Soil-water characteristic curve rapid testing method based on water-gas two-phase flow

Abstract

The invention discloses a rapid soil-water characteristic curve testing method based on water-gas two-phase flow, which comprises the following steps: S1, constructing a rapid soil-water characteristic curve testing system which comprises a pressure control system, an automatic control and data acquisition system and a soil sample device; s2, an unsaturated seepage test is carried out, and the change process of pore pressure and overflow water quantity along with time in the seepage process of the soil sample is obtained in real time; s3, on the basis of the test data, an inversion analysis method combining water-gas two-phase flow numerical simulation and a grid search method is adopted, and the optimal parameter value of the soil-water characteristic curve of the soil body is obtained through calculation; according to the invention, the soil-water characteristic curve of the soil sample can be rapidly obtained, and the test result can comprehensively reflect the water-gas coupling characteristic of the unsaturated soil in a wide matrix suction range and is closer to the macroscopic soil-water characteristic of the soil body.

Description

Technical Field

[0001] The invention relates to the technical field of hydraulic and geotechnical engineering, and in particular to a soil-water characteristic curve rapid testing method based on water-gas two-phase flow. Background Art

[0002] The soil-water characteristic curve reflects the change of soil matrix suction under different water content conditions, directly affects soil strength, stability and water migration behavior, and is crucial in geotechnical engineering. The soil-water characteristic curve can be used to evaluate hydraulic properties such as foundation settlement, slope stability and permeability coefficient of unsaturated soil. It is of great significance to predict the deformation and strength characteristics of soil, optimize structural design, and simulate groundwater movement. It is the basic constitutive relationship for water-soil-force coupling analysis.

[0003] Traditional test methods for obtaining soil-water characteristic curves mainly include: ① Pressure plate method, which controls the external air pressure to discharge the water in the soil, thereby measuring the water content under different suction conditions. This method can measure soil-water characteristic curve data from low to medium suction ranges, and it takes a long time to reach each suction equilibrium state. ② Filter paper method, which uses the hygroscopicity of filter paper to indirectly measure the matrix suction and total suction of the soil sample, and measures the soil-water characteristic curve through the suction balance between the filter paper and the soil sample. This method is simple to operate and low in cost, and is particularly suitable for measuring soil-water characteristic curves in a high suction range (usually >1000kPa), but the test cycle of the water potential balance between the filter paper and the soil sample is long, and the accuracy of the test results is greatly affected by environmental factors. ③ Steam balance method, which measures the soil-water characteristic curve by controlling the water vapor pressure around the soil sample, is particularly suitable for measuring soil suction under a higher matrix suction range (>1500kPa). This method takes a long time to reach water vapor equilibrium, and the uniformity of water distribution in soil samples with high suction is difficult to ensure. The test is easily affected by environmental conditions such as temperature and humidity, and is not applicable to low matrix suction ranges. Therefore, it is urgent to propose a device and method for quickly testing soil-water characteristic curves. Summary of the invention

[0004] In order to overcome the above-mentioned shortcomings, the present invention provides a rapid testing method for soil-water characteristic curve based on water-gas two-phase flow, which can quickly obtain the soil-water characteristic curve of the soil sample. The test results can comprehensively reflect the water-gas coupling characteristics of unsaturated soil in a wide range of matrix suction, which is closer to the macroscopic soil-water characteristics of the soil.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a soil-water characteristic curve rapid testing method based on water-gas two-phase flow, which comprises the following steps:

[0006] Step S1: construct a soil-water characteristic curve rapid test system, including a pressure control system, an automatic control and data acquisition system, and a soil sample device;

[0007] Step S2: Conduct an unsaturated seepage test to obtain the time-varying process of pore pressure and overflow water volume during the seepage of the soil sample in real time;

[0008] Step S3: Based on the test data, an inversion analysis method combining water-gas two-phase flow numerical simulation with a grid search method is used to calculate the optimal parameter values ​​of the soil-water characteristic curve of the soil.

[0009] Furthermore, in step S1, the pressure control system includes an air compressor, a buffer, an air source, a valve and a water source. The air compressor is used to pressurize the test device to control the flow pressure of water and air in the test. A buffer is provided at the outlet of the air compressor to avoid impact on soil samples and instruments during pressurization and decompression, and reduce the impact of pressure fluctuations on test results.

[0010] The automatic control and data acquisition system includes a solenoid valve, a relay module, a pressure sensor, an acquisition card, a water collection bottle, an electronic balance and a computer. The pressure sensor is used to continuously monitor the real-time pressure data in the test system, the water collection bottle is used to collect the water overflowing from the bottom of the soil sample, and the electronic balance is used to weigh and record the overflowing water.

[0011] The soil sample set includes sponge, gravel, soil sample and PVC pipe.

[0012] Furthermore, the solenoid valve is connected and communicated with a relay module, and the computer controls the switch state of the solenoid valve through the relay module.

[0013] Furthermore, the pressure sensor establishes a communication connection with an acquisition card, and the acquisition card converts the electrical signal collected by the pressure sensor into a digital signal and transmits it to a computer, thereby realizing real-time collection of pressure data during the test process.

[0014] Furthermore, the soil sample is placed in a PVC tube, which is composed of sponge, gravel, soil sample, gravel and sponge from top to bottom.

[0015] Furthermore, the sponge at the bottom of the soil sample device is connected to an outlet pipe, the outlet pipe leads to a water collecting bottle, the mouth of the water collecting bottle is covered with a plastic film to reduce or eliminate the impact of water evaporation on the test, and the water collecting bottle is placed on an electronic balance; the electronic balance has an RS-232 serial port communication to achieve communication with a computer and record the weighing data in the computer.

[0016] Furthermore, the step S2 is specifically as follows:

[0017] Step 2.1: Test preparation and sample loading: Fill the sample step by step, and evenly apply cementitious material on the wall of the sample loading device, so as to use it as a medium to embed the soil sample tightly, reduce the gap between the soil sample and the surrounding wall, hinder the movement of water and gas through the wall channel, and thus prevent the occurrence of wall seepage; at the same time, measure the density, porosity, saturation and saturated permeability of the soil sample to provide initial conditions and material parameters for numerical back calculation;

[0018] Step 2.2: Check the air tightness of the device and saturate the sample: After checking that the air tightness of the device is good, open the water supply solenoid valve until the soil sample is saturated and then close the water supply solenoid valve;

[0019] Step 2.3: Conduct unsaturated permeability test: After the soil sample is saturated, apply air pressure to it and conduct a soil-water property test. Collect and record the air pressure at the top of the sample and the cumulative overflow water at the bottom in real time, and draw a curve of the cumulative overflow water and air pressure changing with time.

[0020] Furthermore, the step S3 is specifically as follows:

[0021] Step 3.1: Select the unsaturated soil-water behavior model;

[0022] Step 3.2: Initialize the parameter vector P j The upper and lower boundaries of the value range and Generate grid points in the parameter space, divide each parameter into N intervals, and use the following formula to calculate the specific parameter value P of the grid node j (k):

[0023]

[0024] Step 3.3: Numerical simulation of water-gas two-phase flow: For each parameter combination, the initial conditions and boundary conditions for solving the water-gas two-phase flow are given, and the water-gas two-phase flow coupling solution is performed to calculate the change process of pore gas pressure, pore water pressure and saturation degree in the simulated soil sample;

[0025] Step 3.4: Calculate the objective function: Calculate the cumulative outflow from the numerical results of the water-gas two-phase flow;

[0026]

[0027] In the formula, ρ w represent the pore water pressure gradient and water density, respectively, dS is the microarea on the area domain, Γ represents the boundary of the computational domain, and l represents the index variable of the summation symbol;

[0028] Calculate the NRMSE value of the grid point value in each parameter value interval as the objective function;

[0029]

[0030] In the formula, The test value representing the cumulative overflow water volume, is the average value of the overflow water volume in the test. represents the predicted value of overflow water volume in water-gas two-phase flow simulation, k′ is the intrinsic permeability, is the relative permeability coefficient of water, μ w is the viscosity of water, g is the acceleration of gravity; the best fitting soil-water characteristic curve of the soil sample can be obtained through the optimal parameters corresponding to the minimum value of NRMSE;

[0031] Step 3.5: Find the optimal value by comparing the NRMSE value of each grid node of the parameter; if the optimal parameter combination is found, proceed to step 3.6; otherwise, determine a smaller interval of the optimal parameter value and go to step 3.2;

[0032] Step 3.6: Output the optimal parameter values ​​of soil-water characteristic curve.

[0033] Furthermore, the step 3.1 is specifically as follows: the model proposed by van Genuchten, Mualem, and Corey is selected to describe soil-water characteristics, and the expressions thereof are respectively:

[0034] van Genuchten soil-water characteristic curve model:

[0035]

[0036] The relative permeability function of water phase proposed by Mualem is:

[0037]

[0038] The relationship between gas phase relative permeability and saturation proposed by Corey:

[0039]

[0040] Where: S is the matrix suction; P0 is the air intake value, λ represents the curve shape parameter, S rr is the residual saturation; S r is the water saturation; and represent the water phase and gas phase permeabilities, respectively.

[0041] Furthermore, the step 3.3 is specifically as follows: the control equation for the water-gas two-phase flow coupling solution is:

[0042]

[0043] Where: φ, S rThey represent the porosity and water saturation of the medium respectively; is the gradient operator; μ w , μ g represent the viscosity coefficient of water and gas respectively; and k represent the relative permeability and intrinsic permeability of water and gas respectively; p w 、p g are pore water pressure and pore gas pressure respectively; ρ g is the density of the gas.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1) The present invention does not require the soil sample to reach a suction equilibrium state, which greatly shortens the test cycle and greatly improves the test efficiency of the soil-water characteristic curve.

[0046] 2) The present invention combines the advantages of water-gas two-phase flow numerical simulation and grid search method to seek the optimal values ​​of soil-water characteristic parameters of soil samples. The water-gas two-phase flow simulation fully considers the water-gas coupling process inside the unsaturated soil. The grid search method can avoid falling into the local optimal value, which greatly improves the test accuracy.

[0047] 3) The automatic control and data acquisition system of the test device can realize automatic control of the test process and real-time data acquisition, avoid errors introduced by improper manual operation, support multi-point and continuous testing, and help improve the speed and data quality of soil-water characteristic curve testing.

[0048] 4) The present invention can quickly obtain the soil-water characteristic curve of the soil sample, and the test results can comprehensively reflect the water-gas coupling characteristics of unsaturated soil in a wide range of matrix suction, which is closer to the macroscopic soil-water characteristics of the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flow chart of a rapid test method of soil-water characteristic curve based on water-gas two-phase flow;

[0050] Figure 2 It is a structural diagram of the soil-water characteristic curve rapid test system;

[0051] Figure 3 is a curve of cumulative overflow water volume and air pressure changing with time in the embodiment;

[0052] Figure 4 It is the distribution diagram of the objective function NRMSE in the target domain;

[0053] Figure 5 It is a comparison chart between the predicted value of cumulative overflow water volume and the test result value. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] Example 1: Figure 1 As shown, a soil-water characteristic curve rapid testing method based on water-gas two-phase flow comprises the following steps:

[0056] Step S1: construct a soil-water characteristic curve rapid test system, which mainly includes three parts: pressure control system, automatic control and data acquisition system, and soil sample device;

[0057] Step S2: Conduct an unsaturated seepage test to obtain the time-varying process of pore pressure and overflow water volume during the seepage of the soil sample in real time;

[0058] Step S3: Based on the test data, an inversion analysis method combining water-gas two-phase flow numerical simulation with a grid search method is used to calculate the optimal parameter values ​​of the soil-water characteristic curve of the soil.

[0059] Preferably, the step S1 is specifically as follows: the test system is as follows Figure 2 As shown, the pressure control system includes an air compressor, a buffer, an air source, a valve and a water source. The air compressor is used to pressurize the test device to control the flow pressure of water and air in the test. A buffer is provided at the outlet of the air compressor, which is filled with gravel and can slowly and evenly apply pressure to avoid impact on soil samples and instruments during pressurization and pressure relief, and reduce the impact of pressure fluctuations on test results; the automatic control and data acquisition system includes an electromagnetic valve, a relay module, a pressure sensor, an acquisition card, a water collection bottle, an electronic balance and a computer. The electromagnetic valve can apply air pressure or water pressure to the soil sample through automatic switch control. The pressure sensor can continuously monitor the real-time pressure data in the test system. The water collection bottle is used to collect water overflowing from the bottom of the soil sample. The electronic balance is used to weigh and record the overflowed water; the soil sample device includes a sponge, gravel, soil sample and a PVC pipe.

[0060] Preferably, the solenoid valve is connected and communicated with a relay module, and the computer can control the switch state of the solenoid valve through the relay module.

[0061] Preferably, the pressure sensor establishes a communication connection with an acquisition card, and the acquisition card converts the electrical signal collected by the pressure sensor into a digital signal and transmits it to a computer, thereby realizing real-time collection of pressure data during the test process.

[0062] Preferably, the soil sample is placed in a PVC tube, which is arranged from top to bottom in the order of sponge, gravel, soil sample, gravel, and sponge.

[0063] Preferably, gravel is laid at the upper and lower ends of the soil sample device to reduce erosion damage to the soil sample, a sponge is placed on the top to evenly apply air pressure to the sample, and a sponge is placed on the bottom to filter overflow water to ensure the accuracy of the test results.

[0064] Preferably, the sponge at the bottom of the soil sample device system is connected to an outlet pipe, which leads to a water collecting bottle. The mouth of the water collecting bottle is covered with a layer of plastic film to reduce or eliminate the impact of water evaporation on the test. The water collecting bottle is placed on an electronic balance.

[0065] Preferably, the electronic balance has an RS-232 serial communication port, which can communicate with a computer and record the weighing data in the computer.

[0066] Preferably, the step S2 is specifically:

[0067] Step 2.1 Test preparation and sample loading: The sample size used in this test is 75 mm in height and 45 mm in diameter. The sample is filled step by step during loading. This test divides the soil sample into 5 parts, and the side walls of the sample loading device are processed step by step. Then each soil sample is poured into the sample loading device and compacted. The thickness of the soil sample after each compaction is 15 mm, and the sample is compacted as evenly as possible. And apply cementitious material on the wall of the sample loading device, which can not only effectively reduce the gap between the soil sample and the side wall and prevent the occurrence of side wall seepage, but also make the soil sample more tightly embedded in it, thereby further improving the stability and reliability of the sample. At the same time, the density, porosity, saturation and saturated permeability of the soil sample are measured. The soil sample used in this test is red soil in the Three Gorges Reservoir area, and its apparent density is measured to be 2.1g / cm 3 , the porosity is 0.32, the natural saturation is 0.45, and the saturated permeability coefficient of the sample is 2.0×10 -5 cm / s;

[0068] Step 2.2 Check the air tightness of the device and saturate the sample: Before the test, use an air compressor to pressurize the device and check whether the device, especially the interface, is leaking. After 30 minutes of pressurization, the pressure drops by less than 2m, indicating that the air tightness of this test device meets the requirements. After checking that the air tightness of the device is good, open the water supply solenoid valve until the soil sample is saturated and close the water supply solenoid valve;

[0069] Step 2.3 Conduct the test: After the sample is saturated, close the water supply solenoid valve, open the air supply solenoid valve, and apply 300kPa of air pressure to the top of the sample. Under the action of the air pressure, the pore water in the sample will gradually overflow, causing the sample saturation to gradually decrease. Continue to maintain this air pressure until the amount of water overflowing no longer increases. During this process, collect and record the changes in the air pressure at the top of the sample and the cumulative amount of water overflowing at the bottom in real time, import the data into the computer and save it, and draw a curve of the cumulative amount of water overflowing and the change of air pressure over time (such as Figure 3 ). Figure 3 It can be seen that the measured overflow water volume changes in an obvious exponential relationship with time. Within the initial 200 minutes, the cumulative overflow water volume rapidly increased to about 7.9 g. Subsequently, the overflow water volume gradually reached a stable value, indicating that the movement of water and gas in the pores has reached a stable stage.

[0070] Preferably, the step S3 is specifically:

[0071] Step 3.1: Select the unsaturated soil-water behavior model;

[0072] The model proposed by van Genuchten, Mualem, and Corey is selected to describe soil-water characteristics, and its expressions are:

[0073] 1) van Genuchten soil-water characteristic curve model

[0074]

[0075] 2) Water phase relative permeability function proposed by Mualem

[0076]

[0077] 3) Corey's proposed relationship between gas phase relative permeability and saturation

[0078]

[0079] Where: S is the matrix suction; P0 is the air intake value, λ represents the curve shape parameter, S rr is the residual saturation; S r is the water saturation; and represent the water phase and gas phase permeabilities, respectively.

[0080] Step 3.2: Initialize the parameter vector P j The upper and lower boundaries of the value range and Generate grid points in the parameter space, divide each parameter into N intervals, and use the following formula to calculate the specific parameter value P of the grid node j (k):

[0081]

[0082] This test divides each parameter into 5 intervals, namely:

[0083] P0(kPa): [10,60], [10,30], [10,20], [12,16], [14,16]

[0084] λ: [0.1, 0.5], [0.1, 0.3], [0.1, 0.2], [0.13, 0.16], [0.14, 0.16]

[0085] S rr : [0, 0.35], [0, 0.2], [0, 0.1], [0, 0.07], [0.14, 0.16]

[0086] The initial upper and lower bounds of each parameter are: P0[10, 60], λ[0.1, 0.5], S rr [0.02, 0.07].

[0087] Step 3.3: Numerical simulation of water-gas two-phase flow. For each parameter combination, the initial conditions and boundary conditions for solving the water-gas two-phase flow are given, and the water-gas two-phase flow coupling solution is performed to calculate the change process of the pore gas pressure, pore water pressure and saturation degree in the simulated soil sample. The control equation for the water-gas two-phase flow coupling solution is:

[0088]

[0089] Where: φ, S r They represent the porosity and water saturation of the medium respectively; is the gradient operator; μ w , μ g represent the viscosity coefficient of water and gas respectively; and k represent the relative permeability and intrinsic permeability of water and gas respectively; p w 、p g are the pore water pressure and pore gas pressure, respectively. w , g are the densities of water and gas respectively;

[0090] Step 3.4: Calculate the objective function. Calculate the cumulative outflow from the numerical results of the water-gas two-phase flow.

[0091]

[0092] In the formula, represents the pore water pressure gradient, dS is the micro area on the area domain, Γ represents the boundary of the computational domain, and l represents the index variable of the summation symbol;

[0093] The NRMSE value of the grid point value in each parameter value interval is calculated as the objective function.

[0094]

[0095] In the formula, The test value representing the cumulative overflow water volume, is the average value of the overflow water volume in the test. represents the predicted value of overflow water volume in water-gas two-phase flow simulation, k′ is the intrinsic permeability, is the relative permeability coefficient of water, μ w is the viscosity of water, and g is the acceleration of gravity. The best fitting water and air relative permeability of the soil sample can be obtained through the optimal parameters corresponding to the minimum NRMSE value;

[0096] Step 3.5: Find the optimal value by comparing the NRMSE value of each grid node of the parameter. If the optimal parameter combination is found, proceed to step 3.6; otherwise, determine a smaller interval for the optimal parameter value and go to step 3.2. When the minimum NRMSE value obtained in this experiment is 0.038, output the optimal parameter value;

[0097] Step 3.6: Output the optimal parameter values ​​of soil-water characteristic curve {P0, λ, S rr} is {15kPa, 0.15, 0.05}.

[0098] Figure 4 The distribution diagram of the objective function NRMSE in the target domain shows that there are multiple parameter combinations that achieve the local minimum NRMSE value in the parameter space, which further highlights the highly nonlinear nature of the soil-water property inversion problem; in addition, the existence of multiple minimum points in the objective function domain means that when other optimization strategies are adopted, the algorithm is easily limited to a local optimal solution and cannot reach the global optimal solution. It can be seen that the method proposed in this patent is a reliable way to seek the global optimal solution.

[0099] In order to verify the reliability of the proposed test method, the cumulative overflow water volume calculated by the inversion parameters was compared and analyzed with the measured values, such as Figure 5 As shown, the two agree well, indicating that this method is feasible.

[0100] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The embodiments and features in the embodiments of the present application can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A rapid test method for soil-water characteristic curve based on water-gas two-phase flow, characterized by: It includes the following steps: Step S1: construct a soil-water characteristic curve rapid test system, including a pressure control system, an automatic control and data acquisition system, and a soil sample device; Step S2: Conduct an unsaturated seepage test to obtain the time-varying process of pore pressure and overflow water volume during the seepage of the soil sample in real time; Step S3: Based on the test data, an inversion analysis method combining water-gas two-phase flow numerical simulation with a grid search method is used to calculate the optimal parameter values ​​of the soil-water characteristic curve of the soil.

2. A soil-water characteristic curve rapid testing method based on water-gas two-phase flow according to claim 1, characterized in that: In step S1, the pressure control system comprises an air compressor (1), a buffer (2), an air source (3), a valve (8) and a water source (9); the air compressor (1) is used to pressurize the test device to control the flow pressure of water and air in the test; a buffer (2) is provided at the outlet of the air compressor (1) to avoid impact on the soil sample and the instrument during the pressurization and depressurization process, thereby reducing the influence of pressure fluctuations on the test results; The automatic control and data acquisition system comprises a solenoid valve (4), a relay module (5), a pressure sensor (6), an acquisition card (7), a water collection bottle (14), an electronic balance (15) and a computer (16), wherein the pressure sensor (6) is used to continuously monitor the real-time data of the pressure in the test system, the water collection bottle (14) is used to collect the amount of water overflowing from the bottom of the soil sample, and the electronic balance (15) is used to weigh and record the amount of overflowing water; The soil sample device comprises a sponge (10), gravel (11), a soil sample (12) and a PVC pipe (13).

3. The method for rapid testing soil-water characteristic curve based on water-gas two-phase flow according to claim 2 is characterized in that: The solenoid valve (4) is connected to the relay module (5) for communication, and the computer (16) controls the switch state of the solenoid valve (4) through the relay module (5).

4. The method for rapid testing soil-water characteristic curve based on water-gas two-phase flow according to claim 2 is characterized in that: The pressure sensor (6) establishes a communication connection with the acquisition card (7), and the acquisition card (7) converts the electrical signal collected by the pressure sensor (6) into a digital signal and transmits it to the computer (16), thereby realizing real-time collection of pressure data during the test process.

5. The method for rapid testing soil-water characteristic curve based on water-gas two-phase flow according to claim 2 is characterized in that: The soil sample is placed in a PVC pipe (13), which is arranged from top to bottom in the order of a sponge (10), gravel (11), a soil sample (12), gravel (11), and a sponge (10).

6. The method for rapid testing soil-water characteristic curve based on water-gas two-phase flow according to claim 2 is characterized in that: The sponge (10) at the bottom of the soil sample device is connected to an outlet pipe, which leads to a water collecting bottle (14). The mouth of the water collecting bottle (14) is covered with a plastic film to reduce or eliminate the influence of water evaporation on the test. The water collecting bottle (14) is placed on an electronic balance (15); the electronic balance (15) has an RS-232 serial port communication to realize communication with a computer (16) and record the weighing data in the computer.

7. The method for rapid testing soil-water characteristic curve based on water-gas two-phase flow according to claim 1 is characterized in that: The step S2 is specifically as follows: Step 2.1: Test preparation and sample loading: Fill the sample step by step, and evenly apply cementitious material on the wall of the sample loading device, so as to use it as a medium to embed the soil sample tightly, reduce the gap between the soil sample and the surrounding wall, hinder the movement of water and gas through the wall channel, and thus prevent the occurrence of wall seepage; at the same time, measure the density, porosity, saturation and saturated permeability of the soil sample to provide initial conditions and material parameters for numerical back calculation; Step 2.2: Check the air tightness of the device and saturate the sample: After checking that the air tightness of the device is good, open the water supply solenoid valve until the soil sample is saturated and then close the water supply solenoid valve; Step 2.3: Conduct unsaturated permeability test: After the soil sample is saturated, apply air pressure to it and conduct a soil-water property test. Collect and record the air pressure at the top of the sample and the cumulative overflow water at the bottom in real time, and draw a curve of the cumulative overflow water and air pressure changing with time.

8. The method for rapid testing soil-water characteristic curve based on water-gas two-phase flow according to claim 1 is characterized in that: The step S3 is specifically as follows: Step 3.1: Select the unsaturated soil-water behavior model; Step 3.2: Initialize the parameter vector P j The upper and lower boundaries of the value range and Generate grid points in the parameter space, divide each parameter into N intervals, and use the following formula to calculate the specific parameter value P of the grid node j (k): Step 3.3: Numerical simulation of water-gas two-phase flow: For each parameter combination, the initial conditions and boundary conditions for solving the water-gas two-phase flow are given, and the water-gas two-phase flow coupling solution is performed to calculate the change process of pore gas pressure, pore water pressure and saturation degree in the simulated soil sample; Step 3.4: Calculate the objective function: Calculate the cumulative outflow from the numerical results of the water-gas two-phase flow; In the formula, ρ w represent the pore water pressure gradient and water density, respectively, dS is the microarea on the area domain, Γ represents the boundary of the computational domain, and l represents the index variable of the summation symbol; Calculate the NRMSE value of the grid point value in each parameter value interval as the objective function; In the formula, The test value representing the cumulative overflow water volume, is the average value of the overflow water volume tested in the experiment, represents the predicted value of overflow water volume in water-gas two-phase flow simulation, k′ is the intrinsic permeability, is the relative permeability coefficient of water, μ w is the viscosity of water, g is the acceleration of gravity; the best fitting soil-water characteristic curve of the soil sample can be obtained through the optimal parameters corresponding to the minimum value of NRMSE; Step 3.5: Find the optimal value by comparing the NRMSE value of each grid node of the parameter; if the optimal parameter combination is found, proceed to step 3.6; otherwise, determine a smaller interval of the optimal parameter value and go to step 3.2; Step 3.6: Output the optimal parameter values ​​of soil-water characteristic curve.

9. The method for rapid testing soil-water characteristic curve based on water-gas two-phase flow according to claim 3 is characterized in that: The step 3.1 is specifically as follows: select the model proposed by van Genuchten, Mualem, and Corey to describe soil-water characteristics, and the expressions thereof are: van Genuchten soil-water characteristic curve model: The relative permeability function of water phase proposed by Mualem: The relationship between gas phase relative permeability and saturation proposed by Corey: Where: S is the matrix suction; P0 is the air intake value, λ represents the curve shape parameter, S rr is the residual saturation; S r is the water saturation; and represent the water phase and gas phase permeabilities, respectively.

10. The method for rapid testing soil-water characteristic curve based on water-gas two-phase flow according to claim 3, characterized in that: The step 3.3 is specifically as follows: the control equation for the water-gas two-phase flow coupling solution is: Where: φ, S r They represent the porosity and water saturation of the medium respectively; is the gradient operator, μ w , μ g represent the viscosity coefficient of water and gas respectively; and k represent the relative permeability and intrinsic permeability of water and gas respectively; p w 、p g are pore water pressure and pore gas pressure respectively; ρ g is the gas density.

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