Method for accurately acquiring unsaturated permeability coefficient of earth-rock mixture

Abstract

The invention discloses a method for accurately acquiring an unsaturated permeability coefficient of a soil-rock mixture, and relates to the technical field of material analysis. The method comprises the following steps: firstly, obtaining a soil-water characteristic curve of a soil-rock mixture in a full suction range through an experiment; then fitting a soil-water characteristic curve by using a VG model to accurately obtain fitting parameters; the saturated permeability coefficient of the soil-rock aggregate is obtained through a constant head permeability test, and finally, based on the fitting parameters and the saturated permeability coefficient, the accurate unsaturated permeability coefficient of the soil-rock aggregate is obtained through calculation by using a Gardner model. According to the method, the unsaturated permeability coefficient of the soil-rock aggregate is obtained through an indirect calculation method, the influence of various uncertain factors possibly existing in direct measurement through experiments is avoided, meanwhile, the accurate unsaturated permeability coefficient of the soil-rock aggregate can be obtained in the experiment times as few as possible, the cost is low, the time is short, and the method is suitable for large-scale popularization and application. The method is suitable for rapidly acquiring the unsaturated permeability coefficient of the soil-rock mixture on a large scale.

Description

Technical Field

[0001] The invention relates to the technical field of material analysis, in particular to analysis of unsaturated permeability coefficient, and in particular to a method for accurately obtaining the unsaturated permeability coefficient of a soil-rock mixture. Background Art

[0002] The unsaturated permeability coefficient of soil-rock mixture is an important parameter of soil-rock mixture permeability. It reflects the conductivity of soil to fluid under unsaturated conditions. It is closely related to factors such as the internal structure, particle size, porosity, and particle shape of the soil-rock mixture. In actual engineering, the permeability characteristics of soil-rock mixture are important factors that restrict engineering design, construction, and even safe operation.

[0003] Soil-water characteristics are the basis for obtaining the permeability of soil-rock mixtures, which can be expressed by soil-water characteristic curves. The soil-water characteristic curve (SWCC) is a curve that describes the relationship between suction and water content in unsaturated soil. The soil-water characteristic curve can reflect the size and distribution of pores in the soil. However, most of the current soil-water characteristic curve tests are conducted in the low suction range. The soil-water characteristic curve of the full suction range is derived using limited data points in the low suction range, which has certain deviations; especially for soil-rock mixtures, due to the special soil pore structure characteristics of soil-rock mixtures, the existing soil-water characteristic curves cannot characterize the soil-water characteristics of the full suction range, and thus it is impossible to obtain an accurate soil-water characteristic curve for the soil-rock mixture, thereby obtaining accurate permeability of the soil-rock mixture.

[0004] Although the permeability characteristics of soil-rock mixture can be characterized by saturated permeability coefficient, the saturated permeability coefficient alone cannot characterize its permeability characteristics in the whole process of saturation-unsaturation. Therefore, it is necessary to obtain the unsaturated permeability coefficient of soil-rock mixture to characterize its permeability characteristics. However, although the unsaturated permeability coefficient of soil-rock mixture can be measured by experiment, the measurement of the unsaturated permeability coefficient of soil-rock mixture is relatively complicated, and the measurement of the unsaturated permeability coefficient of soil-rock mixture with different stone contents requires a large number of experiments, which is costly and time-consuming. Therefore, estimating the unsaturated permeability coefficient of soil-rock mixture by empirical formula is the best way to quickly and accurately obtain the unsaturated permeability characteristics of soil-rock mixture with different stone contents. However, due to the influence of soil-water characteristic curve and stone content, the existing empirical formula cannot directly and accurately obtain the unsaturated permeability coefficient of soil-rock mixture with different stone contents. Therefore, it is necessary to optimize the method of obtaining the unsaturated permeability coefficient to ensure that the unsaturated permeability coefficient of soil-rock mixture with different stone contents can be obtained more accurately. Summary of the invention

[0005] The purpose of the present invention is to propose a method for accurately obtaining the unsaturated permeability coefficient of soil-rock mixtures because the existing empirical formula cannot directly and accurately obtain the unsaturated permeability coefficient of soil-rock mixtures with different stone contents due to the influence of the soil-water characteristic curve and the stone content.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides a method for accurately obtaining the unsaturated permeability coefficient of a soil-rock mixture, comprising the following steps:

[0007] S1. Obtain the saturation of soil-rock mixture with different rock contents through experiments (S e ) and matrix suction (S); based on the saturation and matrix suction, draw the soil-water characteristic curve of the full suction range of soil-rock mixture with different rock contents;

[0008] S2. Use the VG model to fit the soil-water characteristic curve to obtain the values ​​of fitting parameters a, m, and n of soil-rock mixtures with different stone contents; the VG model formula is: In the formula, S e is saturation, S is matrix suction, a, m, n are fitting parameters;

[0009] S3. Obtain the saturated permeability coefficient (K) of soil-rock mixture with different rock contents through constant head permeability test. S );

[0010] S4. Based on the fitting parameters and the saturated permeability coefficient, the unsaturated permeability coefficient (K) of the soil-rock mixture with different stone contents is calculated using the Gardner model; the formula of the Gardner model is: Where k is the unsaturated permeability coefficient, K S is the saturated permeability coefficient, a and n are fitting parameters.

[0011] The invention discloses a method for accurately obtaining the unsaturated permeability coefficient of a soil-rock mixture. First, a soil-water characteristic curve of the soil-rock mixture in the full suction range is obtained through experiments; then, a VG model is used to fit the soil-water characteristic curve to accurately obtain fitting parameters; then, a saturated permeability coefficient of the soil-rock mixture is obtained through a constant head permeability test; finally, based on the fitting parameters and the saturated permeability coefficient, the Gardner model is used to calculate the accurate unsaturated permeability coefficient of the soil-rock mixture; the method obtains the unsaturated permeability coefficient of the soil-rock mixture through an indirect calculation method, thereby avoiding the influence of various uncertain factors that may exist in direct measurement through experiments; meanwhile, the accurate unsaturated permeability coefficient of the soil-rock mixture can be obtained in a minimum number of experiments, with low cost and short time, and is suitable for large-scale rapid acquisition of the unsaturated permeability coefficient of the soil-rock mixture.

[0012] Among them, in step S1, preferably, the saturation and matrix suction of soil-rock mixtures with different stone contents are obtained by the pressure plate method; the structure of the soil-rock mixture is relatively loose, and the changes in the soil-water characteristic curve are concentrated in the low suction range. The pressure plate method is used to obtain the results with higher accuracy.

[0013] Preferably, the specific method of obtaining the saturation and matrix suction of soil-rock mixtures with different rock contents by the pressure plate method includes:

[0014] (1) Specimen preparation: The soil-rock mixture specimen was formed into a non-standard ring knife specimen by static pressure method. The specimen was a cylinder with a diameter of 76 mm and a height of 68 mm. The moisture content of the soil-rock mixture specimen was the natural moisture content (m dry ), the stone content is 30%, 40%, 50% and 60% respectively; the formed test piece is placed in a saturator, and then placed in a vacuum saturation container, immersed in water, and after a vacuum saturation treatment of more than 24 hours, the test piece is obtained;

[0015] (2) Saturated clay plate: Place the side wall of the stainless steel sample chamber on the base, inject airless water to submerge the clay plate, and the water level is about 5 cm above the surface of the clay plate; fill the entire water body and the measurement system with airless water, and remove bubbles; assemble the instrument, apply an air pressure of 5-20 kPa, and continue to drain for more than one hour until there are no obvious bubbles and the clay plate is saturated, thus obtaining a saturated clay plate;

[0016] (3) Water channel flushing: The drainage groove under the clay plate is where bubbles tend to concentrate. During the flushing process, a hand pump is used to apply a very small air pressure to the left measuring tube so that the diffused bubbles under the clay plate flow out with the water in the transparent connecting tube. After the flushing is completed, adjust the water level in the left measuring tube, gas collecting bottle and horizontal capillary tube to the marked scale, and record the original reading (V0) of the right measuring tube.

[0017] (4) Install the test specimen and start the test: After the test specimen is placed, adjust the air pressure in the test chamber to the required pressure value through the pressure control panel; wait until the specimen reaches a state of equilibrium under the suction, that is, the change in water volume is no longer obvious; record the reading (V) of the right measuring tube. The difference between this reading and the previous reading is the change in water volume of the soil sample between the two measurements;

[0018] (5) Pressurize step by step: After the previous pressure test is completed, pressurize step by step and repeat step (4) until all pressure levels are tested. Reduce the air pressure to zero, disassemble the confining pressure chamber, take out the test piece, place the test piece in a 105℃ oven for 8h, and calculate the residual moisture content of the test piece after drying.

[0019] (6) Data processing: The pressure value set at each level of air pressure is the corresponding matrix suction (S) after the specimen soil reaches equilibrium; the saturation (S e) is the mass moisture content of the soil sample at each level of pressure (ω i ).

[0020] Preferably, in step (1), before the sample is formed, particles larger than 20.0 mm are screened out from the sample.

[0021] Preferably, in steps (4) and (5), the air pressure is set to 9 levels, namely 5 kPa, 10 kPa, 20 kPa, 30 kPa, 50 kPa, 100 kPa, 300 kPa, 500 kPa and 1000 kPa, respectively; the preferred air pressure setting level can more accurately measure the saturation and matrix suction data of soil-rock mixtures with different stone contents, so that the soil-water characteristic curve of the soil-rock mixture in the full suction range can be accurately drawn, significantly improving the accuracy of the unsaturated permeability coefficient of the soil-rock mixture.

[0022] Preferably, in step (6), the mass moisture content (ω i ) is calculated as: Among them, ω i ,ω i+1 is the mass water content (%) at the i-th and i+1-th level pressures; V i 、V i+1 is the reading of the right tube under the i-th and i+1-th pressures (ml); ρ is the density of water (g / cm 3 ); m is the dry soil weight of the specimen when it was formed (g).

[0023] Among them, in step S3, the constant head permeability test is carried out according to the "Highway Geotechnical Test Code" (JTG3430-2020).

[0024] Preferably, the saturated permeability coefficient (K S ) is calculated as: Q is the amount of permeated water in time t (cm 3 ), L is the height of the sample between the centers of the two pressure measuring holes (cm), H is the average water level difference (cm), t is the time, and A is the cross-sectional area of ​​the sample (cm 2 ).

[0025] Preferably, since water temperature has a greater influence on the saturated permeability coefficient of soil, especially on soil with a high rock content and a large porosity, step S3 further includes: obtaining the saturated permeability coefficient (K S ) is used to calculate the saturated permeability coefficient when the water temperature is T; the saturated permeability coefficient (K ST ) is calculated as: K S is the experimentally measured saturated permeability coefficient; η Tis the hydrodynamic viscosity coefficient at temperature T℃; η S is the hydrodynamic viscosity at the experimental temperature.

[0026] Preferably, the hydrodynamic viscosity coefficient is obtained by querying Table T0129-1 in the "Highway Geotechnical Test Code" (JTG3430-2020).

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture of the present invention obtains the unsaturated permeability coefficient of the soil-rock mixture by an indirect calculation method, thereby avoiding the influence of various uncertain factors that may exist in direct experimental measurement. At the same time, the accurate unsaturated permeability coefficient of the soil-rock mixture can be obtained in a minimum number of experiments, which is low in cost and time, and is suitable for large-scale rapid acquisition of the unsaturated permeability coefficient of a soil-rock mixture.

[0029] 2. The method for obtaining the unsaturated permeability coefficient of soil-rock mixture of the present invention has carried out targeted optimization on the method for obtaining the saturation and matrix suction of soil-rock mixture with different stone contents by the pressure plate method, so that the saturation and matrix suction data of soil-rock mixture with different stone contents can be obtained more accurately, thereby being able to accurately draw the soil-water characteristic curve of the whole suction range of soil-rock mixture, and significantly improving the accuracy of the unsaturated permeability coefficient of soil-rock mixture.

[0030] 3. The method for obtaining the unsaturated permeability coefficient of the soil-rock mixture of the present invention also takes into account the influence of temperature on the saturated permeability coefficient, and performs targeted optimization and adjustment to make the calculated unsaturated permeability coefficient of the soil-rock mixture more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The soil-water characteristic curve diagram of soil-rock mixture with different stone contents obtained in Example 1 of the present invention;

[0032] Figure 2 The saturated permeability coefficient of the soil-rock mixture obtained in Example 1 of the present invention varies with the rock content;

[0033] Figure 3 This is a graph of the unsaturated permeability coefficient of soil-rock mixtures with different stone contents at 20°C obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies implemented based on the content of the present invention belong to the scope of the present invention.

[0035] Embodiment 1:

[0036] A method for accurately obtaining the unsaturated permeability coefficient of a soil-rock mixture comprises the following steps:

[0037] S1. Obtain the saturation of soil-rock mixture with different rock contents by pressure plate method (S e ) and matrix suction (S); based on the saturation and matrix suction, the soil-water characteristic curve ( Figure 1 );

[0038] The specific methods of the pressure plate method include:

[0039] (1) Specimen preparation: The soil-rock mixture sample (particles larger than 20.0 mm were screened out) was formed into a non-standard ring knife specimen by static pressure method. The specimen was a cylinder with a diameter of 76 mm and a height of 68 mm. The moisture content of the soil-rock mixture sample was the natural moisture content (m dry ), the stone content is 30%, 40%, 50% and 60% respectively; the formed test piece is placed in a saturator, and then placed in a vacuum saturation container, immersed in water, and after a vacuum saturation treatment of more than 24 hours, the test piece is obtained;

[0040] (2) Saturated clay plate: Place the side wall of the stainless steel sample chamber on the base, inject airless water to submerge the clay plate, and the water level is about 5 cm above the surface of the clay plate; fill the entire water body and the measurement system with airless water, and remove bubbles; assemble the instrument, apply an air pressure of 5-20 kPa, and continue to drain for more than one hour until there are no obvious bubbles and the clay plate is saturated, thus obtaining a saturated clay plate;

[0041] (3) Water channel flushing: The drainage groove under the clay plate is where bubbles tend to concentrate. During the flushing process, a hand pump is used to apply a very small air pressure to the left measuring tube so that the diffused bubbles under the clay plate flow out with the water in the transparent connecting tube. After the flushing is completed, adjust the water level in the left measuring tube, gas collecting bottle and horizontal capillary tube to the marked scale, and record the original reading (V0) of the right measuring tube.

[0042] (4) Install the test specimen and start the test: After the test specimen is placed, adjust the air pressure in the test chamber to the required pressure value through the pressure control panel; wait until the specimen reaches a state of equilibrium under the suction, that is, the change in water volume is no longer obvious; record the reading (V) of the right measuring tube. The difference between this reading and the previous reading is the change in water volume of the soil sample between the two measurements;

[0043] (5) Pressurize step by step: After the previous pressure test is completed, pressurize step by step (the air pressure is set to 9 levels, namely 5 kPa, 10 kPa, 20 kPa, 30 kPa, 50 kPa, 100 kPa, 300 kPa, 500 kPa and 1000 kPa), and repeat step (4) until the experiment of all pressure levels is completed; reduce the air pressure to zero, disassemble the confining pressure chamber, take out the test piece, place the test piece in a 105 ° C oven for 8 hours, and calculate the residual moisture content of the test piece after drying;

[0044] (6) Data processing: The pressure value set at each level of air pressure is the corresponding matrix suction (S) after the specimen soil reaches equilibrium; the saturation (S e ) is the mass moisture content of the soil sample at each level of pressure (ω i ); mass moisture content of the test soil sample (ω i ) is calculated as: Among them, ω i ,ω i+1 is the mass water content (%) at the i-th and i+1-th level pressures; V i , V i+1 is the reading of the right tube under the i-th and i+1-th pressures (ml); ρ is the density of water (g / cm 3 ); m is the dry soil weight of the specimen when it was formed (g);

[0045] S2. Using VG model The soil-water characteristic curve was fitted to obtain the values ​​of fitting parameters a, m, and n for soil-rock mixtures with different rock contents (see Table 1);

[0046] Table 1 Soil-water characteristic curve fitting parameters

[0047]

[0048]

[0049] S3. Through the constant head permeability test (Highway Geotechnical Test Code), the saturated permeability coefficient (K S );

[0050] Saturated permeability coefficient (K S ) is calculated as: Q is the amount of permeated water in time t (cm 3 ), L is the height of the sample between the centers of the two pressure measuring holes (cm), H is the average water level difference (cm), t is the time, and A is the cross-sectional area of ​​the sample (cm 2 );

[0051] The saturated permeability coefficient (K S) based on the calculation results, the saturated permeability coefficient at a water temperature of 20°C was obtained (see Table 2, Figure 2 ); saturated permeability coefficient when water temperature is 20℃ (K ST ) is calculated as: K S is the experimentally measured saturated permeability coefficient; η T is the hydrodynamic viscosity coefficient at a temperature of 20°C; η s is the hydrodynamic viscosity coefficient at the experimental temperature;

[0052] Table 2 Permeability coefficient of soil-rock mixture

[0053]

[0054] The hydrodynamic viscosity coefficient is obtained by querying Table T0129-1 in the "Highway Geotechnical Test Code" (JTG3430-2020);

[0055] S4. Based on the fitting parameters and saturated permeability coefficient, the Gardner model was used The unsaturated permeability coefficient (K) of soil-rock mixture with different rock contents was calculated and plotted as a curve (see Figure 3 ).

Claims

1. A method for accurately obtaining the unsaturated permeability coefficient of a soil-rock mixture, characterized in that: The following steps are involved: S1. Obtain the saturation and matrix suction of soil-rock mixtures with different stone contents through experiments; draw the soil-water characteristic curve of the full suction range of soil-rock mixtures with different stone contents according to the saturation and matrix suction; S2. Use the VG model to fit the soil-water characteristic curve to obtain the values ​​of fitting parameters a, m, and n of soil-rock mixtures with different stone contents; the VG model formula is: In the formula, S e is saturation, S is matrix suction, a, m, n are fitting parameters; S3. Obtain the saturated permeability coefficient of soil-rock mixture with different rock contents through constant head permeability test; S4. Based on the fitting parameters and the saturated permeability coefficient, the unsaturated permeability coefficient of the soil-rock mixture with different stone contents is calculated using the Gardner model; the formula of the Gardner model is: Where k is the unsaturated permeability coefficient, K S is the saturated permeability coefficient, a and n are fitting parameters.

2. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 1, characterized in that: In step S1, the saturation and matrix suction of soil-rock mixtures with different rock contents are obtained by the pressure plate method.

3. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 2, characterized in that: The specific methods for obtaining the saturation and matrix suction of soil-rock mixtures with different rock contents by the pressure plate method include: (1) Specimen preparation: The soil-rock mixture sample was formed into a non-standard ring knife specimen by static pressure method. The specimen was a cylinder with a diameter of 76 mm and a height of 68 mm. The moisture content of the soil-rock mixture sample was the natural moisture content, and the stone content was 30%, 40%, 50%, and 60% respectively. The formed specimen was placed in a saturator, and then placed in a vacuum saturation container, immersed in water, and subjected to vacuum saturation treatment for more than 24 hours to obtain the specimen to be tested. (2) Saturated clay plate: Place the side wall of the stainless steel sample chamber on the base, inject airless water to submerge the clay plate, and the water level is about 5 cm above the surface of the clay plate; fill the entire water body and the measurement system with airless water, and remove bubbles; assemble the instrument, apply an air pressure of 5-20 kPa, and continue to drain for more than one hour until there are no obvious bubbles and the clay plate is saturated, thus obtaining a saturated clay plate; (3) Water channel flushing: The drainage groove under the clay plate is where bubbles are easily concentrated. During the flushing process, a hand pump is used to apply a very small air pressure to the left measuring tube so that the diffused bubbles under the clay plate flow out with the water in the transparent connecting tube. After the flushing is completed, adjust the water level in the left measuring tube, gas collecting bottle and horizontal capillary tube to the marked scale, and record the original reading of the right measuring tube. (4) Install the test specimen and start the test: After the test specimen is placed, adjust the air pressure in the test chamber to the required pressure value through the pressure control panel; wait until the specimen reaches a state of equilibrium under the suction, that is, the change in water volume is no longer obvious; record the reading of the right measuring tube, and the difference between this reading and the previous reading is the change in water volume of the soil sample between the two measurements; (5) Pressurize step by step: After the previous pressure test is completed, pressurize step by step and repeat step (4) until all pressure levels are tested. Reduce the air pressure to zero, disassemble the confining pressure chamber, take out the test piece, place the test piece in a 105℃ oven for 8h, and calculate the residual moisture content of the test piece after drying. (6) Data processing: The pressure value set at each level of air pressure is the corresponding matrix suction after the specimen soil reaches a state of equilibrium; the saturation is the mass moisture content of the specimen soil sample at each level of pressure.

4. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 3, characterized in that: In step (1), before the sample is formed, particles larger than 20.0 mm are screened out from the sample.

5. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 3, characterized in that: In steps (4) and (5), the air pressure is set to 9 levels, namely 5kPa, 10kPa, 20kPa, 30kPa, 50kPa, 100kPa, 300kPa, 500kPa and 1000kPa.

6. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 3, characterized in that: In step (6), the mass moisture content of the test soil sample is calculated as: Among them, ω i ,ω i+1 is the mass water content at the i-th and i+1-th level pressures; V i 、V i+1 is the reading of the right measuring tube under the i-th and i+1-th level air pressures; ρ is the density of water; m is the dry soil weight when the specimen is formed.

7. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 1, characterized in that: In step S3, the constant head permeability test is carried out according to the Highway Geotechnical Test Code.

8. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 1, characterized in that: In step S3, the calculation formula of the saturated permeability coefficient is: Q is the amount of permeable water in time t, L is the height of the sample between the centers of the two pressure measuring holes, H is the average water level difference, t is time, and A is the cross-sectional area of ​​the sample.

9. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 1, characterized in that: Step S3 also includes: based on the saturated permeability coefficient of the soil-rock mixture obtained through experiments, calculating the saturated permeability coefficient when the water temperature is T; the saturated permeability coefficient (K ST ) is calculated as: K S is the experimentally measured saturated permeability coefficient; η T is the hydrodynamic viscosity coefficient at temperature T℃; η S is the hydrodynamic viscosity at the experimental temperature.

10. The method for obtaining the unsaturated permeability coefficient of a soil-rock mixture according to claim 9, characterized in that: The hydrodynamic viscosity coefficient is obtained by querying Table T0129-1 in the Highway Geotechnical Test Code.

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