Method and system for determining minimum waterproof thickness of clay layer in mining area

Abstract

The invention discloses a method and system for determining the minimum waterproof thickness of a clay layer in a mining area, and relates to the technical field of evaluation of the minimum waterproof thickness of the clay layer. Constructing an elastic foundation beam mechanical model according to the geological data; unconsolidated formation parameters of the elastic foundation beam mechanical model are determined through geological data and laboratory tests; determining the tensile failure minimum thickness according to the maximum tensile stress of the beam end; determining the shear failure minimum thickness according to the maximum shear force of the beam end; sensitivity analysis is conducted on the unconsolidated formation parameters, and the minimum water-resisting layer thickness under different working conditions is obtained; and obtaining the minimum waterproof thickness of the clay layer based on the minimum waterproof layer thicknesses under different working conditions. Aiming at the problem that the water insulation performance of a clay layer is damaged due to the development of a water flowing fractured zone in coal mining, the bearing capacity of the clay layer in a tensile and shear failure mode is quantified by constructing a mechanical model, targeted water prevention and control measures can be formulated in advance, and water inrush accidents are prevented.

Description

Technical Field

[0001] This invention relates to the field of minimum waterproof thickness assessment technology for clay layers, and more specifically to a method and system for determining the minimum waterproof thickness of clay layers in mining areas. Background Technology

[0002] In the process of large-scale coal mining, mine water hazards have become increasingly prominent, severely restricting safe production and sustainable development in coal mines. In mining areas with special geological conditions such as shallow coal seams, thick loose layers covering thin bedrock, and thick loess cover, water-conducting fracture zones caused by mining activities can extend upwards, potentially affecting the bedrock and the overlying clay layer. Although clay layers naturally possess a certain degree of water-impermeability, when water-conducting fracture zones develop to a considerable height, they can disrupt the original water-impermeable structure of the strata, leading to fracture development and a significant decrease in the water-impermeability of the clay layer.

[0003] Under conditions of thick loose layers and thin bedrock, the bedrock is prone to full-thickness fractures, and the loose layer bends and sinks along with the bedrock. In this case, the water-tightening capacity of the clay layer depends on its bottom lithology, thickness, and the degree of mining deformation. Predicting the development height of water-conducting fracture zones and assessing the water-tightening capacity of clay layers often relies on empirical formulas or simple geological analysis methods. However, these methods often fail to accurately account for the combined effects of complex geological conditions, mining techniques, and other factors.

[0004] Therefore, in complex situations where water-conducting fracture zones may affect clay layers, how to provide a method and system for determining the minimum water-resistant thickness of clay layers in mining areas, accurately assess the water-resistant capacity of clay layers, and thus provide a reliable basis for mine water inrush prevention is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method and system for determining the minimum water-impermeable thickness of clay layers in mining areas. Addressing the problem of water-conducting fracture zones developing during coal mining leading to the degradation of the water-impermeable performance of clay layers, the invention simplifies the clay layer as a beam structure situated on an elastic foundation. A mechanical model is constructed to quantify its bearing capacity under tensile and shear failure modes. By assessing the water-impermeable capacity of the clay layer, targeted water control measures can be formulated in advance to prevent water inrush accidents, providing crucial data support for mining area water resource planning and ecological environmental protection.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for determining the minimum waterproof thickness of clay layers in mining areas, comprising: Collect geological data from the mining area; Based on the geological data, an elastic foundation beam model considering aquifer water pressure and self-weight load was established. The loose layer parameters of the elastic foundation beam mechanical model were determined by geological data and laboratory tests. The uniaxial tensile strength of the soil is calculated based on the maximum tensile stress at the beam end, and the minimum thickness h1 for tensile failure is determined. Calculate the total shear resistance based on the maximum shear force at the beam end, and determine the minimum thickness h2 required for shear failure. Sensitivity analysis was performed on the parameters of the loose layer to obtain the minimum waterproof layer thickness under different working conditions; Based on the minimum waterproof layer thickness under different working conditions, the minimum tensile failure thickness h1 and the minimum shear failure thickness h2 under different parameter states are compared, and the larger value is taken as the minimum waterproof layer thickness h of the clay layer.

[0007] Preferably, based on the geological data, a geological model is established, and schematic diagrams of the two zones along the dip direction of the working face, a mechanical model diagram, and an elastic foundation beam model diagram are drawn. An elastic foundation beam model considering aquifer water pressure and self-weight load is established; wherein, the two zones include a water-conducting fracture zone and a collapse zone; The caving zone is located directly above the goaf, with its bottom in direct contact with the ore layer; the water-conducting fracture zone is located above the caving zone, and above the water-conducting fracture zone is a clay layer.

[0008] Preferably, the loose layer parameters include, but are not limited to, aquifer water pressure, clay layer elastic modulus, internal cohesion, internal friction angle, subgrade coefficient, and soil density.

[0009] Preferably, based on the maximum tensile stress at the beam end Calculate the uniaxial tensile strength of soil Determine the minimum thickness h1 required to withstand tensile failure; make The minimum thickness of the impermeable clay layer required to meet the tensile failure requirement is calculated and denoted as h1.

[0010] Preferably, based on the maximum shear force at the beam end Calculate the total shear strength Determine the minimum thickness h2 required for shear failure; make The minimum thickness of the impermeable clay layer required to meet the tensile failure requirement is calculated and denoted as h2.

[0011] Preferably, the total shear strength includes: cohesive shear term, self-weight-lateral pressure shear term, and self-weight-distributed force shear term, as shown in the following formula: ; In the formula: It is an internal cohesive force; It is the internal friction angle; The effective thickness of the clay layer subjected to shear stress; This is the coefficient of pressure on the stationary side; The unit weight of the clay layer; This refers to the effective cover height above the clay layer.

[0012] Preferably, the maximum tensile stress at the beam end is: ; in, The beam end bending moment is represented by h; h represents the minimum waterproof thickness of the clay layer. The uniaxial tensile strength of the soil is calculated based on the tangency of the Mohr circle and the straight line: ; In the formula: For internal cohesion, It is the internal friction angle.

[0013] Preferably, based on the minimum waterproof layer thickness under different working conditions, the waterproof layer thickness is used as the independent variable. , For the dependent variable, a program was developed to obtain the results under different parameter combinations. Relationship with the thickness of the waterproof layer Relationship between the thickness of the waterproof layer and the thickness of the waterproof layer; in, , Each refers to , ; Indicates the uniaxial tensile strength of soil. This indicates the maximum tensile stress at the beam end; Indicates the total shear strength. This indicates the maximum shear force at the beam end.

[0014] Preferably, a system for determining the minimum waterproof thickness of clay layers in a mining area includes: The data collection module is used to collect geological data from the mining area; The model building module is used to build an elastic foundation beam model that considers aquifer water pressure and self-weight load based on the geological data. The loose layer parameter determination module is used to determine the loose layer parameters of the elastic foundation beam mechanical model through geological data and laboratory tests. The module for determining the minimum thickness for tensile failure is used to calculate the uniaxial tensile strength of the soil based on the maximum tensile stress at the beam end, and to determine the minimum thickness for tensile failure h1. The module for determining the minimum thickness for shear failure is used to calculate the total shear resistance based on the maximum shear force at the beam end and to determine the minimum thickness h2 for shear failure. The loose layer parameter analysis module is used to perform sensitivity analysis on the loose layer parameters to obtain the minimum waterproof layer thickness under different working conditions. The minimum waterproof thickness determination module for clay layers is used to compare the minimum tensile failure thickness h1 and the minimum shear failure thickness h2 under different working conditions, and take the larger value as the minimum waterproof thickness h of the clay layer.

[0015] As can be seen from the above technical solutions, compared with the prior art, the present invention discloses a method and system for determining the minimum water-proof thickness of clay layer in mining area, which has the following beneficial effects: (1) The present invention uses the elastic foundation beam theory as the core mechanical model, establishes a mechanical model through theoretical derivation, quantifies the ultimate bearing capacity of clay layer under tension and shear, and combines multi-parameter sensitivity analysis to form a scientific thickness design logic, which is applicable to the calculation effect of minimum water-proof layer of clay layer at different burial depths.

[0016] (2) The present invention transforms the evaluation of water-proofing capacity into bending-shear failure mechanical analysis, considering the dual failure modes of tensile failure and shear failure, and determines the minimum water-proof layer thickness through conservative parameter values ​​and multi-scheme sensitivity analysis.

[0017] (3) The present invention constructs a logical system of model establishment, parameter determination, damage calculation and result analysis, with supporting flowcharts and cases, which are convenient for engineering technicians to apply directly. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 A flowchart illustrating a method for determining the minimum waterproof thickness of a clay layer in a mining area, provided as an embodiment of the present invention.

[0020] Figure 2 A schematic diagram of a geological model provided for an embodiment of the present invention.

[0021] Figure 3 This is a schematic diagram of the two zones in the working surface direction provided in an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of an elastic foundation beam model provided in an embodiment of the present invention.

[0023] Figure 5 Provided for embodiments of the present invention A schematic diagram showing the relationship between the thickness of the waterproof layer and the change in the thickness of the waterproof layer.

[0024] Figure 6 Provided for embodiments of the present invention A schematic diagram showing the relationship between the thickness of the waterproof layer and the change in the thickness of the waterproof layer. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] This invention discloses a method for determining the minimum waterproof thickness of clay layers in mining areas, such as... Figure 1 As shown, it includes: Step A: Collect geological data of the mining area; Specifically, geological data and mining plans for the mining area should be collected to clarify the relative location, occurrence, thickness, water content, and water-impermeability of coal seams, bedrock, and loose layers.

[0027] Step B: Based on the geological data, establish an elastic foundation beam model that considers aquifer water pressure and self-weight load; Specifically, based on the data collected in step A, a geological model is established, and schematic diagrams of the two zones (water-conducting fracture zone and collapse zone) along the working face tilt direction, mechanical model diagrams, and elastic foundation beam model diagrams are drawn. The mechanical model of the elastic foundation beam is then established and solved.

[0028] Step C: Determine the loose layer parameters of the elastic foundation beam mechanical model through geological data and laboratory tests; Step D: Determine the minimum thickness h1 of the waterproof clay layer based on the tensile failure, calculate the uniaxial tensile strength of the soil based on the maximum tensile stress at the beam end, and determine the minimum thickness h1 for tensile failure. Step E: Determine the minimum thickness h2 of the impermeable clay layer based on the shear failure, calculate the total shear resistance based on the maximum shear force at the beam end, and determine the minimum thickness h2 for shear failure; Step F: Based on the parameter range determined in Step C, perform sensitivity analysis on the loose layer parameters to obtain the minimum waterproof layer thickness under different working conditions, and plot the thickness- Curve, thickness - curve; Step G: Based on the minimum waterproof layer thickness under different working conditions, compare the minimum tensile failure thickness h1 and the minimum shear failure thickness h2 under different parameter states. Combined with the sensitivity analysis curve, and considering the engineering redundancy design, take the larger value as the minimum waterproof layer thickness h of the clay layer.

[0029] This invention proposes a method for determining the minimum water-tightening thickness of a clay layer within a coal mine's water-conducting fracture zone, based on the elastic foundation beam theory. Specifically, in fully mechanized mining with a thick loose layer in shallow bedrock, the water-conducting fracture zone is allowed to extend to the loose layer above the bedrock. However, if the fractures continue to develop within the clay layer, it is necessary to assess the water-tightening capacity of the effective water-tightening clay layer. Based on the elastic foundation beam theory, an analysis is conducted using a mechanical model and incorporating tensile and shear failure theories to evaluate the water-tightening capacity of the clay layer above the fracture zone as an effective water-tightening layer. This yields a safe threshold for the thickness of the effective water-tightening clay layer, determining its minimum thickness to prevent water inrush from the coal seam roof caused by the loose aquifer, thus providing a theoretical basis for water inrush prevention.

[0030] Specifically, based on the geological data, a geological model is established, and schematic diagrams of the two zones along the dip direction of the working face, a mechanical model diagram, and an elastic foundation beam model diagram are drawn. An elastic foundation beam model considering aquifer water pressure and self-weight load is established; wherein, the two zones include a water-conducting fracture zone and a collapse zone; The caving zone is located directly above the goaf, with its bottom in direct contact with the ore layer; the water-conducting fracture zone is located above the caving zone, and above the water-conducting fracture zone is a clay layer.

[0031] Specifically, in step B: analyze the geological model, determine the distribution pattern of the "two zones", and draw a schematic diagram of the distribution of the "two zones". (1) Collapse zone: after coal seam mining, the directly overhead rock layer is broken, collapses and accumulates in the goaf, with irregularity and fragmentation; (2) Water-conducting fracture zone: the area where the rock layer above the collapse zone develops a fracture network due to bending and fracturing, which has water-conducting capacity and is the main channel for mine water hazards. Collapse zone: located directly above the goaf, in the shape of an "irregular trapezoid", with the bottom directly in contact with the coal seam, and the height is about 2 to 5 times the mining thickness (in fully mechanized mining, the height of the collapse zone can reach 10 to 20m due to the large mining height). Water-conducting fracture zone: located above the collapse zone, in the shape of a "saddle", and the height can reach 10 to 25 times the mining thickness.

[0032] For horizontally layered media, the clay layer above the water-conducting fracture zone is simplified as an "infinitely long elastic foundation beam" or a "finite-length beam (with a finite working face slope)". Using the beam's deflection differential equation and boundary conditions (fixed end displacement, rotation angle is 0), combined with the beam function in trigonometric (hyperbolic) form as the beam's characteristic function (corresponding to the beam's deflection, rotation angle, bending moment, and shear force), the beam end bending moment is derived. and shear force The analytical solution is shown in the following equation: (1) (2) (3) (4) (5) (6) In the formula: The overlying load is the sum of the water pressure of the loose aquifer and the self-weight of the effective impermeable layer. The characteristic coefficient has a value of (k / 4EI). 0.25 Where k is the subgrade coefficient (MPa / m); E is the elastic modulus; and I is the moment of inertia of the cross section, which is related to the beam height. The length of the foundation beam is taken as the inclined length of the working surface.

[0033] Specifically, in step C, the loose layer parameters include aquifer water pressure. Elastic modulus of clay layer Internal cohesion internal friction angle Bed coefficient soil density Parameters such as these.

[0034] Specifically, (i) aquifer water pressure

[0035] The determination of aquifer water pressure q (hydraulic load acting on the clay layer) needs to consider the aquifer type (unconfined aquifer, confined aquifer) and the hydrogeological conditions of the mining area (water level depth, aquifer thickness, etc.), and is obtained through theoretical analysis, field testing, or empirical derivation. Taking theoretical derivation as an example: (1) Distinguish between aquifer types Unconfined aquifer: Above the first stable impermeable layer below the surface, with a free water surface, the water pressure is affected by the water level depth (vertical distance from the free water surface to the clay layer) and the buoyancy of the soil.

[0036] Confined aquifer: It is constrained by impermeable layers above and below, and the groundwater is under pressure (the water level is higher than the top slab). The water pressure is affected by the height of the confined aquifer (the vertical distance from the top slab to the confined aquifer) and the specific weight of the water.

[0037] (2) Calculation of water pressure in unconfined aquifers

[0038] In unconfined aquifers, the water pressure on the clay layer is pore water pressure, which conforms to the hydrostatic pressure distribution: .

[0039] : is the specific gravity of water (commonly used in engineering). ); : The vertical distance from the middle of the loose aquifer to the free surface of the unconfined water (measured by hydrogeological boreholes and water level observation wells).

[0040] (2) Calculation of water pressure in confined aquifers

[0041] In confined aquifers, water pressure is determined by the height of the confined water level and is independent of the depth of the aquifer's top slab. .

[0042] This is the vertical distance from the clay layer to the confined water level (the confined water level needs to be determined through long-term observation wells and hydrogeological exploration).

[0043] (ii) Soil density

[0044] Soil density is generally determined in two ways: (1) Indoor test method: Take undisturbed clay samples and determine the density using the ring cutter method (for slightly disturbed soil samples) or the wax sealing method (for easily broken soil samples). (2) The natural density range of general clay layers: (1.7~2.1g / cm³) 3 (The density of soft clay is lower than that of hard clay; if regional geological data is available, the local clay layer density statistics can be directly used.)

[0045] (iii) Soil cohesion and internal friction angle

[0046] There are generally three methods to determine the internal cohesion and internal friction angle of soil: (1) Indoor triaxial test: Through consolidated undrained test or consolidated drained test, obtain multiple sets of triaxial test results with different confining pressures, and draw the Mohr-Coulomb strength envelope. The intercept of the envelope fitting is the internal cohesion, and the slope corresponds to the tangent of the internal friction angle. (2) In-situ direct shear test: Shear box is buried in the clay layer in the field, and normal force and shear force are applied in stages. The "shear stress-displacement" curve is drawn to determine the peak shear strength. (3) Refer to the "Engineering Geology Handbook" or adjacent engineering data in the mining area and look up the table according to the "hardness" of the clay layer.

[0047] (iv) Elastic modulus of soil

[0048] The elastic modulus of soil is generally determined by three methods: (1) Indoor triaxial test: Test method: Through triaxial compression test, plot the "stress-strain curve", and take the initial tangent modulus (slope of the tangent at the origin of the curve) or secant modulus (slope when the stress is 50% of the compressive strength) as the elastic modulus E. (2) Static cone penetration test (CPT) inversion: Use the cone tip resistance obtained by static cone penetration test to invert through regional empirical relationships. (3) Refer to the "Engineering Geology Handbook" or adjacent engineering data of the mining area, and look up the table according to the "hardness" of the clay layer.

[0049] (v) Subgrade coefficient

[0050] There are generally three methods to determine the subgrade coefficient: (1) In-situ load test: A plate load test is carried out on the surface of the clay layer to obtain the "load-settlement curve" and take the slope of the straight line segment. The shallow clay layer (<5m) is directly tested; the deep clay layer can be indirectly determined by "borehole buried load test". (2) Indoor test inversion: (a) Consolidation test method: The compression modulus is obtained by indoor consolidation test and estimated by empirical relationship; (b) Triaxial test method: The subgrade coefficient is inverted by elastic theory based on the stress-strain curve of the triaxial test. (3) Refer to relevant specifications to determine the range of clay layer subgrade coefficient.

[0051] Specifically, in step D, when the effective thickness of the waterproof clay layer is h, the maximum tensile stress at the beam end is: (7) In the formula: It is calculated using formula (1).

[0052] The uniaxial tensile strength of the soil is calculated based on the tangency of the Mohr circle and the straight line: (8) In the formula: It is an internal cohesive force; The internal friction angle is determined by the parameters in step C.

[0053] make The minimum thickness of the impermeable clay layer required to meet the tensile failure requirement is calculated and denoted as h1.

[0054] Based on the parameters such as the target aquifer water pressure and the elastic modulus of the aquitard clay determined in step C, different parameters are selected to calculate a series of h1.

[0055] Specifically, in step E, the total shear force Q is the ultimate capacity of the clay layer to resist shear failure, which consists of three parts: cohesion shear term, self-weight-lateral pressure shear term, and self-weight-distributed force shear term.

[0056] (9)

[0057] In the formula: It is an internal cohesive force; The internal friction angle is determined by the parameters in step C. The effective thickness of the clay layer subjected to shear stress; This is the coefficient of pressure on the stationary side; The unit weight of the clay layer; This refers to the effective cover height above the clay layer; The static lateral pressure coefficient is calculated using an empirical formula. calculate.

[0058] make , The minimum thickness of the waterproof clay layer that meets the tensile failure requirement is calculated using formula (2) and denoted as h2.

[0059] Based on the parameters determined in step C, such as the target aquifer water pressure and the elastic modulus of the aquitard clay, different parameters are selected to calculate a series of h2 values.

[0060] Specifically, in step F , Each refers to , Referring to steps D and E, with the thickness of the waterproof layer as the independent variable, , For the dependent variable, a program was developed to obtain the results under different parameter combinations. Relationship with the thickness of the waterproof layer Relationship with the thickness of the waterproof layer. Indicates the uniaxial tensile strength of soil. This indicates the maximum tensile stress at the beam end; Indicates the total shear strength. This indicates the maximum shear force at the beam end.

[0061] Specifically, in step G, observe the results obtained in step F. Relationship with the thickness of the waterproof layer A graph showing the relationship between the thickness of the waterproof layer and the parameters. Analysis of different parameter combinations. , The variation pattern of the region with a value greater than 0 is used to determine the h value that satisfies all parameter conditions, which is then used as the minimum waterproof layer thickness.

[0062] This invention relates to the field of determining the minimum water-tight layer thickness of clay layer in the case of water-conducting fracture zone in coal seam roof affecting loose layer. Specifically, it is a method that simplifies the clay layer as a beam structure sitting on an elastic foundation, quantifies its bearing capacity under tensile and shear failure modes by constructing a mechanical model, and then evaluates the effective water-tight layer thickness.

[0063] This invention assesses the minimum water-tightening thickness of clay layers when water-conducting fracture zones in coal mines affect loose layers, based on the elastic foundation beam theory. This embodiment addresses the problem of clay layer water-tightening performance degradation caused by the development of water-conducting fracture zones in coal mining. It simplifies the clay layer as a beam structure situated on an elastic foundation, quantifying its bearing capacity under tensile and shear failure modes through a mechanical model. The core technologies include: establishing an elastic foundation beam model considering aquifer water pressure and self-weight loads; deriving analytical solutions for beam-end bending moments and shear forces; calculating the minimum clay layer thickness meeting tensile and shear requirements based on Mohr-Coulomb strength theory, taking the larger value as the safe thickness; determining the critical thickness range through multi-parameter sensitivity analysis, and finally using the most unfavorable working condition as the prevention threshold. This technology can be used for coal mine waterproof coal pillar design, water inrush risk early warning, and optimization of water control projects, providing a scientific basis for mine water hazard prevention under complex geological conditions.

[0064] In one specific embodiment of the present invention, geological information of a coal mining area is collected. The mining area consists of a horizontal coal seam, a sandstone-mudstone bedrock (50m thick) and a loose layer from bottom to top. The loose layer has a 90m clay water-tight layer at the bottom and a 50m aquifer at the top.

[0065] Based on the collected data, the geological model constructed is as follows: Figure 2 Based on the geological model and mining conditions, the mining height is 8m and the working face width is 200m. The mine adopts fully mechanized longwall mining. Due to the large mining height, the water-conducting fracture zone is significantly developed, potentially affecting the bedrock and upper clay layer. Therefore, a schematic diagram of the "two zones" (water-conducting fracture zone and caving zone) in the direction of the working face is constructed. Figure 3 The model diagram of the elastic foundation beam is as follows: Figure 4 The mechanical model adopted is Equation (1)-(6).

[0066] The water pressure can be calculated to be 3.8 MPa based on the long-term water level observation borehole. The long-term water level observation borehole (full name "long-term water level observation borehole") is a borehole constructed in a specific area. By burying water level observation equipment (such as vibrating wire water level gauge, pressure sensor, etc.), the groundwater level is monitored for a long time and continuously, and the water level change pattern over time is recorded.

[0067] Experimental tests were conducted on the impermeable clay layer in the mining area to obtain shear resistance parameters. , ;density p Based on tests conducted at this mine, the average value is 2050 kg / m³. 3 Test results show that the elastic modulus of the mining area ranges from 7 to 18 MPa, and the subgrade coefficient k is 4.0 × 10⁻⁶. 4 ~10.0×10 4 kN / m 3 .

[0068] Using formulas (7) and (8), the maximum tensile stress at the beam end and the uniaxial tensile strength of the soil under the maximum and minimum elastic moduli are calculated to determine the minimum thickness h1 that satisfies the tensile strength requirement. In this example, the minimum elastic modulus is taken as 7 MPa and the maximum as 18 MPa, and the minimum subgrade coefficient k is taken as 4.0 × 10⁻⁶. 4 kN / m 3 The maximum value is 10.0 × 10 4 kN / m 3 The results are shown in Table 1.

[0069] Calculate the total shear force under the maximum and minimum elastic moduli using formula (9), and determine the minimum thickness h2 that satisfies the shear resistance. In this example, the minimum elastic modulus is taken as 7 MPa and the maximum as 18 MPa, and the minimum subgrade coefficient k is taken as 4.0 × 10⁴ kN / m. 3 The maximum value is 10.0 × 10⁴ kN / m 3 The results are shown in Table 1.

[0070] Based on the calculation process in steps D and E, with water pressure and soil parameters as fixed values ​​(in this example, the maximum and minimum elastic modulus and subgrade coefficient as fixed values), and the thickness of the impermeable layer as the independent variable, , For the dependent variable, write a program to obtain... Relationship with the change in the thickness of the waterproof layer ( Figure 5 ), Relationship with the change in the thickness of the waterproof layer ( Figure 6 ).

[0071] In one specific embodiment of the present invention, a system for determining the minimum waterproof thickness of a clay layer in a mining area includes: The data collection module is used to collect geological data from the mining area; The model building module is used to build an elastic foundation beam model that considers aquifer water pressure and self-weight load based on the geological data. The loose layer parameter determination module is used to determine the loose layer parameters of the elastic foundation beam mechanical model through geological data and laboratory tests. The module for determining the minimum thickness for tensile failure is used to calculate the uniaxial tensile strength of the soil based on the maximum tensile stress at the beam end, and to determine the minimum thickness for tensile failure h1. The module for determining the minimum thickness for shear failure is used to calculate the total shear resistance based on the maximum shear force at the beam end and to determine the minimum thickness h2 for shear failure. The loose layer parameter analysis module is used to perform sensitivity analysis on the loose layer parameters to obtain the minimum waterproof layer thickness under different working conditions. The minimum waterproof thickness determination module for clay layers is used to compare the minimum tensile failure thickness h1 and the minimum shear failure thickness h2 under different working conditions, and take the larger value as the minimum waterproof thickness h of the clay layer.

[0072] This invention provides a method for determining the minimum water-tightening thickness of a clay layer in a mining area. The method determines the minimum water-tightening thickness of the clay layer when the water-conducting fracture zone in the coal seam roof affects the loose layer. The clay layer is simplified as a beam structure sitting on an elastic foundation. By constructing a mechanical model, its bearing capacity under tensile and shear failure modes is quantified, thereby evaluating the effective water-tightening thickness.

[0073] For fully mechanized mining of thick loose layers in shallow bedrock, where water-conducting fracture zones are permitted to extend to the loose layers above the bedrock, and these fractures continue to develop within the clay layer, it is necessary to assess the water-tightening capacity of the effective water-tightening clay layer. Based on the elastic foundation beam theory, this study uses a mechanical model and incorporates tensile and shear failure theories to evaluate the water-tightening capacity of the clay layer above the fracture zone as an effective water-tightening layer. The safe threshold for the thickness of the effective water-tightening clay layer is determined, and its minimum thickness is established to prevent water inrush from the coal seam roof caused by loose aquifers, providing a theoretical basis for water inrush prevention.

[0074] This invention proposes a technique for assessing the minimum water-tightening thickness of clay layers when water-conducting fracture zones in coal mines affect loose layers, based on the elastic foundation beam theory. Addressing the problem of clay layer water-tightening performance degradation caused by the development of water-conducting fracture zones in coal mining, the clay layer is simplified as a beam structure situated on an elastic foundation. A mechanical model is constructed to quantify its bearing capacity under tensile and shear failure modes. The core techniques include: establishing an elastic foundation beam model considering aquifer water pressure and self-weight load; deriving analytical solutions for beam-end bending moments and shear forces; calculating the minimum clay layer thickness meeting tensile and shear requirements based on Mohr-Coulomb strength theory, and taking the larger value as the safe thickness; determining the critical thickness range through multi-parameter sensitivity analysis, and finally using the most unfavorable working condition as the prevention threshold. This technique can be used for coal mine waterproof coal pillar design, water inrush risk early warning, and optimization of water control projects, providing a scientific basis for mine water hazard prevention under complex geological conditions.

[0075] In a specific embodiment of the present invention, consider a coal mine where a thick loose layer covers the coal-bearing strata, and the bedrock above the coal seam is relatively thin. The mining area, from bottom to top, consists of a horizontal coal seam, a sandstone-mudstone bedrock (50m thick), and a loose layer. Below the loose layer is a 90m clay aquitard, and above it is a 50m aquifer. The designed working face width is 200m, and the mining height is 8m. Based on the collected geological information, a diagram is drawn as follows: Figure 2 The geological model shown. Based on the "two-zone" distribution pattern along the working face direction ( Figure 3 Analysis showed that the elastic foundation beam model is suitable for the embodiments of the present invention.

[0076] The aquifer water pressure level was determined to be 3.8 MPa by drilling water level observation wells. Shear parameters were obtained by collecting rock samples for experimental testing or data collection. , ;density p 2050kg / m 3 The elastic modulus ranges from 7 to 18 MPa, and the subgrade coefficient k is 4.0 × 10⁻⁶. 4 ~10.0×10 4 kN / m 3 .

[0077] Based on the parameters, select the maximum and minimum parameters to determine the range of waterproof layer thickness, draw Table 1, and preliminarily determine the minimum waterproof layer thickness.

[0078] Table 1 Calculation scheme for minimum clay waterproof layer thickness h

[0079] Develop a program to calculate the thickness of the waterproof layer as the independent variable based on formulas (1)-(7). , Calculate according to formulas (8) and (9) , .draw Relationship with the change in the thickness of the waterproof layer ( Figure 5 ), Relationship with the thickness of the waterproof layer.

[0080] Figure 5 Middle: Horizontal axis h: clay layer thickness (m); Vertical axis : The tensile strength of the soil is 0.56 MPa, a constant value. This represents the maximum tensile stress at the beam end (varying with h). The critical point is when h = 26.2 m. = At this point, the clay layer just avoids tensile failure; safe zone: when h > 26.2m, < The clay layer is tensile safe; when h < 26.2m, > There is a risk of tearing.

[0081] Figure 6 Middle: Horizontal axis h: clay layer thickness (m); Vertical axis Q represents the total shear strength (which increases with increasing h). The beam end shear force is a constant value, calculated from parameters such as load q = 3.8 MPa. (≈1200kN). Critical point: When h≈4.92m, Q= At this point, the clay layer just does not experience shear failure; safe zone: when h > 4.92m, Q > Shear resistance is safe; when h < 4.92m, Q < There is a risk of shear slip; Figure 5 The lower limit of h is determined to be 26.2m (tensile strength control). Figure 6 This indicates that the shear safety factor is 5.1, and there is no need to consider the shear risk separately.

[0082] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0083] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining the minimum waterproof thickness of a clay layer in a mining area, characterized in that, include: Collect geological data from the mining area; Based on the geological data, an elastic foundation beam model considering aquifer water pressure and self-weight load was established. The loose layer parameters of the elastic foundation beam mechanical model were determined by geological data and laboratory tests. The uniaxial tensile strength of the soil is calculated based on the maximum tensile stress at the beam end, and the minimum thickness h1 for tensile failure is determined. Calculate the total shear resistance based on the maximum shear force at the beam end, and determine the minimum thickness h2 required for shear failure. Sensitivity analysis was performed on the parameters of the loose layer to obtain the minimum waterproof layer thickness under different working conditions; Based on the minimum waterproof layer thickness under different working conditions, the minimum tensile failure thickness h1 and the minimum shear failure thickness h2 under different parameter states are compared, and the larger value is taken as the minimum waterproof layer thickness h of the clay layer.

2. The method for determining the minimum waterproof thickness of a clay layer in a mining area according to claim 1, characterized in that, Based on the geological data, a geological model was established, and schematic diagrams of the two zones along the dipping direction of the working face, a mechanical model diagram, and an elastic foundation beam model diagram were drawn. An elastic foundation beam model considering aquifer water pressure and self-weight load was established; wherein, the two zones include a water-conducting fracture zone and a collapse zone; The caving zone is located directly above the goaf, with its bottom in direct contact with the ore layer; the water-conducting fracture zone is located above the caving zone, and above the water-conducting fracture zone is a clay layer.

3. The method for determining the minimum waterproof thickness of a clay layer in a mining area according to claim 1, characterized in that, The loose layer parameters include, but are not limited to, aquifer water pressure, clay layer elastic modulus, internal cohesion, internal friction angle, subgrade coefficient, and soil density.

4. The method for determining the minimum waterproof thickness of a clay layer in a mining area according to claim 1, characterized in that, Based on the maximum tensile stress at the beam end Calculate the uniaxial tensile strength of soil Determine the minimum thickness h1 required to withstand tensile failure; make The minimum thickness of the impermeable clay layer required to meet the tensile failure requirement is calculated and denoted as h1.

5. The method for determining the minimum waterproof thickness of a clay layer in a mining area according to claim 1, characterized in that, Based on the maximum shear force at the beam end Calculate the total shear strength Determine the minimum thickness h2 required for shear failure; make The minimum thickness of the impermeable clay layer required to meet the tensile failure requirement is calculated and denoted as h2.

6. The method for determining the minimum waterproof thickness of a clay layer in a mining area according to claim 5, characterized in that, The total shear strength includes: cohesion shear term, self-weight-lateral pressure shear term, and self-weight-distributed force shear term, as shown in the following formula: ； In the formula: It is an internal cohesive force; It is the internal friction angle; The effective thickness of the clay layer subjected to shear stress; This is the coefficient of pressure on the stationary side; The unit weight of the clay layer; This refers to the effective cover height above the clay layer.

7. The method for determining the minimum waterproof thickness of a clay layer in a mining area according to claim 4, characterized in that, The maximum tensile stress at the beam end is: ； in, The beam end bending moment is represented by h; h represents the minimum waterproof thickness of the clay layer. The uniaxial tensile strength of the soil is calculated based on the tangency of the Mohr circle and the straight line: ； In the formula: For internal cohesion, It is the internal friction angle.

8. The method for determining the minimum waterproof thickness of a clay layer in a mining area according to claim 1, characterized in that, Based on the minimum waterproof layer thickness under different working conditions, with the waterproof layer thickness as the independent variable. , For the dependent variable, a program was developed to obtain the results under different parameter combinations. Relationship with the thickness of the waterproof layer Relationship between the thickness of the waterproof layer and the thickness of the waterproof layer; in, , Each refers to , ; Indicates the uniaxial tensile strength of soil. This indicates the maximum tensile stress at the beam end; Indicates the total shear strength. This indicates the maximum shear force at the beam end.

9. A system for determining the minimum water-impermeable thickness of a clay layer in a mining area, using the method for determining the minimum water-impermeable thickness of a clay layer in a mining area as described in any one of claims 1-8, characterized in that, include: The data collection module is used to collect geological data from the mining area; The model building module is used to build an elastic foundation beam model that considers aquifer water pressure and self-weight load based on the geological data. The loose layer parameter determination module is used to determine the loose layer parameters of the elastic foundation beam mechanical model through geological data and laboratory tests. The module for determining the minimum thickness for tensile failure is used to calculate the uniaxial tensile strength of the soil based on the maximum tensile stress at the beam end, and to determine the minimum thickness for tensile failure h1. The module for determining the minimum thickness for shear failure is used to calculate the total shear resistance based on the maximum shear force at the beam end and to determine the minimum thickness h2 for shear failure. The loose layer parameter analysis module is used to perform sensitivity analysis on the loose layer parameters to obtain the minimum waterproof layer thickness under different working conditions. The minimum waterproof thickness determination module for clay layers is used to compare the minimum tensile failure thickness h1 and the minimum shear failure thickness h2 under different working conditions, and take the larger value as the minimum waterproof thickness h of the clay layer.

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