A method for judging the water-blocking properties of heterogeneous equivalent water-retaining layers based on ecological water levels.

Abstract

This invention discloses a method for judging the water-blocking properties of heterogeneous equivalent aquitards based on ecological water levels, comprising the following steps: Step 1, determining the stratigraphic distribution of the working face in the mining area and analyzing the thickness of each stratum; the stratigraphic distribution consists of, from bottom to top, coal seams, bedrock layers, weathered bedrock aquifers, Baode Formation laterite layers, Lishi Formation loess layers, and loose unconfined aquifers; based on the critical constraint of ecological water levels, sandy loess is equivalent to a homogeneous loess or laterite aquitard of a certain thickness. Taking into account the influence of factors such as water head pressure, mining disturbance, lithological structure, permeability coefficient, and rock strata mechanical parameters, the rock strata properties are simplified, and the permeability coefficient of complex soil combinations is equivalently represented, forming a unified standard for the effective thickness of key aquitards. This clarifies the water-blocking performance and distribution characteristics of the rock strata, achieving an equivalent, standardized, and quantitative assessment of the effective thickness of key aquitards, greatly improving the accuracy of delineating weak water-blocking areas.

Description

Technical Field

[0001] This invention belongs to the field of shallow groundwater protection and mine water hazard prevention, specifically involving a method for judging the water-blocking property of a heterogeneous equivalent water-blocking layer based on ecological water level. Background Technology

[0002] A certain mining area has huge coal reserves, but the climate is arid, water resources are scarce, and the environmental carrying capacity is poor, making it a typical "coal-rich—water-poor—fragile ecosystem" region. Figure 1 As shown, the loess of the Lishi Formation and the red soil of the Baode Formation together form a key impermeable soil layer beneath a loose, water-rich unconfined aquifer in the area.

[0003] Although both soil layers possess good water-blocking properties, their spatial distribution is uneven, with some areas exhibiting thinner or even pinch-out layers. Furthermore, the loess layer contains interlayers of fine and medium sandy soils, exhibiting heterogeneity. Its overall permeability and thickness are unclear, making it difficult to accurately define the effective water-blocking thickness of the critical water-blocking layer and the zoning of water loss risk areas. Mining activities conducted without knowing the effective thickness of the critical water-blocking layer may indirectly connect water-conducting fractures to loose unconfined aquifers, increasing the risk of water inrush at the working face. This could lead to shallow groundwater loss, ecological water levels falling below critical values, and surface vegetation degradation, hindering water-conserving coal mining operations.

[0004] In arid to semi-arid climate zones, the reasonable ecological water level depth should be 1.5–5.0 m. When the water level depth exceeds 5 m, surface vegetation becomes unhealthy. Therefore, controlling the groundwater level depth within 5 m during coal mining is a crucial prerequisite for achieving water-conserving coal mining. As a precious water source maintaining the regional ecological and geological environment, loose unconfined aquifers are of great significance for maintaining surface ecology and biodiversity, and are the main and target aquifers for water resource protection in coal mining. The Lishi Formation loess and Baode Formation red soil are located between the loose unconfined aquifer and the weathered bedrock aquifer. Their water-blocking capacity is directly related to the safety of coal mine production and plays a vital role in achieving regional water-conserving coal mining and ecological environmental protection. However, in some areas, although the key water-blocking soil layer is relatively thick, the presence of a large amount of fine sand and medium sand in the Lishi Formation loess layer reduces the soil viscosity, increases the permeability coefficient, weakens the effective water-blocking capacity, and results in a smaller actual effective water-blocking thickness. Under the influence of hydraulic gradient, loose unconfined aquifers in areas with weak impermeable soil layers will continuously seep downwards to replenish weathered bedrock aquifers, resulting in a waste of shallow groundwater resources, groundwater levels falling below the ecological water level, and impacting surface vegetation and the ecological environment. Furthermore, the increased water volume in weathered bedrock aquifers after being replenished by loose unconfined aquifers can indirectly affect the production safety of underground working faces.

[0005] Currently, the determination of the water-blocking performance of key water-retaining soil layers is mainly based on linear inference from their thickness. Most of the research objects are homogeneous single soil layers under ideal conditions. There is little research on the equivalent permeability coefficient of heterogeneous composite soil or sandy soil layers. There is no unified evaluation method for the effective water-retaining layer thickness based on mine production and ecological water level protection. The critical thickness is still difficult to define accurately.

[0006] Therefore, the key to achieving shallow groundwater protection and ecological environment stability lies in how to standardize the treatment of heterogeneous soil layers, use ecological water levels to critically constrain the effective water-resistant thickness, accurately identify the weak water-blocking areas of key water-resistant soil layers, and reduce the loss and waste of groundwater resources according to local conditions. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a method for judging the water-blocking properties of heterogeneous equivalent water-blocking layers based on ecological water levels. This method solves the technical problem in existing technologies that cannot perform standardized treatment of heterogeneous composite soil layers and calculate the effective water-blocking thickness using ecological water levels, thus making it impossible to accurately determine the weak water-blocking areas of key water-blocking soil layers.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for determining the water-blocking property of a heterogeneous equivalent impermeable layer based on ecological water level includes the following steps: Step 1: Determine the stratigraphic distribution of the working face in the mining area and analyze the thickness of each stratum; The geological strata are distributed from bottom to top as follows: coal seam, bedrock layer, weathered bedrock aquifer, Baode Formation laterite layer, Lishi Formation loess layer and loose unconfined aquifer. Step 2: Obtain measured data on the development height of the water-conducting fracture zone in the mining area, and establish the development height of the water-conducting fracture zone based on the measured data. The calculation formula is used to calculate the development height of the water-conducting fracture zone at any position i. ; (1) in: M is the coal seam thickness, in meters; and It is a constant; l i Let be the measured height of the water-conducting fracture zone at the i-th location, in meters. l This is the calculated value for the development height of the water-conducting fracture zone. ,m; n represents the sampling location for obtaining the measured value of the development height of the water-conducting fracture zone; Step 3: Based on the comparison between the thickness of each stratum obtained in Step 1 and the development height of the water-conducting fracture zone obtained in Step 2... The conductivity status is obtained, and the critical waterproof layer and its thickness L are determined based on the conductivity status. The aforementioned connectivity conditions include the top boundary of the water-conducting fracture zone reaching the weathered bedrock aquifer, the top boundary of the water-conducting fracture zone reaching the Baode Formation red soil layer, the top boundary of the water-conducting fracture zone reaching the Lishi Formation loess layer, and the top boundary of the water-conducting fracture zone reaching the loose unconfined aquifer. Step four: Determine the seepage state of the critical impermeable layer with thickness L. If it is seepage of unsaturated clay, it has effective water-blocking performance; otherwise, it does not. Calculate the effective water-blocking thickness of the critical impermeable layer. The effective water-blocking thickness of the critical impermeable layer is the critical value of the effective water-blocking thickness of a single homogeneous loess layer under ecological water level constraints. L e Critical value of effective water-impermeable thickness of homogeneous Baode Formation laterite layer L b Proceed to step five, in which... ; (6) (7) in: D e The ecological water level depth is measured in meters (m). K e denoted as the permeability coefficient of the Lishi Formation loess, in m / d; K b Let be the permeability coefficient of the Baode Formation laterite, in m / d; h z The elevation of the water level at the ground surface, in meters (m). h a The elevation of the water level in the weathered bedrock aquifer is shown in meters (m). v r The vertical seepage velocity of the loose unconfined aquifer is expressed in m / d. Step 5: The sandstone layer of thickness N beneath the loose aquifer is taken as a heterogeneous equivalent aquitard, and its critical aquitard equivalent permeability coefficient is determined. The sandstone layer mentioned is either the laterite layer of the Baode Formation or the loess layer of the Lishi Formation. (8) N = N 1+ N 2+… N j+ …+ N p (9) in: k i Let m be the permeability of the j-th equivalent rock layer. 2 ; ρ The density of the water flow is kg / m³. 3 ; g The acceleration due to gravity is m / s². 2 ; μ Where is the fluid viscosity, Pa·s; k 0j Let m be the initial permeability of the j-th equivalent rock layer. 2 ; ε j Let be the volumetric strain of the j-th equivalent rock layer, % φ 0j Let be the initial porosity of the j-th equivalent rock layer, %; p The equivalent number of rock layers to be considered; N j Let j be the thickness of the equivalent rock layer, in meters. Step 6: Calculate the equivalent thickness of the heterogeneous equivalent waterproof layer according to the following formula. ; (10) in: ΔH is the head pressure difference between the two ends of the heterogeneous equivalent aquitard, in meters (m). Step 7: Determine the equivalent thickness of the heterogeneous equivalent waterproof layer. Is it not less than the critical value L of the effective water-resistant thickness of a single homogeneous loess layer? e Or the critical value of the effective water-resistant thickness L of a single homogeneous red soil layer b If so, the heterogeneous equivalent waterproof layer can achieve effective waterproofing; otherwise, the heterogeneous equivalent waterproof layer cannot achieve effective waterproofing.

[0010] This invention also includes the following technical features: In step three, the key waterproof layer and its thickness L are determined based on the conductivity: If the top boundary of the water-conducting fracture zone reaches the weathered bedrock aquifer, then the thickness L of the critical aquifer is equal to the thickness of the aquifer in the Baode Formation laterite. h b The sum of the thickness of the water-impermeable layer of the Lishi Formation loess h s Equal to the top elevation of the loess layer h 1. Elevation of the bottom slab of the reduced red soil layerh 2, that is: L = h b + h s = h 1– h 2(2) If the top boundary of the water-conducting fracture zone reaches the Baode Formation laterite layer, then the thickness L of the critical aquitard is equal to the residual thickness of the Baode Formation laterite layer. h bc With the thickness of the loess layer of Lishi Group h s The sum of these values ​​equals the elevation of the top slab of the loess layer. h 1. Reduce the height of the water-conducting fracture zone h i Elevation of coal seam floor h 0, that is: L = h bc + h s = h 1- h i - h 0 (3) If the top boundary of the water-conducting fracture zone reaches the loess layer of the Lishi Formation, then the thickness L of the critical aquitard is equal to the residual thickness h of the loess layer of the Lishi Formation. sc It equals the elevation of the top slab of the loess layer h1 minus the height of the water-conducting fracture zone h. i And the elevation of the coal seam floor, h0, that is: L = h sc = h 1- h i - h 0 (4) If the top boundary of the water-conducting fracture zone reaches the loose unconfined aquifer, then the thickness L of the critical aquitard is 0.

[0011] Compared with the prior art, the beneficial technical effects of this invention are: This invention, based on the critical constraint of ecological water level, equates sandy loess to a homogeneous loess or red soil impermeable layer of a certain thickness. By comprehensively considering the influence of factors such as water head pressure, mining disturbance, lithological structure, permeability coefficient, and rock strata mechanical parameters, it simplifies rock strata properties, equivalences the permeability coefficient of complex soil combinations, and forms a unified standard for the effective thickness of the critical impermeable layer. This clarifies the impermeability performance and distribution characteristics of the rock strata, achieving an equivalent, standardized, and quantitative assessment of the effective thickness of the critical impermeable layer. This significantly improves the accuracy of delineating weak water-blocking areas and solves the technical problem in existing technologies that cannot uniformly standardize heterogeneous soil combinations and calculate the effective impermeable thickness using ecological water level, thus failing to accurately determine the weak water-blocking areas of the critical impermeable soil layer. Attached Figure Description

[0012] Figure 1 Schematic diagram of overburden failure and aquifer water loss during coal seam mining Figure 2. Schematic diagram of the strata connected by the water-conducting fracture zone, where (a) the water-conducting fracture zone reaches the weathered bedrock aquifer, (b) the water-conducting fracture zone reaches the red soil layer of the Baode Formation, (c) the water-conducting fracture zone reaches the loess layer of the Lishi Formation, and (d) the water-conducting fracture zone reaches the loose unconfined aquifer. Figure 3 Schematic diagram of ecological water level depth; Figure 4 Equivalent schematic diagram of a heterogeneous equivalent waterproof layer; Figure 5 Quaternary loess lithology and structure in different geological boreholes at coal mining faces Figure 6 The relationship between the equivalent thickness of loess in the Lishi Group and the working water inflow.

[0013] The specific content of the present invention will be further explained in detail below with reference to the embodiments. Detailed Implementation

[0014] It should be noted that, unless otherwise specified, all components in this invention are those known in the art.

[0015] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0016] This invention provides a method for determining the water-blocking property of a heterogeneous equivalent impermeable layer based on ecological water level, comprising the following steps: Step 1: Determine the stratigraphic distribution of the working face in the mining area and analyze the thickness of each stratum; The stratigraphic distribution is as follows, from bottom to top: coal seam, bedrock layer, weathered bedrock aquifer, Baode Formation laterite layer, Lishi Formation loess layer and loose unconfined aquifer; Step 2: Obtain measured data on the development height of the water-conducting fracture zone in the mining area, and establish the development height of the water-conducting fracture zone based on the measured data. The calculation formula is used to calculate the development height of the water-conducting fracture zone at any position i. ; (1) in: M is the coal seam thickness, in meters; and It is a constant; l i Let be the measured height of the water-conducting fracture zone at the i-th location, in meters. l This is the calculated value for the development height of the water-conducting fracture zone. ,m; n represents the sampling location for obtaining the measured value of the development height of the water-conducting fracture zone; Step 3: Based on the comparison between the thickness of each stratum obtained in Step 1 and the development height of the water-conducting fracture zone obtained in Step 2... The conductivity status is obtained, and the critical waterproof layer and its thickness L are determined based on the conductivity status. The conductivity conditions include the top boundary of the water-conducting fracture zone reaching the weathered bedrock aquifer, the top boundary of the water-conducting fracture zone reaching the Baode Formation red soil layer, the top boundary of the water-conducting fracture zone reaching the Lishi Formation loess layer, and the top boundary of the water-conducting fracture zone reaching the loose unconfined aquifer. Step four: Determine the seepage state of the critical impermeable layer with thickness L. If it is seepage of unsaturated clay, it has effective water-blocking performance; otherwise, it does not. Calculate the effective water-blocking thickness of the critical impermeable layer. The effective water-blocking thickness of the critical impermeable layer is the critical value of the effective water-blocking thickness of a single homogeneous loess layer under ecological water level constraints. L e Critical value of effective water-impermeable thickness of homogeneous Baode Formation laterite layer L b Proceed to step five, in which... ; (6) (7) in: D e The ecological water level depth is measured in meters (m). K e denoted as the permeability coefficient of the Lishi Formation loess, in m / d; Kb Let be the permeability coefficient of the Baode Formation laterite, in m / d; h z The elevation of the water level at the ground surface, in meters (m). h a The elevation of the water level in the weathered bedrock aquifer is shown in meters (m). v r The vertical seepage velocity of the loose unconfined aquifer is expressed in m / d. Step 5: The sandstone layer of thickness N beneath the loose aquifer is taken as a heterogeneous equivalent aquitard, and its critical aquitard equivalent permeability coefficient is determined. The sandstone layers are either the laterite layers of the Baode Formation or the loess layers of the Lishi Formation. (8) N = N 1+ N 2+… N j+ …+ N p (9) in: k i Let m be the permeability of the j-th equivalent rock layer. 2 ; ρ The density of the water flow is kg / m³. 3 ; g The acceleration due to gravity is m / s². 2 ; μ Where is the fluid viscosity, Pa·s; k 0j Let m be the initial permeability of the j-th equivalent rock layer. 2 ; ε j Let be the volumetric strain of the j-th equivalent rock layer, % φ 0j Let be the initial porosity of the j-th equivalent rock layer, %; p The equivalent number of rock layers to be considered; N j Let j be the thickness of the equivalent rock layer, in meters. Step 6: Calculate the equivalent thickness of the heterogeneous equivalent waterproof layer according to the following formula. ; (10) in: ΔH is the head pressure difference between the two ends of the heterogeneous equivalent aquitard, in meters (m). Step 7: Determine the equivalent thickness of the heterogeneous equivalent waterproof layer. Is it not less than the critical value L of the effective water-resistant thickness of a single homogeneous loess layer? e Or the critical value of the effective water-resistant thickness L of a single homogeneous red soil layer b If so, the heterogeneous equivalent waterproof layer can achieve effective waterproofing; otherwise, the heterogeneous equivalent waterproof layer cannot achieve effective waterproofing.

[0017] In the above scheme, based on the critical constraint of ecological water level, sandy loess is equivalent to a homogeneous loess or red soil impermeable layer of a certain thickness. Taking into account the influence of factors such as water head pressure, mining disturbance, lithological structure, permeability coefficient, and rock strata mechanical parameters, the rock strata properties are simplified, and the permeability coefficient of complex soil combinations is equivalent to form a unified standard for the effective thickness of the key impermeable layer. This clarifies the impermeability performance and distribution characteristics of the rock strata, achieving an equivalent, standardized, and quantitative assessment of the effective thickness of the key impermeable layer. This greatly improves the accuracy of delineating weak water-blocking areas and solves the technical problem in existing technologies that cannot uniformly standardize heterogeneous soil combinations and calculate the effective impermeable thickness using ecological water level, thus making it impossible to accurately determine the weak water-blocking areas of the key impermeable soil layer.

[0018] In step one, a comprehensive exploration method is employed to collect regional geological data and drilling data, directly revealing the lithology and structure of the strata. Pumping or injection tests are then conducted using boreholes to accurately determine the water-bearing capacity, permeability coefficient, and distribution of aquitards in the shallow surface Salawusu Formation. For the sand-bearing loess aquitard, indoor geotechnical tests are required using core samples to determine the number, thickness proportion, spatial continuity, and contact relationship between sand layers within the loess layer and the upper and lower loess layers.

[0019] In step four, the seepage of unsaturated clay is difficult to achieve effective flow due to the hydrophilicity and expansibility of clay, the small actual cross-sectional area of ​​the water flow, the large degree of tortuosity of the flow path, and the large resistance of the pore channels under low hydraulic gradient.

[0020] When the hydraulic gradient increases or the soil is fully saturated, a stable saturated Darcy flow can form. When the hydraulic gradient is constant, if the vertical seepage flow Qr of the overlying aquifer equals the seepage flow Qg of the critical aquifer, it proves that a stable Darcy flow exists between the two, and effective water blocking cannot be achieved. If the vertical seepage flow Qr of the overlying aquifer is greater than the seepage flow Qg of the critical aquifer, then effective water blocking can be achieved.

[0021] See Figure 4 In steps six and seven, to simplify the properties of the key impermeable layer in complex heterogeneous soil composites, the thickness is... The sandy loess layer is equivalent to a single loess layer or a single red soil layer of a certain thickness, with equivalent thicknesses of M respectively. e M b The permeability coefficients are K e K b Suppose that different types of sandy loess can divide the Lishi Formation loess into layers p, then the thicknesses of the different layers are N1, N2, ... N i , ...N p The permeability coefficients are K1, K2, ... K i , ...K p .

[0022] This invention also includes the following technical features: Referring to Figure 2, in step three, the key waterproof layer and its thickness L are determined based on the conductivity: If the top boundary of the water-conducting fracture zone reaches the weathered bedrock aquifer, then the thickness L of the critical aquifer is equal to the thickness of the aquifer in the Baode Formation laterite. h b The sum of the thickness of the water-impermeable layer of the Lishi Formation loess h s Equal to the top elevation of the loess layer h 1. Elevation of the bottom slab of the reduced red soil layer h 2, that is: L = h b + h s = h 1– h 2(2) If the top boundary of the water-conducting fracture zone reaches the Baode Formation laterite layer, then the thickness L of the critical aquitard is equal to the residual thickness of the Baode Formation laterite layer. h bc With the thickness of the loess layer of Lishi Group h s The sum of these values ​​equals the elevation of the top slab of the loess layer. h 1. Reduce the height of the water-conducting fracture zone h i Elevation of coal seam floor h 0, that is: L = h bc + h s = h 1- h i - h 0 (3) If the top boundary of the water-conducting fracture zone reaches the loess layer of the Lishi Formation, then the thickness L of the critical aquitard is equal to the residual thickness h of the loess layer of the Lishi Formation. sc It equals the elevation of the top slab of the loess layer h1 minus the height of the water-conducting fracture zone h.i And the elevation of the coal seam floor, h0, that is: L = h sc = h 1- h i - h 0 (4) If the top boundary of the water-conducting fracture zone reaches the loose unconfined aquifer, then the thickness L of the critical aquitard is 0.

[0023] In the above scheme, the top boundary of the water-conducting fracture zone reaches the loose unconfined aquifer: the water-blocking property judgment method based on the heterogeneous equivalent aquifer of ecological water level. If some areas have missing Baode Formation red soil layer and Lishi Formation loess layer, or the height of the water-conducting fracture zone reaches the loose unconfined aquifer, that is, the height of the water-conducting fracture zone (h) i The sum of the elevations of the coal seam floor and the bottom plate (h0) is greater than the elevation of the loess roof (h1). h i + h0>h1(5) At this point, the thickness L of the critical aquitard is 0. The loose unconfined aquifer is connected to the underlying weathered bedrock aquifer, creating a hydraulic connection. The loose unconfined aquifer will indirectly replenish the weathered bedrock aquifer through overflow, leading to an increase in the water volume of the weathered bedrock aquifer and increasing the risk of water inrush at the working face.

[0024] Project Cases: Taking the key impermeable soil layer overlying a coal mining face in the Yushen mining area as an example, the Quaternary Lishi Formation loess layer is widely distributed throughout the area, with only a few missing sections on the western wing of the mining area. The borehole-exposed thickness ranges from 0 to 65.95 m, with an average of 17.18 m. The lithology is mainly yellow and brownish-yellow sub-clay and sub-sandy. The lithological structure of the Quaternary Lishi Formation loess revealed by different geological boreholes (K1~K6) in a certain coal mining face is shown below. Figure 5 As shown.

[0025] The borehole data reveals that the overlying Lishi Formation strata on the working surface are 18.9–33.6 m thick, with an average of 24.5 m. The loess layer is 5.5–30 m thick, with an average of 16.2 m, accounting for 66.1% of the total. The loess layer contains fine and medium sandy soils with high permeability, ranging from 3.6–13.4 m thick, with an average of 8.3 m, accounting for 33.9%. In boreholes K4 and K5, the Quaternary Lishi Formation loess is relatively thin, while the fine and medium sand layers are thicker, accounting for 70.9% and 57.8% respectively.

[0026] Measured height of water-conducting fracture zone development in the mining area l iThe average value is 196.58 m, and the coal seam thickness M is 8~11.1 m. Substituting this into equation (1), we can obtain the corrected prediction formula for the development height of the water-conducting fracture zone, which conforms to the lithological characteristics of this mining area: (11) The actual coal seam thickness M of a certain coal mining face is 9.5m. Substituting it into equation (11), we can obtain that the height of the water-conducting fracture zone of the working face is about 181.4~185.0m. Its top boundary does not enter the key water-impermeable soil layer. Therefore, the residual thickness of the key water-impermeable layer of the working face is the complete thickness of the complete loess layer.

[0027] Here, the ecological water level depth D of the loose unconfined aquifer is determined. e =5 m is used as the critical constraint standard for calculating the effective impermeable soil layer thickness, and the ground surface elevation h z =1250 m, water level elevation of weathered bedrock aquifer h a =1190 m, loess permeability coefficient K e =4.87×10 -3 m / d, vertical seepage recharge velocity of loose unconfined aquifer v r =4.37×10 -3 Substituting m / d into equation (6), we can obtain the critical value of the effective water-retaining thickness of a single homogeneous loess layer under ecological water level constraints as L. e >46 m.

[0028] Based on the borehole findings from K1 to K6, the lithological structure of the loess layer in the Lishi Formation was determined, and a heterogeneous equivalent impermeable layer was constructed. The corresponding rock strata properties and hydraulic parameters were then substituted into equation (8) to determine the equivalent permeability coefficient of the heterogeneous equivalent impermeable layer. Then, substituting it into equation (10), we obtain the equivalent thickness of the heterogeneous equivalent waterproof layer. As shown in Table 2.

[0029] Table 2 Equivalent Waterproof Layer for Heterogeneous Structures

[0030] As mentioned above, the critical value of the effective water-retaining thickness of the single homogeneous loess layer under ecological water level constraints is L. e A thickness greater than 46 m indicates that a single, homogeneous loess layer can effectively impermeable the soil. However, the equivalent thickness of a heterogeneous equivalent impermeable layer... All values ​​are less than the critical value L of the effective water-retaining thickness of the loess layer in a single homogeneous Lishi group under ecological water level constraints. eThis means that it cannot effectively block water and has poor water-proofing performance. The loose unconfined aquifer will continue to seep downwards and replenish the weathered bedrock pore-fracture confined aquifer, causing the water volume in the weathered bedrock aquifer to increase and threatening the production safety of the underground mining face.

[0031] Furthermore, to determine the relationship between the equivalent thickness of the Lishi Formation loess layer and the water inflow at the working face when the heterogeneous equivalent aquitard is equivalent to the Lishi Formation loess layer, and to verify the water-retaining performance of loess with different equivalent thicknesses, the water inflow changes during the advance of the coal mining face from the initial cut to near borehole K6 were monitored. Figure 6 As shown.

[0032] During the advancement of the working face, the water inflow gradually increased. The equivalent thickness of the loess layer in the Lishi Formation at boreholes K1 and K2 was relatively large, at 30.06 m and 24.82 m respectively. When the working face advanced to the vicinity of these two boreholes, the water inflow showed a slow upward trend, with the difference in water inflow between the two boreholes being only 15 m. 3 / h. The equivalent thickness of the loess layer in the Lishi Formation at boreholes K4 and K5 is relatively small, at 5.62 m and 6.40 m respectively. When the working face advances to the vicinity of the two boreholes, the water inflow at the working face increases sharply, and the difference in water inflow between the two boreholes reaches 115 m. 3 / h.

[0033] Therefore, the loess of the Lishi Formation at K4 and K5 is a weak water-blocking area with an insufficient equivalent thickness to prevent the downward seepage of the overlying loose aquifer, thus indirectly increasing the water inflow at the working face. While the loess at K1 and K2 also cannot effectively block water, its larger equivalent thickness results in a longer downward seepage path for the loose aquifer, leading to a smaller amount of water actually reaching the working face. Therefore, it has better water-blocking properties compared to the loess of the Lishi Formation at K4 and K5.

[0034] The analysis results of the above engineering cases show that the equivalent method of the effective thickness of the key water-blocking layer based on ecological water level constraints can accurately obtain the water-blocking thickness of the soil layer, overcome the difficulty of equivalence and quantitative calculation of the permeability coefficient of heterogeneous and complex soil layers, realize the precise location of the weak points of water blocking, provide scientific support for reducing the loss of shallow groundwater and preventing the risk of underground water inrush, and have important significance for promoting the coordinated development of ecological protection and safe production in mining areas.

Claims

1. A method for judging water-blocking property of a non-homogeneous equivalent aquiclude based on an ecological water level, characterized by, Includes the following steps: Step 1: Determine the stratigraphic distribution of the working face in the mining area and analyze the thickness of each stratum; The geological strata are distributed from bottom to top as follows: coal seam, bedrock layer, weathered bedrock aquifer, Baode Formation laterite layer, Lishi Formation loess layer and loose unconfined aquifer. Step 2: Obtain measured data on the development height of the water-conducting fracture zone in the mining area, and establish the development height of the water-conducting fracture zone based on the measured data. The calculation formula is used to calculate the development height of the water-conducting fracture zone at any position i. ; （1） in: M is the coal seam thickness, in meters; with is constant; l i hi is the measured value of the development height of the water-conducting fracture zone at the i-th location, m; l For the development of water-conducting fracture zone height calculation value, , ; n represents the sampling location for obtaining the measured value of the development height of the water-conducting fracture zone; Step three, according to the thickness of each stratum obtained in step one and the height of the water flowing fractured zone obtained in step two , to obtain the conduction condition, and determine the key water-resisting layer and its thickness L according to the conduction condition; The aforementioned connectivity conditions include the top boundary of the water-conducting fracture zone reaching the weathered bedrock aquifer, the top boundary of the water-conducting fracture zone reaching the Baode Formation red soil layer, the top boundary of the water-conducting fracture zone reaching the Lishi Formation loess layer, and the top boundary of the water-conducting fracture zone reaching the loose unconfined aquifer. Step four: Determine the seepage state of the critical impermeable layer with thickness L. If it is seepage of unsaturated clay, it has effective water-blocking performance; otherwise, it does not. Calculate the effective water-blocking thickness of the critical impermeable layer. The effective water-blocking thickness of the critical impermeable layer is the critical value of the effective water-blocking thickness of a single homogeneous loess layer under ecological water level constraints. L e Critical value of effective water-impermeable thickness of homogeneous Baode Formation laterite layer L b Proceed to step five, in which... ; （6） （7） in: D e Ecological water depth, m; K e K is the hydraulic conductivity of the loess, m / d; K b K is the hydraulic conductivity of the red soil in the Baode group, m / d; h z Water level of the ground surface, m; h a Water level elevation of weathered bedrock aquifer, m; v r Vp is the vertical seepage velocity of the loose subterranean water layer, m / d; Step 5: The sandstone layer of thickness N beneath the loose aquifer is taken as a heterogeneous equivalent aquitard, and its critical aquitard equivalent permeability coefficient is determined. The sandstone layer mentioned is either the laterite layer of the Baode Formation or the loess layer of the Lishi Formation. （8） N = N 1+ N 2+… N j+ …+ N p （9） in: k i Kj, the permeability of the jth equivalent rock layer, m 2 ; ρ water flow density, kg / m 3 ; g g is the gravitational acceleration, m / s2 2 ; μ Where is the fluid viscosity, Pa·s; k 0j Kj initial permeability for the jth equivalent rock layer, m 2 ; ε j Vj is the volume strain of the jth layer of equivalent rock. φ 0j initial porosity of the jth equivalent rock layer p the number of equivalent rock layers to be considered; N j thickness of the equivalent rock layer for the jth layer, m; Step six, calculate the equivalent thickness of the heterogeneous equivalent aquiclude according to the following formula ; （10） in: ΔH is the head pressure difference between the two ends of the heterogeneous equivalent aquitard, in meters (m). Step 7: Determine the equivalent thickness of the heterogeneous equivalent waterproof layer. Is it not less than the critical value L of the effective water-resistant thickness of a single homogeneous loess layer? e Or the critical value of the effective water-resistant thickness L of a single homogeneous red soil layer b If so, the heterogeneous equivalent waterproof layer can achieve effective waterproofing; otherwise, the heterogeneous equivalent waterproof layer cannot achieve effective waterproofing.

2. The method for determining the water-blocking capacity of a heterogeneous equivalent water-retaining layer based on ecological water level as described in claim 1, characterized in that, In step three, the key waterproof layer and its thickness L are determined based on the conductivity: If the top boundary of the water-conducting fracture zone reaches the weathered bedrock aquifer, then the thickness L of the critical aquifer is equal to the thickness of the aquifer in the Baode Formation laterite. h b The sum of the thickness of the water-impermeable layer of the Lishi Formation loess h s Equal to the top elevation of the loess layer h 1. Elevation of the bottom slab of the reduced red soil layer h 2, that is: L = h b + h s = h 1– h 2（2） If the top boundary of the water-conducting fracture zone reaches the Baode Formation laterite layer, then the thickness L of the critical aquitard is equal to the residual thickness of the Baode Formation laterite layer. h bc With the thickness of the loess layer of Lishi Group h s The sum of these values ​​equals the elevation of the top slab of the loess layer. h 1. Reduce the height of the water-conducting fracture zone h i Elevation of coal seam floor h 0, that is: L = h bc + h s = h 1- h i - h 0（3） If the top boundary of the water-conducting fracture zone reaches the loess layer of the Lishi Formation, then the thickness L of the critical aquitard is equal to the residual thickness h of the loess layer of the Lishi Formation. sc It equals the elevation of the top slab of the loess layer h1 minus the height of the water-conducting fracture zone h. i And the elevation of the coal seam floor, h0, that is: L = h sc = h 1- h i - h 0（4） If the top boundary of the water-conducting fracture zone reaches the loose unconfined aquifer, then the thickness L of the critical aquitard is 0.

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