Method for simulating soil moisture migration in coal mining fractured area

Abstract

The invention discloses a method for simulating soil moisture migration in a coal mining fractured area. The method comprises the following steps: 1, collecting measurement data; 2, preprocessing the collected and measured data; 3, acquiring soil hydraulic characteristic parameters of the coal mining fractured region; and 4, establishing a coal mining fractured region model, and performing simulation according to the established matrix domain moisture migration equation and fracture domain moisture migration equation. The method is simple in step and reasonable in design, the established coal mining fractured region model is divided into the fracture region and the matrix region, the water migration equations are established for the fracture region and the matrix region respectively for simulation, the soil water content of the coal mining fractured region is obtained, the soil water migration condition of the fractured region is effectively adapted, and the method has good application prospects. The moisture migration simulation accuracy is improved, and the soil moisture migration rate and the moisture movement path can be predicted subsequently according to the soil moisture content.

Description

Technical Field

[0001] The invention belongs to the technical field of soil moisture migration simulation, and in particular relates to a soil moisture migration simulation method in a coal mining crack area. Background Art

[0002] The Loess Plateau is the main coal producing area in my country. With the advancement of coal technology, the mining areas in the Loess Plateau have basically formed a high-intensity and high-efficiency underground mining model. However, large-scale underground coal mining has caused serious surface cracks, causing extensive and severe surface damage to the mining areas in the Loess Plateau. The surface cracks caused by underground coal mining have a direct impact on soil moisture and its migration process, resulting in increasingly prominent and serious ecological and environmental damage problems in the region. However, it is difficult to obtain soil moisture migration during the development of cracks. The existing soil moisture migration simulation methods are mainly aimed at homogeneous soils under natural conditions. Mining cracks change the soil structure, soil moisture evaporation rate and migration path, increase the complexity of moisture migration, and cause the hydraulic characteristics of the crack area to be quite different from those of the soil in the natural state. Due to the change of its own migration path and the existence of uneven hydraulic characteristics, the existing soil moisture migration simulation methods cannot be directly applied to mining crack areas.

[0003] Therefore, there is a lack of a reasonably designed method for simulating soil moisture migration in coal mining crack areas. The established coal mining crack area model is divided into crack domain and matrix domain, and moisture migration equations are established for the crack domain and matrix domain respectively for simulation, so as to obtain the soil moisture content in the coal mining crack area, effectively adapt to the soil moisture migration in the crack area, and improve the accuracy of moisture migration simulation. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for simulating soil moisture migration in coal mining crack areas in view of the deficiencies in the above-mentioned prior art. The method has simple steps and reasonable design. The established coal mining crack area model is divided into a crack domain and a matrix domain, and moisture migration equations are established for the crack domain and the matrix domain respectively for simulation, so as to obtain the soil moisture content in the coal mining crack area, effectively adapt to the soil moisture migration situation in the crack area, and improve the accuracy of moisture migration simulation.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for simulating soil moisture migration in coal mining crack areas, characterized in that the method comprises the following steps:

[0006] Step 1: Collection of measurement data:

[0007] Step 101: During the set total monitoring time, the crack depth, lower crack width and upper crack width in the coal mining crack area to be studied are obtained by using the crack monitoring module; the soil water content, soil water suction and soil porosity in the coal mining crack area to be studied are obtained by using the soil monitoring module; the rainfall intensity, temperature and total solar radiation in the coal mining crack area to be studied are obtained by using the meteorological module;

[0008] Step 102, measuring the soil texture in the coal mining crack area to be studied, and obtaining soil texture data of the coal mining crack area to be studied;

[0009] Step 103, record the crack depth as the first type of measurement data, record the lower crack width as the second type of measurement data, record the upper crack width as the third type of measurement data, record the soil moisture content as the fourth type of measurement data, record the soil water suction as the fifth type of measurement data, record the soil porosity as the sixth type of measurement data, record the rainfall intensity as the seventh type of measurement data, record the temperature as the eighth type of measurement data, and record the total solar radiation as the ninth type of measurement data;

[0010] Step 2: Preprocessing of collected measurement data:

[0011] Step 201: preprocessing the first category to the ninth category of measurement data using a computer to obtain the first category to the ninth category of measurement data after preprocessing;

[0012] Step 202, performing mean processing on the pre-processed measurement data of the first category to the ninth category respectively, to obtain the measured mean value of the crack depth, the mean value of the lower crack width, the mean value of the upper crack width, the mean value of the soil moisture content, the mean value of the soil water suction, the mean value of the soil porosity, the mean value of the rainfall intensity, the mean value of the air temperature and the mean value of the total solar radiation; wherein the mean value of the crack depth, the mean value of the lower crack width and the mean value of the upper crack width are recorded as crack data, and the mean value of the soil moisture content, the mean value of the soil water suction, the mean value of the soil porosity, the mean value of the rainfall intensity, the mean value of the air temperature and the mean value of the total solar radiation are recorded as simulation initial parameters;

[0013] Step 3: Obtain soil hydraulic characteristic parameters in coal mining crack areas:

[0014] Step 301, using a computer to plot each point of the pre-processed fifth category measurement data and the pre-processed fourth category measurement data with soil water suction as the horizontal coordinate and soil water content as the vertical coordinate;

[0015] Step 302: Using a computer to perform curve fitting based on the points of the pre-processed fifth category measurement data and the pre-processed fourth category measurement data, the residual moisture content θ is obtained. r , saturated water contentθ s, a first soil porosity related parameter α, a second soil porosity related parameter n and a third soil porosity related parameter m;

[0016] Step 303: Using a computer according to the formula The unsaturated hydraulic conductivity function K(θ) is obtained; where K s is the saturated hydraulic conductivity; θ represents the independent variable of soil moisture content;

[0017] Step 4: Establish a coal mining fracture area model and perform simulation based on the established matrix domain water migration equation and fracture domain water migration equation:

[0018] Step 401, using a computer and hydrus software to establish a cross-sectional diagram of the coal mining crack area to be studied according to the crack data in step 202, recorded as the coal mining crack area model 0BGA, and set the simulation initial parameters and boundary initial conditions; wherein, the soil area 10 cm away from the crack area boundary in the coal mining crack area model 0BGA is set as the crack area, and the remaining soil area is set as the matrix area;

[0019] Step 402, using a computer and hydrus software to mesh the coal mining fracture area model OBGA with equally spaced grids to obtain a coal mining fracture area grid model;

[0020] Step 403: Use a computer to establish a matrix domain water migration equation, as follows:

[0021] Among them, C a is the specific water density of the matrix domain, θ a is the soil moisture function in the matrix domain, t is time, represents the partial derivative with respect to time t, represents the partial derivative about the x direction, h a is the water potential in the matrix domain, represents the partial derivative about the z direction, K(θ a ) represents the value of the independent variable of soil moisture content θ a Unsaturated hydraulic conductivity at ;

[0022] The water migration equation in the crack domain is established by computer, as follows:

[0023] Among them, C c is the specific water density in the fracture domain, θ c is the soil moisture function in the crack domain, h c is the water potential in the fracture domain, K(θ c ) represents the value of the independent variable of soil moisture content θ c The unsaturated hydraulic conductivity at wis the dual-domain water exchange term, Γ l is the laminar exchange term, Γ i is the horizontal imbibition exchange term, ξ a is the volume ratio of the matrix domain, ξ c is the volume ratio of the crack domain, α w is the water conversion rate, K c-a is the saturated hydraulic conductivity at the junction of the two domains, and W is the mean width of the crack, g is the acceleration of gravity, and v is the soil compression coefficient; l f is the wetted length of the left side of the crack, l r is the wetted length of the right side of the crack, Indicates about l f The partial guide, Indicates about l r The partial derivative of

[0024] Step 404: using a computer to compile the established matrix domain water migration equation and fracture domain water migration equation to generate a DLL file and load it into the hydrus software;

[0025] Step 405: Use a computer to use Hydras software to set the time step and the total simulation time, simulate the coal mining crack area grid model according to the established matrix domain moisture migration equation and crack domain moisture migration equation, and obtain the soil moisture content of each node in the coal mining crack area grid model.

[0026] The above-mentioned method for simulating soil moisture migration in coal mining crack areas is characterized by: step 401, the specific process is as follows:

[0027] Step 4011, using a computer and using the geometry module Geometry in the hydrus software to establish a coal mining crack area model 0BGA; wherein the x direction of the coal mining crack area model 0BGA is the crack width direction, and the z direction of the coal mining crack area model 0BGA is the crack depth upward; the coal mining crack area model 0BGA includes a crack area CDBF and a soil area, the soil area 10 cm away from the boundary of the crack area is the crack domain, and the remaining soil area is the matrix domain;

[0028] Step 4012, using a computer to obtain the boundary 0B, boundary BC, boundary CD, boundary DE, boundary EF, boundary FG, boundary GA and boundary AO of the coal mining fracture area model 0BGA;

[0029] Step 4013: Use a computer to input soil texture data, soil porosity mean, residual water content, saturated water content, saturated hydraulic conductivity K using hydrus software. s, the first soil pore related parameter α, the second soil pore related parameter n, the third soil pore related parameter m;

[0030] Step 4014, using a computer to use hydrus software to set initial boundary conditions; wherein, boundary BC, boundary DE, and boundary FG are fixed flux boundaries, and the average soil moisture content and the average soil water suction measured in step 202 are assigned to boundary BC and boundary FG; boundary AO is set as a free drainage boundary, boundary OB and boundary GA are zero flux boundaries, and boundaries CD and boundary EF on both sides of the crack area do not participate in water migration;

[0031] Step 4015: Use a computer to input the mean rainfall intensity, mean temperature and mean total solar radiation in step 202 using the hydrus software.

[0032] The above-mentioned method for simulating soil moisture migration in coal mining crack areas is characterized in that: in the process of simulating the grid model of coal mining crack areas using hydrus software on a computer, the water content of point C is recorded as The water content at point D is recorded as if Greater than or equal to θ s ,and Less than θ s , then the computer uses the hydrus software to set the boundaries BC and FG as variable flux boundaries, the boundary DE as a variable flux boundary, the boundaries CD and EF as variable flux boundaries, the boundary AO as a free drainage boundary, and the boundaries OB and GA as zero flux boundaries;

[0033] if Greater than or equal to θ s ,and Greater than or equal to θ s , the computer uses the hydrus software to set the boundaries BC, DE and FG as constant head boundaries, the boundaries CD and EF as unpressurized seepage free surface boundaries, the boundary AO as the free drainage boundary, and the boundaries OB and GA as the zero flux boundaries.

[0034] The above-mentioned method for simulating soil moisture migration in coal mining crack areas is characterized in that: step 201, the specific process is as follows:

[0035] Step A: During the set total monitoring time, the first to ninth category measurement data measured at the set sampling time are sent to the computer; wherein the i-th category measurement data at the j-th sampling time is recorded as a ij ; i is a positive integer, and 1≤i≤I, I represents the total number of measurement data types, j is a positive integer, and 1≤j≤J, J represents the total number of samples;

[0036] Step B: Process the i-th type of measurement data at J sampling moments using a computer to obtain the variance σ of the i-th type of measurement data i and mean μ i , and judge the i-th type of measurement data, if 0<α ij -μ i |<3σ i , it is judged as a normal value; otherwise, a ij Determined as an outlier;

[0037] Step C, repeat step B multiple times to obtain the normal value of the i-th type of measurement data and the abnormal value of the i-th type of measurement data; wherein the number of abnormal values ​​of the i-th type of measurement data is recorded as

[0038] Step D: Use computer to judge if Then the mean of the normal value of the i-th category measurement data is assigned to the abnormal value to obtain the i-th category measurement data after preprocessing;

[0039] if Then linear interpolation, exponential smoothing and cubic spline interpolation are selected to fit and replace outliers respectively, and the i-th category measurement data after three types of fitting and replacing outliers are obtained, and the i-th category measurement data after the fitting and replacing outliers with the smallest root mean square error among the three types of fitting and replacing outliers is selected as the i-th category measurement data after preprocessing; wherein, Indicates rounding up.

[0040] The above-mentioned method for simulating soil moisture migration in a coal mining crack area is characterized in that: step 302, the specific process is as follows:

[0041] Step 3021, using a computer to set each point of soil water suction and soil water content to fit a three-stage segmented fitting function, as follows:

[0042] Among them, θ A (S) represents the soil moisture function of the first fitting curve, θ r is the residual water content, θ s is the saturated water content, S is the independent variable of soil water suction, α is the first relevant parameter of soil pores, n is the second relevant parameter of soil pores, m is the third relevant parameter of soil pores, and θ B (S) represents the soil moisture function of the second fitting curve, S′ represents the soil water suction when the soil air enters the soil, θ C (S) represents the soil moisture function of the third fitting curve, S a Indicates the horizontal coordinate of the first inflection point on the fitting curve, S bRepresents the horizontal coordinate of the second inflection point on the fitting curve;

[0043] Step 3022: Use a computer to perform curve fitting on each point in step 301 according to the three-stage piecewise fitting function set in step 3021, and obtain the parameters of the three-stage piecewise fitting function; wherein the parameters of the three-stage piecewise fitting function include residual water content θ r , saturated water contentθ s , soil pore first related parameter α, soil pore second related parameter n and soil pore third related parameter m.

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

[0045] 1. The method of the present invention has simple steps and reasonable design, and solves the problem that the current soil moisture migration simulation method cannot be directly applied to mining crack areas.

[0046] 2. The coal mining fracture area model of the present invention is divided into fracture domain and matrix domain, and matrix domain moisture migration equation and fracture domain moisture migration equation are established for the fracture domain and matrix domain respectively, thereby effectively adapting to the different characteristics of the fracture domain and the matrix domain, effectively adapting to the soil moisture migration situation in the fracture area, and improving the accuracy of moisture migration simulation.

[0047] 3. The matrix domain moisture migration equation and the crack domain moisture migration equation established by the present invention are used to simulate the grid model of coal mining crack areas, which can adapt to the simulation of soil moisture migration state under cracks with different requirements, have a wide range of applications, and reliable simulation results.

[0048] 4. The present invention collects and pre-processes the measurement data in advance and then inputs it into the subsequent coal mining crack area grid model for simulation operation, thereby improving the accuracy of prediction.

[0049] 5. The present invention facilitates the subsequent prediction of soil moisture migration rate and moisture movement path according to soil moisture content, provides guidance for reducing negative environmental impacts, and also provides a theoretical basis for subsequent ecological restoration of mining areas.

[0050] In summary, the method of the present invention has simple steps and reasonable design. The established coal mining crack area model is divided into a crack domain and a matrix domain, and water migration equations are established for the crack domain and the matrix domain respectively for simulation, so as to obtain the soil moisture content in the coal mining crack area, effectively adapt to the soil moisture migration situation in the crack area, improve the accuracy of water migration simulation, and facilitate the subsequent prediction of soil moisture migration rate and moisture movement path according to soil moisture content.

[0051] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The figure is a flowchart of the method of the present invention.

[0053] Figure 2 It is a schematic diagram of the coal mining fracture area model of the present invention.

[0054] Figure 3 This is a diagram showing the simulation results of soil moisture migration according to the present invention. DETAILED DESCRIPTION

[0055] like Figure 1 and Figure 2 As shown, the method for simulating soil moisture migration in coal mining crack areas of the present invention comprises the following steps:

[0056] Step 1: Collection of measurement data:

[0057] Step 101: During the set total monitoring time, the crack depth, lower crack width and upper crack width in the coal mining crack area to be studied are obtained by using the crack monitoring module; the soil water content, soil water suction and soil porosity in the coal mining crack area to be studied are obtained by using the soil monitoring module; the rainfall intensity, temperature and total solar radiation in the coal mining crack area to be studied are obtained by using the meteorological module;

[0058] Step 102, measuring the soil texture in the coal mining crack area to be studied, and obtaining soil texture data of the coal mining crack area to be studied;

[0059] Step 103, record the crack depth as the first type of measurement data, record the lower crack width as the second type of measurement data, record the upper crack width as the third type of measurement data, record the soil moisture content as the fourth type of measurement data, record the soil water suction as the fifth type of measurement data, record the soil porosity as the sixth type of measurement data, record the rainfall intensity as the seventh type of measurement data, record the temperature as the eighth type of measurement data, and record the total solar radiation as the ninth type of measurement data;

[0060] Step 2: Preprocessing of collected measurement data:

[0061] Step 201: preprocessing the first category to the ninth category of measurement data using a computer to obtain the first category to the ninth category of measurement data after preprocessing;

[0062] Step 202, performing mean processing on the pre-processed measurement data of the first category to the ninth category respectively, to obtain the measured mean value of the crack depth, the mean value of the lower crack width, the mean value of the upper crack width, the mean value of the soil moisture content, the mean value of the soil water suction, the mean value of the soil porosity, the mean value of the rainfall intensity, the mean value of the air temperature and the mean value of the total solar radiation; wherein the mean value of the crack depth, the mean value of the lower crack width and the mean value of the upper crack width are recorded as crack data, and the mean value of the soil moisture content, the mean value of the soil water suction, the mean value of the soil porosity, the mean value of the rainfall intensity, the mean value of the air temperature and the mean value of the total solar radiation are recorded as simulation initial parameters;

[0063] Step 3: Obtain soil hydraulic characteristic parameters in coal mining crack areas:

[0064] Step 301, using a computer to plot each point of the pre-processed fifth category measurement data and the pre-processed fourth category measurement data with soil water suction as the horizontal coordinate and soil water content as the vertical coordinate;

[0065] Step 302: Using a computer to perform curve fitting based on the points of the pre-processed fifth category measurement data and the pre-processed fourth category measurement data, the residual moisture content θ is obtained. r , saturated water contentθ s , a first soil porosity related parameter α, a second soil porosity related parameter n and a third soil porosity related parameter m;

[0066] Step 303: Using a computer according to the formula The unsaturated hydraulic conductivity function K(θ) is obtained; where K s is the saturated hydraulic conductivity; θ represents the independent variable of soil moisture content;

[0067] Step 4: Establish a coal mining fracture area model and perform simulation based on the established matrix domain water migration equation and fracture domain water migration equation:

[0068] Step 401, using a computer and hydrus software to establish a cross-sectional diagram of the coal mining crack area to be studied according to the crack data in step 202, recorded as the coal mining crack area model 0BGA, and set the simulation initial parameters and boundary initial conditions; wherein, the soil area 10 cm away from the crack area boundary in the coal mining crack area model 0BGA is set as the crack area, and the remaining soil area is set as the matrix area;

[0069] Step 402, using a computer and hydrus software to mesh the coal mining fracture area model OBGA with equally spaced grids to obtain a coal mining fracture area grid model;

[0070] Step 403: Use a computer to establish a matrix domain water migration equation, as follows:

[0071] Among them, C a is the specific water density of the matrix domain, θ a is the soil moisture function in the matrix domain, t is time, represents the partial derivative with respect to time t, represents the partial derivative about the x direction, h a is the water potential in the matrix domain, represents the partial derivative about the z direction, K(θ a ) represents the value of the independent variable of soil moisture content θ a Unsaturated hydraulic conductivity at ;

[0072] The water migration equation in the crack domain is established by computer, as follows:

[0073] Among them, C c is the specific water density in the fracture domain, θ c is the soil moisture function in the crack domain, h c is the water potential in the fracture domain, K(θ c ) represents the value of the independent variable of soil moisture content θ c The unsaturated hydraulic conductivity at w is the dual-domain water exchange term, Γ l is the laminar exchange term, Γ i is the horizontal imbibition exchange term, ξ a is the volume ratio of the matrix domain, ξ c is the volume ratio of the crack domain, α w is the water conversion rate, K c-a is the saturated hydraulic conductivity at the junction of the two domains, and W is the mean width of the crack, g is the acceleration of gravity, and v is the soil compression coefficient; l f is the wetted length of the left wall of the crack, l r is the wetted length of the right side of the crack, Indicates about l f The partial guide, Indicates about l r The partial derivative of

[0074] Step 404: using a computer to compile the established matrix domain water migration equation and fracture domain water migration equation to generate a DLL file and load it into the hydrus software;

[0075] Step 405: Use a computer to use Hydras software to set the time step and the total simulation time, simulate the coal mining crack area grid model according to the established matrix domain moisture migration equation and crack domain moisture migration equation, and obtain the soil moisture content of each node in the coal mining crack area grid model.

[0076] In this embodiment, step 401, the specific process is as follows:

[0077] Step 4011, using a computer and using the geometry module Geometry in the hydrus software to establish a coal mining crack area model 0BGA; wherein the x direction of the coal mining crack area model 0BGA is the crack width direction, and the z direction of the coal mining crack area model 0BGA is the crack depth upward; the coal mining crack area model 0BGA includes a crack area CDBF and a soil area, the soil area 10 cm away from the boundary of the crack area is the crack domain, and the remaining soil area is the matrix domain;

[0078] Step 4012, using a computer to obtain the boundary 0B, boundary BC, boundary CD, boundary DE, boundary EF, boundary FG, boundary GA and boundary AO of the coal mining fracture area model 0BGA;

[0079] Step 4013: Use a computer to input soil texture data, soil porosity mean, residual water content, saturated water content, saturated hydraulic conductivity K using hydrus software. s , the first soil pore related parameter α, the second soil pore related parameter n, the third soil pore related parameter m;

[0080] Step 4014, using a computer to use hydrus software to set initial boundary conditions; wherein, boundary BC, boundary DE, and boundary FG are fixed flux boundaries, and the average soil moisture content and the average soil water suction measured in step 202 are assigned to boundary BC and boundary FG; boundary AO is set as a free drainage boundary, boundary OB and boundary GA are zero flux boundaries, and boundaries CD and boundary EF on both sides of the crack area do not participate in water migration;

[0081] Step 4015: Use a computer to input the mean rainfall intensity, mean temperature and mean total solar radiation in step 202 using the hydrus software.

[0082] In this embodiment, the water content of point C is recorded as The water content at point D is recorded as if Greater than or equal to θ s ,and Less than θ s , then the computer uses the hydrus software to set the boundaries BC and FG as variable flux boundaries, the boundary DE as a variable flux boundary, the boundaries CD and EF as variable flux boundaries, the boundary AO as a free drainage boundary, and the boundaries OB and GA as zero flux boundaries;

[0083] if Greater than or equal to θ s ,and Greater than or equal to θ s , the computer uses the hydrus software to set the boundaries BC, DE and FG as constant head boundaries, the boundaries CD and EF as unpressurized seepage free surface boundaries, the boundary AO as the free drainage boundary, and the boundaries OB and GA as the zero flux boundaries.

[0084] In this embodiment, step 201, the specific process is as follows:

[0085] Step A: During the set total monitoring time, the first to ninth category measurement data measured at the set sampling time are sent to the computer; wherein the i-th category measurement data at the j-th sampling time is recorded as a ij ; i is a positive integer, and 1≤i≤I, I represents the total number of measurement data types, j is a positive integer, and 1≤j≤J, J represents the total number of samples;

[0086] Step B: Process the i-th type of measurement data at J sampling moments using a computer to obtain the variance σ of the i-th type of measurement data i and mean μ i , and judge the i-th type of measurement data, if 0<α ij -μ i |<3σ i , it is judged as a normal value; otherwise, a ij Determined as an outlier;

[0087] Step C, repeat step B multiple times to obtain the normal value of the i-th type of measurement data and the abnormal value of the i-th type of measurement data; wherein the number of abnormal values ​​of the i-th type of measurement data is recorded as

[0088] Step D: Use computer to judge if Then the mean of the normal value of the i-th category measurement data is assigned to the abnormal value to obtain the i-th category measurement data after preprocessing;

[0089] if Then linear interpolation, exponential smoothing and cubic spline interpolation are selected to fit and replace outliers respectively, and the i-th category measurement data after three types of fitting and replacing outliers are obtained, and the i-th category measurement data after the fitting and replacing outliers with the smallest root mean square error among the three types of fitting and replacing outliers is selected as the i-th category measurement data after preprocessing; wherein, Indicates rounding up.

[0090] In this embodiment, step 302, the specific process is as follows:

[0091] Step 3021, using a computer to set each point of soil water suction and soil water content to fit a three-stage segmented fitting function, as follows:

[0092] Among them, θ A (S) represents the soil moisture function of the first fitting curve, θ r is the residual water content, θ s is the saturated water content, S is the independent variable of soil water suction, α is the first relevant parameter of soil pores, n is the second relevant parameter of soil pores, m is the third relevant parameter of soil pores, and θ B (S) represents the soil moisture function of the second fitting curve, S′ represents the soil water suction when the soil air enters the soil, θ C (S) represents the soil moisture function of the third fitting curve, S a Indicates the horizontal coordinate of the first inflection point on the fitting curve, S b Represents the horizontal coordinate of the second inflection point on the fitting curve;

[0093] Step 3022: Use a computer to perform curve fitting on each point in step 301 according to the three-stage piecewise fitting function set in step 3021, and obtain the parameters of the three-stage piecewise fitting function; wherein the parameters of the three-stage piecewise fitting function include residual water content θ r , saturated water contentθ s , soil pore first related parameter α, soil pore second related parameter n and soil pore third related parameter m.

[0094] In this embodiment, the sampling time is set to 1 hour / time to 5 hours / time; the total monitoring time is set to 7 days.

[0095] In this embodiment, when the soil in the coal mining crack area to be studied is loess, the soil compression coefficient v is 0.05.

[0096] In this embodiment, when the soil in the coal mining crack area to be studied is loess, the saturated hydraulic conductivity K s 0.01m / s.

[0097] In this embodiment, the mean value W of the width of the crack is the mean value of the upper width of the crack + the mean value of the lower width of the crack / 2.

[0098] In this embodiment, in actual use, the soil water suction S′ is 1.84 kPa when the soil air is inhaled.

[0099] In this embodiment, in actual use, the grid spacing is 1 cm.

[0100] In this embodiment, during the actual simulation in step 405, the total simulation time is 300 minutes and the time step is 1.

[0101] In this embodiment, in the simulation under different crack data, the crack data is set to be micro cracks, small cracks, medium cracks and large cracks. When micro cracks, small cracks, medium cracks and large cracks exist, the number of discrete grids is set to 2588, 2487, 2321 and 2209 respectively. Among them, the upper widths of micro cracks, small cracks, medium cracks and large cracks are 1.69 cm, 8.12 cm, 11.42 cm and 18.98 cm respectively, and the corresponding upper widths are 0.5 cm, 5 cm, 7 cm and 10 cm respectively.

[0102] In this embodiment, the depth of the coal mining fracture area model 0BGA is 100 cm and the width is 120 cm.

[0103] In this embodiment, the regions with micro cracks, small cracks, medium cracks and large cracks are fitted through steps 301 and 302 respectively, and the parameters shown in Table 1 are obtained:

[0104]

[0105] In this embodiment, Figure 3As shown in the figure, it can be seen that in the initial period before soil moisture migration, the initial soil moisture content gradually increases with the increase of depth, and the soil moisture content of each horizontal layer is basically consistent, showing a layered uniform distribution; but the moisture content around the crack and the crack wall is slightly lower than the moisture content of the corresponding horizontal layer, and the larger the crack size, the lower the moisture content; the soil at the bottom of the crack wall is also affected by the crack, and the soil moisture content presents a "point source" dry distribution with the bottom of the crack as the center, and the larger the crack size, the lower the surrounding moisture content. The surface soil moisture content of medium-sized cracks and large cracks is basically consistent with that of micro-small cracks and small cracks; when the soil moisture migration infiltrates for 10 minutes, the soil at the top of the crack is not saturated. When the soil moisture migration infiltrates for 30 minutes, the soil at the top of the crack first appears saturated, but due to the influence of soil texture and structure, the moisture migration has not reached 1 / 4 of the depth at this time, which is consistent with the actual situation. As the soil water migration and infiltration time increases, the soil water around the cracks shows the characteristics of uneven migration and the unevenness gradually increases, that is, the water forms preferential flow along the cracks, especially in large cracks, the preferential flow is more obvious, and the preferential flow of small and medium cracks is initially revealed, but there is almost no preferential flow phenomenon in micro cracks. When the soil water migration and infiltration is 60 minutes, the surface soil is basically saturated. The medium and large cracks are affected by the horizontal absorption and infiltration of the crack wall, which accelerates the downward movement of the wetting front, that is, the preferential flow phenomenon is aggravated. The preferential flow of small cracks gradually appears, but the wetting front of micro cracks moves downward in parallel, and there is almost no preferential flow phenomenon. When the soil water migration and infiltration is 120 minutes, the infiltration rate of micro cracks remains unchanged, the wetting peak moves downward in parallel, and there are signs of preferential flow around the cracks of small cracks, but the overall is not strong, while the infiltration rate around the medium and large cracks is faster, and the preferential flow is significant; when the soil water migration and infiltration is 300 minutes, the entire area of ​​micro cracks, small cracks, medium cracks and large cracks is saturated. The simulation effect is good and can reflect the soil moisture movement more accurately.

[0106] In summary, the method of the present invention has simple steps and reasonable design. The established coal mining crack area model is divided into a crack domain and a matrix domain, and water migration equations are established for the crack domain and the matrix domain respectively for simulation, so as to obtain the soil moisture content in the coal mining crack area, effectively adapt to the soil moisture migration situation in the crack area, improve the accuracy of water migration simulation, and facilitate the subsequent prediction of soil moisture migration rate and moisture movement path according to soil moisture content.

[0107] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for simulating soil moisture migration in coal mining crack areas, characterized in that: The method comprises the following steps: Step 1: Collection of measurement data: Step 101: During the set total monitoring time, the crack depth, lower crack width and upper crack width in the coal mining crack area to be studied are obtained by using the crack monitoring module; the soil water content, soil water suction and soil porosity in the coal mining crack area to be studied are obtained by using the soil monitoring module; the rainfall intensity, temperature and total solar radiation in the coal mining crack area to be studied are obtained by using the meteorological module; Step 102, measuring the soil texture in the coal mining crack area to be studied, and obtaining soil texture data of the coal mining crack area to be studied; Step 103, record the crack depth as the first type of measurement data, record the lower crack width as the second type of measurement data, record the upper crack width as the third type of measurement data, record the soil moisture content as the fourth type of measurement data, record the soil water suction as the fifth type of measurement data, record the soil porosity as the sixth type of measurement data, record the rainfall intensity as the seventh type of measurement data, record the temperature as the eighth type of measurement data, and record the total solar radiation as the ninth type of measurement data; Step 2: Preprocessing of collected measurement data: Step 201: preprocessing the first category to the ninth category of measurement data using a computer to obtain the first category to the ninth category of measurement data after preprocessing; Step 202, performing mean processing on the pre-processed measurement data of the first category to the ninth category respectively, to obtain the measured mean value of the crack depth, the mean value of the lower crack width, the mean value of the upper crack width, the mean value of the soil moisture content, the mean value of the soil water suction, the mean value of the soil porosity, the mean value of the rainfall intensity, the mean value of the air temperature and the mean value of the total solar radiation; wherein the mean value of the crack depth, the mean value of the lower crack width and the mean value of the upper crack width are recorded as crack data, and the mean value of the soil moisture content, the mean value of the soil water suction, the mean value of the soil porosity, the mean value of the rainfall intensity, the mean value of the air temperature and the mean value of the total solar radiation are recorded as simulation initial parameters; Step 3: Obtain soil hydraulic characteristic parameters in coal mining crack areas: Step 301, using a computer to plot each point of the pre-processed fifth category measurement data and the pre-processed fourth category measurement data with soil water suction as the horizontal coordinate and soil water content as the vertical coordinate; Step 302: Using a computer to perform curve fitting based on the points of the pre-processed fifth category measurement data and the pre-processed fourth category measurement data, the residual moisture content θ is obtained. r , saturated water contentθ s , a first soil porosity related parameter α, a second soil porosity related parameter n and a third soil porosity related parameter m; Step 303: Using a computer according to the formula The unsaturated hydraulic conductivity function K(θ) is obtained; where K s is the saturated hydraulic conductivity; θ represents the independent variable of soil moisture content; Step 4: Establish a coal mining fracture area model and perform simulation based on the established matrix domain water migration equation and fracture domain water migration equation: Step 401, using a computer and hydrus software to establish a cross-sectional diagram of the coal mining crack area to be studied according to the crack data in step 202, recorded as the coal mining crack area model 0BGA, and set the simulation initial parameters and boundary initial conditions; wherein, the soil area 10 cm away from the crack area boundary in the coal mining crack area model 0BGA is set as the crack area, and the remaining soil area is set as the matrix area; Step 402, using a computer and hydrus software to mesh the coal mining fracture area model OBGA with equally spaced grids to obtain a coal mining fracture area grid model; Step 403: Use a computer to establish a matrix domain water migration equation, as follows: Among them, C a is the specific water density of the matrix domain, θ a is the soil moisture function in the matrix domain, t is time, represents the partial derivative with respect to time t, represents the partial derivative about the x direction, h a is the water potential in the matrix domain, represents the partial derivative about the z direction, K(θ a ) represents the value of the independent variable of soil moisture content θ a Unsaturated hydraulic conductivity at ; The water migration equation in the crack domain is established by computer, as follows: Among them, C c is the specific water density in the fracture domain, θ c is the soil moisture function in the crack domain, h c is the water potential in the fracture domain, K(θ c ) represents the value of the independent variable of soil moisture content θ c The unsaturated hydraulic conductivity at w is the dual-domain water exchange term, Γ l is the laminar exchange term, Γ i is the horizontal imbibition exchange term, ξ a is the volume ratio of the matrix domain, ξ c is the volume ratio of the crack domain, α w is the water conversion rate, K c-a is the saturated hydraulic conductivity at the junction of the two domains, and W is the mean width of the crack, g is the acceleration of gravity, and v is the soil compression coefficient; l f is the wetted length of the left wall of the crack, l r is the wetted length of the right side of the crack, Indicates about l f The partial guide, Indicates about l r The partial derivative of Step 404: using a computer to compile the established matrix domain water migration equation and fracture domain water migration equation to generate a DLL file and load it into the hydrus software; Step 405: Use a computer to use Hydras software to set the time step and the total simulation time, simulate the coal mining crack area grid model according to the established matrix domain moisture migration equation and crack domain moisture migration equation, and obtain the soil moisture content of each node in the coal mining crack area grid model.

2. A method for simulating soil moisture migration in coal mining crack areas according to claim 1, characterized in that: Step 401, the specific process is as follows: Step 4011, using a computer and using the geometry module Geometry in the hydrus software to establish a coal mining crack area model 0BGA; wherein the x direction of the coal mining crack area model 0BGA is the crack width direction, and the z direction of the coal mining crack area model 0BGA is the crack depth upward; the coal mining crack area model 0BGA includes a crack area CDBF and a soil area, the soil area 10 cm away from the boundary of the crack area is the crack domain, and the remaining soil area is the matrix domain; Step 4012, using a computer to obtain the boundary 0B, boundary BC, boundary CD, boundary DE, boundary EF, boundary FG, boundary GA and boundary AO of the coal mining fracture area model 0BGA; Step 4013: Use a computer to input soil texture data, soil porosity mean, residual water content, saturated water content, saturated hydraulic conductivity K using hydrus software. s , the first soil pore related parameter α, the second soil pore related parameter n, the third soil pore related parameter m; Step 4014, using a computer to use hydrus software to set initial boundary conditions; wherein, boundary BC, boundary DE, and boundary FG are fixed flux boundaries, and the average soil moisture content and the average soil water suction measured in step 202 are assigned to boundary BC and boundary FG; boundary AO is set as a free drainage boundary, boundary OB and boundary GA are zero flux boundaries, and boundaries CD and boundary EF on both sides of the crack area do not participate in water migration; Step 4015: Use a computer to input the mean rainfall intensity, mean temperature and mean total solar radiation in step 202 using the hydrus software.

3. A method for simulating soil moisture migration in coal mining crack areas according to claim 2, characterized in that: In the process of simulating the grid model of coal mining crack area using hydrus software, the water content of point C is recorded as The water content at point D is recorded as if Greater than or equal to θ s ,and Less than θ s , then the computer uses the hydrus software to set the boundaries BC and FG as variable flux boundaries, the boundary DE as a variable flux boundary, the boundaries CD and EF as variable flux boundaries, the boundary AO as a free drainage boundary, and the boundaries OB and GA as zero flux boundaries; if Greater than or equal to θ s ,and Greater than or equal to θ s , the computer uses the hydrus software to set the boundaries BC, DE and FG as constant head boundaries, the boundaries CD and EF as unpressurized seepage free surface boundaries, the boundary AO as the free drainage boundary, and the boundaries OB and GA as the zero flux boundaries.

4. A method for simulating soil moisture migration in coal mining crack areas according to claim 1, characterized in that: Step 201, the specific process is as follows: Step A: During the set total monitoring time, the first to ninth category measurement data measured at the set sampling time are sent to the computer; wherein the i-th category measurement data at the j-th sampling time is recorded as a ij ; i is a positive integer, and 1≤i≤I, I represents the total number of measurement data types, j is a positive integer, and 1≤j≤J, J represents the total number of samples; Step B: Process the i-th type of measurement data at J sampling moments using a computer to obtain the variance σ of the i-th type of measurement data i and mean μ i , and judge the i-th type of measurement data. If 0<αij-μi|<3σi, it is judged as a normal value; otherwise, aij is judged as an abnormal value; Step C: Repeat step B multiple times to obtain the normal value of the i-th type of measurement data and the abnormal value of the i-th type of measurement data; wherein the number of abnormal values ​​of the i-th type of measurement data is recorded as N ζi ; Step D: Use computer to judge if Then the mean of the normal value of the i-th category measurement data is assigned to the abnormal value to obtain the i-th category measurement data after preprocessing; if Then linear interpolation, exponential smoothing and cubic spline interpolation are selected to fit and replace outliers respectively, and the i-th category measurement data after three types of fitting and replacing outliers are obtained, and the i-th category measurement data after the fitting and replacing outliers with the smallest root mean square error among the three types of fitting and replacing outliers is selected as the i-th category measurement data after preprocessing; wherein, Indicates rounding up.

5. A method for simulating soil moisture migration in coal mining crack areas according to claim 1, characterized in that: Step 302, the specific process is as follows: Step 3021, using a computer to set each point of soil water suction and soil water content to fit a three-stage segmented fitting function, as follows: Among them, θ A (S) represents the soil moisture function of the first fitting curve, θ r is the residual water content, θ s is the saturated water content, S is the independent variable of soil water suction, α is the first relevant parameter of soil pores, n is the second relevant parameter of soil pores, m is the third relevant parameter of soil pores, and θ B (S) represents the soil moisture function of the second fitting curve, S′ represents the soil water suction when the soil air enters the soil, θ C (S) represents the soil moisture function of the third fitting curve, S a Indicates the horizontal coordinate of the first inflection point on the fitting curve, S b Represents the horizontal coordinate of the second inflection point on the fitting curve; Step 3022: Use a computer to perform curve fitting on each point in step 301 according to the three-stage piecewise fitting function set in step 3021, and obtain the parameters of the three-stage piecewise fitting function; wherein the parameters of the three-stage piecewise fitting function include residual water content θ r , saturated water contentθ s , soil pore first related parameter α, soil pore second related parameter n and soil pore third related parameter m.

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