Method for selecting reserved section of normal fault coal pillar

Abstract

The invention discloses a method for selecting a reserved section of a normal fault coal pillar, which belongs to the technical field of normal fault area coal pillar reservation, and realizes precision and scientization of section selection through a closed-loop process of classification and screening of drilling data, multi-factor quantitative matching, dynamic judgment of a dangerous section and segmentation adaptation verification. The method comprises the following specific steps: collecting normal fault geological parameters and drilling data, and screening an effective coal seam-aquifer interlayer spacing according to a drilling penetration state; calculating the absolute value of the difference value between the fault fall and the effective interlayer spacing, and judging the most dangerous section in combination with a preset safety threshold value; executing the process on the long extension fault sections, and determining each section of target section; and iteratively optimizing the parameters through mining feedback data. The method breaks through the limitation of traditional single-factor decision, improves the accuracy of section selection, effectively reduces the risk of water inrush accidents, reduces the waste of coal pillar resources on the premise of guaranteeing safety, and provides key technical support for refined mining of a normal fault area of a coal mine.

Description

Technical Field

[0001] This invention belongs to the technical field of coal pillar retention in normal fault areas, and specifically relates to a method for selecting the coal pillar retention profile in normal fault areas. Background Technology

[0002] In underground coal mining, normal faults are common geological structures. Their characteristic of "downward movement of the hanging wall and upward movement of the footwall" can cause changes in the relative positions of aquifers and coal seams: when the fault displacement increases, the footwall aquifer is more likely to approach the hanging coal seam; when the fault displacement decreases, the hanging wall aquifer is more likely to approach the footwall coal seam. Both situations can lead to safety accidents such as water inrush and roof collapse. Therefore, the rational selection of the coal pillar profile in normal faults is a core prerequisite for determining the width of the coal pillar and ensuring mining safety.

[0003] Current techniques for selecting coal pillar profiles along normal faults rely solely on fault elevation difference (e.g., selecting profiles with larger elevation differences in the hanging wall and smaller differences in the footwall), neglecting the crucial factor of the coal seam-aquifer spacing. When the fault elevation difference and spacing are close, the "connection risk" between the aquifer and coal seam is highest. Selecting profiles based solely on elevation difference can lead to overlooking high-risk areas or excessive profile selection, resulting in resource waste. Furthermore, the techniques fail to classify borehole penetration status, directly using spacing data measured across faults (e.g., the distance between the hanging wall coal seam and the footwall aquifer). This type of data cannot reflect the true relative positions of the coal seam and aquifer, easily leading to profile selection bias. Summary of the Invention

[0004] The purpose of this invention is to provide a method for selecting the profile for leaving coal pillars in normal faults, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for selecting a profile for retaining a coal pillar in a normal fault, comprising the following steps:

[0006] S1. Collect relevant geological parameters and borehole data of the normal fault. The geological parameters include fault location, fault displacement, coal seam distribution range and aquifer distribution range. The borehole data includes borehole trajectory, type of penetrated strata and measured value of coal seam-aquifer spacing.

[0007] S2. Based on the penetration state of the borehole into the normal fault, the validity of the coal seam-aquifer spacing data collected in S1 is determined, specifically including:

[0008] Status A: The borehole only exposed the coal seam on the hanging wall of the fault, did not penetrate the fault, and directly measured the interlayer distance between the coal seam on the hanging wall and the aquifer on the hanging wall. This interlayer distance is determined to be the true interlayer distance and is retained as valid data.

[0009] Status B: The borehole penetrates the coal seam on the hanging wall of the fault but does not expose the aquifer in the hanging wall. It directly penetrates the fault and exposes the aquifer in the footwall. The measured interlayer spacing is the cross-fault spacing between the coal seam on the hanging wall and the aquifer in the footwall. This is considered invalid data and is discarded.

[0010] Status C: The borehole passes through the coal seam on the hanging wall of the fault, the fault fracture zone, and the coal seam on the footwall in sequence, and finally exposes the water-bearing stratum on the footwall. The interlayer distance between the coal seam on the footwall and the water-bearing stratum on the footwall is determined as the equivalent effective interlayer distance and is retained as valid data.

[0011] S3. Extract the effective interlayer spacing data filtered in S2, match it with the fault drop at the corresponding location, and establish a correspondence table between fault drop and effective interlayer spacing.

[0012] S4. Calculate the absolute value of the difference between the fault drop and the effective interlayer spacing for each group in S3, and compare the absolute value of the difference with a preset safety threshold: if the absolute value of the difference is less than or equal to the preset safety threshold, the location is determined to be a candidate point of the most dangerous profile; if the absolute value of the difference is greater than the preset safety threshold, the location is determined to be a low-risk profile point.

[0013] S5. From the most dangerous profile candidate points determined in S4, and in combination with the mining requirements of the hanging wall / footwall of the normal fault, select the candidate point that is closest to the mining face and has the largest impact range as the final target profile.

[0014] S6. If the extension length of the normal fault is greater than the preset segmentation threshold, the fault is divided into multiple continuous segments along the strike. Steps S1-S5 are repeated for each segment to determine the target profile to be left in each segment.

[0015] Preferably, in S1, the fault displacement is obtained by geological exploration drilling, downhole geophysical exploration combined with total station measurement, and the coal seam-aquifer spacing is determined by borehole core sampling, borehole television imaging and conductivity sensor combined.

[0016] Preferably, in S2, if the coverage of effective interlayer spacing data is <80%, Kriging interpolation is used to supplement the effective interlayer spacing data in the missing areas.

[0017] Preferably, in S4, the preset safety threshold is determined based on the water-bearing capacity of the aquifer, the thickness of the coal seam, and the integrity of the rock mass in the area where the normal fault is located: when the water-bearing capacity of the aquifer is strong, i.e., the unit water yield is >10L / (min·m), the coal seam thickness is <2m, and the rock mass integrity coefficient is <0.6, the preset safety threshold is set to 3 to 5m;

[0018] When the aquifer has moderate water-bearing capacity (i.e., unit water yield is 1-10 L / (min·m), coal seam thickness is 2-5 m, and rock mass integrity coefficient is 0.6-0.8, the preset safety threshold is set to 5-8 m.

[0019] When the aquifer has weak water-bearing capacity (i.e., unit water yield < 1 L / (min·m), coal seam thickness > 5 m, and rock mass integrity coefficient > 0.8), the preset safety threshold is set to 8-12 m.

[0020] Preferably, the specific requirements for mining the hanging wall / footwall of a normal fault are as follows: when mining the coal seam on the hanging wall of a normal fault, the candidate point with the smallest absolute value of the difference between the fault displacement and the effective interlayer spacing of the hanging wall is selected first; when mining the coal seam on the footwall of a normal fault, the candidate point with the smallest absolute value of the difference between the fault displacement and the equivalent effective interlayer spacing of the footwall is selected first.

[0021] Preferably, in S5, if there are multiple candidate points for the most dangerous profile, they are sorted according to the priority of the absolute value of the difference from small to large and the distance from the mining face from near to far, and the candidate point ranked first is selected as the target profile.

[0022] Preferably, step S6 further includes collecting water inrush risk monitoring data at the target profile during the mining process, verifying the rationality of the profile selection, and if the monitoring data is abnormal, returning to step S4 to adjust the preset safety threshold and reselect the target profile.

[0023] Preferably, the preset segmentation threshold is determined based on the fault strike length and geological homogeneity: when the fault strike length is >500m and the geological condition difference rate along the line is >15%, it is segmented into segments of 100-200m in length; when the fault strike length is ≤500m or the geological condition difference rate is ≤15%, no segmentation is required, and steps S1 to S5 are executed as a whole.

[0024] Preferably, the abnormal judgment criteria for the water inrush risk monitoring data are as follows: when the increase in water pressure around the coal seam is greater than 0.5 MPa within 24 hours, or the increase in rock permeability is greater than 20% within 24 hours, the preset safety threshold needs to be lowered by 10% to 20%, and S4 and S5 need to be re-executed to select a new target profile.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] 1. This invention abandons the traditional single-factor decision-making model that relies solely on fault displacement. By integrating the two key factors of fault displacement and the coal seam-aquifer spacing, and combining the classification and screening of borehole data, it effectively eliminates invalid data across faults, ensuring the authenticity and validity of the spacing data. Simultaneously, through quantitative comparison of the absolute value of the difference with dynamic safety thresholds, it accurately identifies the most dangerous profile candidate points, avoiding subjective errors from manual experience-based judgments. This effectively improves the matching degree between profile selection and actual geological risks, providing a reliable basis for the design of coal pillar widths and, to a certain extent, reducing the risk of water inrush caused by profile selection deviations.

[0027] 2. The preset safety threshold of this invention is dynamically adjusted according to the differences in aquifer water content, coal seam thickness, and rock mass integrity. The preset segmented threshold is flexibly set in combination with fault strike length and geological homogeneity, which is suitable for the geological characteristics of high, medium and low risk areas, and can meet the requirements for selecting normal fault profiles with long extension and strong geological heterogeneity. It breaks the limitation of the traditional one-size-fits-all method and can be widely applied to normal fault coal pillar retention scenarios with different geological conditions.

[0028] 3. This invention accurately identifies the most dangerous profiles and optimizes the width of coal pillars in high-risk areas, avoiding resource waste caused by excessive pillar placement in traditional methods. Simultaneously, it rationally controls the pillar placement range in low-risk areas, maximizing the release of recoverable resources. Combined with dynamic feedback from water inrush risk monitoring data during mining, it effectively reduces the risks of accidents such as water inrush and roof collapse, while also minimizing coal pillar resource waste, achieving a dual improvement in coal mine safety and resource utilization efficiency. Attached Figure Description

[0029] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0030] Figure 2 This is a cross-section with a large elevation difference in this invention;

[0031] Figure 3 This is a cross-section with a small drop in elevation, as described in this invention.

[0032] Figure 4 This is a distribution map of the target profile locations of the Wugou Yangliu Fault segment in this invention;

[0033] Figure 5 This is a diagram showing the coal and rock pillar layout for this invention. Detailed Implementation

[0034] 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.

[0035] Example 1

[0036] Please see Figure 1 This invention provides a method for selecting the profile for retaining coal pillars in normal faults, comprising the following steps:

[0037] S1. Collect relevant geological parameters and borehole data of normal faults. Geological parameters include fault location, fault displacement, coal seam distribution range and aquifer distribution range. Borehole data includes borehole trajectory, type of penetrated strata and measured value of coal seam-aquifer spacing.

[0038] S2. Based on the penetration state of the borehole into the normal fault, the validity of the coal seam-aquifer spacing data collected in S1 is determined, specifically including:

[0039] Status A: The borehole only exposed the coal seam on the hanging wall of the fault, did not penetrate the fault, and directly measured the interlayer distance between the coal seam on the hanging wall and the aquifer on the hanging wall. This interlayer distance is determined to be the true interlayer distance and is retained as valid data.

[0040] Status B: The borehole penetrates the coal seam on the hanging wall of the fault but does not expose the aquifer in the hanging wall. It directly penetrates the fault and exposes the aquifer in the footwall. The measured interlayer spacing is the cross-fault spacing between the coal seam on the hanging wall and the aquifer in the footwall. This is considered invalid data and is discarded.

[0041] Status C: The borehole passes through the coal seam on the hanging wall of the fault, the fault fracture zone, and the coal seam on the footwall in sequence, and finally exposes the water-bearing stratum on the footwall. The interlayer distance between the coal seam on the footwall and the water-bearing stratum on the footwall is determined as the equivalent effective interlayer distance and is retained as valid data.

[0042] S3. Extract the effective interlayer spacing data filtered in S2, match it with the fault drop at the corresponding location, and establish a correspondence table between fault drop and effective interlayer spacing.

[0043] S4. Calculate the absolute value of the difference between the fault drop and the effective inter-layer spacing for each group in S3, and compare the absolute value of the difference with the preset safety threshold: if the absolute value of the difference is less than or equal to the preset safety threshold, the location is determined to be the candidate point of the most dangerous profile; if the absolute value of the difference is greater than the preset safety threshold, the location is determined to be a low-risk profile point.

[0044] S5. From the most dangerous profile candidate points determined in S4, and in combination with the mining requirements of the hanging wall / footwall of the normal fault, select the candidate point that is closest to the mining face and has the largest impact range as the final target profile.

[0045] S6. If the extension length of the normal fault is greater than the preset segmentation threshold, the fault is divided into multiple continuous segments along the strike. Steps S1-S5 are repeated for each segment to determine the target profile to be left in each segment.

[0046] Further, in S1, two types of core data were collected from the normal fault area. Geological parameters were obtained through geological exploration reports and downhole geophysical exploration (seismic exploration, electromagnetic exploration), including fault location, fault displacement (measurement accuracy ≤ ±0.5m), coal seam distribution range, and aquifer distribution range (such as Taihu limestone aquifer and Ordovician limestone aquifer). Data from all exploration boreholes in the area were also collected, including borehole trajectories (whether they crossed faults), types of strata penetrated (coal seam, fault fracture zone, aquifer), and measured values ​​of the coal seam-aquifer spacing (determined through core sampling and borehole television imaging, accuracy ≤ ±0.3m).

[0047] S2. Borehole Data Classification and Filtering. Based on the borehole's penetration status into the normal fault, filter valid inter-layer spacing data and exclude invalid data to ensure data authenticity:

[0048] State A (True Interlayer Spacing): The borehole only drills into the hanging wall of the fault, and after exposing the hanging wall coal seam, continues drilling to the hanging wall aquifer without crossing the fault. The spacing between the hanging wall coal seam and the hanging wall aquifer measured at this time is the true interlayer spacing, which directly reflects the relative position of the hanging wall coal seam and the aquifer, and is retained as valid data.

[0049] Status B (Invalid Data): After the borehole penetrates the hanging coal seam, it does not encounter the hanging aquifer, but directly penetrates the fault and exposes the footing aquifer. The distance between the hanging coal seam and the footing aquifer measured at this time is the distance across the fault, which is affected by fault displacement and cannot reflect the true risk, so it is discarded.

[0050] State C (Equivalent Effective Interlayer Spacing): The borehole sequentially passes through the hanging wall coal seam, the fault fracture zone, and the footwall coal seam, finally revealing the footwall aquifer. The footwall coal seam-footwall aquifer spacing measured at this point is considered equivalent and retained as valid data because the normal fault only causes displacement of the hanging wall and does not change the relative relationship between the coal seam and aquifer within the hanging wall.

[0051] If the coverage rate of effective interlayer spacing data is less than 80% (the number of boreholes corresponding to the effective data / the total number of boreholes is less than 80%), Kriging interpolation is used to supplement the missing data. The interpolation error is controlled within ±0.5m to ensure data integrity.

[0052] S3. Multi-factor quantitative matching. Extract the effective interlayer spacing data after S2 filtering and establish a corresponding relationship table according to borehole location - fault displacement - effective interlayer spacing. For example, at a certain borehole location, the fault displacement is 45m and the effective interlayer spacing is 44m, forming a 45m-44m matching group, which intuitively reflects the coupling relationship between the fault and the aquifer at this location.

[0053] S4. Hazard Profile Determination. The absolute value of the difference is introduced as a hazard quantification indicator. Specifically, the absolute value of the difference between the fault drop and the effective inter-layer spacing (|fault drop - inter-layer spacing|) is calculated for each fault group. A preset safety threshold is set, which is dynamically adjusted according to the regional geological conditions.

[0054] For high-risk areas (aquifers with high water content: unit inflow > 10 L / (min·m), coal seam thickness < 2 m, rock mass integrity coefficient < 0.6), the threshold is set at 3-5 m.

[0055] For medium-risk areas (aquifer with moderate water content: 1-10 L / (min·m), coal seam thickness 2-5m, rock mass integrity coefficient 0.6-0.8), the threshold is set at 5-8m.

[0056] For low-risk areas (aquifers with weak water content: <1L / (min・m), coal seam thickness >5m, rock mass integrity coefficient >0.8), the threshold is set to 8-12m.

[0057] Comparative Judgment: If |drop - interlayer spacing| ≤ threshold, this location is the most dangerous profile candidate point (the risk of connection between the aquifer and the coal seam is the highest). If |drop - interlayer spacing| > threshold, it is a low-risk profile point (the risk is controllable and does not need to be prioritized).

[0058] S5. Target Profile Determination. Based on the mining requirements of the hanging wall / footwall of the normal fault, the final target profile is determined from the most dangerous candidate points: When mining the hanging wall coal seam, priority is given to the candidate point closest to the hanging wall mining face (the hanging wall coal seam is affected by the footwall aquifer, so the candidate point must cover the hanging wall mining area). When mining the footwall coal seam, priority is given to the candidate point closest to the footwall mining face (the footwall coal seam is affected by the hanging wall aquifer, so the candidate point must cover the footwall mining area). If multiple candidate points exist, they are sorted by the absolute value of the difference between their values ​​(from smallest to largest) and their distance from the working face (from closest to farthest), and the point ranked first is selected as the target profile.

[0059] S6. Segmented Adaptation and Verification Iteration. For long-extended positive faults, local risk adaptation and dynamic optimization are implemented:

[0060] Segmentation determination: If the fault strike length is >500m and the geological condition difference rate along the line is >15% (difference rate = (maximum drop - minimum drop) / average drop × 100%), segment according to the length of 100-200m, repeat S1 to S5 for each segment, and determine the target profile of each segment (e.g., a long fault is divided into 5 segments, and 1 target profile is selected for each segment).

[0061] Mining verification: During the coal pillar retention and mining process corresponding to the target profile, real-time monitoring of water inrush risk data (water pressure around the coal seam and rock permeability) is conducted.

[0062] Iterative optimization: If the monitoring data is abnormal (water pressure increase in 24h > 0.5MPa or permeability increase in 24h > 20%), it indicates that the current threshold is too high and needs to be lowered by 10%-20%. Steps S4-S5 should be executed again to update the target profile and ensure that the risk is controllable.

[0063] In S1, the fault displacement was obtained through geological exploration boreholes, downhole geophysical exploration, and total station measurements. The coal seam-aquifer spacing was determined through borehole core sampling, borehole television imaging, and conductivity sensors.

[0064] Furthermore, during fault displacement measurement, the spacing between geological exploration boreholes was controlled at 50-80m. Downhole geophysical exploration employed a combination of transient electromagnetic instruments and high-density electrical resistivity tomography (EDT), with the total station's measurement accuracy calibrated to ±0.2mm to ensure fault displacement data error ≤0.5m. For determining the coal seam-aquifer interlayer spacing, the borehole core sampling interval was 0.5m, the borehole television imaging resolution was adjusted to 0.1mm, and the conductivity sensor monitoring frequency was 1 time / minute. Multiple methods were used for cross-verification to ensure interlayer spacing data deviation ≤0.3m.

[0065] In S2, if the effective interlayer spacing data coverage is less than 80%, Kriging interpolation is used to supplement the effective interlayer spacing data in the missing areas.

[0066] Furthermore, when using Kriging interpolation to supplement data, the effective data is first tested for normality, and outliers that deviate from the mean by 3 times the standard deviation are removed. Then, the interpolation search radius is set to 50m and the grid resolution is 10m×10m. Cross-validation is used to ensure that the interpolation error is ≤0.5m. The supplemented data must have a consistency of ≥90% with the surrounding effective borehole data before it can be used.

[0067] In S4, the preset safety threshold is determined based on the water-bearing capacity of the aquifer, the thickness of the coal seam, and the integrity of the rock mass in the area where the normal fault is located: when the water-bearing capacity of the aquifer is strong, i.e., the unit water yield is >10L / (min·m), the coal seam thickness is <2m, and the rock mass integrity coefficient is <0.6, the preset safety threshold is set to 3 to 5m.

[0068] When the aquifer has moderate water-bearing capacity (i.e., unit water yield is 1-10 L / (min·m), coal seam thickness is 2-5 m, and rock mass integrity coefficient is 0.6-0.8, the preset safety threshold is set to 5-8 m.

[0069] When the aquifer has weak water-bearing capacity (i.e., unit water yield < 1 L / (min·m), coal seam thickness > 5 m, and rock mass integrity coefficient > 0.8), the preset safety threshold is set to 8-12 m.

[0070] Furthermore, before determining the preset safety threshold, it is necessary to collect geological disaster case data, aquifer dynamic monitoring data, and coal seam mining records for the past 5 years in the area, establish a multi-factor correlation analysis model, and iteratively verify the safety threshold under different combinations of water-bearing capacity, coal seam thickness, and rock mass integrity to ensure that the threshold setting meets the safety control requirements while avoiding excessive conservatism that could lead to resource waste.

[0071] Specifically, when mining coal seams on the hanging wall of a normal fault, the candidate point with the smallest absolute value of the difference between the fault displacement and the effective interlayer spacing of the hanging wall is selected first. When mining coal seams on the footwall of a normal fault, the candidate point with the smallest absolute value of the difference between the fault displacement and the equivalent effective interlayer spacing of the footwall is selected first.

[0072] Furthermore, when mining the hanging wall or footwall coal seam, it is necessary to first use three-dimensional geological modeling technology to restore the spatial relationship between the fault, coal seam, and aquifer, clarify the relative distance and influence range between the mining face and the fault, and select candidate points that need to cover the maximum risk area in the direction of the working face advance, and the distance from the edge of the working face should be ≤50m, to ensure that the profile protection effectively covers the mining operation range.

[0073] In S5, if there are multiple candidate points for the most dangerous profile, they are sorted by the absolute value of the difference from smallest to largest and the distance from the mining face from closest to farthest, and the candidate point ranked first is selected as the target profile.

[0074] Furthermore, when ranking multiple candidate points for the most dangerous profiles, the absolute value of the difference accounts for 60% of the weight, while the distance from the working face accounts for 40%. If the difference in distance between a candidate point and the working face is ≤30m, priority is given to ranking by the absolute value of the difference. If the absolute value of the difference is ≤1m, priority is given to ranking by distance. The ranking process must be presented in a quantitative calculation table to ensure that the selection logic is traceable.

[0075] S6 also includes collecting water inrush risk monitoring data at the target profile during the mining process to verify the rationality of the profile selection. If the monitoring data is abnormal, return to S4 to adjust the preset safety threshold and reselect the target profile. The preset segmentation threshold is determined based on the fault strike length and geological homogeneity: when the fault strike length is >500m and the geological condition difference rate along the line is >15%, segments are made in lengths of 100-200m; when the fault strike length is ≤500m or the geological condition difference rate is ≤15%, no segmentation is required, and steps S1 to S5 are executed as a whole.

[0076] Furthermore, during the data collection for water inrush risk monitoring, 3-5 monitoring points are arranged at the target profile in a triangular or rectangular distribution. High-precision pressure sensors (range 0-10 MPa, accuracy ±0.01 MPa) are used for water pressure monitoring, and rock permeability is determined through borehole water pressure tests (test pressure 0.3-0.5 MPa). Monitoring data is transmitted in real-time to the ground monitoring center, forming a 24-hour continuous data curve for easy anomaly identification. When determining the preset segmentation thresholds, the geological condition difference rate is calculated by weighting the coefficients of variation of fault displacement, aquifer water-bearing capacity, and coal seam thickness, with weights of 0.4, 0.3, and 0.3, respectively. Segmentation must be combined with geological structural nodes along the fault strike (such as fault inflection points and intersections of branch faults). The coefficient of variation of geological conditions within each segment should be ≤0.15 to ensure relatively uniform geological conditions within the segment.

[0077] After performing the segmentation operation, for the faults that need to be segmented, the key indicators such as unit water inflow, coal seam thickness and rock mass integrity coefficient are recalculated based on the geological parameters of each segment area, and an independent safety threshold range is set for each segment according to the aforementioned preset safety threshold setting method.

[0078] Furthermore, within each segment, candidate points are selected according to the predetermined mining requirements of the hanging wall / footwall of the normal fault. Specifically, for hanging wall mining, the point with the smallest absolute value of the difference between the fault displacement and the effective interlayer spacing of the hanging wall is selected; for footwall mining, the point with the smallest absolute value of the difference between the fault displacement and the equivalent effective interlayer spacing of the footwall is selected. If multiple candidate points for the most dangerous profile exist within a segment, they are also prioritized according to the absolute value of the difference from smallest to largest and the distance from the mining face from closest to farthest, to determine the target profile for that segment.

[0079] During the mining of each segment, water inrush risk monitoring data are collected at the corresponding target profile. The rationality of the selection of target profiles for each segment is verified based on the data. If any abnormality is found in the monitoring data, the process immediately returns to step S4 of the corresponding segment to adjust the preset safety threshold and reselect the target profile for that segment.

[0080] The criteria for judging abnormalities in water inrush risk monitoring data are as follows: if the increase in water pressure around the coal seam is greater than 0.5 MPa within 24 hours, or the increase in rock permeability is greater than 20% within 24 hours, the preset safety threshold should be lowered by 10% to 20%, and S4 and S5 should be re-executed to select a new target profile.

[0081] Furthermore, if abnormal monitoring data still occur in two consecutive selected target profiles during the reselection process, the geological structure of the normal fault needs to be reassessed, including the remeasurement and analysis of key parameters such as the width of the fault fracture zone, the thickness of the fault gouge, and the lithological combination on both sides of the fault. Based on the reassessment results, the preset segmentation thresholds can be adjusted or the profile selection method can be changed.

[0082] Furthermore, when there are multiple small associated faults near a normal fault, these associated faults need to be included in the overall analysis system, and their impact on the selection of coal pillar profiles should be comprehensively considered. The associated faults should be subject to similar risk assessment and treatment as the main fault analysis method.

[0083] Example 2

[0084] Please see Figures 2-5 Taking the Wugou Yangliu Fault (a normal fault with a strike length of 620m and a drop of 140-420m, the main aquifer being the Taihui aquifer) of the Yuandian No. 1 Coal Mine of Huaibei Mining Co., Ltd. as an example, the implementation process of this method is explained in detail:

[0085] S1. Parameters and Data Acquisition. Geological parameters, obtained through geophysical surveys, show a fault strike length of 620m, with elevation drops distributed along the fault as follows: 140-200m (eastern section), 200-300m (central section), and 300-420m (western section). The coal seam is designated as No. 10 coal seam, with a thickness of 3.2-4.5m. The Taihu aquifer has a unit yield of 8.5L / (min·m) (moderate water-bearing capacity) and a rock mass integrity coefficient of 0.72. Data from 22 exploration boreholes in the fault area were then collected, recording the penetration status and measured inter-layer spacing for each borehole.

[0086] S2. Borehole data classification and filtering. The 22 boreholes are classified according to their penetration status:

[0087] Status A (actual interlayer spacing): The seven boreholes only exposed the upper coal seam and the upper Taihui aquifer, without penetrating the fault. The measured interlayer spacing was 42-48m, and was retained as valid data.

[0088] Status B (Invalid Data): Six boreholes penetrated the upper coal seam and then directly penetrated the fault to the lower aquifer. The measured distance between the faults was 55-62m, so they were discarded.

[0089] State C (Equivalent Effective Interlayer Spacing): Nine boreholes penetrated the hanging coal seam, fault, and footwall coal seam, and the spacing between the footwall coal seam and the footwall Taihui aquifer was measured to be 40-46m, which was retained as valid data.

[0090] Effective data coverage = (7+9) / 22≈72.7%<80%. Kriging interpolation was used to supplement the effective interlayer spacing data of the 5 missing areas (interpolation 43-47m), and finally 16 sets of effective data were formed.

[0091] S3. Multi-factor quantitative matching. A correspondence is established based on "drilling location - fault displacement - effective inter-layer spacing," with some data as follows:

[0092] Drilling location Fault elevation drop (m) Effective interlayer spacing (m) East Section 1# 165 45 Middle Section 5# 250 44 West Section 9# 380 46 Middle Section 12# 45 44

[0093] S4. Hazardous Profile Determination: This area is classified as medium-risk (medium water content, coal seam thickness 3.2-4.5m, rock mass integrity 0.72), with a preset safety threshold of 5m. The absolute values ​​of the differences are calculated as follows: East Section 1# |165-45|=120m>5m (low risk). Middle Section 5# |250-44|=206m>5m (low risk). West Section 9# |380-46|=334m>5m (low risk). Middle Section 12# |45-44|=1m≤5m (candidate point for the most dangerous profile). Additionally, West Section 15# borehole (48m drop, 46m interlayer spacing) was discovered, with an absolute difference of 2m≤5m, and is also listed as a candidate point.

[0094] S5. Target Profile Determination. The mine plans to mine the lower coal seam, sorted by absolute value of the difference between the coal seams (smallest to largest) and distance from the working face (closest to furthest).

[0095] Middle section 12# (difference 1m, 120m from the lower working face).

[0096] West Section 15# (difference 2m, 280m from the lower working face).

[0097] Section 12# in the middle section was selected as the core target profile, and section 15# in the western section was selected as the secondary candidate profile.

[0098] S6. Segmentation and Verification Iteration. Segmentation determination: The fault strike length is 620m > 500m, and the geological condition difference rate is (420-140) / 280×100% = 100% > 15%. Divide the fault into three segments of 200m each: East Segment (0-200m), Middle Segment (200-400m), and West Segment (400-620m). Repeat steps S1 to S5 for the East and West Segments, and select one low-risk profile as the target profile for each segment.

[0099] Mining verification: During the mining of the coal pillar corresponding to the No. 12 section in the middle section, the water pressure around the coal seam increased by 0.3 MPa over 24 hours (normal), and the rock mass permeability remained stable.

[0100] Iterative optimization: No abnormal data, preset safety threshold is maintained at 5m, target profile does not need to be adjusted.

[0101] Furthermore, when determining the width of the fault coal pillar based on the fault coal pillar layout diagram, the hanging wall of the normal fault descends while the footwall rises. The greater the elevation difference, the closer the aquifer in the footwall is to the coal seam in the hanging wall, and the greater the impact on mining. Therefore, when drawing the layout diagram of the fault hanging wall coal pillar, a profile with a large elevation difference should be selected, such as... Figure 2 Similarly, the smaller the elevation difference, the closer the aquifer in the hanging wall is to the coal seam in the footwall, and the greater the impact during mining. Therefore, when drawing the layout of the coal and rock pillars in the footwall of a normal fault, a profile with a small elevation difference should be selected, such as... Figure 3 The Wugou Yangliu Fault has a vertical drop of 140–420 m, classifying it as a large-drop fault. The most dangerous sections are those with a drop close to (equal to, higher than, or lower than) the distance between the coal seam and the ash layer, requiring the construction of fault pillars. Sections with a drop significantly higher or lower than the distance between the coal seam and the ash layer do not require fault pillars. Furthermore, due to the large length of the fault, fault pillars need to be constructed in segments. Based on this, the locations of the fault pillar construction sections, including the control points for the maximum width of the fault pillars and the control points for not constructing fault pillars, were determined.

[0102] Figure 4 The fault drop at the section location is 45m, and the distance between the coal seam and the aquifer is 44m. This location is the most dangerous because the drop and the interlayer distance are close. Therefore, this location was chosen as the section location. A coal-rock pillar layout diagram is drawn as follows. Figure 5The final coal pillar width was determined to be 71m. This method makes the selection of profiles more reasonable and accurate, providing more accurate and powerful data support for the study of fault coal pillar retention. By reasonably retaining the coal pillar, the safety of coal mining is ensured while maximizing the release of coal, bringing the greatest economic benefits to the coal mine. Using this method, three target profiles were selected in the Wugou Yangliu Fault (low risk in the eastern section, high risk in the middle section, and low risk in the western section). The coal pillar retention width of the core profile in the middle section (45m drop, 44m interlayer spacing) was determined to be 71m, which is 16.5% less than the traditional 85m width selected only based on the drop. The newly recovered resource volume in the middle section alone was 21,000 tons. No water inrush or roof anomalies occurred during mining, and the safety was significantly improved.

[0103] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to the above embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for selecting the profile for retaining a coal pillar in a normal fault, characterized in that, Includes the following steps: S1. Collect relevant geological parameters and borehole data of the normal fault. The geological parameters include fault location, fault displacement, coal seam distribution range and aquifer distribution range. The borehole data includes borehole trajectory, type of penetrated strata and measured value of coal seam-aquifer spacing. S2. Based on the penetration state of the borehole into the normal fault, the validity of the coal seam-aquifer spacing data collected in S1 is determined, specifically including: Status A: The borehole only exposed the coal seam on the hanging wall of the fault, did not penetrate the fault, and directly measured the interlayer distance between the coal seam on the hanging wall and the aquifer on the hanging wall. This interlayer distance is determined to be the true interlayer distance and is retained as valid data. Status B: The borehole penetrates the coal seam on the hanging wall of the fault but does not expose the aquifer in the hanging wall. It directly penetrates the fault and exposes the aquifer in the footwall. The measured interlayer spacing is the cross-fault spacing between the coal seam on the hanging wall and the aquifer in the footwall. This is considered invalid data and is discarded. Status C: The borehole passes through the coal seam on the hanging wall of the fault, the fault fracture zone, and the coal seam on the footwall in sequence, and finally exposes the water-bearing stratum on the footwall. The interlayer distance between the coal seam on the footwall and the water-bearing stratum on the footwall is determined as the equivalent effective interlayer distance and is retained as valid data. S3. Extract the effective interlayer spacing data filtered in S2, match it with the fault drop at the corresponding location, and establish a correspondence table between fault drop and effective interlayer spacing. S4. Calculate the absolute value of the difference between the fault drop and the effective interlayer spacing for each group in S3, and compare the absolute value of the difference with a preset safety threshold: if the absolute value of the difference is less than or equal to the preset safety threshold, the location is determined to be a candidate point of the most dangerous profile; if the absolute value of the difference is greater than the preset safety threshold, the location is determined to be a low-risk profile point. S5. From the most dangerous profile candidate points determined in S4, and in combination with the mining requirements of the hanging wall / footwall of the normal fault, select the candidate point that is closest to the mining face and has the largest impact range as the final target profile. S6. If the extension length of the normal fault is greater than the preset segmentation threshold, the fault is divided into multiple continuous segments along the strike. Steps S1-S5 are repeated for each segment to determine the target profile to be left in each segment.

2. The method for selecting the profile for leaving a coal pillar in a normal fault according to claim 1, characterized in that, In S1, the fault displacement is obtained by geological exploration drilling, downhole geophysical exploration combined with total station measurement, and the coal seam-aquifer spacing is determined by drilling core sampling, borehole television imaging and conductivity sensor combined.

3. The method for selecting the profile for leaving a coal pillar in a normal fault according to claim 1, characterized in that, In S2, if the effective interlayer spacing data coverage is less than 80%, Kriging interpolation is used to supplement the effective interlayer spacing data in the missing areas.

4. The method for selecting the profile for leaving a coal pillar in a normal fault according to claim 1, characterized in that, In S4, the preset safety threshold is determined based on the water-bearing capacity of the aquifer, the thickness of the coal seam, and the integrity of the rock mass in the area where the normal fault is located: when the water-bearing capacity of the aquifer is strong, i.e., the unit water inflow is >10L / (min·m), the coal seam thickness is <2m, and the rock mass integrity coefficient is <0.6, the preset safety threshold is set to 3 to 5m. When the aquifer has moderate water-bearing capacity (i.e., unit water yield is 1-10 L / (min·m), coal seam thickness is 2-5 m, and rock mass integrity coefficient is 0.6-0.8, the preset safety threshold is set to 5-8 m. When the aquifer has weak water-bearing capacity (i.e., unit water yield < 1 L / (min·m), coal seam thickness > 5 m, and rock mass integrity coefficient > 0.8), the preset safety threshold is set to 8-12 m.

5. The method for selecting the profile for leaving a coal pillar in a normal fault according to claim 1, characterized in that, The specific requirements for mining the hanging wall / footwall of a normal fault are as follows: when mining coal seams in the hanging wall of a normal fault, the candidate point with the smallest absolute value of the difference between the fault displacement and the effective interlayer spacing in the hanging wall is selected first; when mining coal seams in the footwall of a normal fault, the candidate point with the smallest absolute value of the difference between the fault displacement and the equivalent effective interlayer spacing in the footwall is selected first.

6. The method for selecting the profile for leaving a coal pillar in a normal fault according to claim 1, characterized in that, In S5, if there are multiple candidate points for the most dangerous profile, they are sorted by the absolute value of the difference from smallest to largest and the distance from the mining face from closest to farthest, and the candidate point ranked first is selected as the target profile.

7. The method for selecting the profile for leaving a coal pillar in a normal fault according to claim 1, characterized in that, S6 also includes collecting water inrush risk monitoring data at the target profile during the mining process to verify the rationality of the profile selection. If the monitoring data is abnormal, return to S4 to adjust the preset safety threshold and reselect the target profile.

8. The method for selecting the profile for leaving a coal pillar in a normal fault according to claim 1, characterized in that, The preset segmentation threshold is determined based on the fault strike length and geological homogeneity: when the fault strike length is >500m and the geological condition difference rate along the line is >15%, it is segmented into segments of 100-200m in length; when the fault strike length is ≤500m or the geological condition difference rate is ≤15%, no segmentation is required, and steps S1 to S5 are executed as a whole.

9. The method for selecting the profile for leaving a coal pillar in a normal fault according to claim 7, characterized in that, The abnormal judgment criteria for the water inrush risk monitoring data are as follows: when the increase in water pressure around the coal seam is greater than 0.5 MPa within 24 hours, or the increase in rock permeability is greater than 20% within 24 hours, the preset safety threshold needs to be lowered by 10% to 20%, and S4 and S5 need to be re-executed to select a new target profile.

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