Evaluation method for water-preserved mining in terms of in-situ protection of confined water in mine floor

Abstract

Disclosed in the present invention is an evaluation method for water-preserved mining in terms of the in-situ protection of confined water in a mine floor. The method comprises the following steps: determining the average distance between a mined coal seam floor and an aquifer, the average thickness of the aquifer, the average permeability, a working face length and an advancing distance; measuring the average depth of a fractured zone in the mined floor, and the average thickness and average permeability of rock strata below the fractured zone, so as to obtain an equivalent permeability; measuring and statistically analyzing the water pressure of a confined aquifer, and determining a target water pressure; calculating an allowable water loss during coal mining; determining a critical equivalent permeability coefficient; comparing the equivalent permeability with the critical equivalent permeability, and comparing a calculated water inflow with a water inflow for safe mining at a working face; and finally determining the feasibility of water-preserved mining during which the in-situ protection of confined water in a mine floor can be achieved. In the present invention, on the basis of the dynamic water storage and release characteristics of a confined aquifer and the overall water resistance performance of effective barrier strata in a mined floor, an evaluation method for water-preserved mining during which in-situ protection of confined water in a mine floor can be achieved is provided, and the method involves simple operations and has strong applicability in the field.

Description

A method for determining water-conserving mining under in-situ protection of confined water in the base plate Technical Field

[0001] This invention relates to the field of water-conserving mining technology, and in particular to a method for judging water-conserving mining in situ with confined water protection on the bottom plate. Background Technology

[0002] Most of my country's coal seams have high-pressure aquifers such as Ordovician limestone and Taiyuan limestone on their floor, and the coal reserves are abundant. In-situ water-conserving mining of the confined aquifers on the floor has become one of the urgent needs for the coordinated development of coal resource development and water resource protection in China.

[0003] Water-conserving mining has always been a hot topic in academia, and the concepts and technologies for water-conserving mining are becoming increasingly sophisticated and mature. For in-situ protection of roof water, preliminary technologies / methods have been developed, using the height of water-conducting fracture zones and the stability of key water-resistant layers or groups of water-resistant layers as evaluation indicators. Chinese scholars have achieved rich research results in the prevention and control of confined water inrush in the floor, and have proposed theories and evaluation methods for floor water inrush by analyzing the deformation and failure characteristics of the mining-induced floor and the depth of fracture development, effectively guiding safe mine production. Examples include the "vulnerability index method," the "five-graph double-coefficient method," and the "water inrush coefficient method." Scholars have shifted from "water hazard prevention" of confined water in the floor to "in-situ water-conserving mining" of confined water in the floor, but the relevant research results have the following shortcomings:

[0004] ① Existing research pays less attention to in-situ protection of the bottom water and focuses more on safe mining. It has proposed corresponding technologies to increase the water-blocking performance of the bottom (such as grouting reinforcement) and early warning technologies. Water-conserving mining and safe mining should be coordinated and the complementary model of the two should be fully utilized.

[0005] ② Existing methods such as the stability of the key water-resistant layer of the base plate and the water inrush coefficient method can provide some reference for the in-situ protection of the base plate water, but they do not consider the differences and heterogeneity of the water properties of the rock strata. A quantitative analysis of the overall water-blocking performance of the effective water-resistant layer should be conducted to directly provide a water-retaining mining discrimination method for the in-situ protection of the base plate confined water.

[0006] ③ It is not only necessary to focus on the stability of the confined aquifer within the mining area, but also to ensure the stability of the confined aquifer outside the mining influence area. That is, it is necessary to prevent the confined aquifer outside the mining area from being replenished through the confined aquifer within the mining area, and to prevent the confined aquifer outside the influence area from only draining without replenishment. The traditional condition that the replenishment of the aquifer within the mining influence area equals the leakage of the working face should not be taken as the critical condition. Furthermore, since confined aquifers are generally thick and have sufficient replenishment, a large leakage of the working face will seriously affect the safe mining of the working face. The in-situ protection of the floor water should have its own special characteristics.

[0007] Chinese invention patent: Publication number "CN110749533B", titled "A method for identifying water-retaining coal mining based on equivalent aquitard thickness". This patent discloses a method for identifying water-retaining coal mining based on the thickness of an equivalent aquitard. The specific steps are: determining the thickness M of each overburden stratum. i and the total thickness M of the overburden; test the permeability coefficient K of each layer of the overburden after mining. i ; Calculate the equivalent permeability coefficient K of the overburden. v Determine the aquifer water level depth H0 and recharge rate V. 补给 Determine the post-mining aquifer head height ΔH; calculate the critical equivalent aquifer thickness M required for water-conserving coal mining. 等效 The critical equivalent water-tight layer thickness M 等效 The feasibility of water-retaining mining of the coal seam is ultimately determined by comparing the total thickness M of all strata from the coal seam roof to the aquitard. This technical solution, based on the changes in the overall permeability coefficient and leakage hydrophysical properties of the overlying strata before and after mining, provides a direct method for determining the feasibility of water-retaining coal mining with roof aquifer protection, based on the essential water-retaining properties of the strata. This method is more accurate, faster, and has strong practical applicability in the field. However, this technical solution does not consider the influence of fractured zones (fractured zones have minimal impact on the water-blocking performance of strata, but they reduce the hydraulic gradient from the aquifer to the working face, leading to an increase in the critical equivalent water-blocking thickness), does not consider the differences and heterogeneity of the hydrophysical properties of the strata (permeability coefficients vary at different locations in the floor due to differences in their own hydrophysical properties and stress states), and does not consider the stability of aquifers outside the mining-affected area. It only assumes the boundary condition that the aquifer infiltration and recharge are equal, meaning that downstream aquifers outside the mining-affected area will have no recharge. Furthermore, if the aquifer recharge is large, complete infiltration will affect the safe mining of the working face. Summary of the Invention

[0008] To address the issue that existing technologies fail to consider the differences and heterogeneity of rock strata hydraulic properties and the stability of aquifers, relying solely on the assumption of equal infiltration and recharge boundary conditions, which can negatively impact safe mining operations, this invention proposes a water-conserving mining discrimination method for in-situ protection of confined aquifers. This method fully considers the differences and heterogeneity of rock strata hydraulic properties, balances both water-conserving mining and safe mining modes, and features a simple, highly operable, and easily applicable field application method.

[0009] This invention is achieved through the following technical solution, including the following steps:

[0010] S1. Determine the average distance M between the bottom of the mined coal seam and the aquifer, and the average thickness M of the aquifer. 承 Average penetration rate K 承 With working surface length L 面 and propulsion distance length L 推 ;

[0011] S2, The average depth M of the mining floor fracture zone was detected. 破 The average thickness of each impermeable rock layer below the fracture zone is M i Average penetration rate K i And the equivalent permeability K of the layered heterogeneous substrate eq ;

[0012] S3, Detect and count the total time t 总 Water pressure P of confined aquifers at different time periods i Determine the target water pressure P of the target (in-situ water-retaining) confined aquifer. 目 The measured water pressure P i and target water pressure P 目 By comparison, the pressure P exceeding the target water pressure was obtained. 目 The water pressure P of the confined aquifer 超 and water pressure P i Exceeding the target water pressure P 目 Time t;

[0013] S4. Based on the target water pressure P obtained in step S3 目 With water pressure P 超 And time t, substitute into the formula Permitted water resource loss S during coal mining 允 ;

[0014] In the formula, μ is the hydrodynamic viscosity coefficient, with units of Pa·s;

[0015] S5. The water pressure P obtained in step S3 i and the allowable water loss from coal mining S obtained in step S4 允 Substitute into the formula The critical equivalent permeability coefficient K of the water-resistant rock layer in the mining floor was obtained. 临界 ;

[0016] In the formula, t 总 Total detection time, in days (d); K 临界 The critical equivalent permeability coefficient of the water-resistant rock strata at the bottom of the mining area is given in D; P. 工 The working face water pressure is expressed in MPa.

[0017] S6. Determine the feasibility of in-situ protection of the confined water in the bottom plate for water-retaining mining;

[0018] S61. The equivalent permeability K of the layered heterogeneous substrate obtained in step S2. eq The critical equivalent permeability coefficient K of the water-resistant rock layer in the mining floor obtained in step S5. 临界 Compare, if K eq >K 临界If K eq ≤K 临界 Then proceed to step S62;

[0019] S62, the equivalent permeability K of the layered heterogeneous substrate. eq Average depth M of the mining floor fracture zone 破 The average distance M between the bottom of the coal seam and the aquifer, and the length L of the working face. 面 , Propulsion distance length L 推 and water pressure P i Substitute into the formula The unit time flow rate Q within the total time range is obtained. 涌 If Q does not exist 涌 ≥Q 安 If the continuous duration is more than 5 days, in-situ protection of the bottom plate against pressurized water can be achieved; if Q exists... 涌 ≥Q 安 If the continuous duration exceeds 5 days, in-situ protection of the bottom plate against pressurized water cannot be achieved.

[0020] In the formula, Q 安 The water inflow volume is measured in cubic meters (m³) to ensure safe mining at the working face. 3 / d.

[0021] Furthermore, step S2 includes the following steps:

[0022] S21, at the working surface length L 面 and propulsion distance length L 推 A×B boreholes were arranged within the mining area to obtain the depth of the bottom fracture zone, the thickness of each rock layer below the fracture zone, and the permeability.

[0023] S22. Calculate the average depth M of the mining-induced floor fracture zone based on the depths of several fractured zones, the thicknesses of each rock layer, and the permeability detected in step S21. 破 and the average thickness M of each rock layer below the fracture zone i and average penetration rate K i ;

[0024] S23, the average depth M of the mining floor fracture zone obtained in step S22. 破 and the average thickness M of each rock layer below the fracture zone i and average penetration rate K i Substitute into the formula The equivalent permeability K of the layered heterogeneous substrate is obtained. eq ;

[0025] In the formula, i = 1, 2, 3...n, and n is the number of rock strata below the fracture zone.

[0026] Furthermore, in step S1, the average distance M between the bottom of the mined coal seam and the aquifer, and the average thickness M of the aquifer are obtained by on-site drilling and by reviewing the mine's geological and hydrogeological exploration reports and mine development plan. 承 Average penetration rate K 承 With working surface length L 面 and propulsion distance length L 推 .

[0027] Furthermore, in step S2, the depth detection of the fractured zone of the base plate is mainly based on on-site water pressure testing, supplemented by parallel electrical resistivity tomography. The thickness of each rock layer below the fractured zone is obtained by on-site drilling. The average thickness M of each rock layer below the fractured zone is obtained by averaging the thicknesses of several rock layers below the fractured zone. i The average permeability K of each rock layer below the fracture zone i The mean value is obtained by calculating the mean value after pressure testing during the drilling process.

[0028] Furthermore, in step S2, the values ​​of A and B are 10 and 5 respectively, and the distance between the working face direction and the dip measurement points is L. 推 / 9、L 面 / 4.

[0029] Furthermore, the total detection time in step S3 is t. 总 The cycle is one year, and different time periods are divided into four quarters.

[0030] Furthermore, in step S3, the target water pressure P 目 The method for determining the target water pressure P is as follows: calculate the average water pressure of the confined water in spring and autumn, and take the maximum value as the target water pressure P. 目 .

[0031] Furthermore, in step S4, the confined aquifer water pressure P exceeding the target water pressure is statistically analyzed in both summer and winter confined aquifer conditions. 超 And time t.

[0032] 1. Further, in step S5, the critical equivalent permeability coefficient K of the water-impermeable strata at the bottom of the mining area is calculated. 临界 At that time, the amount of water resources lost during coal mining will be allowed to reach S. 允 Averaged over a year; working face water pressure P 工 The values ​​were obtained from on-site testing.

[0033] Furthermore, in step S62, Q 安 The value is 1000m 3 / d.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The discrimination method provided by this invention not only focuses on the stability of aquifers within the mining area, but also ensures the stability of aquifers outside the mining influence area, that is, it does not disrupt the recharge of aquifers through the mining area, and prevents the situation where aquifers outside the mining influence area only discharge and do not recharge. Attached Figure Description

[0036] Figure 1 is a flowchart of the discrimination method of the present invention.

[0037] Figure 2 is a schematic diagram of the damage to the water-resistant rock strata structure in the bottom plate after mining and the layout of measuring points.

[0038] Figure 3 shows the water pressure P of the confined aquifer at different time periods in Example 1. i With target water pressure P 目 Dotted line graph.

[0039] Figure 4 shows the water inflow Q per unit time within the total time range of Example 1. 涌 Dotted line graph. Detailed Implementation

[0040] The advantages and features of the present invention will be illustrated and explained by the following non-limiting description of preferred embodiments, which are given by way of example only with reference to the accompanying drawings.

[0041] As shown in Figure 1, this invention provides a water-retaining mining discrimination method for in-situ protection of confined water in the bottom plate, the specific steps of which are as follows:

[0042] Step S1: By drilling on-site and reviewing the mine's geological and hydrogeological exploration reports and mine development plan, the average distance M between the bottom of the mined coal seam and the aquifer, and the average thickness M of the aquifer are obtained. 承 Average penetration rate K 承 With working surface length L 面 and propulsion distance length L 推 .

[0043] Step S2: Detect the average depth M of the fracture zone in the mining floor. 破 The average thickness of each impermeable rock layer below the fracture zone is M i Average penetration rate K i And the equivalent permeability K of the layered heterogeneous substrate eq .

[0044] Step S21, in the working surface length L 面 and propulsion distance length L 推 A×B boreholes were arranged within the mining area to obtain the depth of the fracture zone, the thickness of each rock layer below the fracture zone, and the permeability.

[0045] Step S22: Calculate the average depth M of the mining-induced floor fracture zone based on the depth of several floor fracture zones, the thickness of each rock layer, and the permeability detected in step S21. 破 and the average thickness M of each rock layer below the fracture zone i and average penetration rate K i .

[0046] Step S23: The average depth M of the mining bottom plate fracture zone obtained in step S22 is... 破 and the average thickness M of each rock layer below the fracture zone i and average penetration rate K i Substitute into the formula The equivalent permeability K of the layered heterogeneous substrate is obtained. eq .

[0047] In the formula, M is the average distance from the bottom of the mined coal seam to the aquifer, in meters; 破 M represents the average depth of the fractured zone in the mining floor, in meters (m). i K represents the average thickness of all rock layers below the fracture zone, in meters. i The average permeability of the rock layers below the fracture zone is expressed in D; i = 1, 2, 3...n, where n is the number of rock layers below the fracture zone.

[0048] As a preferred method, the depth of the fractured zone in the base plate is primarily determined by on-site water pressure testing, supplemented by parallel electrical resistivity tomography (EDS) to ensure the reliability of the test results. The thickness of each rock layer below the fractured zone is obtained through on-site drilling, and the average thickness M of the rock layers below the fractured zone is calculated by averaging the thicknesses of several layers below the fractured zone. i The average permeability K of each rock layer below the fracture zone i The mean value is obtained by calculating the mean value after pressure testing during the drilling process.

[0049] Preferably, in the working face length L 面 and propulsion distance length L 推 Within the mining area, A×B borehole measuring points are arranged, with values ​​of 10 and 5 for A and B, respectively. The spacing between the measuring points along the strike and dip of the working face is L. 推 / 9、L 面 / 4.

[0050] Step S3: Detect and calculate the total time t. 总 Water pressure P of confined aquifers at different time periods i Determine the target water pressure P of the target (in-situ water-retaining) confined aquifer. 目 The water pressure P of the confined aquifer obtained from the test will be... i The target water pressure P of the target (in-situ water-retaining) confined aquifer 目 By comparison, the pressure P exceeding the target water pressure was obtained. 目The water pressure P of the confined aquifer 超 And the water pressure P of the confined aquifer i Exceeding the target water pressure P 目 The time t.

[0051] As a preferred option, the total detection time is t. 总 The cycle is one year, divided into four quarters. The target water pressure P of the confined aquifer (in-situ water retention) is... 目 The method for determining the target water pressure P is as follows: Considering that the water pressure of confined aquifers is relatively stable in spring and autumn, the average water pressure of the confined aquifers in spring and autumn is calculated, and the maximum value is taken as the target water pressure P. 目 .

[0052] Step S4: Based on the target water pressure P obtained in step S3 目 The pressure P of the confined aquifer exceeds the target water pressure 超 And time t, substitute into the formula Permitted water resource loss S during coal mining 允 .

[0053] In the formula, P 目 The target water pressure for the confined aquifer (in-situ water retention) is expressed in MPa; P 超 The pressure of the confined aquifer exceeding the target pressure is expressed in MPa; t is the time it takes for the pressure of the confined aquifer to exceed the target pressure, expressed in days; S 允 The allowable amount of water loss during coal mining is expressed in cubic meters (m³). 3 μ is the hydrodynamic viscosity coefficient, with units of Pa·s.

[0054] As a preferred option, the confined aquifer water pressure P exceeding the target water pressure 超 The time t is measured within the range of the confined aquifer state in summer and winter.

[0055] Step S5: Based on the water pressure P of the confined aquifer obtained in step S3... i and the allowable water loss from coal mining S obtained in step S4 允 Substitute into the formula The critical equivalent permeability coefficient K of the mining-induced floor aquifer is obtained, which enables in-situ protection of the confined water in the floor (post-mining water loss and water loss due to permissible coal mining). 临界 .

[0056] In the formula, L 推 The distance the working face advances is measured in meters (m); t 总 Total monitoring time, in days; P i The water pressure of the confined aquifer at different time periods is expressed in MPa; K 临界 The critical equivalent permeability coefficient of the water-resistant rock strata at the bottom of the mining area is given in D; P.工 The water pressure at the working face is expressed in MPa.

[0057] Calculate the critical equivalent permeability coefficient K of the water-resistant rock layer at the bottom of the mining area. 临界 At that time, the amount of water resources lost during coal mining will be allowed to reach S. 允 Averaged over each day of the year. When pressurized water flows to the working face, it becomes free water, with a water pressure P. 工 The value is 0 MPa.

[0058] Step S6: Determine the feasibility of in-situ protection of the confined water in the bottom plate for water-retaining mining.

[0059] Step S61: Calculate the equivalent permeability K of the layered heterogeneous substrate obtained in step S2. eq The critical equivalent permeability coefficient K of the water-resistant rock layer in the mining floor obtained in step S5. 临界 Compare, if K eq >K 临界 If K eq ≤K 临界 If, after the coal seam is mined, it is necessary to further determine whether in-situ protection of the confined water on the floor has been achieved, then proceed to step S62.

[0060] Step S62, if K eq ≤K 临界 The equivalent permeability K of the layered heterogeneous substrate eq Average depth M of the mining floor fracture zone 破 The average distance M between the bottom of the coal seam and the aquifer, and the length L of the working face. 面 , Propulsion distance length L 推 and water pressure P i Substitute into the formula The water inflow rate Q per unit time within the total time range is obtained. 涌 To ensure safe mining at the working face, if Q does not exist... 涌 ≥Q 安 If the continuous duration is more than 5 days, in-situ protection of the bottom plate against pressurized water can be achieved; if Q exists... 涌 ≥Q 安 If the continuous duration is more than 5 days, in-situ protection of the bottom plate against pressurized water cannot be achieved.

[0061] In the formula, Q 涌 The water flow rate per unit time is expressed in meters (m³). 3 / d;Q 安 The water inflow volume is measured in cubic meters (m³) to ensure safe mining at the working face. 3 / d. As a preferred option, Q 安 The value is 1000m 3 / d.

[0062] Example 1

[0063] This embodiment takes a working face in a mine in Shanxi, my country, threatened by a confined aquifer as an example. After the bottom plate was reinforced by grouting, the water inflow of the bottom plate was significantly reduced. The purpose is to determine whether the confined aquifer in the bottom plate has been protected in situ.

[0064] Step S1: Review the mine's geological and hydrogeological exploration report and mine development plan to determine the average distance M between the bottom of the mined coal seam and the aquifer, and the average thickness M of the aquifer. 承 Average penetration rate K 承 With working surface length L 面 and propulsion distance length L 推 As shown in Table 1.

[0065] Table 1. Relevant parameters of aquifer and working face

[0066] Step S2: Within the mining area consisting of a 100m working face and a 600m advancing distance, 10×5 borehole measuring points are arranged (see Figure 2 for a schematic diagram). The spacing between the measuring points for the working face strike and dip is 66m and 25m, respectively. The average depth M of the fractured zone of the mining floor is determined using traditional segmented water pressure testing. 破 The average thickness of each rock layer below the fractured zone of the floor after mining is 20m. i and average penetration rate K i See Table 2.

[0067] Table 2. Information on the underlying rock strata below the fracture zone.

[0068] The average thickness M of each impermeable rock layer below the fracture zone in Table 2 is... i and average penetration rate K i Substitute into the formula The equivalent permeability of the layered heterogeneous substrate was calculated to be 1.76 × 10⁻⁶. 3 D.

[0069] Step S3: Based on the hydrological observation well, test the water pressure of the confined aquifer over a period of one year, as shown in Figure 3. Calculate the average water pressure of the confined aquifer in spring and autumn, which are 4.45 MPa and 5.56 MPa respectively. Take the maximum value as the target water pressure P. 目 That is, 5.56 MPa. The water pressure P of the confined aquifer exceeding the target water pressure in summer and winter is statistically analyzed. 超 And time t.

[0070] Step S4: Increase the water pressure P of the confined aquifer, which exceeds the target water pressure. 超 And time t, substitute into the formula Calculate the allowable water loss S during coal mining 允It is 293266.3m 3 .

[0071] Step S5: Based on the water pressure P of the confined aquifer obtained in step S3... i The allowable water loss from coal mining determined in step S4, S 允 And combined with the P determined by field tests 工 Substitute The critical equivalent permeability of the mining-induced floor aquitard strata, calculated to be sufficient for in-situ protection of the confined water in the floor (including post-mining water loss and water loss due to permissible coal mining), is 2.77 × 10⁻⁶. 3 D.

[0072] Step S6: Calculate the equivalent permeability K of the layered heterogeneous substrate obtained in step S2. eq The critical equivalent permeability coefficient K of the water-resistant rock layer in the mining floor obtained in step S5. 临界 Comparison, K eq ≤K 临界 After coal seam mining, it should be further determined whether in-situ protection of the confined water floor has been achieved.

[0073] Based on the water pressure P of the confined aquifer obtained in step S3 i Substitute into the formula (can be simplified to) Calculate the inflow rate Q per unit time within the total time range. 涌 As shown in Figure 4, Q does not exist. 涌 ≥1000m 3 In the case of / d, continuous time of more than 5 days, it can achieve in-situ protection of the bottom plate against pressurized water.

[0074] In addition to the above embodiments, the present invention may have other implementation methods. All technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for determining water-retaining mining under in-situ protection of confined water in the base plate, characterized in that, Includes the following steps: S1. Determine the average distance M between the bottom of the mined coal seam and the aquifer, and the average thickness M of the aquifer. 承 Average penetration rate K 承 With working surface length L 面 and propulsion distance length L 推 ; S2, The average depth M of the fractured zone on the floor of the mined coal seam was obtained. 破 The average thickness M of each rock layer below the fracture zone i Average permeability K of each rock layer below the fracture zone i And the equivalent permeability K of the layered heterogeneous substrate. eq ; S3, Detect and count the total time t 总 Water pressure P of confined aquifer at different time periods i Determine the target water pressure P of the target confined aquifer. 目 The water pressure P of the confined aquifer obtained from the test will be... i and target water pressure P 目 By comparison, the pressure P exceeding the target water pressure was obtained. 目 The water pressure P of the confined aquifer 超 And the water pressure P of the confined aquifer i Exceeding the target water pressure P 目 Time t; S4. Based on the target water pressure P obtained in step S3 目 With water pressure P 超 And time t, substitute into the formula Permitted water resource loss S during coal mining 允 ; In the formula, μ is the hydrodynamic viscosity coefficient, with units of Pa·s; S5. The water pressure P obtained in step S3 i and the allowable water loss from coal mining S obtained in step S4 允 Substitute into the formula The critical equivalent permeability coefficient K of the water-impermeable strata at the bottom of the mined coal seam was obtained. 临界 ; In the formula, t 总 Total testing time, in days; K 临界 The critical equivalent permeability coefficient of the water-impermeable strata at the bottom of the coal seam, expressed in D; P 工 The working face water pressure is expressed in MPa. S6. Determine the feasibility of in-situ protection of the confined water in the bottom plate for water-retaining mining; S61. The equivalent permeability K of the layered heterogeneous substrate obtained in step S2. eq The critical equivalent permeability coefficient K of the water-resistant rock layer in the mining floor obtained in step S5. 临界 Compare, if K eq >K 临界 If K eq ≤K 临界 Then proceed to step S62; S62, the equivalent permeability K of the layered heterogeneous substrate. eq Average depth M of the mining floor fracture zone 破 The average distance M between the bottom of the coal seam and the aquifer, and the length L of the working face. 面 , Propulsion distance length L 推 and water pressure P i Substitute into the formula The unit time flow rate Q within the total time range is obtained. 涌 If Q does not exist 涌 ≥Q 安 If the continuous duration is more than 5 days, in-situ protection of the bottom plate against pressurized water can be achieved; if Q exists... 涌 ≥Q 安 If the continuous duration exceeds 5 days, in-situ protection of the bottom plate against pressurized water cannot be achieved. In the formula, Q 安 The water inflow volume is measured in cubic meters (m³) to ensure safe mining at the working face. 3 / d.

2. The water-retaining mining discrimination method for in-situ protection of confined water in the bottom plate according to claim 1, characterized in that: Step S2 includes the following steps: S21, at the working surface length L 面 and propulsion distance length L 推 A×B boreholes were arranged within the mining area to obtain the depth of the bottom fracture zone, the thickness of each rock layer below the fracture zone, and the permeability. S22. Calculate the average depth M of the mining-induced floor fracture zone based on the depths of several fractured zones, the thicknesses of each rock layer, and the permeability detected in step S21. 破 and the average thickness M of each rock layer below the fracture zone i and average penetration rate K i ; S23, the average depth M of the mining floor fracture zone obtained in step S22. 破 and the average thickness M of each rock layer below the fracture zone i and average penetration rate K i Substitute into the formula The equivalent permeability K of the layered heterogeneous substrate is obtained. eq ; In the formula, i = 1, 2, 3...n, and n is the number of rock strata below the fracture zone.

3. The water-retaining mining discrimination method for in-situ protection of confined water in the bottom plate according to claim 2, characterized in that: In step S1, the average distance M between the bottom of the mined coal seam and the aquifer, and the average thickness M of the aquifer are obtained by on-site drilling and by reviewing the geological and hydrogeological exploration report and the mine development plan. 承 Average penetration rate K 承 With working surface length L 面 and propulsion distance length L 推 .

4. The water-retaining mining discrimination method for in-situ protection of confined water in the bottom plate according to claim 2, characterized in that: In step S2, the depth of the fractured zone of the base plate is mainly determined by on-site water pressure testing, supplemented by parallel electrical resistivity tomography. The thickness of each rock layer below the fractured zone is obtained by on-site drilling. The average thickness M of each rock layer below the fractured zone is obtained by averaging the thicknesses of several rock layers below the fractured zone. i The average permeability K of each rock layer below the fracture zone i The mean value is obtained by calculating the mean value after pressure testing during the drilling process.

5. The water-retaining mining discrimination method for in-situ protection of confined water in the bottom plate according to claim 2, characterized in that: In step S2, the values ​​of A and B are 10 and 5 respectively, and the distance between the working face direction and the dip measurement points is L. 推 / 9、L 面 / 4.

6. The water-retaining mining discrimination method for in-situ protection of confined water in the bottom plate according to claim 2, characterized in that: The total detection time in step S3 is t. 总 The cycle is one year, and different time periods are divided into four quarters.

7. The water-retaining mining discrimination method for in-situ protection of confined water in the bottom plate according to claim 2, characterized in that: In step S3, the target water pressure P 目 The method for determining the target water pressure P is as follows: calculate the average water pressure of the confined water in spring and autumn, and take the maximum value as the target water pressure P. 目 .

8. The water-retaining mining discrimination method for in-situ protection of confined water in the base plate according to claim 2, characterized in that: In step S4, the confined aquifer water pressure P exceeding the target water pressure is statistically analyzed in both summer and winter confined aquifer conditions. 超 And time t.

9. The water-retaining mining discrimination method for in-situ protection of confined water in the bottom plate according to claim 2, characterized in that: In step S5, the critical equivalent permeability coefficient K of the water-retaining rock layer at the bottom of the mining area is calculated. 临界 At that time, the amount of water resources lost during coal mining will be allowed to reach S. 允 Averaged over a year; working face water pressure P 工 The values ​​were obtained from on-site testing.

10. The water-retaining mining discrimination method for in-situ protection of confined water in the base plate according to claim 2, characterized in that: In step S62, Q 安 The value is 1000m 3 / d.

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