Coal seam floor water inrush evaluation method applied to different types of fault structures

Abstract

The application discloses a coal seam floor water inrush evaluation method applied to different types of fault structures and belongs to the technical field of coal seam floor water inrush evaluation. The method is based on an original water inrush coefficient formula, is improved and optimized in combination with geological conditions and water inrush characteristics of the Xinwen coalfield, builds four types of fault water inrush models, i.e., a hidden conductive type, a hidden isolated type, an exposed type and a penetrating type, and is verified by using actual field data and numerical simulation. The evaluation method comprehensively considers factors such as water enrichment of an aquifer, fault length and inclination, depth of a floor water-conducting damage zone, relative thickness of a water-resisting layer and width of a safety water-resisting coal (rock) column, improves the scientificity and accuracy of floor water inrush evaluation in a fault structure region, and provides certain guidance for floor structure water inrush evaluation of the Xinwen coalfield and even similar geological condition mines.

Description

Technical Field

[0001] This invention relates to the field of coal seam floor water inrush evaluation technology, specifically to a method for evaluating coal seam floor water inrush applicable to different types of fault structures. Background Technology

[0002] Coal has long dominated my country's energy consumption structure, playing an irreplaceable role in ensuring national energy security and stable economic and social development. Mine water hazards are the second largest disaster after gas, severely restricting coal mining. The Xinwen Coalfield, an important coal production base in East China, has seen its shallow coal resources gradually depleted after years of mining. Currently, it mainly mines the deeper Lower Coal Seams 11, 13, and 15. With the continuous increase in mining intensity and depth, floor water hazards have become a key factor restricting the mining of the Lower Coal Seams in the Xinwen Coalfield.

[0003] Chinese scientists have conducted numerous experiments and made some progress in assessing the risk of water inrush at the coal seam floor. The water inrush coefficient is widely used in assessing the risk of water hazards at the coal mine floor. However, in practical applications, it has been found that the water inrush coefficient method mainly considers two factors: aquifer water pressure and aquitard thickness. For areas with complex geological structures, especially those with fault structures, the assessment results often deviate from the actual situation. The "Detailed Rules for Coal Mine Water Prevention and Control" issued by the State Administration of Coal Mine Safety clearly stipulates that the water inrush coefficient in sections where the floor is damaged by geological structures should generally not exceed 0.06 MPa / m, and in sections where the aquitard is intact and without structural damage, it should not exceed 0.1 MPa / m. However, in some areas of the Xinwen coalfield, due to unique geological conditions and fault structures, even with a water inrush coefficient below 0.06 MPa / m, floor water hazards still occur frequently.

[0004] This shows that the existing technology needs further improvement. Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating water inrush in coal seam floor structures applicable to different types of fault structures. Based on the original water inrush coefficient formula, and combined with the geological conditions and water inrush characteristics of the Xinwen Coalfield, the water inrush coefficient is improved and optimized to construct a water inrush coefficient that can reflect different types of fault structures (hidden conductive type, hidden isolated type, exposed type, and through type). The method is verified by actual field data and numerical simulation, aiming to provide some guidance for evaluating water inrush in the floor structure of the Xinwen Coalfield and even mines with similar geological conditions.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for evaluating coal seam floor water inrush in different types of fault structures includes the following steps: a. In cases where water from the aquifer in the ground in the roadway or working face surges into the water-conducting fault under the combined effects of fault activation and coal seam floor failure, even though the mining activities do not directly expose the fault, it is classified as a hidden conducting fault water inrush. The formula for the water inrush coefficient of this fault structure is shown in Equation (1): (1); In formula (1): T The coefficient of water inrush. k w The aquifer's water-bearing capacity influence coefficient; P The water pressure of the aquifer at the bottom plate; M The thickness of the waterproof layer at the bottom of the coal seam; β The reduction factor is the combined resistance to damage of the fault zone and the water-conducting failure zone relative to the sandstone. C p The depth of the water-conducting failure zone of the bottom plate; L The fault length; a The fault dip angle; b. Developed within the aquitard, not directly penetrating to the bottom aquifer, with a certain thickness of water-conducting fault relative to the aquifer between its bottom and the aquifer, it is classified as a concealed isolation fault for water inrush. The formula for the water inrush coefficient of this fault structure is shown in equation (2): (2); In formula (2): h The thickness of the top of the Ordovician limestone aquifer relative to the waterproof layer; c. Water-conducting faults that develop within the aquitard or water-conducting failure zone of the floor and are exposed during the mining of the working face or the excavation of the roadway are classified as exposed fault water inrushes. The formula for the water inrush coefficient of this fault structure is shown in equation (3): (3); In equation (3): max( C p , L sin a () represents the larger value of the vertical length between the water-conducting failure zone of the base plate and the fault; d. Water-conducting faults that develop from the aquifer at the bottom of the coal seam and directly penetrate the entire coal seam are classified as through-fault water inrush. The formula for the water inrush coefficient of this fault structure is shown in equation (4): (4); In equation (4): L 1 represents the width of the water-resistant coal pillar.

[0007] In the above-mentioned evaluation method for coal seam floor water inrush in different types of fault structures, in step a, in the case of water inrush in a concealed conductive fault, the high-pressure water in the aquifer flows into the mine through the fault and the water-conducting failure zone of the floor, causing water damage to the coal seam floor.

[0008] In the above-mentioned coal seam floor water inrush evaluation method applied to different types of fault structures, in step b, for the water inrush from hidden isolated faults, under the coupled action of mining stress and high water pressure, the water in the aquifer overcomes the barrier of the relatively water-resistant layer, enters the fault damage zone, and then surges into the mine through the water-conducting damage zone, resulting in a water inrush accident.

[0009] In the above-mentioned coal seam floor water inrush evaluation method applied to different types of fault structures, in step c, for the water inrush from exposed faults, under high-pressure conditions, the water-conducting channel becomes more unobstructed, and the confined water passes through the water-resistant layer and then surges into the mine through the fault, thus triggering a water inrush accident.

[0010] In the above-mentioned coal seam floor water inrush evaluation method applied to different types of fault structures, in step d, for the water inrush from through-going faults, the high-confined water in the aquifer passes through the fault, the floor water-conducting damage zone, and the safety water-resistant coal (rock) pillar and then enters the mine, thus triggering floor water disasters.

[0011] In the above-mentioned coal seam floor water inrush evaluation method applied to different types of fault structures, when the unit water inflow q ≤ 0.1, k w the value is taken as 0.5; when the unit water inflow 0.1 < q ≤ 0.5, k w the value is taken as 1; when the unit water inflow q ≥ 5, k w the value is taken as 2.

[0012] Compared with the prior art, the present invention brings the following beneficial technical effects: (1) The present invention proposes a coal seam floor water inrush evaluation method applied to different types of fault structures, which improves the water inrush coefficient. The improved water inrush coefficient comprehensively considers factors such as the water-richness of the aquifer, the length and dip angle of the fault, the depth of the floor water-conducting damage zone, the thickness of the relatively water-resistant layer, and the width of the safety water-resistant coal (rock) pillar, thus enhancing the scientificity and accuracy of the floor water inrush evaluation in the fault structure area; the water inrush coefficients of the hidden conduction type, hidden isolation type, and exposed type are about 50% higher than the original water inrush coefficient, and the high-risk areas highly coincide with the locations of actual water inrush accidents; the water inrush coefficient of the through-going type is about 158% higher than the original water inrush coefficient in the water inrush area, and the evaluated water inrush area is the same as the simulation result. The improved water inrush coefficient can more reasonably and accurately evaluate the floor water inrush risk in the fault structure area, providing a theoretical basis and technical reference for the water prevention and control work in mines with similar geological conditions.

[0013] (2) The water inrush coefficients for concealed conductive, concealed isolated, and exposed types were verified using the 81501 working face of Liangzhuang Mining in Xinwen Coalfield as an engineering example. The results show that the improved water inrush coefficient can effectively evaluate the water inrush risk area. Its calculated value is generally about 50% higher than the original water inrush coefficient in the fault development area. The high-risk area has good consistency with the actual location of water inrush accidents, which proves the accuracy of the fault structure water inrush coefficient. Attached Figure Description

[0014] The present invention will be further described below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a hidden conductive fault with water inrush. Figure 2 This is a schematic diagram of a water inrush along a concealed isolation fault. Figure 3 To reveal a schematic diagram of water inrush along a fault; Figure 4 This is a schematic diagram of a water inrush along a penetrating fault. Figure 5 The image shows the detection results of the 81501 transient electromagnetic method. Figure 6 This is a schematic diagram of the geological structure of the 81501 working face; Figure 7 This is a stratigraphic columnar section of the 81501 working face. Figure 8 Contour map of the original water inrush coefficient of the 81501 working face; Figure 9 Contour map of water inrush coefficient for fault-structured working face 81501; Figure 10 This is a schematic diagram of the numerical model; Figure 11 This is a graph showing the variation of pore water pressure. Figure 12 This is a graph showing the variation of the water inrush coefficient. Figure 13 This is a diagram showing the evolution of pore water pressure during the mining process; In the picture: M The thickness of the waterproof layer at the bottom of the coal seam is in meters (m). C p The depth of the water-conducting failure zone of the bottom plate is in meters (m). h The thickness of the top of the Ordovician limestone aquifer relative to the impermeable layer is in meters (m). L The fault length is in meters (m). a The fault dip angle, H 1 represents the width of the safety water-resistant coal (rock) pillar, in meters; H 2 represents the height of confined water rise within the fault, in meters (m). L 1 represents the width of the water-resistant coal (rock) pillar, in meters. Detailed Implementation

[0015] This invention proposes a method for evaluating water inrush in the coal seam floor applicable to different types of fault structures. To make the advantages and technical solutions of this invention clearer and more explicit, the invention will be further described below with reference to specific embodiments.

[0016] The main technical concept of this invention is to construct four types of fault water inrush models, namely, concealed conduction type, concealed isolation type, exposed type, and through type, to explain the water inrush mechanism of the corresponding fault types, to improve the original water inrush coefficient, and to propose different types of fault structure-type water inrush coefficients.

[0017] 1.1 Optimization of Fault-Based Water Inrush Coefficient: High-pressure water in the aquifer at the bottom of the coal seam enters the goaf through water-conducting channels, thus forming water hazards at the coal seam floor. Statistics show that approximately 80% of coal seam floor water hazards are caused by the activation of water-conducting faults. The Xinwen coalfield has well-developed fault structures, and in past mining operations, the activation of water-conducting faults has triggered numerous floor water hazard events, severely restricting mining operations in this coalfield. Based on this, and building upon previous research, this invention proposes both through-fault and non-through-fault water inrush models. The non-through-fault models include exposed, concealed conductive, and concealed isolated types. The corresponding water inrush mechanisms are analyzed, and the water inrush coefficient is optimized to improve its applicability in assessing water inrush hazard in fault-based areas.

[0018] 1.1.1 Correlation Analysis between Aquifer Water-Bearing Capacity and Water Inrush Coefficient

[0019] Based on the analysis of 24 water inrush data from coal mines such as Liangzhuang, Xiezhuang, Huafeng, and Suncun in the Xinwen Coalfield and surrounding coalfields, the unit inflow of water at each water inrush point and the total water inrush volume were correlated based on the scale of the water inrush point, as shown in Table 1.

[0020] Table 1 shows that small-scale water inrushes mainly occur in weakly water-bearing aquifers, and the number of such inrushes accounts for a relatively small proportion; medium- or strong aquifers mainly experience medium-sized water inrushes, accounting for the largest proportion of such inrushes; and extremely strong aquifers mainly experience large and extra-large water inrushes. Small-scale water inrushes are more likely to occur when q ≤ 0.1 L / (s·m); medium-scale water inrushes are more likely to occur in the range of 0.1 L / (s·m) < q ≤ 5 L / (s·m); and large and extra-large water inrushes are more likely to occur when q > 5.0 L / (s·m).

[0021] Table 1. Statistical correlation between water inrush scale and aquifer water-bearing capacity

[0022] It can be seen that the water inrush from the coal seam floor is related to the water richness of the aquifer. Under the complete rock stratum with a certain thickness of the water-resisting layer, the stronger the water richness of the bottom aquifer in the mining area, the greater the possibility of water inrush. When the aquifer q ≤ 0.1 L / (s·m), small water inrushes mainly occur. Since the water source intensity of the aquifer is insufficient, it can be effectively controlled during the mining process. In this case, the water inrush coefficient should be weakened; when the aquifer 0.1 L / (s·m) < q ≤ 5 L / (s·m), medium-sized or larger water inrushes mostly occur, which conforms to the current situation of most water inrushes from the coal seam floor. Using the existing water inrush coefficient is relatively reasonable; when the aquifer q ≥ 5 L / (s·m), large and extremely large water inrushes are likely to occur, and corresponding measures should be taken to prevent water inrush from the floor. Therefore, the influence coefficient of aquifer water richness ( k w ) can be introduced to reflect the influence of aquifer water richness on the water inrush accident from the floor, k w and the assignment is shown in Table 2.

[0023] Table 2 Values of the influence coefficient of aquifer water richness (k w )

[0024] 1.2. Analysis of the water inrush process of fault structural type

[0025] 1.2.1. Water inrush from hidden conductive faults

[0026] A hidden conductive fault refers to a water-conducting fault in which, although not directly exposed during mining activities, the water in the bottom aquifer can flow into the roadway or working face under the combined action of fault activation and the coal seam floor failure zone, as shown in Figure 1 . Its water inrush mechanism is that the high-pressure water in the aquifer flows into the mine through the fault and the water-conducting failure zone of the floor, thus causing water disasters on the coal seam floor.

[0027] The strength of the coal seam floor failure zone and the fault is lower than that of the sandstone layer, but it can still play a certain role in resisting damage. Therefore, when calculating the water inrush coefficient of fault structural type, a reduction coefficient β is introduced to represent the anti-damage ability of the fault and the water-conducting failure zone relative to the sandstone. Considering the water inrush mechanism of hidden conductive faults and the influence of aquifer water richness, the water inrush coefficient formula is modified as shown in formula (1).

[0028] (1).

[0029] 1.2.2. Water inrush from hidden isolated faults

[0030] A hidden isolated fault refers to a water-conducting fault that develops within the water-resisting layer, does not directly penetrate to the bottom aquifer, and there is a certain thickness of relatively water-resisting layer between its bottom and the aquifer, as shown in Figure 2As shown. Although this type of fault is not exposed during the mining or tunneling process, its existence may still serve as a potential water-conducting channel. The water inrush mechanism is that under the coupled effect of mining stress and high water pressure, water in the aquifer must overcome the barrier of the relatively impermeable layer, enter the fault failure zone, and then flow into the mine through the water-conducting failure zone, forming a water inrush accident.

[0031] When water inrushes through concealed isolated faults, the water pressure must first overcome the resistance of the relative impermeable layer between the fault bottom and the aquifer, making the inrush mechanism more complex. In this case, the water-blocking capacity of the relative impermeable layer at the top of the aquifer should be fully considered. Such relative impermeable layers are commonly found at the top of the Ordovician limestone aquifer in the Xinwen coalfield. Although this relative impermeable layer is not directly penetrated by the fault, its thickness and integrity directly affect the ease with which water pressure is transmitted to the fault zone. If this relative impermeable layer is thick and has good integrity, it can effectively hinder the transmission of water pressure and reduce the risk of fault activation and water conduction; conversely, if it is thin or has weak links such as primary fractures, it is prone to damage under high water pressure and mining stress, allowing water pressure to be transmitted to the fault through this layer, thereby inducing water inrush. Therefore, based on the inrush mechanism of concealed isolated faults, the inrush coefficient is modified to Equation (2).

[0032] (2).

[0033] 1.2.3. Exposing fault-related water inrush

[0034] An exposed fault refers to a water-conducting fault that develops within the aquitard or water-conducting failure zone of the floor and is exposed during the mining process or tunnel excavation. In other words, the tunnel or working face is in direct contact with the fault. Figure 3 As shown, the mechanism of water inrush is that under high pressure, the unobstructed flow of the water conduit is significantly enhanced. The pressurized water passes through the aquitard and then surges into the mine via the fault, thus triggering a water inrush accident. Compared with concealed faults, water inrush from exposed faults is characterized by a clear path, rapid response, and concentrated water volume, thus posing a higher risk.

[0035] Due to the combined effects of the fault zone and the base failure zone, the rock mass strength in the water-conducting channel is significantly reduced, which can be appropriately increased during the calculation process. β The value of the water inrush coefficient is modified according to equation (3) based on the location of the fault development: (3).

[0036] 1.2.4 Water inrush through a penetrating fault

[0037] A penetrating fault is a water-conducting fault that develops from the aquifer at the bottom of the coal seam and directly penetrates the entire coal seam, such as... Figure 4As shown in the diagram, this type of fault connects the hydraulic system between the aquifer and the coal seam in the floor. It is easily activated under mining conditions. The water inrush mechanism involves high-pressure water from the aquifer passing through the fault, the water-conducting failure zone in the floor, and the safety-preventing water-blocking coal (rock) pillar before entering the mine, thus triggering floor water hazards. Due to the strong penetration and clear water-conducting path of this type of fault, once activated, it often causes sudden and large-volume water inrush disasters, seriously threatening safe mine production.

[0038] When water surges through a fault zone, the main water-blocking component is the safety and water-proof coal (rock) pillar. H 1) Its width and lithological combination directly determine its water-blocking capacity. When constructing the formula for the water inrush coefficient of the through-fault type, the effective water-blocking thickness of the safe water-blocking coal (rock) pillar needs to be introduced. Based on this, the water inrush coefficient of the through-fault type is modified to formula (4): (4).

[0039] The width of the waterproof coal (rock) pillar and the height of the pressurized water rise can be calculated using formula (5) based on the width of the waterproof coal (rock) pillar: (5).

[0040] Combining formulas (4) and (5), the coefficient for water inrush through a fault is given by formula (6): (6).

[0041] The formula for calculating the water inrush coefficient in fault-related structures fully considers parameters such as the water-bearing capacity of the aquifer at the coal seam floor, fault type, fault length, and dip angle. Compared to the original formula, it is more targeted and integrates more mechanisms, making it more applicable to fault-structured areas and providing more accurate evaluation. This provides a more scientific and reliable theoretical tool and evaluation basis for solving the problem of fault-activated water inrush in deep mining of the Xinwen Coalfield and similar geological structures.

[0042] 2.1 Evaluation and analysis were conducted using the methods described above.

[0043] 2.1.1 Overview of the Evaluation Area: Liangzhuang Mining is located in Xintai City, Shandong Province, in the central part of the Xinwen Coalfield. During the mining of the lower coal seam, it faces the threat of pressurized water from the Ordovician limestone floor. The 81501 working face is located in the northern part of the mine, mining the 15 coal seam of the lower coal seam. The overall structure is a monocline, with a mining elevation range of -580 to -800 m and an average coal thickness of 1.45 m. The mining method is full-height mining in one pass, with the roof managed by the caving method.

[0044] The structural region of the bottom plate of the 81501 working face was probed using transient electromagnetic methods. Figure 5The results showed that the faults within the working face were relatively well-developed, with most faults distributed in the eastern part of the working face, with elevation differences ranging from 0 to 9.5 m. These faults included both concealed conductive and concealed isolated types. The exposure revealed the existence of three types of non-penetrating faults within the working face, such as... Figure 6 As shown. The immediate base is siltstone, about 2.3m thick, which is easily broken; the basic base is an alternating layer of siltstone and fine sandstone, up to 21.1m thick, with hard lithology and obvious bedding.

[0045] The aquifer is mainly composed of Xuhui and Ordovician limestone strata at its base. Figure 7 The Xuhui aquifer is located approximately 25 m below the No. 15 coal seam, with an average thickness of 14.8 m. It is deeply buried, without surface water recharge, and is primarily composed of still water, classifying it as a weak aquifer. The Ordovician aquifer is located approximately 75 m below the No. 15 coal seam, with a thickness exceeding 800 m. Its water-bearing capacity is heterogeneous, with localized areas exhibiting moderate to weak water abundance. The initial water level ranges from -72.3 to -468.3 m, with a unit inflow rate between 0.1 and 25 m³ / h. The maximum water pressure of the aquifer is 4.35 MPa, classifying it as a strong aquifer. A groundwater inrush occurred at the Ordovician aquifer at a depth of 206 m from the working face, with a peak flow rate of 176 m³ / h. Investigation revealed that the inrush was caused by the activation of a fault in the floor due to mining activities. Therefore, using the groundwater inrush at the 81501 working face as a background, this study analyzes the accuracy of the inrush coefficients for concealed conductive, concealed isolated, and exposed fault types.

[0046] 2.1.2 Evaluation of the original water inrush coefficient

[0047] The water inrush coefficient of the 81501 working face in Liangzhuang Mining was calculated using the original formula. The results show that the water inrush coefficient value of the working face is 0.050~0.058 MPa / m. Figure 8 According to the "Detailed Rules for Water Prevention and Control in Coal Mines," the water inrush coefficient in sections with structural damage to the floor should generally not exceed 0.06 MPa / m, and in sections with intact aquitards and no structural damage, it should not exceed 0.1 MPa / m. Therefore, the 81501 working face did not have a water inrush risk. However, a delayed water inrush occurred at 206 m from the cut-off point, with a peak water volume of 176 m³ / h. This indicates that using only the original water inrush coefficient for evaluation deviates somewhat from the actual water inrush situation on site.

[0048] A deeper analysis reveals that the primary reason lies in the fact that the original formula for calculating the water inrush coefficient did not adequately consider the weakening effect of fault structures developed within the working face on the water-tightness of the foundation. Faults are well-developed within the 81501 working face, with multiple faults ranging from 0 to 9.5 meters in elevation in the eastern region, encompassing concealed conductive, concealed isolating, and exposed faults. The presence of these faults means that the actual effective water-tight layer thickness may be far less than the average thickness of 75 meters, while also providing potential channels for groundwater uplift and migration. This leads to inaccurate evaluation results of the original water inrush coefficient, making it difficult to effectively predict the water inrush risk in fault-prone areas.

[0049] 2.1.3 Assessment of the risk of sudden water inrush

[0050] When using the fault-based water inrush coefficient for hazard assessment, it is necessary to analyze the values ​​of each calculation element step by step. Geological exploration revealed that the Ordovician limestone layer is a strong aquifer with a maximum water pressure of 4.35 MPa and a water-bearing capacity of 0.1 < q ≤ 5 L / (s·m). Table 2 shows the influence coefficient k of the aquifer's water-bearing capacity. w Taking 1; after the working face was mined, the depth of the water-conducting failure of the bottom plate was measured to be approximately 23 m using a double-ended water plug; there is a 2.5 m layer of siltstone at the top of the Ordovician limestone aquifer, which has low permeability, thus the relative thickness of the aquitard is 2.5 m; according to the geological data of Liangzhuang Mining, the resistance to failure of the bottom plate water-conducting failure zone and the fault is approximately 0.35 times that of the sandstone, therefore... β The value is 0.35. Formulas (1)-(3) are used to calculate the water inrush coefficient in the fault structure area. In the non-fault area, the original formula (T=P / M) is used to calculate the water inrush coefficient at different locations in the working face, such as Figure 9 As shown.

[0051] The fault-based water inrush coefficient ranges from 0.050 to 0.077 MPa / m, representing an increase of approximately 50% compared to the original coefficient. Specifically, the water inrush coefficient in the densely faulted areas of the eastern and north-central parts of the working face is generally higher than 0.06 MPa / m, reaching a maximum of 0.077 MPa / m, indicating a risk of water inrush. In actual mining operations, a water inrush accident occurred in the eastern part of the working face, with the inrush point located within the predicted risk area, highly consistent with the prediction results of the fault-based water inrush coefficient. Based on the original water inrush coefficient evaluation results, the entire 81501 working face is considered a safe zone. Therefore, the original water inrush coefficient has certain limitations in evaluating fault areas. The fault-based water inrush coefficient evaluation method can more accurately identify high-risk water inrush areas controlled by fault structures, overcoming the shortcomings of the original water inrush coefficient, which does not consider the influence of faults and leads to overly optimistic evaluation results. This provides strong theoretical support for accurate early warning and prevention of fault-based water inrush.

[0052] 2.1.4 Numerical Simulation Analysis of Water Inrush Through a Penetrating Fault

[0053] The DF19 fault exists in the western part of the 81501 working face of Liangzhuang Mining. In order to ensure safe mining, a 50-75 m fault protection coal (rock) pillar is left. Based on this fault, a three-dimensional numerical calculation model of the through-type fault is established, and the rationality of the calculation formula of the through-type water inrush coefficient is analyzed.

[0054] 2.1.4.1 Model Establishment and Parameter Determination

[0055] The through-type fault model is 200 m long, 150 m high, and 100 m wide. To accurately display the calculation results, the roof, floor, and fault sections of the coal seam are subjected to mesh refinement. Figure 10 As shown in the figure. The bottom and sides of the model are constrained by normal displacement, simulating a coal seam depth of approximately 900 m. A vertical stress of 22 MPa is applied to the top, with a horizontal lateral pressure coefficient of 1.5. The aquifer is the Ordovician limestone layer at the bottom, with a water pressure of 4.35 MPa. The hydraulic gradient decreases from bottom to top. The model's permeability boundary condition is impermeable around the edges and permeable at the top. During simulated excavation, a single full-height mining operation was adopted. A 30 m boundary coal pillar was left on the left side of the model, with an excavation step distance of 5 m. Excavation stopped 10 m from the fault, with 18 steps in total. The Mohr-Coulomb strength criterion was used as the yield criterion for the coal-rock mass. Based on relevant rock mechanics test results, the calculation parameters for each rock layer used in the numerical simulation are shown in Table 2. To collect and observe changes in water pressure in the fault and aquifer during mining, a monitoring point was set up every 20 m along the fault direction from the top of the Ordovician limestone aquifer, named monitoring points 1, 2, 3, 4, and 5 from bottom to top.

[0056] Table 2 Rock strata property parameters in the model

[0057] 2.1.4.2 Analysis of Pore Water Pressure Evolution

[0058] Changes in pore water pressure during mining, such as Figure 13 As shown, Figure 13 When the excavation reaches 10 m, under the action of mining stress, the stress pore water pressure on the bottom plate of the coal seam shows a local upward trend, the fault is initially activated, and the confined water in the aquifer begins to rise along the fault. Figure 13 In section (b), when the excavation reached 30 m, the distribution range of pore water pressure within the fault zone was further expanded, and the confined water was guided up to the coal along the fault without any spread. Figure 13 When the middle (c) section was excavated to 50 m, the pore water pressure continued to rise and spread laterally at the location of the coal seam and the floor siltstone. This indicates that under the influence of mining, the water-conducting fault zone of the coal seam floor further developed into a connecting fault, the degree of fault activation increased, and the water-conducting capacity was enhanced. Figure 13When the excavation reaches 70 m, the range of confined water diffusion further increases. By outlining the 0.5 MPa water pressure contour line with white lines, it can be observed that the contour line has extended to the goaf. The water pressure contour line in the fault profile is slightly concave, indicating that the water pressure is released at this time and the water flows into the goaf.

[0059] Extract pore water pressure from measuring points 1 to 5 and plot the variation curves. Figure 11 At measuring point 1, located within the aquifer, the initial water pressure was high at 4.17 MPa. During excavation, it only fluctuated slightly, decreasing before increasing slightly, and remained stable at around 4 MPa. Measuring points 2-5 generally showed an upward trend in water pressure, decreasing slightly in the later stages of excavation. The magnitude of the increase varied significantly between different points, with lower pressure values ​​observed the farther the measuring point was from the aquifer. Overall, the water pressure changes at different depths within the fault exhibited a characteristic of "rapid initial growth at shallow points and high initial water pressure with stable changes at deeper points," indicating that under the influence of mining, confined water was guided up the fault and eventually flowed into the goaf.

[0060] 2.2 Flood Risk Assessment

[0061] During the model excavation, the depth of the water-conducting failure of the bottom plate was about 22 m. The water pressure value of the aquifer at the bottom of the fault at measuring point 1 was extracted. The original water inrush coefficient and the water inrush coefficient of the through-fault type were calculated using the original formula (T=P / M) and (6) respectively, and the water inrush coefficient variation curve was obtained. Figure 12 The initial water inrush coefficient remained relatively stable within the range of 0.050–0.060 MPa / m, with only slight fluctuations at excavation distances of 25–35 m, consistently below 0.060 MPa / m, thus remaining within the safe zone. The water inrush coefficient of the fault-penetrating type exhibited a trend of "slow increase—rapid growth—sharp rise at a high level." Within the first 35 m of excavation, the water inrush coefficient slowly increased from 0.045 MPa / m to 0.064 MPa / m, remaining within the safe zone, with a low probability of floor water damage. After 35 m of excavation, the area entered a relatively dangerous zone, with the water inrush coefficient increasing rapidly, reaching 0.1 MPa / m at 60 m. At this stage, confined water in the aquifer diffused in the siltstone of the floor and was guided up to the coal seam, increasing the risk of floor water inrush. After 60 m, the water inrush coefficient rose sharply, reaching 0.139 MPa / m at 75 m, indicating floor water inrush.

[0062] The original water inrush coefficient has limitations in evaluating water inrushes through faults, resulting in unsatisfactory evaluations and significant deviations from actual conditions. The optimized through-fault water inrush coefficient can effectively and accurately evaluate water inrushes in this type of structure, with evaluation results consistent with numerical simulations and actual conditions. Specifically, at 35 m excavation depth and a 45 m wide water-resistant coal pillar, confined water has risen along the fault to the coal seam, and a small amount of seepage occurs at the working face, indicating a possibility of floor water damage. The original water inrush coefficient, 0.054 MPa / m, is below 0.06 MPa / m and fails to assess the risk of water inrush. However, the through-fault water inrush coefficient, 0.064 MPa / m, is 18.5% higher than the original coefficient, indicating a risk of water inrush and providing a more scientific and accurate evaluation for this stage of water inrush. At 70 m excavation depth and a 10 m wide water-resistant coal pillar, the floor water-conducting fault zone is connected to the fault, and confined water surges into the mine, causing floor water inrush. At this point, the original water inrush coefficient is 0.053 MPa / m, and the water inrush coefficient of the through-type fault is 0.137 MPa / m, which is 158% higher than the original water inrush coefficient. Relatively speaking, the evaluation of the fault water inrush coefficient is more accurate.

[0063] In summary, the evaluation results of this invention are more reasonable and further verify the accuracy of the method of this invention.

[0064] Any parts not mentioned in this invention can be achieved by referring to existing technologies.

[0065] Those skilled in the art should recognize that the above embodiments are only used to illustrate this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of protection claimed in this application.

Claims

1. A coal seam floor water inrush evaluation method applied to different types of fault structures, characterized in that, The steps are as follows: a. In cases where water from the aquifer in the ground in the roadway or working face surges into the water-conducting fault under the combined effects of fault activation and coal seam floor failure, even though the mining activities do not directly expose the fault, it is classified as a hidden conducting fault water inrush. The formula for the water inrush coefficient of this fault structure is shown in Equation (1): （1）； In formula (1): T is a water inrush coefficient; k w is a water-bearing layer water enrichment influence coefficient; P is a floor water-bearing layer water pressure; M is a coal seam floor aquiclude thickness; β is a reduction coefficient of the comprehensive anti-damage ability of the fault zone and the water-conducting damage zone relative to sandstone; C p is a floor water-conducting damage zone depth; L is a fault length; a is a fault dip angle; b. Developed within the aquitard, not directly penetrating to the bottom aquifer, with a certain thickness of water-conducting fault relative to the aquifer between its bottom and the aquifer, it is classified as a concealed isolation fault for water inrush. The formula for the water inrush coefficient of this fault structure is shown in equation (2): （2）； In formula (2): h The thickness of the top of the Ordovician limestone aquifer relative to the waterproof layer; c. Water-conducting faults that develop within the aquitard or water-conducting failure zone of the floor and are exposed during the mining of the working face or the excavation of the roadway are classified as exposed fault water inrushes. The formula for the water inrush coefficient of this fault structure is shown in equation (3): （3）； In equation (3): max( C p , L sin a () represents the larger value of the vertical length between the water-conducting failure zone of the base plate and the fault; d. Water-conducting faults that develop from the aquifer at the bottom of the coal seam and directly penetrate the entire coal seam are classified as through-fault water inrush. The formula for the water inrush coefficient of this fault structure is shown in equation (4): （4）； In equation (4): L 1 represents the width of the water-resistant coal pillar.

2. The method for evaluating coal seam floor water inrush in different types of fault structures according to claim 1, characterized in that: In step a, during the water inrush caused by the hidden fault, the high-pressure water in the aquifer flows into the mine through the fault and the water-conducting failure zone of the floor, causing water damage to the coal seam floor.

3. The method for evaluating coal seam floor water inrush in different types of fault structures according to claim 1, characterized in that: In step b, the water inrush from the concealed isolation fault occurs when, under the coupled action of mining stress and high water pressure, water in the aquifer overcomes the barrier of the relatively impermeable layer, enters the fault failure zone, and then flows into the mine through the water-conducting failure zone, forming a water inrush accident.

4. The method for evaluating coal seam floor water inrush in different types of fault structures according to claim 1, characterized in that: In step c, the fault-induced water inrush occurs when, under high pressure, the water-conducting channel becomes more unobstructed, allowing pressurized water to pass through the aquitard and then flow into the mine via the fault, thus triggering a water inrush accident.

5. The method for evaluating coal seam floor water inrush in different types of fault structures according to claim 1, characterized in that: In step d, the fault-penetrating water inrush occurs when high-pressure water in the aquifer passes through the fault, the water-conducting failure zone of the floor, and the safety water-proof coal pillar before entering the mine, thereby causing floor water damage.

6. The method for evaluating coal seam floor water inrush in different types of fault structures according to claim 1, characterized in that: When the specific yield q ≤ 0.1, k w the value is 0.5; when the specific yield 0.1 < q ≤ 0.5, k w the value is 1; when the specific yield q ≥ 5, k w the value is 2.

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