Actual hydraulic slope calculation method and system based on fluid-structure interaction effect

Abstract

The invention discloses an actual hydraulic slope calculation method and system based on a fluid-solid coupling effect, belongs to the technical field of coal mine water prevention and control, and solves the problem of how to calculate an actual hydraulic slope value in a water guide channel after overlying strata water guide fractures extend to a loose aquifer under the influence of the coupling effect of mining-induced stress and confined water of a loose formation. According to the method, the fluid-solid coupling effect generated by coupling of mining-induced stress and confined water is comprehensively considered, different permeability coefficient change rules existing in an elastic undamaged area and a plastic damaged area are put forward and embedded into a numerical calculation model, and a water guide channel of a loose aquifer is found out according to pore pressure and seepage vector distribution; and traversing each grid node of each water guide channel to calculate an actual hydraulic slope interval under the influence of the mining-induced stress and the confined water coupling effect, thereby being beneficial to carrying out seepage failure resistance evaluation under the geological condition and the influence of the mining-induced stress and the confined water coupling effect. Therefore, a theoretical basis is provided for the setting of safe mining of the working face of the sand-prevention and collapse-prevention safe coal pillar.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal mine water control, and relates to a method and system for calculating the actual hydraulic gradient based on the fluid-solid coupling effect. Background Art

[0002] Coal mining areas in East China, North China and other regions of China are generally covered by Neogene and Quaternary unconsolidated confined aquifers. Mining under the near unconsolidated aquifer is extremely likely to induce geological disasters such as water inrush and sand bursting, posing a huge challenge to the safe production of coal mines.

[0003] According to Article 87 of the "Coal Mine Water Control Rules", "When mining under water bodies, the waterproof and water-resisting coal (rock) pillars shall be designed and reserved in accordance with the principle of combining the fracture angle with the waterproof and water-resisting coal (rock) pillars required by the water body mining grade. Among them: when mining with sand-proof and collapse-proof coal (rock) pillars reserved, the critical hydraulic gradients of the overlying soil layer and weathered zone shall be combined to conduct an anti-seepage failure evaluation to ensure that no water inrush and sand bursting accidents occur." In the analysis of the anti-seepage failure of the overlying soil layer and weathered zone rock layer during mining under the loose layer, there are two crucial indicators, namely: the critical hydraulic gradient J1 of water inrush and sand bursting in the soil layer and weathered zone rock layer, and the actual hydraulic gradient J2 of each layer during the mining process. When the actual hydraulic gradient J2 < J1, it is relatively safe and there is no danger of water inrush and sand bursting in the working face; when the actual hydraulic gradient J2 > J1, there is a danger of water inrush and sand bursting in the working face. Therefore, accurately calculating the critical hydraulic gradient J1 and the actual hydraulic gradient J2 of the overlying soil layer and weathered zone rock layer during the coal face mining process will directly affect the safe mining of the working face with sand-proof and collapse-proof coal (rock) pillars reserved under the unconsolidated aquifer.

[0004] For the calculation of the critical hydraulic gradient J1, the commonly used methods are the Terzaghi formula, the formula of Nanjing Hydraulic Research Institute, and the Zamalin formula recommended in the "Interpretation of Coal Mine Water Control Rules", etc., and the minimum value of the calculation results of various methods is determined as the critical hydraulic gradient. However, for the calculation of the actual hydraulic gradient J2 of the overlying soil layer and weathered zone rock layer during the coal face mining process, no specific recommended formula is given.

[0005] In response to this situation, many scholars have taken the mechanism of water and sand burst in mining under loose aquifers as their research target, and have used theoretical analysis, numerical simulation and other research methods to study the actual hydraulic slope of water and sand burst in loose layers under mining conditions, and obtained the actual hydraulic slope calculation expression. For example, the literature "Prediction of sand burst in coal mining under soft sandstone aquifers" (Zhang Yujun, Kang Yonghua, Liu Xiu'e. Journal of China Coal Society, 2006.31(4):429-432) proposed the principle of complete well flow under steady flow conditions based on the single well fixed flow pumping and pressure; for example, the literature "Evaluation Method for Anti-seepage Damage in Mining Near Loose Layers II: Hydraulic Slope Analytical Method" (Dong Guiming, Sui Wanghua, Li Yuzhou, et al. Journal of Engineering Geology, 2023,31(04):1486-1493.) proposed the actual hydraulic slope calculation expression based on the single well fixed drawdown model. According to the research status, the calculation model and derivation process of the above actual hydraulic gradient have the following problems:

[0006] 1. The principle of single-well fixed-flow pumping and pressurized complete well flow is not valid when water and sand bursts occur at the bottom of the aquifer due to the water-conducting fractures. Since the water inflow is not a constant value but changes with time, it is obviously inconsistent with the actual situation to equate it to single-well fixed-flow pumping. At the same time, the water inflow of the aquifer is estimated by the pressurized-unpressurized flow prediction formula. The water inflow of the aquifer is Among them, K is the permeability coefficient of the aquifer; according to Darcy's law, the mine water inflow is derived as Q = KAJ, where Q is the water inflow, K is the permeability coefficient, i is the actual hydraulic gradient, and A is the water flow area, which represents the lateral area of ​​a cylindrical water inflow channel with r as the bottom radius and M as the height of the aquifer thickness, that is, A = 2πrM; the two equations are combined to obtain Under the influence of the coupling effect of mining stress and confined water, when the overburden water-conducting fracture wave aquifer is formed, the soil inside the aquifer is often destroyed. The permeability coefficient in the soil destruction area (plastic failure zone) increases sharply, becoming the main channel for water and sand bursts. Therefore, it is unreasonable to regard the permeability coefficient k1 of the cylindrical water-conducting channel in the theoretical model as the initial permeability coefficient k of the aquifer. The actual hydraulic gradient value calculated by this method is obviously too high, and there will be an order of magnitude difference.

[0007] 2. The following problems exist in the process of deriving the actual hydraulic gradient based on the principle of the single-well fixed drawdown model: Although the model takes into account the disadvantage of non-constant flow during water and sand bursts, water and sand bursts may only occur during the mining process of the working face when the water-conducting fracture zone develops to form a water inrush channel in the aquifer, and water burst is a prerequisite for sand bursts. In this process, the permeability coefficients of the coal seam roof overburden, bedrock weathering zone, and loose layer bottom aquifer in the mining stress influence area will change, and the degree of change is related to the elastic or plastic state in which they are located. In the elastic range, the permeability coefficient changes with the effective stress, and in the plastic damage range, the permeability coefficient is related to the fracture characteristic parameters, and may change by an order of magnitude. Therefore, when the permeability coefficients of the overburden, weathering zone, and aquifer change, it directly affects the calculation results of the actual hydraulic gradient. Conversely, the change in the permeability coefficients of each layer will also affect the stress distribution state. Ignoring the influence of the coupling effect of mining stress and confined water will have a great impact on the calculation results of the hydraulic gradient. Therefore, it is crucial to propose a method that can calculate the actual hydraulic gradient in the water channel based on the fluid-solid coupling effect. Summary of the invention

[0008] The technical solution of the present invention is used to solve the problem of how to calculate the actual hydraulic gradient value in the water-conducting channel when the overburden water-conducting fractures extend to the loose aquifer under the influence of the coupling effect of mining stress and loose layer confined water.

[0009] The present invention solves the above technical problems through the following technical solutions:

[0010] A method for calculating an actual hydraulic gradient based on fluid-solid coupling effect comprises the following steps:

[0011] S1. Obtain soil samples and coal samples from loose aquifers and rock samples from roof overburden strata through geological exploration drilling;

[0012] S2. Determine the parameters required for numerical simulation and establish a numerical calculation model for the actual hydraulic slope;

[0013] S3, setting displacement boundary conditions, stress boundary conditions and failure criteria for the numerical calculation model, inputting the parameters obtained in step S2, starting the solid mechanics mode, and closing the fluid mechanics mode, and performing initial stress balance calculation;

[0014] S4. Using the fish language and following the principle of cell traversal, write the relationship between the permeability coefficient of each layer cell of the overburden rock, bedrock weathering zone, and loose aquifer within the elastic undamaged range and the plastic damaged range;

[0015] S5. Simultaneously start the solid mechanics mode and the fluid mechanics mode, perform excavation calculations on the mining face based on the fluid-solid coupling effect, and find the water-conducting channel of the loose aquifer;

[0016] S6. Using the fish language to traverse each grid node at the top and bottom of the aquifer in each water channel, define a hydraulic gradient function, and calculate the numerical range of the hydraulic gradient in each water channel;

[0017] S7. Traverse the numerical range of the hydraulic gradient in all water-conducting channels, take the maximum and minimum values ​​of the hydraulic gradient as the upper and lower limits of the actual hydraulic gradient, and obtain the actual hydraulic gradient range based on the fluid-solid coupling effect.

[0018] Furthermore, the parameters required for numerical simulation are determined in step S2, and a numerical calculation model of the actual hydraulic gradient is established; specifically: the physical and mechanical parameters and hydraulic parameters of soil and rock samples at each layer are obtained through indoor physical and mechanical tests, hydraulic tests and water pressure test results of loose aquifers; the water level data of the hydrological long observation hole near the mining face and the elevation data of the loose aquifer are obtained to calculate the water pressure p of the loose aquifer; a comprehensive borehole column chart of the mining face is drawn according to the lithology and height of each layer, and the actual hydraulic gradient numerical calculation model is established based on the borehole column chart of the exploration area in the mining face using Flac3D software.

[0019] Furthermore, the physical and mechanical parameters include uniaxial compressive strength Rc, elastic modulus E, tensile strength Rt, cohesion C, internal friction angle The hydraulic parameters include the permeability coefficient k.

[0020] Furthermore, the failure criterion in step S3 is the Mohr-Coulomb yield criterion.

[0021] Furthermore, the expression of the permeability coefficient k1 within the elastic undamaged range in step S4 is as follows:

[0022] k1=k0exp(-ασ)

[0023] Where k0 is the initial permeability coefficient of each unit cell, α is the test parameter, and σ is the effective stress of each unit cell, which is the difference between the mean of the principal stress in the three directions of each unit cell and the pore pressure.

[0024] Furthermore, the permeability coefficient k within the plastic failure range in step S4 is m The expression is as follows:

[0025]

[0026] Where w is the damage variable of rock or soil. For the damaged rock or soil, w>0; To destroy the current porosity of rock or soil, is the initial porosity, is the residual porosity under high stress state, σ is the average effective stress, ζ is the stress sensitivity coefficient, and ζ1 is the damage permeability effect coefficient.

[0027] Furthermore, the expression of the hydraulic gradient function in step S6 is as follows:

[0028]

[0029] In the formula, J n is the hydraulic gradient value in the water channel n, p ni is the pore pressure of each node at the top of the aquifer in the water channel n, and the corresponding coordinates are (x ni ,y ni ), p nj is the pore pressure of each node at the bottom of the aquifer in the water channel n, and the corresponding coordinate is (x nj ,y nj ), H is the thickness of the aquifer, ρ is the density of water, which is 1000 kg / m 3 , g is 9.8m / s 2 .

[0030] Furthermore, the maximum value J of the hydraulic gradient function in step S6 is max With the minimum value J min The expression is as follows:

[0031]

[0032] Furthermore, the range of the actual hydraulic gradient in step S7 is specifically:

[0033] min(J nmin )≤J≤max(J nmax )

[0034]

[0035] Where J is the actual hydraulic gradient.

[0036] The present invention also provides an actual hydraulic gradient calculation system based on fluid-solid coupling effect, comprising a sample collection module, a model building module, an initial stress balance calculation module, a permeability coefficient change module, an excavation calculation module, a hydraulic gradient calculation module and an actual hydraulic gradient calculation module;

[0037] The sample collection module is used to obtain soil samples and coal samples of loose aquifers and rock samples of roof overburden strata through geological exploration drilling;

[0038] The model building module is used to determine the parameters required for numerical simulation and to establish a numerical calculation model for the actual hydraulic gradient;

[0039] The initial stress balance calculation module is used to set displacement boundary conditions, stress boundary conditions and failure criteria for the numerical calculation model, input the parameters obtained by the model establishment module, start the solid mechanics mode, and close the fluid mechanics mode to perform initial stress balance calculation;

[0040] The permeability coefficient change module is used to compile the permeability coefficient change relationship of each layer cell of the overburden rock, bedrock weathering zone, and loose aquifer within the elastic undamaged range and the plastic damaged range by using the fish language according to the principle of cell traversal;

[0041] The excavation calculation module is used to simultaneously start the solid mechanics mode and the fluid mechanics mode, perform excavation calculations on the mining face based on the fluid-solid coupling effect, and find the water-conducting channel of the loose aquifer;

[0042] The hydraulic gradient calculation module is used to traverse each grid node at the top and bottom of the aquifer in each water channel using the fish language, define a hydraulic gradient function, and calculate the numerical range of the hydraulic gradient in each water channel respectively;

[0043] The actual hydraulic gradient calculation module is used to traverse the numerical range of the hydraulic gradient in all water-conducting channels, take the maximum and minimum values ​​of the hydraulic gradient as the upper and lower limits of the actual hydraulic gradient, and obtain the actual hydraulic gradient range based on the fluid-solid coupling effect.

[0044] The advantages of the present invention are as follows: the present invention comprehensively considers the fluid-solid coupling effect produced by the coupling of mining stress and confined water, proposes that there are different permeability coefficient variation laws in the elastic undamaged area and the plastic damaged area and embeds a numerical calculation model, finds the water conduction channel of the loose aquifer according to the pore pressure and seepage vector distribution, traverses each grid node of each water conduction channel to calculate the actual hydraulic gradient interval under the influence of the coupling effect of mining stress and confined water, is conducive to carrying out the anti-seepage damage evaluation under the geological conditions and the coupling effect of mining stress and confined water, thereby providing a theoretical basis for the safe mining of the working face with sand prevention and collapse prevention safety coal pillars, and has excellent guiding significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a flow chart of a method for calculating an actual hydraulic gradient based on fluid-solid coupling effect according to an embodiment of the present invention;

[0046] Figure 2 is a schematic diagram of a numerical calculation model of an actual hydraulic gradient based on fluid-solid coupling effect according to an embodiment of the present invention;

[0047] Figure 3 This is a distribution diagram of the plastic zone when the working face advances 80 m in the embodiment of the present invention;

[0048] Figure 4Schematic diagram of the evolution law of the permeability coefficient of the overburden layer when the working face advances 80m according to an embodiment of the present invention;

[0049] Figure 5 It is a schematic diagram of the evolution law of the permeability coefficient of the aquifer when the working face advances 80m according to an embodiment of the present invention;

[0050] Figure 6 is a distribution diagram of pore pressure and seepage vector when the working face advances 80 m according to an embodiment of the present invention;

[0051] Figure 7 It is a schematic diagram of node traversal calculation in the water diversion channel when the working face advances 80m according to an embodiment of the present invention. DETAILED DESCRIPTION

[0052] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and specific embodiments:

[0054] Embodiment 1

[0055] like Figure 1 Specifically, a method for calculating an actual hydraulic gradient based on a fluid-solid coupling effect is disclosed, comprising the following steps:

[0056] S1. Obtain soil samples and coal samples from loose aquifers and rock samples from roof overburden strata through geological exploration drilling;

[0057] S2. Determine the parameters required for numerical simulation and establish a numerical calculation model for the actual hydraulic slope;

[0058] S21. Obtain the physical and mechanical parameters and hydraulic parameters of soil and rock samples at each layer through indoor physical and mechanical tests, hydraulic tests and water pressure test results of loose aquifers, including uniaxial compressive strength Rc, elastic modulus E, tensile strength Rt, cohesion C, internal friction angle Porosity Permeability coefficient k;

[0059] S22, obtaining water level data of the hydrological long observation hole near the mining working face and the elevation data of the loose aquifer, and calculating the water pressure p of the loose aquifer;

[0060] S23. Draw a comprehensive borehole histogram of the mining face according to the lithology and height of each layer, and use Flac3D software to establish a numerical calculation model of the actual hydraulic gradient based on the borehole histogram of the exploration area in the mining face;

[0061] S3, setting displacement boundary conditions, stress boundary conditions and failure criteria for the numerical calculation model, inputting the parameters obtained in step S2, starting the solid mechanics mode, and closing the fluid mechanics mode, and performing initial stress balance calculation;

[0062] In this embodiment, the displacement boundary conditions include but are not limited to setting some boundaries of the numerical calculation model as fixed displacement boundaries to simulate the constraints of the foundation or surrounding rock and soil, while other unconstrained boundaries are set as free boundaries; the stress boundary conditions include but are not limited to applying stress by setting the initial total stress or through the pressure boundary; the failure criterion adopts the Mohr-Coulomb yield criterion as the material yield standard.

[0063] Flac3D is a numerical simulation software used in geological engineering and civil engineering. When performing initial stress balance calculations, the behavior of the fluid will introduce computational complexity, especially when the initial conditions are not yet balanced. If the model has not reached a steady state, the pressure of the fluid will affect the stress distribution, making the initial calculation results unstable. Turning off the fluid mechanics mode can avoid these unnecessary interactions.

[0064] By running the solver, the initial stress balance calculation is performed. During the calculation process, the numerical calculation model will solve the initial stress field according to the set boundary conditions and input parameters. The initial stress balance calculation provides a stable initial condition for the analysis of fluid-solid coupling effects. By first performing solid mechanics analysis, it can be ensured that the numerical calculation model has a reasonable initial state when entering the fluid analysis.

[0065] S4. Using the fish language, according to the principle of cell traversal, write the relationship between the permeability coefficient of each layer cell of the overburden rock, bedrock weathering zone, and loose aquifer within the elastic undamaged range and the plastic damaged range; the expression of the permeability coefficient k1 within the elastic undamaged range is as follows:

[0066] k1=k0exp(-ασ)

[0067] Where k0 is the initial permeability coefficient of each unit cell, σ is the effective stress of each unit cell, which is the difference between the mean of the principal stress in the three directions of each unit cell and the pore pressure, and α is the test parameter, which can be obtained by fitting the values ​​calculated from the three drop strokes of the drilling pumping experiment with the corresponding drawdown data.

[0068] After the initial stress balance calculation, the disturbance caused by the mining excavation of the working face will lead to a secondary distribution of stress. The stress formed after redistribution in the rock mass under the influence of mining is the mining stress. The mining stress is coupled with the confined water, causing the change of pore pressure in the rock mass, which in turn affects the stress field.

[0069] When the rock mass undergoes plastic failure under the coupling effect of mining stress and confined water pressure, the change in permeability within the plastic failure range is related to factors such as initial porosity, residual porosity, and average effective stress. m The expression is as follows:

[0070]

[0071] Where w is the damage variable of rock or soil. For the damaged rock or soil, w>0; To destroy the current porosity of rock or soil, is the initial porosity, is the residual porosity under high stress state, σ is the average effective stress, ζ is the stress sensitivity coefficient, and is taken as 5.0×10 -8 / Pa, ζ1 is the damage permeability effect coefficient, which is taken as 5.0.

[0072] S5. Simultaneously start the solid mechanics mode and the fluid mechanics mode, perform excavation calculations on the mining face based on the fluid-solid coupling effect, and find the water-conducting channel of the loose aquifer;

[0073] The fluid mechanics mode is turned on in Flac3D to simulate the flow of pore water and its influence on the surrounding rock and soil. The solid mechanics mode can simulate the stress distribution under the fluid-solid coupling effect. The excavation calculation is specifically as follows: according to the actual mining conditions of the coal mining face, the excavation width (i.e. the inclination width of the working face) is set, the single excavation step is 10m, the number of excavation steps is equal to one tenth of the length of the working face, and the boundary effect influence area is set.

[0074] Under the influence of mining stress and confined water coupling effect, when the overburden water-conducting fractures involve the loose aquifer, the soil inside the aquifer is often destroyed. The permeability coefficient increases sharply in the plastic failure area, forming a water-conducting channel, which becomes the channel for major water and sand burst accidents. In the excavation calculation process based on the fluid-solid coupling effect, the development range of the water-conducting fracture zone above the mining face is sought according to the development height and range of the plastic failure area. In the plastic failure area, due to the sharp increase in permeability coefficient, the water-conducting channels of the loose aquifer can be found through the pore pressure change law and seepage vector of the loose aquifer, and are named water-conducting channels 1 to n in sequence.

[0075] S6. Using the fish language to traverse each grid node at the top and bottom of the aquifer in each water channel, define a hydraulic gradient function, and calculate the numerical range of the hydraulic gradient in each water channel;

[0076] The hydraulic gradient function J n The expression is as follows:

[0077]

[0078] In the formula, p ni is the pore pressure of each node at the top of the aquifer in the water channel n, and the corresponding coordinates are (x ni ,y ni ), p nj is the pore pressure of each node at the bottom of the aquifer in the water channel n, and the corresponding coordinate is (x nj ,y nj ), H is the thickness of the aquifer, ρ is the density of water, which is 1000 kg / m 3 , g is 9.8m / s 2 .

[0079] Using fish language to compile a trial algorithm program to find the maximum value J of the hydraulic slope in the water channel n max With the minimum value J min , so the hydraulic gradient value J in the water channel n is n The value range is between J max With J min Between, meet J min <J n <J max , the maximum value of the hydraulic gradient function J max With the minimum value J min The expression is as follows:

[0080]

[0081] S7, traversing the numerical range of hydraulic gradients in all water-conducting channels, taking the maximum and minimum values ​​of the hydraulic gradients as the upper and lower limits of the actual hydraulic gradient, respectively, to obtain the actual hydraulic gradient range based on the fluid-solid coupling effect;

[0082] Under the influence of the coupling effect of mining stress and confined water, the actual hydraulic gradient J of loose aquifers where water and sand burst accidents occur is specifically as follows:

[0083] min(J nmin )≤J≤max(J nmax )

[0084]

[0085] Where, min(Jnmin ) is the lower limit of the actual hydraulic gradient, max(J nmax ) is the upper limit of the actual hydraulic gradient.

[0086] When the maximum value of the actual hydraulic gradient in each water channel is calculated, max(J nmax ) is less than the critical hydraulic slope, no water and sand burst accidents will occur; and when the minimum value of the actual hydraulic slope min(J nmin ) is greater than the critical hydraulic slope, it will cause water and sand burst accidents.

[0087] like Figure 2-7 As shown, the present invention is analyzed by examples and a numerical calculation model is established as shown in Figure 2 As shown in the figure. The fish language is used to compile the formula for the change of the permeability coefficient of each unit cell in the elastic undamaged area and the plastic damaged area, and it is traversed in a loop. When the working face advances 80m, the plastic zone of the overburden develops to the aquifer and communicates with the plastic zone of the aquifer. The plastic zone cloud map (the distribution of the area where the material undergoes plastic deformation under stress) at this moment is shown in the figure. Figure 3 As shown. Figure 4-5 They are respectively the evolution laws of permeability coefficients of overburden strata and aquifers when the working face advances 80m.

[0088] like Figure 6 As shown, according to the pore pressure and seepage vector distribution, the main water-conducting channels of the aquifer are found. In this embodiment, the main water-conducting channels 1 and 2 of the aquifer are found. Figure 7 As shown, the fish language is used to traverse the grid nodes at the top and bottom of the aquifer in the water channel. According to steps S6-S7, the fish language is used to compile a trial algorithm program to calculate the maximum hydraulic slope J in the water channel 1. 1max is 1.14, the minimum hydraulic slope J 1min is 0.74, calculate the maximum hydraulic gradient J in water channel 2 2max is 1.12, the minimum hydraulic slope J 2min =0.71, and the maximum and minimum values ​​of the hydraulic gradients in the two water-conducting channels are taken as the maximum and minimum values ​​of the actual hydraulic gradient, that is, under the influence of the geological conditions and the coupling effect of mining stress and confined water, when the water-conducting fracture zone communicates with the aquifer, the plastic failure zone of the loose aquifer communicates with the water-conducting fracture zone of the overburden rock, and the above two main water-conducting channels are formed. The actual hydraulic gradient range is: 0.71≤J≤1.14. Combined with the critical hydraulic gradient J calculated according to the existing technology, c On this basis, we can carry out the anti-seepage damage evaluation under the influence of geological conditions and the coupling effect of mining stress and pressurized water, so as to provide a theoretical basis for the safe mining of the working face with a safety coal (rock) pillar to prevent sand and collapse.

[0089] The present invention also provides an actual hydraulic gradient calculation system based on fluid-solid coupling effect, comprising a sample collection module, a model building module, an initial stress balance calculation module, a permeability coefficient change module, an excavation calculation module, a hydraulic gradient calculation module and an actual hydraulic gradient calculation module;

[0090] The sample collection module is used to obtain soil samples and coal samples of loose aquifers and rock samples of roof overburden strata through geological exploration drilling;

[0091] The model building module is used to determine the parameters required for numerical simulation and to establish a numerical calculation model for the actual hydraulic gradient;

[0092] The initial stress balance calculation module is used to set displacement boundary conditions, stress boundary conditions and failure criteria for the numerical calculation model, input the parameters obtained by the model establishment module, start the solid mechanics mode, and close the fluid mechanics mode to perform initial stress balance calculation;

[0093] The permeability coefficient change module is used to compile the permeability coefficient change relationship of each layer cell of the overburden rock, bedrock weathering zone, and loose aquifer within the elastic undamaged range and the plastic damaged range by using the fish language according to the principle of cell traversal;

[0094] The excavation calculation module is used to simultaneously start the solid mechanics mode and the fluid mechanics mode, perform excavation calculations on the mining face based on the fluid-solid coupling effect, and find the water-conducting channel of the loose aquifer;

[0095] The hydraulic gradient calculation module is used to traverse each grid node at the top and bottom of the aquifer in each water channel using the fish language, define a hydraulic gradient function, and calculate the numerical range of the hydraulic gradient in each water channel respectively;

[0096] The actual hydraulic gradient calculation module is used to traverse the numerical range of the hydraulic gradient in all water-conducting channels, take the maximum and minimum values ​​of the hydraulic gradient as the upper and lower limits of the actual hydraulic gradient, and obtain the actual hydraulic gradient range based on the fluid-solid coupling effect.

[0097] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating actual hydraulic gradient based on fluid-solid coupling effect, characterized in that: The following steps are involved: S1. Obtain soil samples and coal samples from loose aquifers and rock samples from roof overburden strata through geological exploration drilling; S2. Determine the parameters required for numerical simulation and establish a numerical calculation model for the actual hydraulic slope; S3, setting displacement boundary conditions, stress boundary conditions and failure criteria for the numerical calculation model, inputting the parameters obtained in step S2, starting the solid mechanics mode, and closing the fluid mechanics mode, and performing initial stress balance calculation; S4. Using the fish language and following the principle of cell traversal, write the relationship between the permeability coefficient of the cells of the overburden rock, bedrock weathering zone, and loose aquifer in the elastic undamaged range and the plastic damaged range; S5. Simultaneously start the solid mechanics mode and the fluid mechanics mode, perform excavation calculations on the mining face based on the fluid-solid coupling effect, and find the water-conducting channel of the loose aquifer; S6. Using the fish language to traverse each grid node at the top and bottom of the aquifer in each water channel, define a hydraulic gradient function, and calculate the numerical range of the hydraulic gradient in each water channel; S7. Traverse the numerical range of the hydraulic gradient in all water-conducting channels, take the maximum and minimum values ​​of the hydraulic gradient as the upper and lower limits of the actual hydraulic gradient, and obtain the actual hydraulic gradient range based on the fluid-solid coupling effect.

2. The actual hydraulic gradient calculation method based on fluid-solid coupling effect according to claim 1 is characterized in that: The parameters required for numerical simulation are determined as described in step S2, and a numerical calculation model of the actual hydraulic gradient is established; specifically: the physical and mechanical parameters and hydraulic parameters of soil and rock samples at each layer are obtained through indoor physical and mechanical tests, hydraulic tests and water pressure test results of loose aquifers; the water level data of the hydrological long observation hole near the mining face and the elevation data of the loose aquifer are obtained to calculate the water pressure p of the loose aquifer; a comprehensive borehole column chart of the mining face is drawn according to the lithology and height of each layer, and the actual hydraulic gradient numerical calculation model is established based on the borehole column chart of the exploration area in the mining face using Flac3D software.

3. The actual hydraulic gradient calculation method based on fluid-solid coupling effect according to claim 2 is characterized in that: The physical and mechanical parameters include uniaxial compressive strength Rc, elastic modulus E, tensile strength Rt, cohesion C, internal friction angle The hydraulic parameters include the permeability coefficient k.

4. The actual hydraulic gradient calculation method based on fluid-solid coupling effect according to claim 1 is characterized in that: The failure criterion in step S3 is the Mohr-Coulomb yield criterion.

5. The actual hydraulic gradient calculation method based on fluid-solid coupling effect according to claim 1 is characterized in that: The expression of the permeability coefficient k1 within the elastic undamaged range in step S4 is as follows: k1=k0exp(-ασ) Where k0 is the initial permeability coefficient of each unit cell, α is the test parameter, and σ is the effective stress of each unit cell, which is the difference between the mean of the principal stress in the three directions of each unit cell and the pore pressure.

6. The actual hydraulic gradient calculation method based on fluid-solid coupling effect according to claim 5 is characterized in that: The permeability coefficient k within the plastic failure range described in step S4 m The expression is as follows: Where w is the damage variable of rock or soil. For the damaged rock or soil, w>0; To destroy the current porosity of rock or soil, is the initial porosity, is the residual porosity under high stress state, σ is the average effective stress, ζ is the stress sensitivity coefficient, and ζ1 is the damage permeability effect coefficient.

7. The actual hydraulic gradient calculation method based on fluid-solid coupling effect according to claim 6 is characterized in that: The expression of the hydraulic gradient function in step S6 is as follows: In the formula, J n is the hydraulic gradient value in the water channel n, p ni is the pore pressure of each node at the top of the aquifer in the water channel n, and the corresponding coordinates are (x ni ,y ni ), p nj is the pore pressure of each node at the bottom of the aquifer in the water channel n, and the corresponding coordinate is (x nj ,y nj ), H is the thickness of the aquifer, ρ is the density of water, which is 1000 kg / m 3 , g is 9.8m / s 2 .

8. The actual hydraulic gradient calculation method based on fluid-solid coupling effect according to claim 7 is characterized in that: The maximum value J of the hydraulic gradient function in step S6 max With the minimum value J min The expression is as follows:

9. The actual hydraulic gradient calculation method based on fluid-solid coupling effect according to claim 8 is characterized in that: The range of the actual hydraulic gradient in step S7 is specifically: min(J nmin )≤J≤max(J nmax ) Where J is the actual hydraulic gradient.

10. An actual hydraulic gradient calculation system based on fluid-solid coupling effect, characterized in that: It includes sample collection module, model building module, initial stress balance calculation module, permeability coefficient change module, excavation calculation module, hydraulic slope calculation module and actual hydraulic slope calculation module; The sample collection module is used to obtain soil samples and coal samples of loose aquifers and rock samples of roof overburden strata through geological exploration drilling; The model building module is used to determine the parameters required for numerical simulation and to establish a numerical calculation model for the actual hydraulic gradient; The initial stress balance calculation module is used to set displacement boundary conditions, stress boundary conditions and failure criteria for the numerical calculation model, input the parameters obtained by the model establishment module, start the solid mechanics mode, and close the fluid mechanics mode to perform initial stress balance calculation; The permeability coefficient change module is used to compile the permeability coefficient change relationship of each layer cell of the overburden rock, bedrock weathering zone, and loose aquifer within the elastic undamaged range and the plastic damaged range by using the fish language according to the principle of cell traversal; The excavation calculation module is used to simultaneously start the solid mechanics mode and the fluid mechanics mode, perform excavation calculations on the mining face based on the fluid-solid coupling effect, and find the water-conducting channel of the loose aquifer; The hydraulic gradient calculation module is used to traverse each grid node at the top and bottom of the aquifer in each water channel using the fish language, define a hydraulic gradient function, and calculate the numerical range of the hydraulic gradient in each water channel respectively; The actual hydraulic gradient calculation module is used to traverse the numerical range of the hydraulic gradient in all water-conducting channels, take the maximum and minimum values ​​of the hydraulic gradient as the upper and lower limits of the actual hydraulic gradient, and obtain the actual hydraulic gradient range based on the fluid-solid coupling effect.

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