A method for grading treatment of underlying old goaf in an open coal mine

Abstract

The application discloses a kind of open coal mine underlying old goaf grading disposal method, it is related to open coal mining technical field.The grading disposal method of the application includes: first, obtain the geometry of slope, goaf boundary, residual coal pillar, overburden structure, blasting and mechanical disturbance, hydrogeology and multi-source monitoring parameters;Further, extract key indicators and construct six types of dimensionless coefficient, establish six-coupling risk comprehensive index model, according to which the old goaf is divided into Ⅰ to Ⅳ grade danger level;Then, for different levels, match the differentiated step-by-step disposal scheme, from conventional monitoring to intensive break top and full-face filling;At the same time, the grading results and disposal scheme are corrected by numerical simulation and field monitoring inversion.The method integrates multiple factors into a unified quantitative framework, uses double-criteria grading rules to avoid boundary misjudgment, forms a complete technical closed loop of grading, disposal, verification and correction, and is suitable for main slope scenarios such as working bank, internal discharge bank and end bank.

Description

Technical Field

[0001] This invention relates to the field of open-pit coal mining technology, specifically to a method for graded treatment of old goaf areas under open-pit coal mines. Background Technology

[0002] During open-pit mining, stress redistribution, blasting disturbances, and mechanical vibrations near the working face can affect the stability of the underlying old goaf to varying degrees. As the old goaf gradually approaches the working face, or as the height of damage to the overlying strata continues to increase and the stability of the remaining coal pillars continues to decrease, the impact of the goaf may be transmitted to the working face and the upper part of the slope, thereby inducing slope deformation, settlement, fissure expansion, or even local instability.

[0003] To address the aforementioned issues, scholars and engineers have conducted relevant research. Some studies have used limit equilibrium methods or numerical simulations to solve for the stability coefficient of a single open-pit slope under the influence of goaf, thereby determining the overall safety status of the slope. Other studies have used the characteristics of roof collapse and overlying rock movement in goaf areas to divide the scope of mining-induced impact into zones, providing a reference for delineating hazardous areas.

[0004] At the engineering remediation level, grouting and roof-breaking blasting are two commonly used methods. The former increases the roof's bearing capacity by filling the goaf with grout, while the latter uses blasting to cause the roof rock mass to collapse and expand, filling the goaf to eliminate or reduce its impact on the upper slope. Both methods have achieved certain engineering results under specific working conditions.

[0005] However, the existing technologies mentioned above still have several shortcomings, as follows: (1) Most existing solutions focus on a single aspect of slope stability evaluation or goaf stability evaluation, failing to incorporate multi-source information such as the spatial distance effect between the goaf and the working face, overburden failure transmission conditions, the degree of degradation of residual coal pillars, real-time disturbance intensity, and on-site monitoring anomalies into a unified quantitative evaluation framework. This single-dimensional evaluation model is difficult to fully reflect the actual impact of old goaf on open slopes, resulting in a large deviation between the evaluation results and the actual engineering situation.

[0006] (2) Existing methods lack clear quantitative models for the boundary of hazard levels under different distances, disturbance intensities, and overburden structures. The classification is based on qualitative judgments made by engineering experience. This experience-driven classification method leads to the coexistence of over-treatment and under-treatment in engineering practice. Over-treatment increases unnecessary engineering costs, while under-treatment makes it difficult to effectively ensure safe production in open-pit mines.

[0007] (3) Existing technologies often adopt fixed treatment methods such as single grouting or single roof breaking after anomalies are detected, lacking a differentiated treatment system that matches the risk level step by step. Regardless of the risk status of the goaf, similar treatment methods are used, resulting in excessive intervention in low-risk scenarios and insufficient treatment in high-risk scenarios, and a lack of differentiation in treatment measures for different risk scenarios.

[0008] (4) Existing solutions generally lack a closed-loop process for numerical simulation verification and on-site monitoring feedback correction of grading results and governance effects. The rationality of grading results is difficult to be effectively verified by independent means, and the governance solutions are also difficult to dynamically optimize and adjust according to the actual on-site response, thus failing to form a complete technical closed loop from evaluation to governance to feedback correction.

[0009] Therefore, existing technologies lack a systematic technical solution that integrates hazard classification, matching of treatment methods, numerical simulation verification, and dynamic correction. There is an urgent need to establish a tiered treatment method for the subsurface old goaf in open-pit coal mines that can comprehensively consider the coupling effects of multiple factors and achieve accurate hazard classification and precise matching of treatment measures. Summary of the Invention

[0010] To address the aforementioned technical problems, this invention provides a method for graded treatment of underlying old goaf areas in open-pit coal mines, thereby resolving the issues raised in the background section. The method includes the following steps: A method for graded treatment of old goaf areas beneath open-pit coal mines includes the following steps: (1) Obtain geometric parameters of open-pit coal mine slopes, spatial boundary parameters of old goaf areas, parameters of residual coal pillars, parameters of overburden structure, parameters of blasting and mechanical disturbance, hydrogeological parameters and multi-source monitoring parameters; (2) Extract key indicators characterizing the hazards of old goaf areas during open-pit mining, and construct the goaf influence transmission coefficient. Overburden penetration coefficient Coal pillar instability coefficient Disturbance coefficient Slope vulnerability coefficient and monitoring anomaly coefficient And based on six coefficients, a comprehensive risk index model was established; (3) Determine the hazard level of the old goaf area based on the comprehensive hazard index model, wherein the hazard level includes Level I low hazard, Level II medium hazard, Level III high hazard and Level IV extremely high hazard; (4) Based on the hazard level determined in step (3), output the corresponding graded treatment plan; (5) Correct the hazard level determined in step (3) and the graded treatment plan in step (4) by numerical simulation or on-site monitoring inversion.

[0011] Furthermore, the multi-source monitoring parameters mentioned in step (1) include at least one or a combination of the following: InSAR deformation monitoring data, GNSS displacement data, slope inclination data, microseismic data, blasting vibration velocity data, mechanical vibration data, borehole television data, and pore water pressure data.

[0012] Furthermore, the six coefficients mentioned in step (2) are defined as follows: Influence transmission coefficient: ; in, The horizontal distance from the nearest boundary of the old goaf area to the working wall. This refers to the vertical distance from the top of the old goaf to the critical bearing layer of the slope. The length of the working disturbance characteristic; The vertical critical influence height; and The attenuation coefficient; Overburden penetration coefficient: ; in, The height at which the overlying strata in the old goaf are damaged or connected. The minimum overburden thickness from the top of the old goaf to the surface, the key bearing layer at the bottom of the slope, or the stability control interface of open-pit mining; Coal pillar instability coefficient: ; ; in, The initial strength of the residual coal pillar, The remaining strength of the residual coal pillar, To accumulate the number of blasting disturbances, For the creep strain of the coal pillar, As a water-weakening factor, , , For attenuation parameters; Disturbance coefficient: ; in, The peak velocity of the blast vibration. The threshold value for controlling blasting vibration velocity. This refers to the amplitude of mechanical vibration. The mechanical vibration control threshold, the weights of the blasting disturbance and mechanical disturbance components, satisfy and ; Slope vulnerability coefficient: ; in, For the slope angle, The table shows the slope height; The slope angle control threshold, The slope height control threshold, and meets the following requirements. ; Monitoring anomaly coefficient: ; in This refers to the horizontal displacement of the slope. For vertical settlement, The number of microseismic events per unit time; The threshold for early warning and control of horizontal displacement of slope. The threshold for early warning and control of vertical settlement of slopes. The threshold for early warning and control of microseismic events, and satisfying the following conditions. .

[0013] Furthermore, the comprehensive risk index model mentioned in step (2) is as follows: ; ; in, These are subjective weights derived from expert experience or hierarchical analysis. The objective entropy weights are derived from the distribution of historical samples or real-time data. These are the combined weighting coefficients.

[0014] Furthermore, the method for determining the hazard level in step (3) is as follows: when <0.20、 <0.45 and When the value is less than 0.20, it is directly classified as Level I. When 0.35 <= If <0.55, it is classified as Level II; When 0.55 <= If the value is less than 0.75, it is classified as Level III. when >=0.75 or simultaneously satisfy >=0.60、 >=0.75、 If the value is greater than or equal to 0.60, it is classified as Level IV.

[0015] Furthermore, in step (4): Level I low-risk mining employs conventional mining methods, optimized blasting parameters, and periodic monitoring. For Level II medium-risk areas, local grouting, controlled blasting vibration reduction, drainage, and increased monitoring are employed. Level III high-risk operations employ surface drilling and roof-breaking blasting, utilizing the fracturing and swelling properties of the roof rock to cause the fractured rock mass to collapse and fill the goaf, while simultaneously combining supplementary grouting; Level IV extremely high risk involves dense surface drilling, zonal or segmental top-breaking blasting, and full-section or segmental grouting or paste filling. Work is restricted or suspended before remediation is completed to prevent disturbed mining.

[0016] Furthermore, in the aforementioned surface borehole roof-breaking blasting, the spacing between the roof-breaking boreholes is 8-15 meters, and the final borehole location is near the key control layer of the roof; supplementary grouting is arranged in areas where the roof collapse is insufficient, on both sides of the coal pillar, and in the fracture conduction zone.

[0017] Furthermore, in step (5), a three-dimensional numerical model of the open-pit slope and the old goaf is established using FLAC3D, 3DEC, UDEC or equivalent geotechnical numerical platform. By changing the horizontal distance, vertical distance, residual coal pillar ratio, overburden thickness, peak blasting velocity and mechanical amplitude between the goaf and the working slope, the maximum horizontal displacement, maximum vertical settlement, plastic zone area and overburden failure height of the slope are output.

[0018] Furthermore, based on the simulated horizontal displacement of the slope... Vertical settlement Plastic region area and overburden destruction height Constructing a simulated response index : ; in, , , and These represent the simulated horizontal displacement, vertical settlement, plastic zone area, and overburden failure height of the slope. , , For the corresponding control threshold. According to... Corresponding segmentation rules Mapped to simulated hazard levels ; Using the consistency index The grading results were verified: ; in, The risk level numbers are the risk level predicted by the comprehensive risk index model of this invention. Level I is denoted as 1, Level II as 2, Level III as 3, and Level IV as 4. This is the simulated response level number.

[0019] Furthermore, the method is applicable to the hazard classification and treatment of old goaf areas under the working side, inner side, or end side of open-pit coal mines.

[0020] The present invention provides a method for graded treatment of old goaf areas under open-pit coal mines, which has the following beneficial effects: (1) By constructing six dimensionless coefficients—the goaf influence transmission coefficient, the overburden penetration coefficient, the coal pillar instability coefficient, the disturbance coefficient, the slope vulnerability coefficient, and the monitoring anomaly coefficient—a six-element coupled hazard comprehensive index is established using a weighting method that combines subjective hierarchical analysis weights with objective entropy weights. This model is based on the physical laws that the farther the distance, the weaker the influence; the more difficult the damage to reach the upper reaches, the lower the influence; the more stable the coal pillar, the lower the hazard; and the more obvious the monitoring anomaly, the higher the hazard. It can quantitatively characterize the nonlinear coupling contribution of different factors to the goaf hazard, so that the comprehensive index accurately reflects the actual hazard level.

[0021] (2) Establish a dual-criteria grading rule that combines necessary condition triggering with comprehensive index segmentation to avoid misjudgment of boundary scenarios that may be caused by relying solely on the comprehensive index. When the influence transmission coefficient, overburden penetration coefficient and monitoring anomaly coefficient are all below the corresponding thresholds, it is directly judged as a low-risk level to avoid excessive amplification of long-distance scenarios; when the comprehensive index reaches a high value or the aforementioned three coefficients exceed the threshold at the same time, it is judged as an extremely high-risk level to ensure timely identification of extreme scenarios and complete consistency between the predicted and simulated responses at each level.

[0022] (3) A differentiated treatment system matching the hazard level is formed. The four hazard levels correspond to the treatment plans that are strengthened at each level. A gradient progression relationship is formed in the three dimensions of monitoring frequency, blasting control and treatment intensity. From judgment to treatment to acceptance, a complete closed loop is formed, which effectively avoids over-treatment and under-treatment.

[0023] (4) Establish a two-dimensional closed-loop correction mechanism of numerical simulation and field monitoring. A three-dimensional model is established through a professional numerical simulation platform to output slope displacement, settlement, plastic zone area and overburden failure height. The simulation response index is constructed and mapped to the simulation hazard level. The consistency of the simulation response index with the model prediction level is checked. If there is a discrepancy, the model parameters are corrected through inversion analysis to achieve dynamic matching between the grading results and the simulation and monitoring data.

[0024] (5) The sources of various parameters in the model are clearly defined. Geometric and distance parameters are obtained from geological exploration data, coal and rock mechanics parameters are determined by laboratory tests, attenuation coefficients are obtained from historical data and inversion, combined weights are determined by the combined analytic hierarchy process and entropy weight method, and grading thresholds are determined by a combination of historical cases and simulation results, ensuring that the model has good portability in different mining areas. At the same time, this method is applicable to the old goaf areas under the working slope, inner slope and end slope, covering the main slope types of open-pit coal mines. Attached Figure Description

[0025] Figure 1A schematic diagram showing the location relationship between a Class I low-risk goaf and the working slab; Figure 2 This is a schematic diagram showing the location relationship between the Class II medium-risk goaf and the working sill. Figure 3 A schematic diagram showing the location relationship between the Class III high-risk goaf and the working slab; Figure 4 This is a schematic diagram showing the relationship between the location of a Class IV extremely high-risk goaf and the working slope. Detailed Implementation

[0026] 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.

[0027] I. A method for graded treatment of old goaf areas beneath open-pit coal mines, comprising the following steps: (1) Obtain geometric parameters of open-pit coal mine slopes, spatial boundary parameters of old goaf areas, parameters of residual coal pillars, parameters of overburden structure, parameters of blasting and mechanical disturbance, hydrogeological parameters and multi-source monitoring parameters; among which, the multi-source monitoring parameters include at least one or a combination of the following: InSAR deformation monitoring data, GNSS displacement data, slope inclinometer data, microseismic data, blasting vibration velocity data, mechanical vibration data, borehole television data and pore water pressure data.

[0028] Table 1: Key Indicators and Their Engineering Significance

[0029] (2) Extract key indicators characterizing the hazards of old goaf areas during open-pit mining. For example, horizontal distance. Vertical distance Overburden thickness Top slab failure height Stability of residual coal pillar etc., construct the influence transmission coefficient of goaf. Overburden penetration coefficient Coal pillar instability coefficient Disturbance coefficient Slope vulnerability coefficient and monitoring anomaly coefficient This invention employs a combined weighted six-element coupled hazard comprehensive index model. To reflect the fundamental principle that "the farther the distance, the weaker the impact; the more difficult the damage to reach the source, the lower the impact; the more stable the coal pillar, the lower the hazard; and the more obvious the monitoring anomaly, the higher the hazard," the following coefficient definitions are proposed.

[0030] .

[0031] This characterizes the degree of attenuation of the impact of old mining subsidence areas transmitted to the working slope and key bearing layers. Among them, The horizontal distance from the nearest boundary of the old goaf area to the working wall or the control boundary of the working wall; It is the minimum vertical distance from the top of the old goaf to the lower boundary of the key bearing layer of the slope or the working side disturbance influence; The length of the working disturbance characteristic; The vertical critical influence height; and This is the attenuation coefficient. The larger the value, the easier it is for the impact to be transmitted from the goaf to the working area.

[0032] .

[0033] in, The height at which the overlying strata in the old goaf are damaged or connected. The minimum overburden thickness from the top of the old goaf to the surface, the key bearing layer at the bottom of the slope, or the stability control interface of open-pit mining. The larger the value, the more likely the impact of the goaf is to reach the surface or enter the critical control area of ​​the slope.

[0034] ; .

[0035] in, The initial strength of the residual coal pillar, The remaining strength of the residual coal pillar, To accumulate the number of blasting disturbances, For the creep strain of the coal pillar, As a water-weakening factor, , , This is the attenuation parameter.

[0036] ; ; .

[0037] In the above formula, where, The peak velocity of the blast vibration. The threshold value for controlling blasting vibration velocity. This refers to the amplitude of mechanical vibration. This is the mechanical vibration control threshold, and . and Characterizing slope angle and slope height, , and These represent the horizontal displacement, vertical settlement, and number of microseismic events per unit time of the slope, respectively. Relevant thresholds. , , , , , and It can be determined by on-site control standards, historical anomaly thresholds, or inversion analysis.

[0038] ; .

[0039] in, These are subjective weights derived from expert experience or hierarchical analysis. The objective entropy weights are derived from the distribution of historical samples or real-time data. These are the combined weighting coefficients. By introducing combined weights, this invention maintains the interpretability of engineering experience for the hierarchical boundaries while using objective data to correct the importance of each indicator.

[0040] (3) Establish a comprehensive risk index based on the above coefficients and determine the risk level. The risk levels include Level I (low risk), Level II (medium risk), Level III (high risk), and Level IV (extremely high risk), where: when <0.20、 <0.45 and When <0.20, it is directly judged as Level I; when 0.35<= If <0.55, it is classified as Level II; if 0.55<= When <0.75, it is classified as Level III; when >=0.75 or simultaneously satisfy >=0.60、 >=0.75、 A value >=0.60 indicates a Level IV goaf. To avoid misjudging boundary scenarios due to relying solely on the comprehensive index, this invention employs a dual-criteria model of "necessary condition triggering + comprehensive index segmentation." Level I low-risk goaf areas are far from the working slope, and overburden damage is unlikely to reach the surface or key bearing layers; Level II medium-risk goaf areas have localized impacts that can be transmitted to the bottom of the slope or local bearing areas; Level III high-risk goaf areas have impacts that enter the control range of the working slope and require proactive remediation; Level IV extremely high-risk goaf areas are very close to the working slope or exhibit abrupt changes in monitoring anomalies, posing a significant risk of instability.

[0041] The parameters in the hazard classification model are not arbitrarily selected, but determined based on different sources and stratifications. Geometric parameters, distance parameters, and burial depth parameters are preferably obtained directly from geological exploration data of the mining area, mining engineering drawings, drilling data, and slope measurement results; coal and rock mechanics parameters, initial strength of coal pillars, and overburden threshold parameters are preferably obtained from uniaxial compression tests, splitting tests, triaxial tests, creep tests, and similar material tests; attenuation coefficients... , , and attenuation parameters , It can be obtained from historical data of similar mining areas, test results and numerical simulation inversion; the expert experience weight in the combined weight can be determined by the analytic hierarchy process, and the objective entropy weight can be calculated from the distribution of historical samples or online monitoring data; the optimal threshold for risk level segmentation is determined by comprehensively considering historical instability cases, on-site safety control standards and the inflection point characteristics of simulation results.

[0042] For high-risk and extremely high-risk areas where surface boreholes are used for fractured and expanded filling, the borehole spacing, fault top position, charge quantity, and grouting quantity are preferably determined by joint inversion based on the spatial scale of the goaf, overburden lithology, roof thickness, and allowable disturbance level, thereby avoiding over-treatment or under-treatment.

[0043] (4) Output the corresponding graded treatment plan according to the hazard level. The grade number obtained according to the present invention is output according to the graded treatment method that matches its grade. Grade I adopts conventional mining, blasting parameter optimization and periodic inspection; Grade II adopts local grouting, controlled blasting and vibration reduction, drainage and intensified monitoring; Grade III adopts surface drilling and roof breaking blasting, using the fracture and expansion properties of the roof rock to make the broken rock mass collapse and fill the goaf, and at the same time combine supplementary grouting; Grade IV adopts dense surface drilling, zoned or segmented roof breaking blasting and full-section or segmented grouting / paste filling, and restricts or suspends work to help prevent disturbance mining before the treatment is completed.

[0044] Table 2: Rules for Classifying Hazard Levels

[0045] (5) The hazard level and response plan are corrected by numerical simulation or on-site monitoring inversion.

[0046] To verify whether the hazard classification results match reality, this invention establishes a three-dimensional numerical simulation verification scheme for open-pit slopes and old goaf areas. Preferably, FLAC3D, 3DEC, UDEC, or equivalent geotechnical numerical platforms are used to establish a model including the working slope, overburden structure layers, old goaf area, and residual coal pillars. The model is then modified by changing the horizontal distance between the goaf area and the working slope. Vertical distance The simulation measures residual coal pillar ratio, overburden thickness, peak blasting velocity, and mechanical amplitude, outputting the maximum horizontal displacement, maximum vertical settlement, plastic zone area, and overburden failure height of the slope. Based on the simulation results, a verification level is constructed, and its consistency with the predicted level of the comprehensive hazard index is verified. This hazard classification method reflects both distance effects and overburden transfer conditions, and combines residual coal pillar stability, real-time disturbance, and the degree of anomalies monitored in the field. Furthermore, it develops a tiered treatment plan adapted to the hazard level, addressing the problems of unclear hazard level classification, lack of hierarchical treatment measures, and difficulty in verifying consistency through numerical simulation and field monitoring in existing technologies.

[0047] To facilitate mapping simulation results to simulated hazard levels, a simulation response index can be further defined. : .

[0048] in, , , and These represent the simulated horizontal displacement, vertical settlement, plastic zone area, and overburden failure height of the slope. , , For the corresponding control threshold. According to... Corresponding segmentation rules Mapped to simulated hazard levels .

[0049] .

[0050] in, The risk level numbers are the risk level predicted by the comprehensive risk index model of this invention. Level I is denoted as 1, Level II as 2, Level III as 3, and Level IV as 4. This is the simulated response level number. The closer the result is to 1, the more consistent the classification result is with the simulation result.

[0051] Table 3: Example of Simulation Condition Matrix

[0052] The above operating conditions indicate that as the distance between the goaf and the working face decreases, the residual coal pillar ratio decreases, and the overburden transmission conditions intensify, the hazard level increases, which is consistent with engineering practice. The reliability of the classification method of this invention can be verified by comparing the predicted and simulated hazard levels.

[0053] II. Detailed Implementation Methods and Engineering Examples

[0054] Example 1: Hazard Classification and Treatment of Underlying Old Goaf in an Open-Pit Coal Mine

[0055] Taking the old goaf beneath the left working face of an open-pit coal mine as an example. The slope height of this working face... The slope is 150m long and the angle of the slope is... The angle is 37°. The horizontal distance between the roof of the old goaf and the control boundary of the working face is... The minimum vertical distance from the top slab to the lower boundary of the critical load-bearing layer is 46m. The characteristic length of the working side disturbance is 25m. Take 80m as the critical vertical influence height. Take 60m, attenuation coefficient Take 0.90, Take 0.80. Minimum overburden thickness in old goaf areas. The overlying strata failure height is 72m, obtained from previous numerical analysis and monitoring inversion. It is 51m.

[0056] Initial strength of residual coal pillar The pressure was 10.86 MPa, and the cumulative number of blasting disturbances was 10.86 MPa. For 120 cycles, the creep strain of the coal pillar The water weakening factor is 0.09. The attenuation parameter is 0.35. Take 0.0030, Take 1.80, Take 0.90. Peak blast velocity. The speed is 6.5 cm / s, and the control threshold is... 10 cm / s; mechanical amplitude The control threshold is 0.32 mm. It is 0.50mm; take =0.60, =0.40. Slope angle control threshold. The slope angle is 45°, and the slope height control threshold is... It is 180m; take =0.50, =0.50. The horizontal displacement of the slope was monitored. The vertical settlement is 0.16m. The value is 0.23m, and the number of microseismic events per unit time is... The value is 14; corresponding to the control threshold. 0.25m 0.35m 20; take =0.40, =0.30, =0.30.

[0057] (a) Calculation of risk factor.

[0058] ; ; ; ; ; ; .

[0059] Based on historical data of the mining area and the results of entropy weight correction, the combined weight is taken as follows: =0.20, =0.18, =0.18, =0.14, =0.12, =0.18.

[0060] Since 0.55 <= The value is less than 0.75, therefore the area is classified as a Level III high-risk zone. This classification is consistent with the engineering phenomenon that "the impact of the goaf has entered the control range of the working face, but has not yet reached the point where a complete shutdown of mining is necessary."

[0061] (II) Corresponding handling plan.

[0062] For the aforementioned Class III high-risk area, before the working face gets closer, the present invention lays out boreholes along the control boundary of the working face from the ground surface, drills to the target roof layer above the old goaf and performs sectional roof breaking blasting, so that the roof rock mass is broken and the goaf is filled by the collapse of the rock fragmentation; after the roof fragmentation and filling, the remaining insufficiently filled areas are supplemented with grouting to form a combined treatment mode of "roof fragmentation and filling + grouting reinforcement".

[0063] Preferably, the spacing between boreholes in the faulted area is controlled at 8-15m, and the final borehole location is near the key control layer of the roof. Supplementary grouting is preferably arranged in areas where the roof collapse is insufficient, on both sides of the coal pillar, and in the fracture conduction zone to improve the overall support capacity of the roof-overburden system in the goaf. After the treatment is completed, dynamic evaluation will continue to be conducted using InSAR, GNSS, microseismic, and slope inclinometer data. Work can only proceed normally when the level drops to Level II or below.

[0064] (III) Engineering explanation of graded treatment.

[0065] For the same mining area, if operating conditions A, B, C, and D are substituted into the model of this invention, a hazard classification result that gradually increases from level I to level IV can be obtained, corresponding to progressively enhanced remediation measures from conventional monitoring and local grouting, to fractured roof filling, and then to dense drilling fractured roof and full-section filling. Therefore, this invention can not only achieve quantitative hazard assessment, but also provide targeted remediation paths for different hazard levels.

[0066] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for graded treatment of old goaf areas beneath open-pit coal mines, characterized in that, Includes the following steps: (1) Obtain geometric parameters of open-pit coal mine slopes, spatial boundary parameters of old goaf areas, parameters of residual coal pillars, parameters of overburden structure, parameters of blasting and mechanical disturbance, hydrogeological parameters and multi-source monitoring parameters; (2) Extract key indicators characterizing the hazards of old goaf areas during open-pit mining, and construct the goaf influence transmission coefficient. Overburden penetration coefficient Coal pillar instability coefficient Disturbance coefficient Slope vulnerability coefficient and monitoring anomaly coefficient And based on six coefficients, a comprehensive risk index model was established; The six coefficients are defined as follows: Influence transmission coefficient: ； in, The horizontal distance from the nearest boundary of the old goaf area to the working wall. This refers to the vertical distance from the top of the old goaf to the critical bearing layer of the slope. The length of the working disturbance characteristic; The vertical critical influence height; and The attenuation coefficient; Overburden penetration coefficient: ； in, The height at which the overlying strata in the old goaf are damaged or connected. The minimum overburden thickness from the top of the old goaf to the surface, the key bearing layer at the bottom of the slope, or the stability control interface of open-pit mining; Coal pillar instability coefficient: ； ； in, The initial strength of the residual coal pillar, The remaining strength of the residual coal pillar, To accumulate the number of blasting disturbances, For the creep strain of the coal pillar, As a water-weakening factor, , , For attenuation parameters; Disturbance coefficient: ； in, The peak velocity of the blast vibration. The threshold value for controlling blasting vibration velocity. This refers to the amplitude of mechanical vibration. The mechanical vibration control threshold, the weights of the blasting disturbance and mechanical disturbance components, and the following conditions must be met: ; Slope vulnerability coefficient: ； in, For the slope angle, This refers to the slope height; The slope angle control threshold, The slope height control threshold is set, and it satisfies the following conditions: ; Monitoring anomaly coefficient: ； in This refers to the horizontal displacement of the slope. For vertical settlement, The number of microseismic events per unit time; The threshold for early warning and control of horizontal displacement of slope. The threshold for early warning and control of vertical settlement of slopes. The threshold for early warning and control of microseismic events, and satisfying the following conditions. ; (3) Determine the hazard level of the old goaf area based on the comprehensive hazard index model, wherein the hazard level includes Level I low hazard, Level II medium hazard, Level III high hazard and Level IV extremely high hazard; (4) Based on the hazard level determined in step (3), output the corresponding graded treatment plan; (5) Correct the hazard level determined in step (3) and the graded treatment plan in step (4) by numerical simulation or on-site monitoring inversion.

2. The method according to claim 1, characterized in that, The multi-source monitoring parameters mentioned in step (1) include any one or a combination of the following: InSAR deformation monitoring data, GNSS displacement data, slope inclinometer data, microseismic data, blasting vibration velocity data, mechanical vibration data, borehole television data, and pore water pressure data.

3. The method according to claim 1, characterized in that, The risk comprehensive index model mentioned in step (2) is as follows: ； ； in, These are subjective weights derived from expert experience or hierarchical analysis. The objective entropy weights are derived from the distribution of historical samples or real-time data. These are the combined weighting coefficients.

4. The method according to claim 3, characterized in that, The method for determining the hazard level in step (3) is as follows: when <0.20、 <0.45 and When the value is less than 0.20, it is directly classified as Level I. When 0.35 <= If <0.55, it is classified as Level II; When 0.55 <= If the value is less than 0.75, it is classified as Level III. when >=0.75 or simultaneously satisfy >=0.60、 >=0.75、 If the value is greater than or equal to 0.60, it is classified as Level IV.

5. The method according to claim 1, characterized in that, In step (4): Level I low-risk mining employs conventional mining methods, optimized blasting parameters, and periodic monitoring. For Level II medium-risk areas, local grouting, controlled blasting vibration reduction, drainage, and increased monitoring are employed. Level III high-risk operations employ surface drilling and roof-breaking blasting, utilizing the fracturing and swelling properties of the roof rock to cause the fractured rock mass to collapse and fill the goaf, while simultaneously combining supplementary grouting; Level IV extremely high risk involves dense surface drilling, zonal or segmental top-breaking blasting, and full-section or segmental grouting or paste filling. Work is restricted or suspended before remediation is completed to prevent disturbed mining.

6. The method according to claim 1, characterized in that, In step (5), FLAC3D, 3DEC, UDEC or equivalent geotechnical numerical platform are used to establish a three-dimensional numerical model of the open slope and old goaf. By changing the horizontal distance, vertical distance, residual coal pillar ratio, overburden thickness, peak blasting velocity and mechanical amplitude between the goaf and the working wall, the maximum horizontal displacement, maximum vertical settlement, plastic zone area and overburden failure height of the slope are output.

7. The method according to claim 6, characterized in that, Constructing a simulated response index : ； in, , , and These represent the simulated horizontal displacement, vertical settlement, plastic zone area, and overburden failure height of the slope. , , and For the corresponding control threshold; according to Corresponding segmentation rules Mapped to simulated response level number ; Using the consistency index The grading results were verified: ； in, The risk level is determined by the comprehensive risk index model. Level I is denoted as 1, Level II as 2, Level III as 3, and Level IV as 4.

8. The method according to claim 1, characterized in that, The method is applicable to the risk classification and treatment of old goaf areas under the working side, inner side, or end side of open-pit coal mines.

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