Measuring system and method for simultaneously determining soil water characteristic curve and unsaturated hydraulic conductivity

Abstract

The application discloses a kind of simultaneously determining the measurement system and method of soil water characteristic curve and unsaturated permeability coefficient, comprising: sample chamber, pressure chamber, water supply side, drainage side, manual valve, differential pressure gauge, solenoid valve, PC end and electronic scale.PC end is connected with electronic scale, for recording experimental data;Sample chamber is used to place sample, pressure chamber is used to place sample chamber and pressurization, drainage side and water supply side are each provided with three burettes, and are divided into standard burette and measuring burette, wherein standard burette applies variable head method to measure permeability coefficient in permeation experiment, measuring burette is used to measure the change amount of soil water volume, differential pressure gauge is used to measure the head pressure difference of standard burette and measuring burette and connect solenoid valve to realize the automatic control of soil water inlet and drainage.The application has the advantages that: water level is adjusted using solenoid valve, to realize the automation of measurement process;SWCC curve and permeability coefficient can be simultaneously measured;Instrument cost is low, and measurement result accuracy is higher.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical engineering, and particularly relates to an improved system and method for measuring unsaturated soil water characteristic curve (SWCC) and unsaturated permeability coefficient. BACKGROUND

[0002] In most engineering projects, the soil is often in an unsaturated state, i.e., unsaturated soil. Compared with saturated soil, the properties of unsaturated soil in engineering projects change greatly when the proportion of the three phases changes greatly. This often brings many difficulties to geotechnical engineering and environmental engineering. These difficulties not only hinder the construction of projects, but also cause certain losses. At present, the properties of unsaturated soil are mainly estimated according to the soil water characteristic curve (SWCC), and the shear strength, permeability, diffusion characteristics, and bulk strain of unsaturated soil can be effectively determined through the soil water characteristic curve. The soil water characteristic curve reflects the relationship between the matric suction and the water content in the unsaturated soil, and embodies the water-holding capacity of the soil under the action of matric suction. A typical soil water characteristic curve is shown in FIG. 1. Figure 1

[0003] The permeability coefficient of unsaturated soil is an important parameter for analyzing the stability of soil slopes under rainfall, the migration of underground sewage in solid waste landfills, and problems in filling engineering. The unsaturated permeability coefficient is related to the water content, and the value of the unsaturated permeability coefficient changes constantly with the change of the matric suction, and the change range can span several orders of magnitude, so it is difficult to accurately measure the unsaturated permeability coefficient. At present, the measurement methods of the unsaturated permeability coefficient are generally divided into two types: direct measurement method and indirect prediction method. The indirect method is to predict the unsaturated permeability coefficient of the soil from the theoretical aspect according to the basic physical properties of the soil, such as the pore size. For a long time, the permeability coefficient of unsaturated soil is obtained indirectly through the soil water characteristic curve, which is only an empirical method, and the theoretical system is not mature. The direct method is to measure the permeability coefficient by measuring the pore water pressure and water content through the unsaturated permeability test. The direct measurement method is divided into steady-state method and non-steady-state method, and the difference between the two methods is whether the hydraulic gradient changes with time. The direct measurement method has a long test time and high cost, but the obtained permeability coefficient is reliable.

[0004] Prior art one

[0005] ​Currently, the conventional instrument for determining the soil water characteristic curve of unsaturated soil is the pressure plate apparatus. The main components of the pressure plate apparatus are a metal pressure chamber and a saturated high air entry value ceramic plate. According to the different air entry values, the common ceramic plates can be divided into 3, 5 and 15 bar. Generally, according to different test soil samples, the appropriate air entry value of the ceramic plate can be selected for the experiment. Below the ceramic plate is a drainage pipeline connected to the outside. The water in the sample will gradually flow out through the ceramic plate pores into the drainage pipeline after a certain pressure is applied, until the pore water pressure and the applied pressure become balanced. When the amount of water flowing out of the pipeline no longer changes, it is considered that the soil sample has reached a balanced state, and the experiment is complete. By applying different pressures, multiple test points can be obtained, and finally the complete soil water characteristic curve can be drawn. For the pressure plate apparatus, a soil sample can also be used to test the complete soil water characteristic curve by continuously applying pressure, and after reaching equilibrium at a certain pressure, the next pressure is applied. Through continuous research by scholars, the accuracy and efficiency of the pressure plate apparatus have been continuously improved.

[0006] Oliveira (Oliveira OM, Marinho FAM (2006) Study of equilibration time in the pressure plate. In: Fourth international conference on unsaturated soil, Carefree, AZ 2 April, pp 1864-1874) pointed out that the change of pressure chamber temperature will cause the change of water vapor in the pressure chamber, which will affect the water content in the soil sample. Li et al. (Li, H., Hou, R., Fan, T. B., et al. Rapid determination of SWCC method based on dynamic multi-step flow principle and improvement of pressure plate apparatus [J]. Chinese Journal of Geotechnical Engineering, 2020, 28(4): 707-715) improved the pressure plate apparatus, which can measure the volume of bubbles generated at the bottom of the ceramic plate during the experiment. Hou et al. (Hou, R. Rapid determination of soil-water characteristic curve model and improvement of test method for unsaturated soil [D]. North China University of Water Resources and Electric Power, 2020) used the improved pressure plate apparatus to test the dynamic multi-step flow method, which greatly shortened the test time of the soil water characteristic curve. Chen et al. (Chen, H., Wei, C. F., Li, H., et al. Overflow water correction weighing method for determining soil-water characteristic curve of unsaturated soil [J]. Rock and Soil Mechanics, 2010(07): 2141-2145) compared the weighing method, overflow water correction weighing method and overflow water weighing method, and the results showed that the saturation of the soil sample determined by the overflow water correction weighing method was larger than that of the other two methods. Based on the traditional pressure plate, Pang et al. improved it by adding an electronic pressure gauge system, an electronic balance and an evaporation correction system, and a temperature control system, which greatly improved the measurement accuracy of the soil water characteristic curve.

[0007] Disadvantages of Prior Art One

[0008] 1. The time for a soil sample to reach equilibrium during the desaturation or saturation process is uncertain. The SWCC measurement for an individual soil sample can last for several months.

[0009] 2. The current method can only be used for SWCC measurement, and cannot be directly used for unsaturated soil permeability coefficient measurement.

[0010] 3. Multiple air pressures need to be adjusted during a single measurement experiment, which is complicated and prone to errors due to manual operation, reducing the experimental accuracy.

[0011] 4. The necessary experimental operations of the pressure plate apparatus, such as "removing the sample for weighing and then placing it back on the ceramic plate", will affect the contact condition between the sample and the ceramic plate, hinder the water transfer between the sample and the ceramic plate, and thus have a significant impact on the test results.

[0012] 5. The ceramic plate is the main component of the pressure plate apparatus. High-pressure gas can pass through the edge of the ceramic plate into the bottom of the ceramic plate, and then enter the drainage pipeline, making the actual suction of the sample less than the controlled suction applied by the high-pressure gas source.

[0013] Prior Art Two

[0014] Steady-state method: The hydraulic gradient is a constant value during the test, and the relationship between the matric suction and the water content is obtained. The steady-state method is mainly conducted indoors and is favored by unsaturated soil scholars due to its economy, advancement, and standardization.

[0015] Klute based on steady-state method, (Klute A. Laboratory measurement of hydraulic conductivity of unsaturated soils [J]. Methods of Soil Analysis. Monograph 9, Part 1, American Society of Agronomy, Madison, WI, 1965; 253-261) designed a test device to determine the permeability coefficient of unsaturated soil. The test principle of the test equipment is to control the gas pressure in the pore during the test by the gas supply device to maintain the constant matric suction. In addition, the water supply device can be used to provide a constant water head force to the top of the sample. Li Aimin et al. carried out corresponding steady-state seepage test on sandy soil and silt, and obtained the relationship between water content and permeability coefficient. Shao Longtan (Shao Longtan, Li Aimin, Wang Zhupen, et al. Development and application of unsaturated soil steady-state seepage test device [J]. Rock and Soil Mechanics, 2005, 27 (11)) and others self-made unsaturated permeability coefficient test instrument, which is simple to operate and shortens the test time to a certain extent. Xu Yongfu et al. (Xu Yongfu, Lan Shouqi, Sun De'an, et al. A new type of test device for measuring the influence of stress state on the permeability coefficient of unsaturated soil [J]. Rock and Soil Mechanics, 2005, 24 (1): 160-16) developed a constant water head test instrument, which measures the permeability coefficient of unsaturated soil under different stress states on the basis of adding radial strain ring and axial strain sensor, and can most intuitively depict the relationship between unsaturated permeability coefficient and stress state. Cui Ying et al. (Xu Yongfu, Lan Shouqi, Sun De'an, et al. A new type of test device for measuring the influence of stress state on the permeability coefficient of unsaturated soil [J]. Rock and Soil Mechanics, 2005, 24 (1): 160-16) added a water gradient control device to the existing GDS unsaturated soil triaxial test instrument, and analyzed the influence of saturation and initial dry density on the permeability coefficient.

[0016] Disadvantages of prior art two

[0017] 1. When the water head changes, the water level needs to be manually corrected, and the water level needs to be adjusted many times in a seepage experiment; 2. The measurement period of the test is long, and the utilization rate of the sample is low; 3. The type of soil suitable for the test is limited; 4. It is very difficult to accurately measure the volume of water discharged; 5. The instrument is expensive. Summary

[0018] The present application provides a measurement system and method for simultaneously determining the soil water characteristic curve and the unsaturated permeability coefficient.

[0019] A kind of measurement system for simultaneously determining soil water characteristic curve and unsaturated permeability coefficient, comprising sample chamber (1), pressure chamber (2), water supply side (3), drainage side (4), manual valve, differential pressure gauge (6), solenoid valve (7), PC end is connected with electronic scale, for recording experimental data, fitting experimental data;

[0020] The sample chamber (1) comprises: upper acrylic disc (11), lower acrylic disc (13) and porous acrylic cylinder (12); the porous acrylic cylinder (12) is between the upper acrylic disc (11) and the lower acrylic disc (13), and the upper acrylic disc (11) and the lower acrylic disc (13) are fixed by four bolts passing through the nuts to form the sample chamber (1); the inside of the upper acrylic disc (11) and the lower acrylic disc (13) is provided with two thin tubes capable of penetrating the inside and outside of the sample chamber (1);

[0021] The porous acrylic cylinder (12) is used to fill soil sample; the surface of the porous acrylic cylinder (12) is provided with a plurality of small holes with a diameter of 2mm; the inner surface of the porous acrylic cylinder (12) is attached with filter paper;

[0022] The inner diameter of the thin tube is 3mm, and the two thin tubes penetrate to the lower surface of the upper acrylic disc (11) through the side of the upper acrylic disc (11); the positions of the two thin tubes are symmetrical;

[0023] The two thin tubes penetrate to the upper surface of the lower acrylic disc (13) through the side of the lower acrylic disc (13), and the positions of the two thin tubes are symmetrical;

[0024] The pressure chamber (2) comprises: upper square iron plate (21), lower square iron plate (22), acrylic cylinder (23) and electronic balance (24);

[0025] The acrylic cylinder (23) is between the upper square iron plate (21) and the lower square iron plate (22), and the acrylic cylinder (23) is fixed by the bolts penetrating through the four corners and the nuts to form the pressure chamber (2); the center of the upper square iron plate (21) is the center of the circle, and six screw holes (211) are uniformly arranged; two screw holes (211) are symmetrically arranged in the middle of the lower square iron plate (22);

[0026] The water supply side (3) comprises: standard burette A (31), coarse measuring burette A (32), fine measuring burette A (33) and water supply tank (34); the standard burette A (31), the coarse measuring burette A (32), the fine measuring burette A (33) and the water supply tank (34) are interconnected through water pipes; the standard burette A (31), the coarse measuring burette A (32) and the fine measuring burette A (33) are switched according to experimental requirements by the manual valve;

[0027] The drainage side (4) includes: a standard burette B (41), a coarse measuring burette B (42), a fine measuring burette B (43), and a drainage tank (44); the standard burette B (41), the coarse measuring burette B (42), the fine measuring burette B (43), and the drainage tank (44) are interconnected by water pipes, and the standard burette B (41), the coarse measuring burette B (42), and the fine measuring burette B (43) can be switched according to experimental requirements by a manual valve;

[0028] The water replenishment tank (8) is connected to the water supply tank (34) and the drainage tank (44) respectively, and is used to replenish the water supply tank (34) and the drainage tank (44);

[0029] The water pipe on the water supply side (3) is connected to a thin pipe on the upper acrylic disc (11) through a screw hole on the upper square iron plate (21). Another thin pipe on the upper acrylic disc (11) is connected to a thin pipe on the lower acrylic disc (13) through a water pipe. Another thin pipe on the lower acrylic disc (13) is connected to the drain side (4) through a screw hole on the upper square iron plate (21) through a water pipe.

[0030] The upper square iron plate (21) has six screw holes (211). One screw hole (211) is connected to the air pressure regulating device for pressure load, and another screw hole (211) is connected to the atmosphere through a manual valve. This valve is installed on the screw hole. When the valve is open, it is the same as the atmosphere, and when the valve is closed, it isolates the instrument from the atmosphere. The remaining two screw holes (211) are sealed with bolts.

[0031] An electronic balance (24) is set in the middle of the lower square iron plate (22), and the sample chamber (1) is placed at the measuring position of the electronic balance (24);

[0032] The two screw holes (211) on the lower square iron plate (22) are used for the power cord and PC output line of the electronic balance (24) to pass through;

[0033] There are three differential pressure gauges (6). One is located between the water pipe connecting the upper acrylic disc (11) and the lower acrylic disc (13) in the sample chamber (1). Another is located between the standard burette A (31) and the coarse measuring burette A (32) / fine measuring burette A (33). The third is located between the standard burette B (41) and the coarse measuring burette B (42) / fine measuring burette B (43).

[0034] There are four solenoid valves (7): one between the sample chamber (1) and the coarse measuring burette A (32) / fine measuring burette A (33), one between the sample chamber (1) and the coarse measuring burette B (42) / fine measuring burette B (43), one between the water supply tank (34) and the coarse measuring burette A (32) / fine measuring burette A (33), and one between the drain tank (44) and the coarse measuring burette B (42) / fine measuring burette B (43).

[0035] Preferably, there are 32 holes in total, distributed at 4 positions spaced 10 mm apart in the height direction and at 8 positions spaced 45 degrees apart in the circumferential direction.

[0036] Preferably, the upper acrylic disc (11) and the lower acrylic disc (13) have a diameter of 160 mm and a thickness of 10 mm. The surfaces of the upper acrylic disc (11) and the lower acrylic disc (13) that contact the porous acrylic cylinder (12) are provided with circular grooves, so that the upper and lower ends of the porous acrylic cylinder (12) are embedded therein.

[0037] Preferably, the standard burette A (31) and standard burette B (41) have an inner diameter of 3 mm and a length of 320 mm in order to minimize the evaporation.

[0038] Preferably, the inner diameter of the coarse measuring burette A (32) and the coarse measuring burette B (42) is 30 mm and the length is 320 mm.

[0039] Preferably, the inner diameter of the fine measuring burette A (33) and the fine measuring burette B (43) is 3 mm and the length is 320 mm.

[0040] Preferably, a manual valve A (5-1) is installed at the water pipe connecting the water supply side (3) and the sample chamber (1), and a manual valve A (5-1) is installed at the water pipe connecting the drainage side (4) and the sample chamber (1);

[0041] A three-way valve (5-2) is installed at the water pipe connecting the water supply tank (34) to the standard burette A (31), the coarse measuring burette A (32), and the fine measuring burette A (33).

[0042] A three-way valve (5-2) is provided at the water pipe connecting the drain tank (44) to the standard burette B (41), the coarse measuring burette B (42), the fine measuring burette B (43) and the drain tank (44);

[0043] Manual valve B (5-3) between standard burette A (31) and coarse measuring burette A (32) / fine measuring burette A (33);

[0044] Manual valve B(5-3) between standard burette B(41) and coarse measuring burette B(42) / fine measuring burette B(43);

[0045] A manual valve C (5-4) is installed at the water pipe between the water supply tank (34) and the water replenishment tank (8);

[0046] A manual valve C (5-4) is installed at the water pipe between the drainage tank (44) and the water supply tank (8);

[0047] A manual valve C (5-4) is installed at the water pipe between the water supply tank (34) and the drainage tank (44).

[0048] This invention also discloses a method for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficients, comprising the following steps:

[0049] S1: Cut PTFE filter paper that is breathable but waterproof into pieces 5cm long and 26cm wide;

[0050] S2: Use silicone to attach PTFE filter paper to the inside of a porous acrylic cylinder; this ensures there are no gaps between the filter papers, the ends of the filter papers, and the sample chamber; by using PTFE filter paper, atmospheric pressure from the surrounding environment will enter the soil sample through the pores, while pore water inside the soil will not leak through the pores.

[0051] S3: Pour water into the porous acrylic cylinder and confirm that there is no leakage on its sides;

[0052] S4: After drying, use the same silicone rubber to attach the membrane filter to the lower end of the porous acrylic cylinder and allow it to dry completely;

[0053] S5: Measure the inner diameter of the porous acrylic cylinder with PTFE filter paper attached, and calculate its volume;

[0054] S6: Calculate the sample mass from the volume of the porous acrylic cylinder and the maximum dry density value obtained from the compaction test;

[0055] S7: Fill the sample chamber with a dry sample;

[0056] S8: Use silicone to attach the membrane filter to the top of the porous acrylic cylinder and let it dry;

[0057] S9: Clamp the metal wire mesh between the top and bottom of the membrane filter and place it in the test sample chamber to measure and record its quality; in addition, install a three-way valve (5-2) at the end of the water pipe leading from the upper acrylic disc (11) and the lower acrylic disc (13) of the sample chamber.

[0058] S10: The prepared sample is gradually depressurized over time. When bubbles gradually stop appearing, it is gradually restored to atmospheric pressure, thereby saturating it.

[0059] S11: To prevent air from entering, remove the sample after closing the three-way valve (5-2) in the water, allow the sample to be filled with water once, and then allow the area around the sample chamber to dry.

[0060] S12: Weigh again; the mass difference between the mass before and after saturation, minus the mass of water in the tube, gives the mass of pore water, from which the initial volume water content is calculated.

[0061] S13: Place the prepared sample on the electronic balance (24) in the pressure chamber (2). Before connecting the water pipe to each instrument, the water pipe needs to be filled with water to remove air.

[0062] S14: Fix the tube, press the "print" button on the scale, and then close the upper square iron plate (21) of the pressure chamber (2); after completing all preparations, wait for the fluctuation of the proportional value to converge;

[0063] S15: Operate manual valve B (5-3) on the water supply side (3) and the drainage side (4), select the coarse measuring burette as the measuring burette; connect the three-way valve (5-2) to the measuring burette;

[0064] S16: Adjust the water level of all burettes from the center of the sample height to a certain height, close the two manual valves B (5-3), determine the reference water level, and then add water until DPT1 and DPT2 are zero. The water level of the water supply tank (34) and the drain tank (44) should be lower than the reference water level.

[0065] S17: Record data;

[0066] S18: Activate the MultiAi creation program and initialize DWL and CI → Start the program in the input order → Select water retention test - drying → START;

[0067] S19: Open the manual switches of the four solenoid valves (7) and open the two manual valves A (5-1);

[0068] S20: Operate the pressure regulating valve to slowly increase the pressure to the load pressure; the suction force at this time is expressed by the following expression:

[0069]

[0070] Where S is the suction force, P is the load pressure, and H is the sample height;

[0071] During the test, if it is necessary to adjust the water level of the water supply tank (34) and the drain tank (44), adjust the manual valve (5) between the water supply tank (8) and the water supply tank (34) and the drain tank (44);

[0072] S21: Based on whether the soil sample has reached equilibrium after 8-10 hours, copy and open the output file and end the test;

[0073] S22: At the end of the test, press the "End" button in the program window and stop saving the data file; in addition, close the manual switches of the four solenoid valves (7) and close the two manual valves A (5-1); close the Tera Term VT window and stop saving the file;

[0074] S23: Switch to unsaturated permeability testing;

[0075] Unsaturated permeability test:

[0076] S24: Open both manual valves B (5-3); with the water level at the beginning of the water retention test drainage process as the center, raise the water level of the reference titration and measurement titration on the water supply side by Δh (mm), and lower the water level of the reference and measurement burettes on the drainage side by Δh (mm); keep the measurement burette and the fine burette on the water supply side at the same water level.

[0077] S25: Close the two manual valves B (5-3), determine the reference water level, and take the zero point of DPT1 and DPT2 if necessary; set the water level of the water supply tank (34) to be about 10 cm higher than the reference water level, and set the water level of the drain tank (44) to be about 10 cm lower than the reference water level.

[0078] S26: Activate Tera Term VT, select File → Log, specify the file name, select "Time", "Appendix" and "Plain Text", and then press the Save button;

[0079] S27: Activate the MultiAi creation program and start the program by entering DWL and CI in the order of initialization → select magnetic permeability test - unsaturated → START;

[0080] S28: Open the manual switches of the four solenoid valves (7), open the two manual valves A (5-1), and start the test; at this time, the suction force on the water supply side at the lower end of the sample and the suction force on the drainage side at the upper end of the sample are represented by the following expressions:

[0081]

[0082]

[0083] Where P is the load pressure and H is the sample height;

[0084] L is the length of the sample, in mm;

[0085] Δh is the difference between the water level in the burette and the water surface height at the beginning of the drainage process in the water retention test;

[0086] S29: During the test, if it is necessary to adjust the water level of the water supply tank (34) / drainage tank (44), adjust the water supply tank (34) and manual valve C (5-4); in addition, when the scale value fluctuates greatly, it is necessary to adjust the water level of the standard burette and measuring burette on the water supply side (3) and the drainage side (4) respectively.

[0087] S30: Copy and open the output file, and check whether the scale value and differential pressure gauge value have reached a stable state;

[0088] S31: After confirming that it is in a stable state, switch the measuring burette on the water supply side (3) to the fine measuring burette; use the fine measuring burette to perform the unsaturated permeation test, and read the position of the water surface in the fine measuring burette and the time it takes to pass through; in the unsaturated permeation test, the initial water level of the fine measuring burette should be maintained at the initial water level of the coarse measuring burette; in addition, the water level change of the fine measuring burette is about 2.5 cm, and it is repeated many times; at this time, when switching to the fine measuring burette, start the timer for the unsaturated permeation test and start recording;

[0089] S32: After completing the unsaturated permeation test, the test is finished; click the end button in the program window and stop saving the data file; at the same time, close the manual switches of the four solenoid valves (7) and close the two manual valves A (5-1); finally close the program Tera Term VT window and stop saving the file.

[0090] Compared with the prior art, the advantages of the present invention are as follows:

[0091] 1. Automating water level regulation using solenoid valves;

[0092] 2. It can simultaneously measure SWCC curves and permeability coefficients;

[0093] 3. The instrument is low in cost and the measurement results are highly accurate. Attached Figure Description

[0094] Figure 1 This is a schematic diagram of the measurement system structure according to an embodiment of the present invention;

[0095] Figure 2 This is a schematic diagram of the sample chamber structure according to an embodiment of the present invention;

[0096] Figure 3 This is a schematic diagram of the acrylic disk structure in an embodiment of the present invention;

[0097] Figure 4 This is a schematic diagram of the porous acrylic cylindrical structure according to an embodiment of the present invention;

[0098] Figure 5 This is a schematic diagram of the pressure chamber structure according to an embodiment of the present invention;

[0099] Figure 6 This is a schematic diagram of the square iron plate structure in an embodiment of the present invention;

[0100] Figure 7 This is a schematic diagram of the square iron plate structure in an embodiment of the present invention. Detailed Implementation

[0101] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0102] like Figure 1 As shown, a measurement system for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficients includes a sample chamber 1, a pressure chamber 2, a water supply side 3, a drainage side 4, a manual valve 5, a differential pressure gauge 6, a solenoid valve 7, and a PC terminal connected to an electronic scale for recording experimental data and fitting experimental data.

[0103] like Figures 2 to 4 As shown, the sample chamber 1 includes: an upper acrylic disc 11, a lower acrylic disc 13, and a porous acrylic cylinder 12. The porous acrylic cylinder 12 is located between the upper acrylic disc 11 and the lower acrylic disc 13. The upper acrylic disc 11 and the lower acrylic disc 13 are fixed together by four bolts passing through a tightening nut, forming the sample chamber 1. Both the upper acrylic disc 11 and the lower acrylic disc 13 have two thin tubes inside, capable of connecting the inside and outside of the sample chamber 1.

[0104] The porous acrylic cylinder 12 is used to fill soil samples. It is a cylinder with an inner diameter of 90 mm, an outer diameter of 100 mm, a thickness of 5 mm, and a height of 50 mm. The surface of the porous acrylic cylinder 12 has several small holes with a diameter of 2 mm. There are 32 such holes in total, distributed at four locations spaced 10 mm apart in the height direction and at eight locations spaced 45 degrees apart in the circumferential direction. Filter paper is attached to the inner surface of the cylinder, allowing air to pass through but preventing water penetration.

[0105] The upper acrylic disc 11 and the lower acrylic disc 13 have a diameter of 160 mm and a thickness of 10 mm. The surfaces of the upper acrylic disc 11 and the lower acrylic disc 13 that contact the porous acrylic cylinder 12 are provided with circular grooves, so that the upper and lower ends of the porous acrylic cylinder 12 are embedded in them.

[0106] The inner diameter of the thin tube is 3mm, and the two thin tubes pass through the side of the upper acrylic disc 11 to the lower surface of the upper acrylic disc 11; the two thin tubes are symmetrically positioned.

[0107] Two thin tubes extend from the side of the lower acrylic disc 13 to its upper surface, and the two tubes are symmetrically positioned. For example... Figures 5 to 7As shown, the pressure chamber 2 includes: an upper square iron plate 21, a lower square iron plate 22, an acrylic cylinder 23, and an electronic balance 24.

[0108] An acrylic cylinder 23 is located between the upper square iron plate 21 and the lower square iron plate 22. Bolts at the four corners of the upper and lower square iron plates 21 and 22 are used to connect them, and the acrylic cylinder 23 is secured by tightening nuts to form a pressure chamber 2. Six screw holes 211 are evenly arranged with the center of the upper square iron plate 21 as the center. Two screw holes 211 are symmetrically arranged in the middle of the lower square iron plate 22.

[0109] The water supply side 3 includes: a standard burette A31, a coarse measuring burette A32, a fine measuring burette A33, and a water supply tank 34; the standard burette A31, the coarse measuring burette A32, the fine measuring burette A33, and the water supply tank 34 are interconnected by water pipes, and the standard burette A31, the coarse measuring burette A32, and the fine measuring burette A33 are switched according to experimental requirements via manual valves.

[0110] The drainage side 4 includes: a standard burette B41, a coarse measuring burette B42, a fine measuring burette B43, and a drainage tank 44; the standard burette B41, the coarse measuring burette B42, the fine measuring burette B43, and the drainage tank 44 are interconnected by water pipes, and the standard burette B41, the coarse measuring burette B42, and the fine measuring burette B43 are switched according to experimental requirements via manual valves.

[0111] To minimize evaporation, the standard burettes A31 and B41 have an inner diameter of 3 mm and a length of 320 mm, and are filled with fine matter.

[0112] The coarse measuring burettes A32 and B42 have an inner diameter of 30 mm and a length of 320 mm, and are filled with coarse material.

[0113] The fine measuring burettes A33 and B43 have an inner diameter of 3 mm and a length of 320 mm, and are filled with fine matter.

[0114] The water replenishment tank 8 is connected to the water supply tank 34 and the drainage tank 44 respectively, and is used to replenish the water supply tank 34 and the drainage tank 44.

[0115] The water pipe on the water supply side 3 is connected to a thin pipe on the upper acrylic disc 11 through a screw hole in the upper square iron plate 21. Another thin pipe on the upper acrylic disc 11 is connected to a thin pipe on the lower acrylic disc 13 through a water pipe. Another thin pipe on the lower acrylic disc 13 is connected to the drain side 4 through a screw hole in the upper square iron plate 21 through a water pipe.

[0116] Of the six screw holes 211 on the upper square iron plate 21, one screw hole 211 connects to a pressure regulating device, which is independent of the system and is a well-developed experimental instrument used for pressure loads. Another screw hole 211 connects to the atmosphere via a manual valve. This valve is installed on the screw hole; opening it allows the instrument to be connected to the atmosphere, while closing it isolates the instrument from the atmosphere. The remaining two screw holes 211 are sealed with bolts.

[0117] An electronic balance 24 is set in the middle of the lower square iron plate 22, and the sample chamber 1 is placed at the measuring position of the electronic balance 24.

[0118] The two screw holes 211 on the lower square iron plate 22 are used for the power cord and PC output line of the electronic balance 24 to pass through.

[0119] There are three differential pressure gauges 6 in total. One is located between the water pipe connecting the upper acrylic disc 11 and the lower acrylic disc 13 in the sample chamber 1. Another is located between the standard burette A31 and the coarse measuring burette A32 / fine measuring burette A33. The third is located between the standard burette B41 and the coarse measuring burette B42 / fine measuring burette B43.

[0120] There are four solenoid valves 7: one is located between sample chamber 1 and coarse measuring burette A32 / fine measuring burette A33, one is located between sample chamber 1 and coarse measuring burette B42 / fine measuring burette B43, one is located between water supply tank 34 and coarse measuring burette A32 / fine measuring burette A33, and one is located between drainage tank 44 and coarse measuring burette B42 / fine measuring burette B43.

[0121] A manual valve A5-1 is installed at the water pipe connecting the water supply side 3 and the sample chamber 1, and a manual valve A5-1 is installed at the water pipe connecting the drainage side 4 and the sample chamber 1.

[0122] A three-way valve 5-2 is installed at the water pipe connecting the water supply tank 34 to the standard burette A31, the coarse measuring burette A32, and the fine measuring burette A33.

[0123] A three-way valve 5-2 is provided at the water pipe connecting the drain tank 44 to the standard burette B41, the coarse measuring burette B42, the fine measuring burette B43 and the drain tank 44.

[0124] Manual valve B5-3 between standard burette A31 and coarse measuring burette A32 / fine measuring burette A33;

[0125] Manual valve B5-3 between standard burette B41 and coarse measuring burette B42 / fine measuring burette B43;

[0126] A manual valve C5-4 is installed at the water pipe between the water supply tank 34 and the water replenishment tank 8;

[0127] A manual valve C5-4 is installed at the water pipe between the drain tank 44 and the water supply tank 8;

[0128] A manual valve C5-4 is installed at the water pipe between the water supply tank 34 and the drainage tank 44.

[0129] A method for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficients includes the following steps: S1: Cut a special filter paper (hereinafter referred to as "PTFE filter paper") with the characteristics that allows air to pass through easily but water to pass through easily under zero pressure difference into 5cm long and 26cm wide pieces.

[0130] S2: PTFE filter paper is attached to the inside of a porous acrylic cylinder using silicone rubber. At this point, there are no gaps between the filter papers, or between the filter paper ends and the sample chamber. By using the PTFE filter paper, atmospheric pressure from the surrounding environment acts on the sample through the pores, while pore water does not leak through the pores.

[0131] S3: Pour water into the porous acrylic cylinder and confirm that there is no leakage on its sides.

[0132] S4: After drying, use the same silicone rubber to attach the membrane filter to the lower end of the porous acrylic cylinder and allow it to dry completely.

[0133] S5: Measure the inner diameter of the porous acrylic cylinder with PTFE filter paper attached, and calculate its volume.

[0134] S6: Calculate the sample mass at 80% compaction from the volume of the porous acrylic cylinder and the maximum dry density value obtained from the compaction test.

[0135] S7: Fill the sample chamber with a dry sample with a compaction degree of 80%. For a single-layer sample, divide it into 5 layers, each 1 cm thick, in a 5 cm high porous acrylic cylinder.

[0136] S8: Use silicone to attach the membrane filter to the top of the porous acrylic cylinder and dry it.

[0137] S9: Clamp the wire mesh between the top and bottom of the membrane filter and place it in the test sample chamber to measure and record its quality. Additionally, install a three-way valve 5-2 at the end of the water pipe leading from the upper acrylic disc 11 and lower acrylic disc 13 of the sample chamber.

[0138] S10: The prepared sample is gradually depressurized over time. When bubbles gradually stop appearing, it is gradually restored to atmospheric pressure, thereby saturating it.

[0139] S11: To prevent air from entering, remove the sample after closing the three-way valve 5-2 in the water, allow the sample to be filled with water once, and then dry the area around the sample chamber.

[0140] S12: Weigh again. Subtract the mass of water in the tube from the mass difference before and after saturation to obtain the mass of pore water, and use this value to calculate the initial volumetric water content.

[0141] S13: The screws on the sample chamber may be loose, so tighten them again after saturation to prevent water leakage and air from entering.

[0142] S14: Place the prepared sample on the electronic balance 24 in pressure chamber 2. Before connecting the water pipes to the instruments, fill the water pipes with water to remove air. Special attention should be paid to the fact that air can easily remain in the solenoid valves and differential pressure gauges. When connecting the pipes to the sample chamber, a pre-connected three-way valve can be used to easily prevent air from entering.

[0143] S15: Secure the tube, press the "Print" button on the scale, and then close the upper square iron plate 21 of pressure chamber 2. After completing all preparations, wait for the fluctuation of the proportional value to converge.

[0144] S16: Operate the manual valves on the water supply side 3 and the drainage side 4, and select the coarse measuring burette as the measuring burette. Connect the three-way valve 5-2 to the measuring burette.

[0145] S17: Adjust the water level of all burettes from the center of the sample height to a certain height (mm), close the two manual valves B5-3, determine the reference water level, and then add water until DPT1 and DPT2 are zero. The water level in the water supply tank 34 and the drain tank 44 should be lower than the reference water level.

[0146] S18: Record data.

[0147] S19: Activate the MultiAi creation program and initialize DWL and CI → Start the program in the input order → Select Water Retention Test - Drying (drainage process of water retention test) → START. If there is a possibility of a large water volume and a significant increase in water level, by setting DWL, the excess water in DWL flows into the water supply and drainage tank, so the water level fluctuation can be kept below a certain value. On the other hand, if the increase in water level is within a range that does not significantly affect suction, etc., setting a large value to DWL eliminates the control of solenoid valve 7, and the increase in water level in the burette can be read intuitively, confirming the wastewater volume.

[0148] S20: Open the manual switches of four solenoid valves 7 and open two manual valves A5-1.

[0149] S21: Operate the pressure regulating valve to slowly increase the pressure to the load pressure (kPa). The suction force (kPa) at this point is expressed by the following expression:

[0150]

[0151] Where S is the suction force, P is the load pressure, and H is the sample height.

[0152] During the test, if it is necessary to adjust the water level of the water supply tank 34 and the drain tank 44, adjust the manual valve 5 between the water replenishment tank 8 and the water supply tank 34 and the drain tank 44.

[0153] S22: Based on whether the soil sample has reached equilibrium after 8-10 hours, copy and open the output file and end the test.

[0154] S23: At the end of the test, press the "End" button in the program window and stop saving the data file. Additionally, close the manual switches of all four solenoid valves 7 and close the two manual valves A5-1. Furthermore, close the Tera Term VT window and stop saving the file.

[0155] S24: Switch to unsaturated permeability test.

[0156] Unsaturated permeability test:

[0157] S25: Open both manual valves B5-3. At the start of the water retention test (drainage process), raise the reference and measuring titration water levels (mm) on the supply side (mm), and set the reference and measuring titration water levels on the drain side 4 (mm). Measuring the water level in the burette on the supply side 3, keeping the fine measuring burette at the same water level. To independently open and close solenoid valve 7, use the DioBit program connected to the A / D / D / A board.

[0158] S26: Close both manual valves B5-3, determine the reference water level, and take the zero points of DPT1 and DPT2 if necessary. Set the water level in the water supply tank 34 to be about 10 cm higher than the reference water level, and set the water level in the drain tank 44 to be about 10 cm lower than the reference water level.

[0159] S27: Activate Tera Term VT, select File → Log, specify the file name, select "Time", "Appendix" and "Plain Text", and then press the Save button.

[0160] S28: Activate the MultiAi creation program and press Initialize → Enter DWL and CI in that order to start the program → Select Magnetic Permeability Test - Unsaturated (Unsaturated Permeability Test) → START.

[0161] S29: Open the manual switches of four solenoid valves 7 and two manual valves A5-1 to begin the test. At this time, the suction force (kPa) on the water supply side at the lower end of the sample and the suction force (kPa) on the drain side 4 at the upper end of the sample are as follows: Assuming the length of the sample is (mm), it can be expressed by the following expressions:

[0162]

[0163]

[0164] Where P is the load pressure and H is the sample height;

[0165] L is the length of the sample, in mm;

[0166] Δh is the difference between the water level in the burette and the water surface at the beginning of the drainage process in the water retention test.

[0167] S30: During the test, if it is necessary to adjust the water level of the water supply tank 34 / drainage tank 44, adjust the water supply tank 34 and the manual valve C5-4. In addition, when the scale value fluctuates greatly, that is, when the water supply and drainage are unbalanced, it is necessary to adjust the standard burette and the measuring titration water level on the water supply side 3 and the drainage side 4 respectively.

[0168] S31: Copy and open the output file to check whether the scale values ​​and differential pressure gauge values ​​have reached a stable state.

[0169] S32: After confirming a stable state, switch the measuring burette on the water supply side 3 to the fine measuring burette. Perform a water level permeability test using the fine measuring burette, and read the water level position in the fine measuring burette and the time taken for it to pass through. During the water level permeability test, the initial water level in the fine measuring burette should be maintained at the initial water level in the coarse measuring burette, and care should be taken to prevent it from increasing. Furthermore, the water level change in the fine measuring burette should be approximately 2.5 cm, and this should be repeated multiple times. At this point, when switching to the fine measuring burette, start the timer for the water level permeability test and record the readings.

[0170] S33: After completing the data collection for the water level permeability test, the test is finished. Click the "End" button in the program window and stop saving the data file. Simultaneously, close the manual switches of all four solenoid valves 7 and close the two manual valves A5-1. Finally, close the Tera Term VT program window and stop saving the file.

[0171] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the implementation methods of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of the present invention.

Claims

1. A measurement system for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficients, characterized in that: It includes a sample chamber (1), a pressure chamber (2), a water supply side (3), a drainage side (4), a manual valve, a differential pressure gauge (6), a solenoid valve (7), a water replenishment tank (8), a PC terminal, and an electronic balance (24); The PC terminal is connected to the electronic balance (24) and is used to record experimental data and fit experimental data. The sample chamber (1) includes: an upper acrylic disc (11), a lower acrylic disc (13), and a porous acrylic cylinder (12); the upper acrylic disc (11) and the lower acrylic disc (13) are connected by the porous acrylic cylinder (12), and the upper acrylic disc (11) and the lower acrylic disc (13) are connected by four bolts passing through and tightening nuts to fix the porous acrylic cylinder (12) to form the sample chamber (1); the upper acrylic disc (11) and the lower acrylic disc (13) are each provided with two thin tubes that can penetrate the inside and outside of the sample chamber (1); The porous acrylic cylinder (12) is used to fill soil samples; the surface of the porous acrylic cylinder (12) is provided with several small holes with a diameter of 2 mm; the inner surface of the porous acrylic cylinder (12) is covered with filter paper; The inner diameter of the thin tube is 3mm. The two thin tubes pass through the side of the upper acrylic disc (11) to the lower surface of the upper acrylic disc (11). The two thin tubes are symmetrically positioned. Two thin tubes pass through the side of the lower acrylic disc (13) to the upper surface of the lower acrylic disc (13), and the two thin tubes are symmetrically positioned. The pressure chamber (2) includes: an upper square iron plate (21), a lower square iron plate (22), an acrylic cylinder (23), and an electronic balance (24); An acrylic cylinder (23) is placed between the upper square iron plate (21) and the lower square iron plate (22). The upper square iron plate (21) and the lower square iron plate (22) are connected by bolts at the four corners and the acrylic cylinder (23) is fixed by tightening nuts to form a pressure chamber (2). Six screw holes (211) are evenly arranged with the center of the upper square iron plate (21) as the center. Two screw holes (211) are symmetrically arranged in the middle of the lower square iron plate (22). The water supply side (3) includes: a standard burette A (31), a coarse measuring burette A (32), a fine measuring burette A (33), and a water supply tank (34); the standard burette A (31), the coarse measuring burette A (32), the fine measuring burette A (33), and the water supply tank (34) are interconnected by water pipes, and the standard burette A (31), the coarse measuring burette A (32), and the fine measuring burette A (33) can be switched according to experimental requirements by a manual valve; The drainage side (4) includes: a standard burette B (41), a coarse measuring burette B (42), a fine measuring burette B (43), and a drainage tank (44); the standard burette B (41), the coarse measuring burette B (42), the fine measuring burette B (43), and the drainage tank (44) are interconnected by water pipes, and the standard burette B (41), the coarse measuring burette B (42), and the fine measuring burette B (43) can be switched according to experimental requirements by a manual valve; The water replenishment tank (8) is connected to the water supply tank (34) and the drainage tank (44) respectively, and is used to replenish the water supply tank (34) and the drainage tank (44); The water pipe on the water supply side (3) is connected to a thin pipe on the upper acrylic disc (11) through a screw hole on the upper square iron plate (21). Another thin pipe on the upper acrylic disc (11) is connected to a thin pipe on the lower acrylic disc (13) through a water pipe. Another thin pipe on the lower acrylic disc (13) is connected to the drain side (4) through a screw hole on the upper square iron plate (21) through a water pipe. The upper square iron plate (21) has six screw holes (211). One screw hole (211) is connected to the air pressure regulating device for pressure load, and another screw hole (211) is connected to the atmosphere through a manual valve. This valve is installed on the screw hole. When the valve is opened, it communicates with the atmosphere, and when the valve is closed, it isolates the instrument from the atmosphere. The remaining two screw holes (211) are sealed with bolts. An electronic balance (24) is set in the middle of the lower square iron plate (22), and the sample chamber (1) is placed at the measuring position of the electronic balance (24); The two screw holes (211) on the lower square iron plate (22) are used for the power cord and PC output line of the electronic balance (24) to pass through; There are three differential pressure gauges (6). One is located between the water pipe connecting the upper acrylic disc (11) and the lower acrylic disc (13) in the sample chamber (1). Another is located between the standard burette A (31) and the coarse measuring burette A (32) / fine measuring burette A (33). The third is located between the standard burette B (41) and the coarse measuring burette B (42) / fine measuring burette B (43). There are four solenoid valves (7): one between the sample chamber (1) and the coarse measuring burette A (32) / fine measuring burette A (33), one between the sample chamber (1) and the coarse measuring burette B (42) / fine measuring burette B (43), one between the water supply tank (34) and the coarse measuring burette A (32) / fine measuring burette A (33), and one between the drain tank (44) and the coarse measuring burette B (42) / fine measuring burette B (43).

2. The measurement system for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficient according to claim 1, characterized in that: There are a total of 32 holes, distributed at 4 locations spaced 10mm apart in the height direction and at 8 locations spaced 45 degrees apart in the circumferential direction.

3. The measurement system for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficient according to claim 1, characterized in that: The upper acrylic disc (11) and the lower acrylic disc (13) have a diameter of 160 mm and a thickness of 10 mm. The surfaces of the upper acrylic disc (11) and the lower acrylic disc (13) that contact the porous acrylic cylinder (12) are provided with circular grooves, so that the upper and lower ends of the porous acrylic cylinder (12) are embedded in them.

4. The measurement system for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficient according to claim 1, characterized in that: The standard burettes A (31) and B (41) are designed to minimize evaporation by having an inner diameter of 3 mm and a length of 320 mm.

5. The measurement system for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficient according to claim 1, characterized in that: The inner diameter of the coarse measuring burette A (32) and the coarse measuring burette B (42) is 30 mm and the length is 320 mm.

6. The measurement system for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficient according to claim 1, characterized in that: The inner diameter of the fine measuring burette A (33) and the fine measuring burette B (43) is 3 mm and the length is 320 mm.

7. The measurement system for simultaneously determining soil-water characteristic curves and unsaturated permeability coefficient according to claim 1, characterized in that: A manual valve A (5-1) is installed at the water pipe connecting the water supply side (3) and the sample chamber (1), and a manual valve A (5-1) is installed at the water pipe connecting the drainage side (4) and the sample chamber (1); A three-way valve (5-2) is installed at the water pipe connecting the water tank (34) to the standard burette A (31), the coarse measuring burette A (32), and the fine measuring burette A (33). A three-way valve (5-2) is provided at the water pipe connecting the drain tank (44) to the standard burette B (41), the coarse measuring burette B (42), the fine measuring burette B (43) and the drain tank (44). Manual valve B (5-3) between standard burette A (31) and coarse measuring burette A (32) / fine measuring burette A (33); Manual valve B(5-3) between standard burette B(41) and coarse measuring burette B(42) / fine measuring burette B(43); A manual valve C (5-4) is installed at the water pipe between the water supply tank (34) and the water replenishment tank (8); A manual valve C (5-4) is installed at the water pipe between the drainage tank (44) and the water supply tank (8); A manual valve C (5-4) is installed at the water pipe between the water supply tank (34) and the drain tank (44).

Images