Coal pillar working face recovery method and system based on isolated coal body and directional pressure relief

Abstract

The application discloses a coal pillar working face recovery method and system based on isolated coal body and directional pressure relief, and belongs to the technical field of coal pillar recovery. The method comprises the following steps: detecting and evaluating the coal pillar to be recovered, dividing the coal pillar into multiple recovery units, and reserving temporary isolated coal bodies between adjacent recovery units; arranging a directional pressure relief structure on the high stress side of the coal pillar, the adjacent side of the goaf or the side of the roadway; supporting the recovery unit to be recovered to form a support control area; recovering in short step distance and section according to the progressive order from low stress to high stress recovery unit; dynamically adjusting the recovery step distance, support density and pressure relief parameters according to the real-time monitoring data in the recovery process; and when the support or filling of the adjacent recovery unit is completed and the surrounding rock deformation tends to be stable, the temporary isolated coal body is recovered again. The application also discloses a recovery system. The application adopts the above method and system, can reduce the stress concentration and roof instability risk in the coal pillar recovery process, and improves the coal pillar recovery rate and recovery operation safety.

Description

Technical Field

[0001] This invention relates to the field of coal pillar recovery technology, and in particular to a method and system for recovering coal pillars in working faces based on isolated coal bodies and directional pressure relief. Background Technology

[0002] During underground coal mining, coal pillars of a certain size are typically left to maintain roadway stability, isolate goaf areas, or protect shafts and chambers. As mining progresses into the middle and later stages, the number of leftover coal pillars increases, resulting in coal resource losses. Recovering these coal pillars can improve resource recovery rates and extend the mine's service life.

[0003] However, abandoned coal pillars typically bear the load of overlying strata for extended periods and are affected by stress transfer from adjacent goaf areas, disturbances during roadway excavation, and deformation of the roof and floor. Significant stress concentration and fracture development may exist within the coal pillar. Directly recovering the entire coal pillar can easily induce problems such as coal wall spalling, roof collapse, support failure, increased roadway deformation, and abnormal gas outbursts.

[0004] Existing coal pillar recovery processes typically have the following shortcomings: 1. The order of recovery mainly relies on experience to determine, and there is a lack of a method for dividing recovery units based on coal pillar risk zoning; 2. The lack of a phased support structure between adjacent recycling units makes it easy for recycling disturbances to accumulate. 3. The delayed treatment of the goaf formed after recovery can easily affect the stability of adjacent roadways and remaining coal seams.

[0005] Therefore, there is an urgent need to propose a method and system for recovering coal pillars in working faces based on isolated coal bodies and directional pressure relief. Summary of the Invention

[0006] The purpose of this invention is to provide a method and system for recovering coal pillar working faces based on isolated coal body and directional pressure relief, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides a method for recovering coal pillars in working faces based on isolated coal seams and directional pressure relief, comprising the following steps: S1. Detect the coal pillar to be recovered and its adjacent roadways, goaf and roof and floor to obtain the coal pillar size, coal seam thickness, roof and floor lithology, goaf boundary, coal pillar stress distribution, roadway deformation state, roof stability and gas occurrence state. S2. Based on the data obtained in S1, the coal pillar to be recovered is divided into multiple recovery units, and a temporary isolation coal body is reserved between two adjacent recovery units; S3. Based on the stress distribution of the coal pillar and the location of the goaf boundary, directional stress relief structures are arranged on the high stress side of the coal pillar, the side adjacent to the goaf, or the side adjacent to the roadway. S4. Arrange advanced and temporary supports in front of and on both sides of the unit to be recovered to form a support control zone before recovery. S5. Perform short-step segmented recovery of the recovery units in the order of progress from low-stress recovery units to high-stress recovery units. S6. Monitor relevant data during the recovery process in real time, and dynamically adjust the recovery step distance, cutting depth, support density and directional pressure relief parameters based on the monitoring data; S7. After a recycling unit has completed recycling, the corresponding goaf space shall be temporarily supported, pressure-relief supported, filled or sealed off. S8. When the adjacent recovery unit has completed support or filling and the surrounding rock deformation rate is lower than the preset stability threshold, the temporary isolation coal body between the adjacent recovery units shall be recovered for a second time.

[0008] Preferably, dividing the coal pillar to be recovered into multiple recovery units includes: Based on the coal pillar size, coal body strength, internal stress distribution of the coal pillar, influence range of the goaf, and stability parameters of the roof and floor, the risk zone of the coal pillar to be recovered is divided. Based on the risk zone classification results, multiple recovery units are determined along the strike or dip direction of the coal pillar, with priority given to recovering low-stress areas and delaying the recovery of high-stress concentrated areas. The width of a single recycling unit ranges from 2m to 12m, and the width of a temporary isolation coal body ranges from 0.5m to 5m.

[0009] Preferably, the directional pressure relief structure includes one or more of the following: pressure relief boreholes, slotted grooves, pre-splitting hole groups, and weakening hole groups. The pressure relief boreholes are arranged along the strike, dip, or height of the coal pillar, and the slotted grooves are arranged on the high-stress side of the coal pillar, the side adjacent to the goaf, the top coal section, or the bottom coal section.

[0010] Preferably, when performing short-step segmented recycling of the recycling unit, adjacent recycling units are not recycled simultaneously and continuously. The next recycling unit is recycled only after the previous recycling unit has completed its support or filling.

[0011] Preferably, the advanced support and temporary support include at least three of the following support methods: anchor bolts, anchor cables, single hydraulic props, π-shaped steel beams, hydraulic supports, telescopic supports, side protection plates, and anti-slab netting.

[0012] Preferably, the monitoring data includes at least three of the following: internal stress of the coal pillar, roof subsidence, roof delamination, sidewall convergence, floor heave, support working resistance, anchor cable stress, frequency of microseismic events, gas concentration, and wind speed.

[0013] Preferably, the deformation rate of the surrounding rock is lower than a preset stability threshold, including at least one of the following: the roof subsidence rate, the approach rate of the two sides, and the support resistance growth rate being lower than the corresponding threshold.

[0014] The present invention also provides a coal pillar working face recovery system based on isolated coal body and directional pressure relief, comprising the following modules: The detection and evaluation module is used to detect the coal pillar to be recovered and its adjacent roadways, goaf and roof and floor, and to obtain the coal pillar size, coal seam thickness, roof and floor lithology, goaf boundary, coal pillar stress distribution, roadway deformation state, roof stability and gas occurrence state. The recycling unit division module is used to divide the coal pillar to be recycled into multiple recycling units based on the data obtained by the detection and evaluation module, and to determine the location and size of the temporary isolation coal body; The directional pressure relief module is used to form a directional pressure relief structure on the high-stress side of the coal pillar, the side adjacent to the goaf, or the side adjacent to the roadway, based on the stress distribution of the coal pillar and the location of the goaf boundary. The segmented recycling module is used to perform short-step segmented recycling of each recycling unit according to a preset recycling sequence; The dynamic support module is used to support the roof, side walls, and goaf before, during, and after recovery. The monitoring and feedback module is used to monitor relevant data in the recovery process in real time, including at least three of the following: internal stress of the coal pillar, roof subsidence, roof delamination, sidewall movement, floor heave, support working resistance, anchor cable stress, frequency of micro-seismic events, gas concentration, and wind speed. The parameter adjustment module is used to adjust the recovery step distance, cutting depth, support density, and decompression parameters based on the data monitored by the monitoring feedback module. The goaf treatment module is used to support, fill, or seal off the goaf space formed after recovery.

[0015] Preferably, the dynamic support module includes an advance support component, a working area support component, and a delayed support component, which are arranged sequentially along the coal pillar recovery direction.

[0016] Preferably, the parameter adjustment module includes a risk assessment unit, a parameter correction unit, and an early warning output unit. The risk assessment unit is used to determine whether the recovery unit meets the conditions for continued recovery, and the parameter correction unit is used to generate adjustment instructions for the recovery step distance, support density, and pressure relief hole parameters.

[0017] Therefore, the coal pillar recovery method and system based on isolated coal body and directional pressure relief described above have the following beneficial effects: (1) By weakening the high stress concentration area through the directional pressure relief structure, the coal pillar is in a more controllable stress release state before recovery, thereby reducing the risk of sudden instability of the coal pillar; (2) By setting up temporary isolation coal bodies between adjacent recycling units, the coal pillars can maintain their phased bearing capacity during the segmented recycling process, thereby improving the stability of the recycling process; (3) By zoning the support, working area support and delayed support, the risk of roof collapse and roadway deformation is reduced and the roof control capability is improved. (4) The monitoring data is directly used to adjust the recovery step distance, support density and decompression parameters, so that the recovery process is shifted from experience control to feedback control, realizing dynamic and precise regulation, effectively reducing the risk of roof accidents and improving the resource recovery rate; (5) Local filling or pressure relief support is carried out on the recovered space to reduce the range of roof collapse and the degree of disturbance to adjacent roadways, thereby reducing the impact of goaf disturbance.

[0018] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0019] Figure 1 This is a flowchart of a coal pillar recovery method based on isolated coal body and directional pressure relief, according to an embodiment of the present invention. Figure 2 This is a plan view of the overall layout of the coal pillar working face of the present invention; Figure 3 This is a diagram showing the layout of the recycling unit and the temporary isolated coal seam in this invention. Figure 4 This is a cross-sectional view of the directional pressure relief structure arrangement of the present invention; Figure 5 This is a diagram showing the support zoning layout of the present invention; Figure Labels 1. First working face; 2. Second working face; 3. Third working face; 4. First recovery unit; 5. Second recovery unit; 6. Third recovery unit; 7. Solid coal; 8. Coal pillar to be recovered; 9. Temporary isolation coal body; 10. Goaf; 11. Secondary recovery area; 12. Pressure relief borehole; 13. Slotted groove; 14. Anchor cable and anchor bolt; 15. Current recovery unit; 16. Movable support; 17. Lagging support component; 18. Local filling. Detailed Implementation

[0020] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] Example like Figure 1 As shown, this invention provides a method for recovering coal pillars in working faces based on isolated coal bodies and directional pressure relief, including the following steps: S1. Detect the coal pillar to be recovered and its adjacent roadways, goaf and roof and floor to obtain the coal pillar size, coal seam thickness, roof and floor lithology, goaf boundary, coal pillar stress distribution, roadway deformation state, roof stability and gas occurrence state.

[0023] S2. Based on the data obtained in S1, the coal pillar to be recovered is divided into multiple recovery units, and a temporary isolation coal body is reserved between two adjacent recovery units.

[0024] Specifically, risk zones are delineated for the coal pillars to be recovered based on their dimensions, coal strength, internal stress distribution, goaf influence range, and roof and floor stability parameters. The coal pillar dimensions characterize its load-bearing capacity; smaller widths and less favorable aspect ratios indicate poorer stability. Coal strength reflects the pillar's resistance to failure; lower strength increases the likelihood of instability. Internal stress distribution assesses load concentration; high stress concentrations at pillar edges or in localized areas can create stress concentration zones and induce localized failure. Goaf influence range analyzes the impact of adjacent goafs on pressure relief, disturbance, and surrounding rock deformation; greater goaf influence weakens pillar stability. Roof and floor stability parameters evaluate the upper and lower boundary constraints; higher roof and floor deformation or breakage increases the risk of pillar instability.

[0025] Based on the above indicators, and according to the comprehensive influence relationship of "bearing capacity—stress state—external disturbance—surrounding rock constraint," each evaluation indicator is graded and assigned a value, and risk judgment rules are established: when the coal pillar size is small, the coal body strength is low, the internal stress concentration is obvious, the goaf disturbance is strong, and the roof and floor stability is poor, it is judged as a high-risk area; when some indicators show an unfavorable state, but the coal pillar still has a certain bearing capacity, it is judged as a medium-risk area; when the coal pillar size is reasonable, the coal body strength is high, the stress distribution is uniform, the goaf influence is weak, and the roof and floor stability is good, it is judged as a low-risk area. Through comprehensive evaluation of multiple indicators, the risk level of different areas of the coal pillar to be recovered is classified, providing a basis for the subsequent mining plan formulation and safety control.

[0026] Specifically, the stress state inside the coal pillar is evaluated using the stress concentration factor: ; In the formula, The stress concentration factor of the coal pillar; This represents the maximum principal stress inside the coal pillar. For the original rock stress; when When <1.5, it is classified as a low-stress zone; when 1.5 ≤ When <2.5, it is classified as a medium stress zone; when When the value is ≥2.5, it is classified as a high stress concentration area. The classification threshold is corrected based on the measured data of the mining area.

[0027] Based on the risk zone delineation, multiple recovery units are determined along the strike or dip direction of the coal pillar, prioritizing the recovery of low-stress areas and delaying the recovery of high-stress concentration areas. The width of a single recovery unit is determined based on the coal pillar width, coal body bearing capacity, and surrounding rock control requirements, preferably ranging from 2m to 12m. Temporary isolation coal bodies are installed between adjacent recovery units. The width of these temporary isolation coal bodies is determined based on the overlying strata load, coal body strength, and stage bearing requirements, preferably ranging from 0.5m to 5m. After adjacent recovery units have been supported or filled and the surrounding rock condition has stabilized, the temporary isolation coal bodies are subjected to secondary recovery to improve the coal pillar resource recovery rate.

[0028] The width of the temporary isolation coal body is determined based on the load of the overlying strata it bears during its phase of bearing, the coal body's bearing capacity, and safety reserve requirements.

[0029] Specifically, the width of the temporary isolation coal body satisfies the following relationship: ; In the formula: The allowable bearing strength of the temporary isolated coal seam, in MPa; The load per unit area of ​​the temporarily isolated coal seam, in MPa; This is for the safety factor.

[0030] The load per unit area of ​​the temporary isolation coal seam is determined based on the weight of the overlying strata and the impact range of mining activities in adjacent recovery units. ; In the formula: The average unit weight of the overlying rock strata is kN / m³. 3 ; The depth of the coal seam is in meters (m). The range of impact from adjacent recovery units is measured in meters (m). The width of the temporary isolation coal seam is in meters (m).

[0031] The minimum width of the temporary isolation coal body is determined based on the above relationships: ; in, The width of the temporary isolation coal body.

[0032] In practical applications, the calculated width is corrected based on the coal seam occurrence conditions, coal strength, degree of mining impact, and safety control requirements.

[0033] Temporary isolation coal bodies serve as phased load-bearing structures during the recovery process of adjacent recovery units, limiting roof subsidence and reducing stress disturbance between adjacent recovery units. Temporary isolation coal bodies are not permanent coal pillars; they require secondary recovery after the adjacent areas have stabilized. By setting up temporary isolation coal bodies, the stability of the recovery process can be improved, resource loss reduced, and the coal resource recovery rate increased.

[0034] S3. Based on the stress distribution of the coal pillar and the location of the goaf boundary, directional stress relief structures are arranged on the high-stress side of the coal pillar, the side adjacent to the goaf, or the side adjacent to the roadway. The directional stress relief structures include one or more of the following: stress relief boreholes, slotted grooves, pre-splitting hole groups, and weakening hole groups. The stress relief boreholes are arranged along the strike, dip, or height of the coal pillar, with a diameter of 42mm to 150mm, a depth of 30% to 90% of the coal pillar width, and a spacing of 0.5m to 3m. Slotted grooves are arranged on the high-stress side of the coal pillar, the side adjacent to the goaf, the top coal area, or the bottom coal area, with a depth of 0.3m to 3m, to create weak stress-relieving surfaces.

[0035] S4. Arrange advanced and temporary supports in front of and on both sides of the unit to be recovered to form a pre-recovery support control zone. The advanced and temporary supports include at least three of the following support methods: anchor bolts, anchor cables, single hydraulic props, π-shaped steel beams, hydraulic supports, telescopic supports, side protection plates, and anti-fracture netting. The advanced support zone is arranged within a range of 5m to 50m in front of the recovery work area.

[0036] S5. Following the progression from low-stress recovery units to high-stress recovery units, the recovery units are divided into short-step segments for recovery. The single-step advance length for each short-step segment is 1m to 10m. After each advance, support reinforcement or surrounding rock condition testing is performed.

[0037] Specifically, the order of recycling is determined as follows: (a) Prioritize the recovery of low-stress recovery units; (b) Delay the recovery of recovery units located near the boundaries of goaf areas, high stress concentration areas, or structural fracture zones; (c) Two adjacent recycling units do not recycle simultaneously or consecutively; (d) The next recovery unit is recovered after the previous recovery unit has been supported or filled.

[0038] S6. Monitor relevant data during the recovery process in real time, and dynamically adjust the recovery step distance, cutting depth, support density, and directional pressure relief parameters based on the monitoring data. Specifically, the monitoring data includes at least three of the following: internal stress of the coal pillar, roof subsidence, roof delamination, sidewall convergence, floor heave, support working resistance, anchor cable stress, frequency of micro-seismic events, gas concentration, and wind speed.

[0039] When the amount of roof delamination, the increase in support working resistance, the increase in internal stress of the coal pillar, or the roadway convergence rate exceeds the corresponding preset threshold, one or more of the following measures shall be implemented: (a) Reduce the recovery step distance; (b) Reduce the depth of a single cut; (c) Increase support density; (d) Supplement with pressure relief drilling; (e) Add temporary support; (f) Suspend the recycling of high-risk recycling units.

[0040] The formula for calculating the tunnel convergence rate is as follows: ; In the formula, This indicates the convergence rate of the tunnel cross section, in mm / d. express The net spatial distance between measuring points in the roadway at any given time (initial cross-sectional distance), in mm; Indicates the last monitoring The net spatial distance between measuring points in the tunnel at any given time, in mm; This indicates the relative convergence of the surrounding rock of the roadway within the interval between two monitoring sessions, in mm. This indicates the time interval between two monitoring sessions, expressed in days (d).

[0041] S7. After a recycling unit is completed, temporary support, pressure relief support, filling, or sealing isolation treatment shall be carried out on the corresponding mined-out space. The support includes an advance support zone, a recycling operation support zone, and a delayed stabilization support zone arranged sequentially along the recycling direction. Filling includes one or more of the following: partial filling, gangue filling, paste filling, high-moisture material filling, and foamed concrete filling.

[0042] S8. When the adjacent recovery unit has completed support or filling and the surrounding rock deformation rate is lower than the preset stability threshold, the temporary isolation coal body between the adjacent recovery units shall be recovered for a second time.

[0043] Specifically, after the adjacent recycling unit completes the recycling operation and the support or filling treatment, the deformation parameters of the surrounding rock in the recycling area are continuously obtained through the monitoring feedback module.

[0044] The surrounding rock deformation parameters include at least three of the following: roof subsidence, sidewall convergence, floor heave, support resistance, and internal stress change of the coal pillar.

[0045] The deformation rate of the surrounding rock was calculated based on continuous monitoring data. ; in: The deformation rate of the surrounding rock; For the first The corresponding deformation or resistance force of the surrounding rock at the time of the next monitoring; For the first The corresponding deformation or resistance force of the surrounding rock at the time of the next monitoring; and These represent the two monitoring times.

[0046] The surrounding rock is considered to have entered a stable stage when one or more of the following conditions are met: (1) The rate of roof sinking is lower than the set threshold; (2) The approach rate of the two sides is lower than the set threshold; (3) The rate of increase in support resistance is lower than the set threshold; (4) The stress changes inside the coal pillar tend to stabilize.

[0047] The preset stability thresholds for the roof subsidence rate, the lateral approach rate, and the support resistance growth rate are determined based on the mine's coal seam occurrence conditions, roof and floor lithology, coal pillar size, and historical monitoring data. When the continuous monitoring time reaches 24h to 72h, and the surrounding rock deformation parameters do not exceed the corresponding stability thresholds, the adjacent recovery unit is determined to have reached a stable state.

[0048] Once the stability criteria are met, the temporary isolated coal body between adjacent recovery units is recycled a second time.

[0049] If, during the monitoring process, the rate of roof subsidence increases, the rate of approach between the two sides increases, the support resistance rises rapidly, or the stress inside the coal pillar reconcentrates, then the secondary recovery of the temporarily isolated coal body should be stopped, and the support reinforcement or directional decompression treatment should be carried out again.

[0050] The present invention also provides a coal pillar working face recovery system based on isolated coal body and directional pressure relief, comprising the following modules: The detection and evaluation module is used to detect the coal pillar to be recovered and its adjacent roadways, goaf, and roof and floor, and to obtain the coal pillar size, coal seam thickness, roof and floor lithology, goaf boundary, coal pillar stress distribution, roadway deformation state, roof stability, and gas occurrence state.

[0051] The recovery unit division module is used to divide the coal pillar to be recovered into multiple recovery units based on the data obtained by the detection and evaluation module, and to determine the location and size of the temporary isolation coal body. Specifically, the recovery unit division module generates a recovery unit layout diagram based on the coal pillar stress distribution, roof stability, goaf proximity, and roadway deformation state, and divides the coal pillar to be recovered into multiple recovery units according to the recovery unit layout diagram.

[0052] The directional pressure relief module is used to form a directional pressure relief structure on the high-stress side of the coal pillar, the side adjacent to the goaf, or the side adjacent to the roadway, based on the stress distribution of the coal pillar and the location of the goaf boundary. Specifically, the directional pressure relief module includes a drilling device, a slotting device, a borehole positioning device, and a pressure relief parameter recording device. The drilling device is used to drill pressure relief boreholes, the slotting device is used to arrange the slots, the borehole positioning device is used to position each borehole, and the pressure relief parameter recording device is used to record the pressure relief parameters.

[0053] The segmented recycling module is used to perform short-step segmented recycling of each recycling unit according to a preset recycling sequence.

[0054] The dynamic support module is used to support the roof, side walls and goaf before, during and after recovery. The support includes an advance support zone, a recovery operation support zone and a delayed stabilization support zone arranged sequentially along the recovery direction. The advance support zone is located within 5m to 50m in front of the recovery operation zone.

[0055] Specifically, the dynamic support module includes advanced support components, work area support components, and delayed support components.

[0056] The monitoring and feedback module is used to monitor relevant data in the recovery process in real time, including at least three of the following: internal stress of the coal pillar, roof subsidence, roof delamination, sidewall movement, floor heave, support working resistance, anchor cable stress, frequency of micro-seismic events, gas concentration, and wind speed.

[0057] Specifically, the monitoring feedback module includes at least three of the following: stress sensor, roof delamination meter, roadway convergence meter, support pressure sensor, anchor cable force gauge, gas sensor, microseismic sensor, and data acquisition terminal.

[0058] The parameter adjustment module is used to adjust the recovery step distance, cutting depth, support density, and decompression parameters based on the data monitored by the monitoring feedback module.

[0059] Specifically, the parameter adjustment module includes a risk assessment unit, a parameter correction unit, and an early warning output unit. The risk assessment unit is used to determine whether the recovery unit meets the conditions for continued recovery, and the parameter correction unit is used to generate adjustment instructions for the recovery step distance, support density, and pressure relief hole parameters.

[0060] The goaf treatment module is used to support, fill, or seal off the goaf space formed after recovery.

[0061] Example 1: Segmented Recovery of Coal Pillars like Figure 2-5 The diagram shows the overall layout of the coal pillar working face, including the first working face 1, the second working face 2, and the third working face 3 arranged sequentially. Solid coal 7 is located on one side of the first working face 1 and the third working face 3. A section of coal pillar is left between two roadways in a certain mine, with one side of the coal pillar adjacent to the goaf 10. The stability of the coal pillar is first evaluated using methods such as borehole inspection, stress testing, roof delamination observation, and roadway convergence observation.

[0062] Based on the evaluation results, the coal pillar is divided into multiple recovery units along the direction. The recovery units include the first recovery unit 4, the second recovery unit 5, and the third recovery unit 6. Each recovery unit includes a coal pillar 8 to be recovered. A temporary isolation coal body 9 is reserved between two adjacent recovery units. The temporary isolation coal body 9 is not mined in the early stage of recovery and is used to form a phased bearing structure between adjacent recovery units.

[0063] Pressure relief boreholes 12 are arranged on the side adjacent to the goaf. The pressure relief boreholes 12 are arranged along the coal pillar strike, and the spacing between the boreholes is determined according to the width of the coal pillar, the strength of the coal body, and the degree of stress concentration. If necessary, slotted grooves 13 are set on the high-stress side of the coal pillar to create a weakening zone in the local coal pillar.

[0064] Advance and temporary support are provided in front of and on both sides of the current recovery unit 15. Specifically, advance support is provided by using anchor cables and anchor bolts 14, support is provided by using movable supports 16 for the work area, and lag support components 17 are used for lag support, forming an advance support area, a work area support area, and a lag stability area.

[0065] During recovery, priority is given to recovering units that are far from the goaf and have lower stress. Each recovery unit is advanced using a short-step approach. After each short-step recovery is completed, temporary support or support reinforcement is immediately implemented.

[0066] Once the first recovery unit has completed support or partial filling, and the roof subsidence rate and roadway convergence rate are below preset thresholds, the adjacent second recovery unit is then recovered. After both adjacent recovery units have stabilized, a secondary recovery zone 11 is formed, and the temporary isolation coal seam between them is recovered a second time.

[0067] Example 2: Coal pillar recovery in adjacent goaf areas For coal pillars adjacent to goaf areas, the goaf side is significantly affected by overlying rock movement, making stress concentration more likely. Before recovery, slotted grooves 13 and pressure-relieving boreholes 12 sets are first arranged on the side adjacent to the goaf area.

[0068] The slotted groove 13 is arranged along the coal pillar direction, and the pressure relief borehole 12 is located inside the slotted groove, forming a directional pressure relief structure of "slotted groove 13 - pressure relief borehole 12 - recovery unit". This structure is used to weaken the continuity of high-stress coal body on the goaf side, making the stress release direction more controllable.

[0069] The recovery sequence proceeds gradually from the stable side of the roadway towards the goaf side. High-risk recovery units near the goaf boundary are recovered later. If a significant increase in roof delamination, support resistance, or the frequency of microseismic events is detected, the recovery unit operation is suspended, and supplementary pressure relief or reinforced support measures are implemented.

[0070] Example 3: Recovery of Coal Pillars with Partial Filling like Figure 4 As shown, under the condition that a large void is formed after the coal pillar is recovered or the roof is broken, a filling retaining wall is immediately set up after each recovery unit is completed, and the recovery space is partially filled 18 by injecting gangue, paste, high water content material or foam concrete.

[0071] The filling area can be the entire recovery space, or only a local area near the roadway side, goaf side, or roof fracture zone. After filling is completed, roof displacement and support resistance continue to be monitored. Once the deformation stabilizes, the adjacent temporary isolation coal seam 9 is then recovered.

[0072] This embodiment is applicable to coal pillar recovery scenarios where the roof is fractured, adjacent roadways are sensitive to deformation, or the goaf has a strong impact.

[0073] Therefore, the coal pillar recovery method and system based on isolated coal body and directional pressure relief described above can reduce stress concentration and roof instability risk during the coal pillar recovery process, and improve the coal pillar recovery rate and recovery operation safety.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for recovering coal pillars at working faces based on isolated coal seams and directional pressure relief, characterized in that, Includes the following steps: S1. Detect the coal pillar to be recovered and its adjacent roadways, goaf and roof and floor to obtain the coal pillar size, coal seam thickness, roof and floor lithology, goaf boundary, coal pillar stress distribution, roadway deformation state, roof stability and gas occurrence state. S2. Based on the data obtained in S1, the coal pillar to be recovered is divided into multiple recovery units, and a temporary isolation coal body is reserved between two adjacent recovery units; S3. Based on the stress distribution of the coal pillar and the location of the goaf boundary, directional stress relief structures are arranged on the high stress side of the coal pillar, the side adjacent to the goaf, or the side adjacent to the roadway. S4. Arrange advanced and temporary supports in front of and on both sides of the unit to be recovered to form a support control zone before recovery. S5. Perform short-step segmented recovery of the recovery units in the order of progress from low-stress recovery units to high-stress recovery units. S6. Monitor relevant data during the recovery process in real time, and dynamically adjust the recovery step distance, cutting depth, support density and directional pressure relief parameters based on the monitoring data; S7. After a recycling unit has completed recycling, the corresponding goaf space shall be temporarily supported, pressure-relief supported, filled or sealed off. S8. When the adjacent recovery unit has completed support or filling and the surrounding rock deformation rate is lower than the preset stability threshold, the temporary isolation coal body between the adjacent recovery units shall be recovered for a second time.

2. The coal pillar recovery method based on isolated coal body and directional pressure relief according to claim 1, characterized in that: The coal pillar to be recovered is divided into multiple recovery units, including: Based on the coal pillar size, coal body strength, internal stress distribution of the coal pillar, influence range of the goaf, and stability parameters of the roof and floor, the risk zone of the coal pillar to be recovered is divided. Based on the risk zone classification results, multiple recovery units are determined along the strike or dip direction of the coal pillar, with priority given to recovering low-stress areas and delaying the recovery of high-stress concentrated areas. The width of a single recycling unit ranges from 2m to 12m, and the width of a temporary isolation coal body ranges from 0.5m to 5m.

3. The coal pillar recovery method based on isolated coal body and directional pressure relief according to claim 1, characterized in that: The directional pressure relief structure includes one or more of the following: pressure relief boreholes, slotted grooves, pre-splitting hole groups, and weakening hole groups. The pressure relief boreholes are arranged along the strike, dip, or height of the coal pillar, while the slotted grooves are arranged on the high-stress side of the coal pillar, the side adjacent to the goaf, the top coal area, or the bottom coal area.

4. The coal pillar recovery method based on isolated coal body and directional pressure relief according to claim 1, characterized in that: When performing short-step segmented recovery of a recovery unit, adjacent recovery units are not recovered simultaneously and continuously. The next recovery unit is recovered only after the previous recovery unit has completed its support or filling.

5. The coal pillar recovery method based on isolated coal body and directional pressure relief according to claim 1, characterized in that: Advanced support and temporary support include at least three of the following support methods: anchor bolts, anchor cables, single hydraulic props, π-shaped steel beams, hydraulic supports, telescopic supports, side protection plates, and anti-slab mesh.

6. The coal pillar recovery method based on isolated coal body and directional pressure relief according to claim 1, characterized in that: The monitoring data includes at least three of the following: internal stress of the coal pillar, roof subsidence, roof delamination, sidewall convergence, floor heave, support working resistance, anchor cable stress, frequency of microseismic events, gas concentration, and wind speed.

7. The coal pillar recovery method based on isolated coal body and directional pressure relief according to claim 1, characterized in that: The deformation rate of the surrounding rock is lower than the preset stability threshold, which includes at least one of the following: the roof subsidence rate, the approach rate of the two sides, and the support resistance growth rate being lower than the corresponding threshold.

8. A coal pillar working face recovery system based on isolated coal body and directional pressure relief, and a coal pillar working face recovery method based on isolated coal body and directional pressure relief according to any one of claims 1-7, characterized in that, Includes the following modules: The detection and evaluation module is used to detect the coal pillar to be recovered and its adjacent roadways, goaf and roof and floor, and to obtain the coal pillar size, coal seam thickness, roof and floor lithology, goaf boundary, coal pillar stress distribution, roadway deformation state, roof stability and gas occurrence state. The recycling unit division module is used to divide the coal pillar to be recycled into multiple recycling units based on the data obtained by the detection and evaluation module, and to determine the location and size of the temporary isolation coal body; The directional pressure relief module is used to form a directional pressure relief structure on the high-stress side of the coal pillar, the side adjacent to the goaf, or the side adjacent to the roadway, based on the stress distribution of the coal pillar and the location of the goaf boundary. The segmented recycling module is used to perform short-step segmented recycling of each recycling unit according to a preset recycling sequence; The dynamic support module is used to support the roof, side walls, and goaf before, during, and after recovery. The monitoring and feedback module is used to monitor relevant data in the recovery process in real time, including at least three of the following: internal stress of the coal pillar, roof subsidence, roof delamination, sidewall movement, floor heave, support working resistance, anchor cable stress, frequency of micro-seismic events, gas concentration, and wind speed. The parameter adjustment module is used to adjust the recovery step distance, cutting depth, support density, and decompression parameters based on the data monitored by the monitoring feedback module. The goaf treatment module is used to support, fill, or seal off the goaf space formed after recovery.

9. The coal pillar recovery system based on isolated coal body and directional pressure relief according to claim 8, characterized in that: The dynamic support module includes an advance support component, a working area support component, and a delayed support component, which are arranged sequentially along the coal pillar recovery direction.

10. The coal pillar recovery system based on isolated coal body and directional pressure relief according to claim 8, characterized in that: The parameter adjustment module includes a risk assessment unit, a parameter correction unit, and an early warning output unit. The risk assessment unit is used to determine whether the recovery unit meets the conditions for continued recovery, and the parameter correction unit is used to generate adjustment instructions for the recovery step distance, support density, and pressure relief hole parameters.

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