easy to produce test errors. There is no reasonable control of the permeability of gas between the specimen and the rubber membrane, and the error caused by the evaporation of the discharged water is not considered; in addition, the measurement accuracy is poor. For soils with low permeability coefficients, such as expansive soils and clay soils, the existing test methods are difficult to meet the test requirements. In addition, considering the actual situation, the permeability of unsaturated soil is not only related to factors such as the size of air pressure, the distribution and connectivity of the pores of the soil itself, but also closely related to the ambient temperature. The temperature of the roadbed soil is affected by the atmospheric environment temperature, and the temperature is always in dynamic change. However, the current equipment for testing the permeability of unsaturated soil is mainly aimed at normal temperature conditions, and does not consider testing under variable temperature conditions. Therefore, it is very meaningful to design a soil permeability test device that can measure soil permeability under different temperature conditions. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention provides a test device and method for testing the permeability of unsaturated soil, which solves the problems existing in the prior art and equipment, such as inaccurate measurement of the permeability characteristics of unsaturated soil, difficulty in measuring soil with a low permeability coefficient, unreasonable traditional method of preparing samples, and failure to consider variable temperature conditions.

[0006] In order to achieve the above-mentioned invention object, the technical scheme adopted by the present invention is: a test device for testing the air permeability of unsaturated soil, comprising an air pressure control sub-device, a test sub-device, a high and low temperature test chamber, an air flow measurement sub-device and a sample making device;

[0007] The air pressure control sub-device is connected to the test sub-device, the high and low temperature test box provides the ambient temperature for the test sub-device, the air flow measurement sub-device is respectively connected to the high and low temperature test box and the test sub-device, the air flow measurement sub-device provides airflow measurement for the test sub-device, and the sample making device makes samples for the test sub-device.

[0008] The beneficial effects of the present invention are as follows: the present invention utilizes an air pressure control sub-device, a test sub-device, a high and low temperature test chamber, an air flow measurement sub-device and a sample preparation device to measure the permeability of a soil with a low permeability coefficient, thereby solving the problem that traditional test devices are difficult to measure soil with a low permeability coefficient, solving the problem of inaccurate measurement of the permeability characteristics of unsaturated soil at present, solving the problem of leakage of samples and rubber membranes in traditional permeability equipment, and solving the error caused by evaporation in the process of measuring gas volume using drainage, and the like. At the same time, the test sub-device of the present invention is combined with the high and low temperature test chamber to solve the problem of changes in the permeability of unsaturated soil under variable temperature conditions. The test sub-device is also equipped with a corresponding reasonable sample preparation device, thereby solving the problem that traditional triaxial sample preparation is not suitable for permeability tests of unsaturated soil.

[0009] Further, the air pressure control sub-device includes a pressurizing system, a first pressure regulating valve, a second pressure regulating valve, a drying bottle, a first U-tube pressure gauge, and a second U-tube pressure gauge;

[0010] The pressurization system is divided into two air pressure channels, wherein a first pressure regulating valve is provided on one air pressure channel, and the one air pressure channel is respectively connected to the drying bottle, the test sub-device and the first U-tube pressure gauge, and a second pressure regulating valve is provided on the other air pressure channel, and the other air pressure channel is connected to the test sub-device, and the second U-tube pressure gauge is connected to the test sub-device.

[0011] The beneficial effect of the above further scheme is that the present invention takes the dryness of the input gas into consideration and first dries the input gas using a drying bottle, which can reduce the influence of the input gas on the moisture content of the sample and improve the accuracy of the test data.

[0012] Further, the test sub-device includes a sample device side mold, a sample device bottom plate, screws, a water-permeable plate, a rubber ring, a rubber membrane and a sample device top plate;

[0013] The side mold of the sample device is connected to the bottom plate of the sample device and the top plate of the sample device by screws respectively; there are two water-permeable plates, which are respectively arranged at the upper and lower ends of the sample in the rubber membrane; the side mold of the sample device is an integrated mold, and the inner cavity of the side mold of the sample device is a cylinder;

[0014] Two symmetrical openings are arranged on the side of the sample device side mold, one of which is connected to another air pressure channel to input a stable confining pressure into the cavity between the sample device side mold and the rubber membrane, and the other opening is connected to the second U-tube pressure gauge to observe the confining pressure of the test device. The top and bottom of the sample device side mold, the inner side of the screw hole of the sample device bottom plate and the inner side of the screw hole of the sample device top plate are all provided with annular shallow grooves for placing the rubber rings, and the positions of the annular shallow grooves on the top and bottom of the sample device side mold correspond to the positions of the annular shallow grooves on the sample device bottom plate and the sample device top plate respectively;

[0015] The structure of the sample device bottom plate and the sample device top plate are the same, and the sample device bottom plate and the sample device top plate are respectively installed at the bottom position and the top position of the sample device side mold in a one-to-one correspondence. The sample device bottom plate and the sample device top plate are each provided with two screw holes, and the sample device bottom plate and the sample device top plate are both provided with openings. The opening on the sample device bottom plate is connected to the drying bottle, and the opening on the sample device top plate is connected to the air flow meter device.

[0016] The beneficial effect of the above further scheme is that, in order to reduce the test error caused by the input gas passing through the gap between the rubber membrane and the sample, the present invention adopts measures such as setting a confining pressure outside the rubber membrane, applying vaseline on the inner wall of the rubber membrane, and fixing the sample and the rubber membrane with a rubber ring. Taking into account the actual situation of the roadbed soil, the high and low temperature test chamber can be used to measure the permeability of unsaturated soil under different temperature conditions.

[0017] Further, the air flow measuring device includes a first air flow measuring device and a second air flow measuring device;

[0018] The first gas flow measuring device is used to measure a gas flow rate less than 1 mL / min, and the first gas flow measuring device includes a gas chamber, a first valve and a second valve;

[0019] The air inlet pipe of the first air flow quantum device is divided into two air flow channels, one of which is connected to the second valve, and the other is connected to the air chamber and the first valve; and the air inlet pipe of the first air flow quantum device is connected to the opening on the top plate of the sample device;

[0020] The second gas flow measuring device is used to measure a gas flow greater than 1 mL / min, and the second gas flow measuring device is connected to an opening on the top plate of the sample device.

[0021] The beneficial effect of the above further scheme is: the present invention takes into account different air flow sizes and adopts different measurement methods. When the soil seepage flow rate is greater than 1mL / min, a soap film flowmeter is used for measurement; when the soil seepage flow rate is less than 1mL / min, a homemade air chamber is used for measurement, which can measure smaller gas flow rates, and the experimental device is simple, the cost is low, and the actual use effect is good.

[0022] Furthermore, the sample making device comprises a sample making device top plate, a sample making device bottom plate, a sample making device column, a sample making mold and a jack;

[0023] The sample preparation device top plate, sample preparation device bottom plate and sample preparation device columns constitute the frame of the sample preparation device, the jack is installed in the middle of the sample preparation device bottom plate, and the sample preparation mold is located above the jack and below the sample preparation device top plate;

[0024] The sample making mold comprises a sample making mold outer mold, a sample making mold inner film, an outer mold fixing screw, a sample making mold top plate and a sample making mold bottom plate;

[0025] The outer mold of the sample making mold can be divided into two halves, and the size of the recess of the outer mold of the sample making mold is the same as the size of the inner membrane of the sample making mold so as to wrap the inner membrane of the sample making mold. The upper and lower ends of the outer side edge of the outer mold of the sample making mold are provided with threads, and the outer mold fixing screws fix the two halves of the outer mold of the sample making mold with screws.

[0026] The inner membrane of the sample preparation mold includes an upper section, a middle section and a lower section, each of which can be divided into two lobes; the upper and lower sections have the same size, and the inner cavity size is 39.1mm in diameter × 65mm in height, and the inner cavity diameter of the middle section is 39.1mm × 80mm in height;

[0027] The top plate of the sample making mold has the same size as the bottom plate of the sample making mold. The top plate of the sample making mold and the bottom plate of the sample making mold are both formed by splicing two upper and lower cylinders. The diameter of the upper cylinder is the same as the inner diameter of the inner membrane of the sample making mold, and the diameter of the lower cylinder is the same as the outer diameter of the outer mold of the sample making mold.

[0028] The beneficial effects of the above further scheme are: the present invention takes into account the disadvantages of the traditional sample preparation method and adopts the static pressure method to prepare the sample; considering that the sealing of both ends of the sample during the compaction process will affect the test results of the unsaturated soil permeability, the cutting method is adopted to cut off the two ends of the soil sample to prepare the standard sample.

[0029] The present invention provides a test method for testing the air permeability of an unsaturated soil, and the test method for testing the air permeability of an unsaturated soil comprises the following steps:

[0030] S1. Check the test device for testing the air permeability of unsaturated soil;

[0031] S2. Prepare the sample by static pressure, and cut the two ends of the prepared sample by cutting during the compaction process, install the cut sample in the test sub-device, and complete the installation of the test sub-device;

[0032] S3. Place the installed test sub-device in a high and low temperature test chamber, connect the air pressure control sub-device, the air flow measurement sub-device and the test sub-device using an air pressure pipe, and use the air flow measurement sub-device to perform measurements to complete the test of the air permeability of the unsaturated soil.

[0033] The beneficial effects of the present invention are as follows: the present invention utilizes an air pressure control sub-device, a test sub-device, a high and low temperature test chamber, an air flow measurement sub-device and a sample preparation device to measure the permeability of a soil with a low permeability coefficient, thereby solving the problem that traditional test devices are difficult to measure soil with a low permeability coefficient, solving the problem of inaccurate measurement of the permeability characteristics of unsaturated soil at present, solving the problem of leakage of samples and rubber membranes in traditional permeability equipment, and solving the error caused by evaporation in the process of measuring gas volume using drainage, and the like. At the same time, the test sub-device of the present invention is combined with the high and low temperature test chamber to solve the problem of changes in the permeability of unsaturated soil under variable temperature conditions. The test sub-device is also equipped with a corresponding reasonable sample preparation device, thereby solving the problem that traditional triaxial sample preparation is not suitable for permeability tests of unsaturated soil.

[0034] Furthermore, the step S2 comprises the following steps:

[0035] S201, installing the inner mold of the sample making mold on the inner cavity of the outer mold of the sample making mold, and fixing the two halves of the outer mold of the sample making mold with the outer mold fixing screws;

[0036] S202, placing the bottom plate of the sample making mold under the sample making mold, filling the determined soil into the cavity of the sample making mold, and installing the top plate of the sample making mold;

[0037] S203, placing the sample making mold on a jack, applying pressure, completely compacting the top plate of the sample making mold into the cavity of the sample making mold, and statically pressing for a preset time;

[0038] S204, after compaction, take out the sample, and cut off both ends of the prepared sample by using a cutting method;

[0039] S205, applying vaseline on the inner surface of the rubber film, and wrapping the sample with the rubber film;

[0040] S206. Place a water-permeable plate at both ends of the sample, and use three rubber rings to bind the rubber membrane and the sample at the upper, middle and lower positions of the sample respectively;

[0041] S207, placing the bound sample in the cavity of the side mold of the sample device, and installing the bottom of the side mold of the sample device, the top of the side mold of the sample device, the bottom plate of the sample device, and the rubber rings of the top plate of the sample device in the annular shallow groove;

[0042] S208. Turn the excess rubber film at both ends of the rubber film wrapping the sample outward to the top edge of the side mold of the sample device, and use screws to connect the side mold of the sample device to the top plate and the bottom plate of the sample device respectively, to complete the installation of the test sub-device.

[0043] The beneficial effects of the above further scheme are: in order to reduce the test error caused by the input gas passing through the gap between the rubber membrane and the sample, the present invention adopts measures such as setting a confining pressure outside the rubber membrane, applying vaseline on the inner wall of the rubber membrane, and fixing the sample and the rubber membrane with a rubber ring. Considering the uniformity of the sample, the static pressure method is used to prepare the sample, and considering that the sealing of the two ends of the soil sample during the compaction process will affect the test results of the unsaturated soil permeability, the cutting method is used to cut off the two ends of the sample to prepare the standard sample.

[0044] Furthermore, step S3 includes the following steps:

[0045] S301, placing the test sub-device in a high and low temperature test chamber, and connecting the air pressure control sub-device, the air flow measurement sub-device and the test sub-device using an air pressure pipeline;

[0046] S302: Use the first air flow measuring device or the second air flow measuring device to perform measurement to complete the test of air permeability of unsaturated soil.

[0047] The beneficial effect of the above further solution is: using two air flow measurement devices solves the problem that traditional test devices are difficult to measure soil with a low permeability coefficient, and solves the problem of inaccurate measurement of the permeability characteristics of unsaturated soil.

[0048] Furthermore, the measurement using the first air flow measuring device in step S302 includes the following steps:

[0049] A1. Preset the temperature of the high and low temperature test chamber. After the sample temperature stabilizes, read the initial readings of the liquid levels of the first U-tube pressure gauge and the second U-tube pressure gauge;

[0050] A2. Squeeze out all the gas in the air chamber, close the first valve, and open the second valve;

[0051] A3. Open the pressurization system, set the confining pressure of the sample sub-device through the second pressure regulating valve, and observe the pressure changes before and after the liquid surface of the second U-tube pressure gauge, and make the confining pressure 10kPa to 20kPa greater than the preset pressure value of the test;

[0052] A4. Open the pressurization system, set the air pressure of the sample sub-device through the first pressure regulating valve, observe the pressure changes before and after the liquid surface of the first U-tube pressure gauge, and adjust the air pressure value input to the sample sub-device to the preset pressure value of the test;

[0053] A5. When the liquid level of the first U-tube pressure gauge stabilizes, open the second valve and close the first valve to allow gas to enter the gas chamber;

[0054] A6. Record the volume change of the air chamber to obtain the air permeability coefficient of the soil, and obtain the air permeability of the unsaturated soil according to the air permeability coefficient of the soil;

[0055] The step S302 uses the second air flow measuring device to measure, including the following steps:

[0056] B1. Preset the temperature of the high and low temperature test chamber. After the sample temperature stabilizes, read the initial readings of the liquid levels of the first U-tube pressure gauge and the second U-tube pressure gauge;

[0057] B2. Open the pressurization system, adjust the confining pressure of the sample sub-device through the second pressure regulating valve, and observe the pressure changes before and after the liquid surface of the second U-tube pressure gauge to make the confining pressure greater than the preset pressure value of the test by 10kPa to 20kPa;

[0058] B3. Open the first pressure regulating valve, observe the pressure changes before and after the liquid level of the first U-tube pressure gauge, and adjust the air pressure entering the test sub-device to the preset pressure value of the test;

[0059] B4. When the liquid level of the first U-tube pressure gauge changes steadily, the soap film flowmeter is turned on to obtain the air permeability coefficient of the soil, and the air permeability of the unsaturated soil is obtained based on the air permeability coefficient of the soil.

[0060] The beneficial effects of the above further scheme are: the test sub-device combined with the high and low temperature test chamber solves the problem of the change of the permeability of unsaturated soil under variable temperature conditions, and the change of the pressure value before and after the U-tube pressure gauge is used to observe the size of the air pressure value, and the air pressure measurement is accurate and low cost. The use of two air flow measurement sub-devices solves the problem that the traditional test device is difficult to measure the soil with a low permeability coefficient, and solves the problem of inaccurate measurement of the permeability characteristics of unsaturated soil.

[0061] Furthermore, the first gas flow measuring device is used to measure a gas flow rate of less than 1 mL / min;

[0062] The second gas flow measuring device is used to measure a gas flow greater than 1 mL / min.

[0063] The beneficial effect of the above further scheme is: the present invention takes into account different air flow sizes and adopts different measurement methods. When the soil seepage flow rate is greater than 1mL / min, a soap film flowmeter is used for measurement; when the soil seepage flow rate is less than 1mL / min, a homemade air chamber is used for measurement, which can measure smaller gas flow rates, and the experimental device is simple, the cost is low, and the actual use effect is good. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 It is a composition diagram of the present invention.

[0065] Figure 2 This is a detailed diagram of the sample sub-device.

[0066] Figure 3 This is a detailed diagram of the sample installation.

[0067] Figure 4 This is a front view disassembled diagram of the inner membrane of the sample preparation device.

[0068] Figure 5 This is a top view of the inner membrane of the sample preparation device.

[0069] Figure 6 The figure is a flow chart of the method of the present invention.

[0070] Among them, 1-air pressure control sub-device, 101-pressurization system, 102-first pressure regulating valve, 103-second pressure regulating valve, 104-drying bottle, 105-first U-tube pressure gauge, 106-second U-tube pressure gauge, 2-test sub-device, 201-side mold of sample device, 202-bottom plate of sample device, 203-screw, 204-water-permeable plate, 205-rubber ring, 206-rubber membrane, 207-top plate of sample device, 3-high and low temperature test box, 4-air flow measurement sub-device, 401-first air Flow measuring device, 4011-air chamber, 4012-first valve, 4013-second valve, 402-second air flow measuring device, 5-sample making device, 501-sample making device top plate, 502-sample making device bottom plate, 503-sample making device column, 504-sample making mold, 5041-sample making mold outer mold, 5042-sample making mold inner film, 5043-outer mold fixing screw, 5044-sample making mold top plate, 5045-sample making mold bottom plate, 505-jack, 6-soap film flowmeter. DETAILED DESCRIPTION

[0071] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0072] like Figure 1 As shown, the present invention provides a test device for testing the air permeability of unsaturated soil, comprising an air pressure control sub-device 1, a test sub-device 2, a high and low temperature test chamber 3, an air flow measurement sub-device 4 and a sample making device 5;

[0073] The air pressure control sub-device 1 is connected to the test sub-device 2, the high and low temperature test box 3 provides the ambient temperature for the test sub-device 2, the air flow measurement sub-device 4 is respectively connected to the high and low temperature test box 3 and the test sub-device 2, the air flow measurement sub-device 4 provides airflow measurement for the test sub-device 2, and the sample making device 5 makes samples for the test sub-device 2.

[0074] The air pressure control sub-device 1 includes a pressurizing system 101, a first pressure regulating valve 102, a second pressure regulating valve 103, a drying bottle 104, a first U-tube pressure gauge 105 and a second U-tube pressure gauge 106;

[0075] The pressurizing system 101 is divided into two air pressure channels, wherein a first pressure regulating valve 102 is provided on one air pressure channel, and the one air pressure channel is respectively connected to the drying bottle 104, the test sub-device 2 and the first U-tube pressure gauge 105, and a second pressure regulating valve 103 is provided on the other air pressure channel, and the other air pressure channel is connected to the test sub-device 2, and the second U-tube pressure gauge 106 is connected to the test sub-device 2.

[0076] like Figure 2 As shown, the test sub-device 2 includes a sample device side mold 201, a sample device bottom plate 202, screws 203, a water-permeable plate 204, a rubber ring 205, a rubber membrane 206 and a sample device top plate 207;

[0077] The sample device side mold 201 is connected to the sample device bottom plate 202 and the sample device top plate 207 respectively through screws 203; there are two water-permeable plates 204, which are respectively arranged at the upper and lower ends of the sample in the rubber membrane 206; the sample device side mold 201 is an integrated mold, and the inner cavity of the sample device side mold 201 is a cylinder;

[0078] Two symmetrical openings are arranged on the side of the sample device side mold 201, one of which is connected to another air pressure channel to input a stable confining pressure into the cavity between the sample device side mold 201 and the rubber membrane 206, and the other opening is connected to the second U-tube pressure gauge 106 to observe the size of the confining pressure of the test device. The top and bottom of the sample device side mold 201, the inner side of the screw 203 hole of the sample device bottom plate 202 and the inner side of the screw 203 hole of the sample device top plate 207 are all provided with annular shallow grooves for placing the rubber ring 205. The positions of the annular shallow grooves on the top and bottom of the sample device side mold 201 correspond to the positions of the annular shallow grooves on the sample device bottom plate 202 and the sample device top plate 207 respectively.

[0079] The sample device bottom plate 202 and the sample device top plate 207 have the same structure, and the sample device bottom plate 202 and the sample device top plate 207 are respectively installed at the bottom position and the top position of the sample device side mold 201 in a one-to-one correspondence. Two screw 203 holes are provided on the sample device bottom plate 202 and the sample device top plate 207. There are openings on the sample device bottom plate 202 and the sample device top plate 207. The openings on the sample device bottom plate 202 are connected to the drying bottle 104, and the openings on the sample device top plate 207 are connected to the air flow meter device 4.

[0080] In this embodiment, the sample device side mold 201 is an integrated mold, and the inner cavity of the sample device side mold 201 is a cylinder with a size of 40mm in diameter and 100mm in height. Two symmetrical openings are arranged on the side of the sample device side mold 201, one opening is connected to the other air pressure channel mentioned above, and a stable confining pressure is input into the cavity between the sample device side mold 201 and the rubber membrane 206, and the other opening is connected to the second U-tube pressure gauge 106 to observe the size of the confining pressure of the test device 2; the top and bottom of the sample device side mold 201, the sample device bottom plate 202 or the sample device top plate 207 are provided with an annular shallow groove for the rubber ring 205, which is convenient for placing the rubber ring 205, and the top and bottom of the sample device side mold 201 correspond to the positions of the annular shallow grooves of the sample device top plate 207 or the sample device bottom plate 202, respectively. The annular shallow grooves are arranged at the top and bottom of the sample device side mold 201 and the inner sides of the screw holes 203 of the sample device bottom plate 202 and the sample device top plate 207 to ensure the airtightness of gas pressurization.

[0081] The sample device bottom plate 202 and the sample device top plate 207 are identical in structure and are installed at the bottom and top of the test device side mold 201 respectively; there are two screw holes on the sample device bottom plate 202 and the sample device top plate 207, which are convenient for the sample device bottom plate 202 and the sample device top plate 207 to be installed one by one with the bottom and top of the test device side mold 201 respectively; the sample device bottom plate 202 and the sample device top plate 207 both have an opening, the sample device top plate 207 is connected to the air flow measurement sub-device 4, and the sample device bottom plate 202 is connected to the air pressure control sub-device 1. The surfaces of the sample device bottom plate 202 and the sample device top plate 207 that contact the sample device side mold 201 are both annular shallow grooves, which are convenient for placing rubber rings 206 for air pressure sealing. The sample device side mold 201 is connected to the sample device bottom plate 202 and the sample device top plate 207 by screws 203. The rubber membrane 206 is used to wrap the sample; two water-permeable plates 204 are provided, which are placed at the upper and lower ends of the sample in the rubber membrane 206 respectively, to prevent the sample from being disturbed and to protect the upper and lower end samples from being damaged by the external pressure.

[0082] The air flow measuring device 4 includes a first air flow measuring device 401 and a second air flow measuring device 402;

[0083] The first gas flow measuring device 401 is used to measure a gas flow rate less than 1 mL / min. The first gas flow measuring device 401 includes a gas chamber 4011, a first valve 4012 and a second valve 4013;

[0084] The air inlet pipe of the first air flow quantum device 401 is divided into two air flow channels, one of which is connected to the second valve 4013, and the other is connected to the air chamber 4011 and the first valve 4012; and the air inlet pipe of the first air flow quantum device 401 is connected to the opening on the top plate 207 of the sample device;

[0085] The second gas flow measuring device 402 is used to measure a gas flow greater than 1 mL / min. The second gas flow measuring device 402 is connected to an opening on the top plate 207 of the sample device.

[0086] In this embodiment, the gas flow measuring sub-device 4 proposes two air flow measurement methods according to the air flow velocity flowing out from the top of the sample in the sample sub-device 2. The first gas flow measuring sub-device 401 includes an air chamber 4011, a first valve 4012, and a second valve 4013, and can measure a gas flow less than 1 mL / min. The second measuring sub-device uses a soap film flowmeter 6 for measurement, and can measure a gas flow greater than 1 mL / min. The first measurement method can measure a situation where the gas flow velocity is relatively small, and the device is simple and practical, while the second measurement method can measure a situation where the gas flow velocity is relatively large.

[0087] The sample preparation device 5 comprises a sample preparation device top plate 501, a sample preparation device bottom plate 502, a sample preparation device column 503, a sample preparation mold 504 and a jack 505;

[0088] The sample preparation device top plate 501, the sample preparation device bottom plate 502 and the sample preparation device upright column 503 constitute the frame of the sample preparation device 5, the jack 505 is installed in the middle of the sample preparation device bottom plate 502, and the sample preparation mold 504 is located above the jack 505 and below the sample preparation device top plate 501;

[0089] like Figure 3 As shown, the sample making mold 504 includes a sample making mold outer mold 5041, a sample making mold inner film 5042, an outer mold fixing screw 5043, a sample making mold top plate 5044 and a sample making mold bottom plate 5045;

[0090] The outer mold 5041 of the sample making mold can be divided into two halves, and the size of the recess of the outer mold 5041 of the sample making mold is the same as the size of the inner membrane 5042 of the sample making mold so as to wrap the inner membrane 5042 of the sample making mold. The upper and lower ends of the outer side edge of the outer mold 5041 of the sample making mold are provided with threads, and the outer mold fixing screws 5043 fix the two halves of the outer mold 5041 of the sample making mold with screws.

[0091] The sample preparation mold inner membrane 5042 includes an upper section, a middle section and a lower section, each of which can be divided into two lobes; the upper and lower sections have the same size, and the inner cavity size is 39.1 mm in diameter × 65 mm in height, and the inner cavity size of the middle section is 39.1 mm in diameter × 80 mm in height;

[0092] The sample making mold top plate 5044 and the sample making mold bottom plate 5045 have the same size. The sample making mold top plate 5044 and the sample making mold bottom plate 5045 are both composed of two upper and lower cylinders. The diameter of the upper cylinder is the same as the inner diameter of the sample making mold inner membrane 5042, and the diameter of the lower cylinder is the same as the outer diameter of the sample making mold outer mold 5041.

[0093] In the present embodiment, the sample preparation device 5 comprises a sample preparation device top plate 501, a sample preparation device bottom plate 502, a sample preparation device column 503, a sample preparation mold 504 and a jack 505. The sample preparation device top plate 501, the sample preparation device bottom plate 502 and the sample preparation device column 503 constitute the overall framework of the sample preparation device 5. The jack 505 is placed in the center of the sample preparation device bottom plate 502, and its function is to provide stable and effective pressure in sample preparation. The sample preparation mold 504 is located above the jack 505 and below the sample preparation device top plate 501. The sample preparation mold 504 consists of a sample preparation mold outer mold 5041, a sample preparation mold inner film 5042, an outer mold fixing screw 5043, a sample preparation mold top plate 5044 and a sample preparation mold bottom plate 5045.

[0094] In this embodiment, the inner membrane 5042 of the sample preparation mold is composed of three sections, and the upper and lower ends have the same size. The inner cavity size of the upper and lower ends is 39.1 mm in diameter × 65 mm in height; the inner cavity size of the middle section is the same as that of the conventional triaxial specimen, which is 39.1 mm in diameter × 80 mm in height. Figure 4 The three sections of the inner film 5042 of the sample preparation mold can be divided into two pieces to facilitate the removal of the sample after molding. Figure 5 As shown in the figure, the outer edges of the two ends of the middle mold within a range of 5mm are cut inwards to reduce half of the thickness, and the inner edges of the two end molds within a range of 5mm where they are connected to the middle mold are cut outwards to reduce half of the thickness, so as to facilitate the mutual connection of the three molds.

[0095] In this embodiment, the outer mold 5041 of the sample making mold can be divided into two parts, each mold is in the shape of "[", and the size of the mold recess is the same as the size of the inner membrane 5042 of the sample making mold, which is used to wrap the inner membrane 5042 of the sample making mold. The upper and lower ends of the outer side edge of the sample making mold outer mold 5041 are provided with threads, and the two halves of the sample making mold outer mold 5041 are fixed by the outer mold fixing screws 5043. The sample making mold top plate 5044 is the same size as the sample making mold bottom plate 5045, and is mainly composed of two cylinders. The diameter of the lower cylinder is the same as the outer diameter of the sample making mold outer mold 5041, and the height is 20mm; the diameter of the upper cylinder is the same as the inner diameter of the sample making mold inner membrane 5042, and the height is 50mm. The function of the sample making mold top plate 5044 and the sample making mold bottom plate 5045 is to compact the soil sample using the protruding cylinder using the jack 505.

[0096] In this embodiment, in the actual road engineering environment, there is a temperature difference between the upper and lower soil layers, and the temperature difference will bring about a saturated vapor pressure difference in the soil pores. Under the action of the air pressure difference, water vapor will migrate. The test sub-device 2 of the present invention uses an air pressure control sub-device 1 to provide an active air pressure difference for the test sample. The air pressure input is realized through the pressurization system 101, and the input air pressure ranges from 0kPa to 100kPa; the pressurization system 101 is divided into two channels, and the pressure is adjusted by two pressure regulating valves respectively; after the air pressure of one channel is adjusted by the first pressure regulating valve 102, the input gas is dried by the drying bottle 104 to prevent the water vapor in the gas from affecting the water content of the sample, and then the air pressure is input to the bottom plate 202 of the sample device, and the air pressure is input to the bottom of the sample through the bottom plate 202 of the sample device, and the air pressure input is accurately measured by the first U-tube pressure gauge 105; after the air pressure pipeline of the other channel is adjusted by the second pressure regulating valve 102, it is input into the cavity between the side mold 201 of the sample device and the rubber membrane 206 to provide a stable confining pressure.

[0097] In this embodiment, the air pressure in the cavity between the sample device side mold 201 and the rubber membrane 206 is the confining pressure of the sample and the rubber membrane 206. By providing a confining pressure value greater than the input air pressure, it is ensured that the input air pressure does not flow out from the side walls of the sample and the rubber membrane.

[0098] In this embodiment, the high and low temperature test box 3 provides an environmental temperature for the sample sub-device 2, and the temperature can be set to -20°C to 50°C to simulate the actual road environment temperature.

[0099] Through the above design, the present invention solves the problem of inaccurate measurement of the current permeability characteristics of unsaturated soil, solves the problem of air leakage between soil samples and rubber membranes in traditional permeability equipment, and solves the error caused by evaporation in the process of measuring gas volume by drainage. The present invention adopts a simple collection device to measure the permeability of soil with a low permeability coefficient, which solves the problem that traditional test devices are difficult to measure soil with a low permeability coefficient. The test sub-device 2 in the present invention is combined with the high and low temperature test box 3 to solve the problem of changes in the permeability of unsaturated soil under variable temperature conditions. The test sub-device 2 is also equipped with a corresponding reasonable sample preparation device, which solves the problem that traditional triaxial sample preparation is not suitable for unsaturated soil permeability test.

[0100] Example 2

[0101] like Figure 6 As shown, the present invention provides a test method for testing the air permeability of unsaturated soil, and the implementation method is as follows

[0102] S1. Check the test device for testing the air permeability of unsaturated soil;

[0103] In this embodiment, at the beginning of the test, the test device for testing the air permeability of unsaturated soil needs to be inspected to check whether each component can operate normally and has normal connection combinations.

[0104] S2. Prepare the sample by static pressure, and cut the two ends of the prepared sample by cutting during the compaction process, install the cut sample in the test sub-device, and complete the installation of the test sub-device. The implementation method is as follows:

[0105] S201, installing the inner mold of the sample making mold on the inner cavity of the outer mold of the sample making mold, and fixing the two halves of the outer mold of the sample making mold with the outer mold fixing screws;

[0106] S202, placing the bottom plate of the sample making mold under the sample making mold, filling the determined soil into the cavity of the sample making mold, and installing the top plate of the sample making mold;

[0107] S203, placing the sample making mold on a jack, applying pressure, completely compacting the top plate of the sample making mold into the cavity of the sample making mold, and statically pressing for a preset time;

[0108] S204, after compaction, take out the sample, and cut off both ends of the prepared sample by using a cutting method;

[0109] S205, applying vaseline on the inner surface of the rubber film, and wrapping the sample with the rubber film;

[0110] S206. Place a water-permeable plate at both ends of the sample, and use three rubber rings to bind the rubber membrane and the sample at the upper, middle and lower positions of the sample respectively;

[0111] S207, placing the bound sample in the cavity of the side mold of the sample device, and installing the bottom of the side mold of the sample device, the top of the side mold of the sample device, the bottom plate of the sample device, and the rubber rings of the top plate of the sample device in the annular shallow groove;

[0112] S208. Turn the excess rubber film at both ends of the rubber film wrapping the sample outward to the top edge of the side mold of the sample device, and use screws to connect the side mold of the sample device to the top plate and the bottom plate of the sample device respectively, to complete the installation of the test sub-device.

[0113] In this embodiment, during the sample preparation stage, the sample is prepared by static pressure using the sample pressing instrument in the device of the present invention. First, the sample preparation mold inner film 5042 is installed in the inner cavity of the sample preparation mold outer mold 5041, and then the two-piece sample preparation mold outer mold 5041 is fixed by the outer mold fixing screws 5043. After that, the sample preparation mold bottom plate 5045 is placed at the lower part of the sample preparation mold 504, the calculated soil is filled into the sample preparation mold 504 cavity, and the sample preparation mold top plate 5044 is installed. Then the sample preparation mold 504 is placed on the jack 505, and pressure is applied to completely compact the sample preparation mold top plate 5044 into the mold cavity, and static pressure is applied for 20 minutes to 30 minutes to ensure the uniformity of sample compaction. After compaction, the sample is taken out. At this time, the sample is longer than the standard sample, and the standard sample in the middle part is cut using a geosaw. The main reason for making the sample longer is that the sample surfaces at the upper and lower ends will block the air permeability pores of the soil due to compaction. In order to ensure the effectiveness of the test, the sample needs to be made longer and only the middle part is cut off to ensure the reasonable effectiveness of the test.

[0114] After the sample is made, first apply a large amount of vaseline on the inner surface of the rubber membrane 206, wrap the rubber membrane 206 around the sample, place a water-permeable plate 204 at the upper and lower ends of the sample, and then use three rubber rings 205 to tie the rubber membrane 206 and the sample at the upper, middle and lower positions of the sample respectively. The above measures are all to prevent gas from flowing out from the rubber membrane 206 and the side wall of the sample to ensure the effectiveness of the test.

[0115] After the sample is made, place the sample in the cavity of the sample device side mold 201, and place the rubber ring 205 of the top or bottom of the sample device side mold 201 and the sample device top plate 207 and the sample device bottom plate 202 in the annular shallow groove. Since the rubber film 206 wrapping the sample is long, the excess rubber film 206 at both ends of the rubber film 206 wrapping the sample is turned outward to the top edge of the sample device side mold 201. Then use screws 203 to connect the sample device side mold 201, the sample device top plate 207 and the sample device bottom plate 202.

[0116] S3. Place the installed test sub-device in a high and low temperature test chamber, connect the air pressure control sub-device, the air flow measurement sub-device and the test sub-device using an air pressure pipe, and use the air flow measurement sub-device to measure, so as to complete the test of the air permeability of the unsaturated soil. The implementation method is as follows:

[0117] S301, placing the test sub-device in a high and low temperature test chamber, and connecting the air pressure control sub-device, the air flow measurement sub-device and the test sub-device using an air pressure pipeline;

[0118] S302: Use the first air flow measuring device or the second air flow measuring device to perform measurement to complete the test of air permeability of unsaturated soil.

[0119] The step S302 uses the first air flow measuring device to perform measurement, including the following steps:

[0120] A1. Preset the temperature of the high and low temperature test chamber. After the sample temperature stabilizes, read the initial readings of the liquid levels of the first U-tube pressure gauge and the second U-tube pressure gauge;

[0121] A2. Squeeze out all the gas in the air chamber, close the first valve, and open the second valve;

[0122] A3. Open the pressurization system, set the confining pressure of the sample sub-device through the second pressure regulating valve, and observe the pressure changes before and after the liquid surface of the second U-tube pressure gauge, and make the confining pressure 10kPa to 20kPa greater than the preset pressure value of the test;

[0123] A4. Open the pressurization system, set the air pressure of the sample sub-device through the first pressure regulating valve, observe the pressure changes before and after the liquid surface of the first U-tube pressure gauge, and adjust the air pressure value input to the sample sub-device to the preset pressure value of the test;

[0124] A5. When the liquid level of the first U-tube pressure gauge stabilizes, open the second valve and close the first valve to allow gas to enter the gas chamber;

[0125] A6. Record the volume change of the air chamber to obtain the air permeability coefficient of the soil, and obtain the air permeability of the unsaturated soil according to the air permeability coefficient of the soil;

[0126] The first gas flow measuring device is used to measure a gas flow rate less than 1 mL / min;

[0127] The step S302 uses the second air flow measuring device to measure, including the following steps:

[0128] B1. Preset the temperature of the high and low temperature test chamber. After the sample temperature stabilizes, read the initial readings of the liquid levels of the first U-tube pressure gauge and the second U-tube pressure gauge;

[0129] B2. Open the pressurization system, adjust the confining pressure of the sample sub-device through the second pressure regulating valve, and observe the pressure changes before and after the liquid surface of the second U-tube pressure gauge to make the confining pressure greater than the preset pressure value of the test by 10kPa to 20kPa;

[0130] B3. Open the first pressure regulating valve, observe the pressure changes before and after the liquid level of the first U-tube pressure gauge, and adjust the air pressure entering the test sub-device to the preset pressure value of the test;

[0131] B4. When the liquid level of the first U-tube pressure gauge changes steadily, the soap film flowmeter is turned on to obtain the air permeability coefficient of the soil, and the air permeability of the unsaturated soil is obtained according to the air permeability coefficient of the soil;

[0132] The second gas flow measuring device is used to measure a gas flow greater than 1 mL / min.

[0133] In this embodiment, after the test device is installed, the test sub-device 2 is placed in the high and low temperature test box 3. Then, the air pressure control sub-device 1, the air flow measurement sub-device 4 and the test sub-device 2 are connected by an air pressure pipeline.

[0134] In this embodiment, during the test, if the airflow measurement method 1 is used for measurement, the main operation steps are as follows:

[0135] First, the temperature of the high and low temperature test box 3 is set according to the test design. After the temperature of the sample is stable, the initial readings of the liquid levels of the two U-tube pressure gauges are measured; the gas in the air chamber 4011 is completely squeezed out, and then the first valve 4012 is closed and the second valve 4013 is opened; the pressurization system 101 is opened, and the confining pressure of the sample sub-device 2 is first adjusted through the second pressure regulating valve 103, and the change of the pressure value before and after the liquid surface of the second U-tube pressure gauge 106 is observed, so that the confining pressure is greater than the pressure value of the test design scheme by 10kPa to 20kPa; then the first pressure regulating valve 102 is opened, and the change of the pressure value before and after the liquid surface of the first U-tube pressure gauge 105 is observed, and the air pressure value input to the sample sub-device 2 is adjusted to the test design pressure value; when the liquid level of the first U-tube pressure gauge 105 changes stably, it means that the gas seepage of the sample has reached a stable state at this time; at this time, the first valve 4012 is opened, and the second valve 4013 is closed to allow the gas to enter the air chamber 4011. The volume change of the air chamber 4011 over a period of time is recorded to calculate the air permeability coefficient of the soil and characterize the air permeability of the sample.

[0136] In this embodiment, solution 1 is applicable to the case where the soil gas seepage flow rate is less than 1 mL / min.

[0137] In this embodiment, during the test, if the airflow measurement method 2 is used for measurement, the main operation steps are as follows:

[0138] First, the temperature of the high and low temperature test box 3 is set according to the test design. After the sample temperature stabilizes, the initial readings of the liquid levels of the two U-tube pressure gauges are measured; the pressurization system 101 is turned on, and the confining pressure of the sample sub-device 2 is adjusted through the second pressure regulating valve 103, and the changes in the pressure values ​​before and after the liquid level of the second U-tube pressure gauge 106 are observed, so that the confining pressure is 10kPa to 20kPa greater than the pressure value of the test design scheme; then the first pressure regulating valve 102 is opened, and the changes in the pressure values ​​before and after the liquid level of the first U-tube pressure gauge 105 are observed, and the air pressure entering the sample sub-device 2 is adjusted to the test design pressure value; when the liquid level change of the first U-tube pressure gauge 105 is stable, it means that the gas seepage of the sample has reached a stable state at this time; the soap film flowmeter 6 can be turned on to directly calculate the gas seepage flow of the soil.

[0139] In this embodiment, scheme 2 is applicable to the case where the soil gas seepage flow rate is greater than 1 mL / min.

[0140] In this embodiment, when the gas phase flow rate is low and the liquid phase movement is ignored, it is feasible to use Darcy's law to describe the gas phase movement, so the gas permeability coefficient of the sample can be calculated as follows:

[0141] v a =Q a / At

[0142] i a =ΔP / ρ a g

[0143] k a =v a / i a =ρ a QUR a / ΔPAt

[0144] Where: Q a is the permeate gas volume (cm 3 ), k a is the permeability coefficient (cm / s), L, A are the sample height (cm) and area (cm 2 ), t is the test duration (s), ρ a is the density of air (g / cm 3 ), g is the acceleration due to gravity (9.8 m / s 2 ).

[0145] Through the above design, the present invention takes into account the dryness of the input gas, and uses a drying bottle 104 to first dry the input gas, which can reduce the influence of the input gas on the moisture content of the sample and improve the accuracy of the test data; in order to reduce the test error caused by the input gas passing through the gap between the rubber membrane 206 and the sample, measures are taken to set a confining pressure outside the rubber membrane 206, apply vaseline on the inner wall of the rubber membrane 206, and use a rubber ring 205 to fix the sample and the rubber membrane 206; considering the actual situation of the roadbed soil, combined with the high and low temperature test box 3, the permeability of unsaturated soil under different temperature conditions can be measured. Different air flow sizes are taken into consideration and different measurement methods are adopted. When the soil seepage flow rate is greater than 1mL / min, a soap film flowmeter is used for measurement; when the soil seepage flow rate is less than 1mL / min, a self-made air chamber is used for measurement, which can measure a smaller gas flow rate. The experimental device is simple, the cost is low, and the actual use effect is good. Considering the disadvantages of traditional sample preparation methods, the static pressure method is used to prepare the sample. Considering that the sealing of both ends of the sample during the compaction process will affect the test results of the unsaturated soil permeability, the cutting method is adopted to cut off both ends of the sample to prepare a standard sample, which solves the problems existing in the existing technology and equipment, such as inaccurate measurement of the permeability characteristics of unsaturated soil, difficulty in measuring soil with a low permeability coefficient, unreasonable traditional sample preparation method, and failure to consider variable temperature conditions.

Claims

1. A test device for testing the air permeability of unsaturated soil, characterized in that: It comprises an air pressure control sub-device (1), a test sub-device (2), a high and low temperature test chamber (3), an air flow measurement sub-device (4) and a sample making device (5); The air pressure control sub-device (1) is connected to the test sub-device (2); the high and low temperature test box (3) provides an ambient temperature for the test sub-device (2); the air flow measurement sub-device (4) is respectively connected to the high and low temperature test box (3) and the test sub-device (2); the air flow measurement sub-device (4) provides air flow measurement for the test sub-device (2); and the sample making device (5) makes a sample for the test sub-device (2); The air pressure control sub-device (1) comprises a pressurizing system (101), a first pressure regulating valve (102), a second pressure regulating valve (103), a drying bottle (104), a first U-tube pressure gauge (105) and a second U-tube pressure gauge (106); The pressurizing system (101) is divided into two air pressure channels, wherein a first pressure regulating valve (102) is provided on one air pressure channel, and the first air pressure channel is respectively connected to the drying bottle (104), the test sub-device (2) and the first U-tube pressure gauge (105), and a second pressure regulating valve (103) is provided on the other air pressure channel, and the other air pressure channel is connected to the test sub-device (2), and the second U-tube pressure gauge (106) is connected to the test sub-device (2); The test sub-device (2) comprises a sample device side mold (201), a sample device bottom plate (202), screws (203), a water-permeable plate (204), a rubber ring (205), a rubber membrane (206) and a sample device top plate (207); The sample device side mold (201) is connected to the sample device bottom plate (202) and the sample device top plate (207) respectively through screws (203); there are two water-permeable plates (204), which are respectively arranged at the upper and lower ends of the sample in the rubber membrane (206); the sample device side mold (201) is an integrated mold, and the inner cavity of the sample device side mold (201) is a cylinder; Two symmetrical openings are arranged on the side of the sample device side mold (201), one of which is connected to another air pressure channel to input a stable confining pressure into the cavity between the sample device side mold (201) and the rubber membrane (206), and the other opening is connected to the second U-tube pressure gauge (106) to observe the confining pressure of the test device. The top and bottom of the sample device side mold (201), the inner side of the screw (203) hole of the sample device bottom plate (202) and the inner side of the screw (203) hole of the sample device top plate (207) are all provided with annular shallow grooves for placing the rubber ring (205). The positions of the annular shallow grooves on the top and bottom of the sample device side mold (201) correspond to the positions of the annular shallow grooves on the sample device bottom plate (202) and the sample device top plate (207) respectively. The sample device bottom plate (202) and the sample device top plate (207) have the same structure, and the sample device bottom plate (202) and the sample device top plate (207) are respectively installed at the bottom position and the top position of the sample device side mold (201) in a one-to-one correspondence. Two screw (203) holes are provided on the sample device bottom plate (202) and the sample device top plate (207). There are openings on the sample device bottom plate (202) and the sample device top plate (207). The openings on the sample device bottom plate (202) are connected to the drying bottle (104), and the openings on the sample device top plate (207) are connected to the air flow meter device (4).

2. The test device for testing the air permeability of unsaturated soil according to claim 1, characterized in that: The air flow measuring device (4) comprises a first air flow measuring device (401) and a second air flow measuring device (402); The first gas flow measuring device (401) is used to measure a gas flow rate of less than 1 mL / min, and the first gas flow measuring device (401) comprises a gas chamber (4011), a first valve (4012) and a second valve (4013); The air inlet pipe of the first air flow measuring device (401) is divided into two air flow channels, one of which is connected to the second valve (4013), and the other is connected to the air chamber (4011) and the first valve (4012); and the air inlet pipe of the first air flow measuring device (401) is connected to an opening on the top plate (207) of the sample device; The second gas flow measuring device (402) is used to measure a gas flow greater than 1 mL / min. The second gas flow measuring device (402) is connected to an opening on the top plate (207) of the sample device.

3. The test device for testing the air permeability of unsaturated soil according to claim 2, characterized in that: The sample making device (5) comprises a sample making device top plate (501), a sample making device bottom plate (502), a sample making device column (503), a sample making mold (504) and a jack (505); The sample preparation device top plate (501), the sample preparation device bottom plate (502) and the sample preparation device upright column (503) constitute the frame of the sample preparation device (5); the jack (505) is installed at the middle position of the sample preparation device bottom plate (502); the sample preparation mold (504) is located above the jack (505) and below the sample preparation device top plate (501); The sample making mold (504) comprises a sample making mold outer mold (5041), a sample making mold inner film (5042), outer mold fixing screws (5043), a sample making mold top plate (5044) and a sample making mold bottom plate (5045); The outer mold (5041) of the sample making mold can be divided into two halves. The size of the recess of the outer mold (5041) of the sample making mold is the same as the size of the inner film (5042) of the sample making mold so as to wrap the inner film (5042) of the sample making mold. The upper and lower ends of the outer side edge of the sample making mold outer mold (5041) are both provided with threads. The outer mold fixing screws (5043) fix the two halves of the outer mold (5041) of the sample making mold by screws. The sample preparation mold inner membrane (5042) includes an upper section, a middle section and a lower section, each of which can be divided into two lobes; the upper and lower sections have the same size, and the inner cavity size is 39.1 mm in diameter and 65 mm in height, and the inner cavity size of the middle section is 39.1 mm in diameter and 80 mm in height; The sample making mold top plate (5044) and the sample making mold bottom plate (5045) have the same size. The sample making mold top plate (5044) and the sample making mold bottom plate (5045) are both formed by splicing two upper and lower cylinders. The diameter of the upper cylinder is the same as the inner diameter of the sample making mold inner film (5042), and the diameter of the lower cylinder is the same as the outer diameter of the sample making mold outer mold (5041).

4. The test method of the test device for testing the air permeability of unsaturated soil according to any one of claims 1 to 3, characterized in that: The test method for testing the air permeability of unsaturated soil comprises the following steps: S1. Check the test device for testing the air permeability of unsaturated soil; S2. Prepare the sample by static pressure, and cut the two ends of the prepared sample by cutting during the compaction process, install the cut sample in the test sub-device, and complete the installation of the test sub-device; S3. Place the installed test sub-device in a high and low temperature test chamber, connect the air pressure control sub-device, the air flow measurement sub-device and the test sub-device using an air pressure pipe, and use the air flow measurement sub-device to perform measurements to complete the test of the air permeability of the unsaturated soil.

5. The test method for testing the air permeability of unsaturated soil according to claim 4, characterized in that: The step S2 comprises the following steps: S201, installing the inner mold of the sample making mold on the inner cavity of the outer mold of the sample making mold, and fixing the two halves of the outer mold of the sample making mold with the outer mold fixing screws; S202, placing the bottom plate of the sample making mold under the sample making mold, filling the determined soil into the cavity of the sample making mold, and installing the top plate of the sample making mold; S203, placing the sample making mold on a jack, applying pressure, completely compacting the top plate of the sample making mold into the cavity of the sample making mold, and statically pressing for a preset time; S204, after compaction, take out the sample, and cut off both ends of the prepared sample by using a cutting method; S205, applying vaseline on the inner surface of the rubber film, and wrapping the sample with the rubber film; S206. Place a water-permeable plate at both ends of the sample, and use three rubber rings to bind the rubber membrane and the sample at the upper, middle and lower positions of the sample respectively; S207, placing the bound sample in the cavity of the side mold of the sample device, and installing the bottom of the side mold of the sample device, the top of the side mold of the sample device, the bottom plate of the sample device, and the rubber rings of the top plate of the sample device in the annular shallow groove; S208. Turn the excess rubber film at both ends of the rubber film wrapping the sample outward to the top edge of the side mold of the sample device, and use screws to connect the side mold of the sample device to the top plate and the bottom plate of the sample device respectively, to complete the installation of the test sub-device.

6. The test method for testing the air permeability of unsaturated soil according to claim 4, characterized in that: The step S3 comprises the following steps: S301, placing the test sub-device in a high and low temperature test chamber, and connecting the air pressure control sub-device, the air flow measurement sub-device and the test sub-device using an air pressure pipeline; S302: Use the first air flow measuring device or the second air flow measuring device to perform measurement to complete the test of air permeability of unsaturated soil.

7. The test method for testing the air permeability of unsaturated soil according to claim 6, characterized in that: The step S302 uses the first air flow measuring device to perform measurement, including the following steps: A1. Preset the temperature of the high and low temperature test chamber. After the sample temperature stabilizes, read the initial readings of the liquid levels of the first U-tube pressure gauge and the second U-tube pressure gauge; A2. Squeeze out all the gas in the air chamber, close the first valve, and open the second valve; A3. Open the pressurization system, set the confining pressure of the sample sub-device through the second pressure regulating valve, and observe the pressure changes before and after the liquid surface of the second U-tube pressure gauge, and make the confining pressure 10kPa to 20kPa greater than the preset pressure value of the test; A4. Open the pressurization system, set the air pressure of the sample sub-device through the first pressure regulating valve, observe the pressure changes before and after the liquid surface of the first U-tube pressure gauge, and adjust the air pressure value input to the sample sub-device to the preset pressure value of the test; A5. When the liquid level of the first U-tube pressure gauge stabilizes, open the second valve and close the first valve to allow gas to enter the gas chamber; A6. Record the volume change of the air chamber to obtain the air permeability coefficient of the soil, and obtain the air permeability of the unsaturated soil according to the air permeability coefficient of the soil; The step S302 uses the second air flow measuring device to measure, including the following steps: B1. Preset the temperature of the high and low temperature test chamber. After the sample temperature stabilizes, read the initial readings of the liquid levels of the first U-tube pressure gauge and the second U-tube pressure gauge; B2. Open the pressurization system, adjust the confining pressure of the sample sub-device through the second pressure regulating valve, and observe the pressure changes before and after the liquid surface of the second U-tube pressure gauge to make the confining pressure greater than the preset pressure value of the test by 10kPa to 20kPa; B3. Open the first pressure regulating valve, observe the pressure changes before and after the liquid level of the first U-tube pressure gauge, and adjust the air pressure entering the test sub-device to the preset pressure value of the test; B4. When the liquid level of the first U-tube pressure gauge changes steadily, the soap film flowmeter is turned on to obtain the air permeability coefficient of the soil, and the air permeability of the unsaturated soil is obtained based on the air permeability coefficient of the soil.

8. The test method for testing the air permeability of unsaturated soil according to claim 7, characterized in that: The first gas flow measuring device is used to measure a gas flow rate less than 1 mL / min; The second gas flow measuring device is used to measure a gas flow greater than 1 mL / min.

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