Method for preventing and controlling rock burst in coal pillar area of stop line in slicing mining of extra-thick coal seam

Abstract

The application relates to the technical field of coal mining engineering, and discloses a method for preventing and treating rock burst in a coal pillar area of a stop-mining line in layer-by-layer mining of an extra-thick coal seam, which comprises the following steps: constructing pressure-relief holes and blasting holes in the peripheral boundary of an air-returning crossheading tunnel to form a pressure-relief space and cut off a stress transmission path; performing primary-stage blasting to construct a foundation pressure-relief zone; performing middle-stage blasting to promote cracks to penetrate into the deep part of the coal body and expand the range of a plastic zone; performing high-stage deep-hole blasting to cut off the continuous medium between the thick and hard rock layer above a goaf and the coal pillar of the stop-mining line, so that the advanced support pressure is forced to shift to the deep part of the goaf; and implementing alternate blasting along the time axis of the blasting to convert impact kinetic energy into multiple small-energy release events, so that micro-cracks are connected into a continuous stress release zone. Through the change of the mechanical properties of the coal and rock body and the distribution of the advanced support pressure, a stable pressure protection zone is formed in front of the working face, high stress is blocked from being conducted to the tunnel, and the hidden danger of rock burst is eliminated.

Description

Technical Field

[0001] This application relates to the field of coal mining engineering technology, specifically a method for preventing rockburst in the coal pillar area of ​​the stop mining line in layered mining of extra-thick coal seams. Background Technology

[0002] During the layered mining of extra-thick coal seams, when the longwall face advances to the stop-mining line area, the coal pillar area at the stop-mining line will experience extremely high concentrated stress due to the combined effects of the advance support pressure ahead of the longwall face and the lateral thrust of the goaf. Under the load of the overlying strata, this high-stress environment can easily induce instantaneous failure of the surrounding rock and release a large amount of energy, resulting in rockburst disasters and causing severe floor heave, side heave, and a sharp reduction in cross-section in the return airway.

[0003] For rockburst prevention in coal pillar areas of closed mining lines, existing technologies typically employ localized decompression and support methods. Common on-site construction techniques mainly include drilling single large-diameter decompression boreholes in the coal seam of the return airway, utilizing the borehole space to cause deformation of the surrounding coal seam to reduce local stress, or carrying out shallow-hole coal seam blasting in the roadway sidewalls to weaken the physical and mechanical strength of the surface coal and rock mass. Simultaneously, on-site engineering utilizes anchor wire mesh and steel canopy support structures to bear the load of the surrounding rock in order to maintain the basic passage and ventilation cross-section of the roadway during mining.

[0004] Existing conventional local decompression technology only changes the mechanical properties of the shallow coal and rock mass in the roadway. It fails to sever the physical and mechanical continuity between the thick, hard rock layer above the goaf and the coal pillar of the stop line. As a result, the huge advance support pressure generated by the overhanging rock layer above can still be smoothly transmitted and superimposed on the surrounding rock area of ​​the return air roadway. It cannot force the high-concentration stress peak to be substantially transferred to the depth of the goaf. As a result, the roadway is always under the direct control of the high stress transmission path, making it difficult to eliminate the hidden danger of rockburst caused by stress concentration from the source. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this application provides a method for preventing rockbursts in the coal pillar area of ​​the stop mining line in layered mining of extra-thick coal seams, which solves the problems mentioned in the background technology.

[0006] To achieve the above objectives, this application provides the following technical solution: a method for preventing rockburst in the coal pillar area of ​​a stop-mining line in layered mining of extra-thick coal seams, comprising constructing pressure relief holes and blasting holes in the cross-section of the return air roadway, constructing large-diameter stress relief holes in the coal body on both sides of the return air roadway, constructing large-diameter pressure relief holes in the floor of the return air roadway, constructing roof blasting holes inside the roof, and constructing coal body blasting holes inside the coal body. The large-diameter stress relief holes in the coal body and the large-diameter pressure relief holes in the floor form a pressure relief space, and the blasting holes are used as pre-designed weak surfaces to cut off the stress transmission path of the continuous medium.

[0007] Initial blasting is performed to construct the basic stress relief zone. Small amounts of explosives are placed inside the coal seam blasting holes and roof blasting holes for initial blasting, creating initial fractures within the surface coal and rock mass. The continuous structure within the surface coal and rock mass is physically weakened by the cutting action of these initial fractures, reducing the equivalent elastic modulus of the surface coal and rock mass. The walls of the large-diameter stress relief holes in the coal seam deform inwards under pressure, releasing stress. The deformation of the hole walls, combined with the initial fractures, produces a plastic softening effect, constructing an initial plastic zone around the roadway, forming the basic stress relief zone.

[0008] Intermediate-order blasting is employed to expand the plastic zone. As the longwall face advances, intermediate-order blasting procedures are carried out inside the coal seam blast holes, with the charge and borehole depth increased in stages. Different types of delayed-action detonators are used to achieve phased detonation, resulting in a stepped spatial distribution of the total energy released by the blast. The expansion force of the explosive gases and the detonation shock wave act alternately on the coal and rock mass surrounding the foundation decompression zone, causing the initial fractures to penetrate and extend deeper into the coal seam. These penetrating fractures intersect and merge, cutting continuous rock strata into discontinuous rock blocks, causing the plastic zone boundary to extend radially from the initial plastic zone into the deeper coal and rock mass, reducing concentrated stress peaks.

[0009] High-order deep-hole blasting is used to cut through thick, hard rock strata. When the longwall face advances to the area threatened by the overhanging roof of the goaf, the roof blasting holes with the designed maximum depth are detonated simultaneously at the same level. The strong shock wave generated by the concentrated detonation cuts off the continuous medium between the thick, hard rock strata above the goaf and the coal pillar of the stop line, forcing the cantilevered thick, hard rock strata to fracture. The fracture of the thick, hard rock strata causes the suspended load borne by the coal pillar of the stop line to lose its continuous transmission medium, and the advance support pressure leaves the roadway area and transfers to the depth of the goaf. The peak displacement of the support pressure caused by the initial, intermediate, and high-order deep-hole blasting accumulates, causing the peak position of the advance support pressure to shift outwards towards the depths away from the roadway wall, forming a stress-relieving zone in the space surrounding the roadway, thus constituting a pressure-stabilizing protection zone.

[0010] Alternating blasting is employed to release energy throughout the blasting operation timeline, alternating multiple rounds of coal body and roof blasting to convert impact kinetic energy into multiple small energy release events. The combined disturbance generated by alternating blasting causes micro-fractures within the coal and rock mass to repeatedly expand and connect with large-diameter stress relief pores in the coal body, forming structurally weak surfaces within the coal and rock mass and connecting them to form a continuous stress relief zone. This continuous stress relief zone exhibits nonlinear pressure relief characteristics; when the surrounding rock is subjected to mining-induced stress disturbance, the micro-fractures close and the structurally weak surfaces undergo plastic slippage. The closure of micro-fractures and plastic slippage generate deformation strain, which, through the increase in the equivalent plastic softening coefficient and the expansion of the equivalent strain, jointly reduces dynamic stress, dissipating mining-induced stress within the continuous stress relief zone and maintaining the stability of the roadway cross-section.

[0011] This application provides a method for preventing rockbursts in the coal pillar area of ​​the cessation line during layered mining of extra-thick coal seams. It has the following beneficial effects: 1. This application constructs a three-dimensional pressure relief network by building pressure relief holes and blasting holes around the roadway perimeter, thus cutting off the stress transmission path. Combined with high-order deep-hole concentrated blasting, this severs the continuous medium between the thick, hard rock strata in the goaf and the coal pillar at the stop line, forcing the advance support pressure to shift deeper into the goaf. The multi-stage blasting causes the peak displacement of the support pressure to accumulate, causing the peak support pressure position to shift further away from the roadway wall, forming a gently sloping pressure-stabilizing protective zone in front of the working face, preventing high stress from being transmitted into the roadway and eliminating the potential for impact damage.

[0012] 2. This application alters the frequency of kinetic energy release by alternately executing multiple rounds of coal seam blasting and roof blasting. Alternating operations transform accumulated impact kinetic energy into multiple small energy release events, preventing the dynamic manifestation of instantaneous roof collapse. The combined blasting disturbance promotes the expansion of micro-fractures within the rock mass, connecting them with stress relief pores to form a continuous stress relief zone. When the surrounding rock is disturbed by mining, the stress relief zone utilizes fracture closure and plastic slippage on weak surfaces to generate deformation strain, absorbing and dissipating the mining kinetic energy within the structure, thus maintaining the stability of the roadway cross-section.

[0013] 3. This application achieves multi-level control of the stress field by implementing a progressive blasting process from shallow to deep, increasing the hole depth and charge amount in stages. The initial blasting creates surface fissures to construct a basic stress relief zone, reducing the elastic modulus of the surrounding rock. The intermediate blasting uses explosive gases to drive the fissures deeper, cutting the rock strata into discontinuous blocks. The stepped release of blasting energy causes the boundary of the plastic zone to extend radially deeper, reducing concentrated stress peaks. This gradient modification alters the mechanical properties of the coal and rock mass, providing deformation buffer space and controlling roadway floor heave deformation. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating the method for preventing rockbursts in the coal pillar area of ​​the cessation line in the layered mining of extra-thick coal seams, as described in this application. Figure 2 This is a schematic diagram of the full-section multi-dimensional pressure relief borehole layout for the rockburst prevention method in the coal pillar area of ​​the cessation line of the layered mining of extra-thick coal seams in this application. Detailed Implementation

[0015] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0016] Example: Please see the appendix Figure 1- Appendix Figure 2 This application provides a method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams, including the following steps: S100 involves constructing pressure relief holes and blasting holes in the cross-section of the return air roadway. Large-diameter stress relief holes for the coal body are constructed on both sides of the return air roadway, and large-diameter pressure relief holes for the floor are constructed on the floor of the return air roadway. Blasting holes are also constructed in the roof and inside the coal body. These large-diameter stress relief holes in the coal body and the large-diameter pressure relief holes in the floor create a pressure relief space. The blasting holes are used as pre-designed weak surfaces to cut off the stress transmission path of the continuous medium.

[0017] S200 performs initial blasting to construct the basic pressure relief zone. Explosives are placed inside the blasting holes in the coal seam and roof to carry out initial blasting, generating initial fractures in the surface coal and rock mass and constructing an initial plastic zone to form the basic pressure relief zone.

[0018] S300 uses intermediate-level blasting to expand the plastic zone. As the longwall face advances, the depth of the blast holes and the amount of explosives per hole are increased. The gas expansion force and detonation shock wave are used to promote the penetration and expansion of the initial fractures into the deeper part of the coal body, reducing the peak value of concentrated stress.

[0019] The S400 employs advanced deep-hole blasting to cut through thick, hard rock strata. When the longwall face advances to the area threatened by the goaf, concentrated blasting is performed on the roof blasting holes to cut off the continuous medium between the thick, hard rock strata above the goaf and the coal pillar at the stop line, forcing the advance support pressure to transfer deeper into the goaf.

[0020] S500 employs alternating blasting to release energy. Along the construction timeline from S200 to S400, multiple rounds of coal seam blasting and roof blasting are performed alternately, converting impact energy into multiple small-energy release events. This causes micro-fractures and large-diameter stress release holes in the coal seam to connect, forming a continuous stress release zone. This isolates the direct effect of mining stress on the return airway roadway, ensuring the safety of the return airway roadway cross-section.

[0021] After establishing the S100 multi-dimensional stress relief network and achieving spatial stress cutoff, a detailed discussion is given regarding the spatial arrangement, mechanical deformation behavior, and stress deflection paths of various types of differentiated boreholes. The three-dimensional stress cutting of various types of differentiated boreholes is specifically achieved through the following sub-steps of S100: S101 employs four types of differentiated boreholes across the entire cross-section of the roadway. Large-diameter stress relief boreholes for coal seams, large-diameter pressure relief boreholes for the floor, roof blasting boreholes, and coal seam blasting boreholes are simultaneously deployed along the return airway cross-section. The diameter of the large-diameter stress relief boreholes for coal seams is set at 150 mm, and they are arranged horizontally or alternately at a downward dip angle of 0 to 15 degrees along the sidewalls of the return airway. The diameter of the large-diameter pressure relief boreholes for the floor is set at 150 mm, and they are arranged perpendicular to the floor of the return airway downwards or obliquely downwards towards the goaf. The depth of the large-diameter pressure relief boreholes for the floor is determined based on the depth of the floor heave slip line. The diameter of the roof blasting boreholes is set at 75 mm, and the depth is set at 45 meters, and they are arranged obliquely upwards towards the working face and above the goaf in thick, hard rock strata. The diameter of the coal seam blasting boreholes is set at 42 mm, and they are arranged between adjacent large-diameter stress relief boreholes for coal seams. For the adjustment of drilling rig parameters and the connection of drill rods, those skilled in the art can select conventional construction techniques based on the hardness of the surrounding rock at the site. The adjustment of drilling rig parameters and the connection of drill rods are well-known technologies in this field and will not be described in detail in the specification.

[0022] S102 utilizes the stress release effect of borehole wall failure and deformation in large-diameter boreholes. After the construction of large-diameter stress release holes in the coal seam and large-diameter pressure relief holes in the floor, the borehole walls are subjected to static high ground stress caused by the supporting pressure from the working face and the lateral thrust. When the external load exceeds the strength of the coal and rock mass, the surrounding rock of the borehole walls of the large-diameter stress release holes in the coal seam and large-diameter pressure relief holes in the floor undergoes shear failure, and the surrounding rock undergoes geometric deformation towards the internal holes, thereby generating a local low-stress zone around the large-diameter borehole group, achieving deformation relief control of the roadway sides and floor. As the effective residual cross-sectional area of ​​the large-diameter boreholes decreases, volume release occurs around the boreholes. The superposition effect of volume release causes the surrounding rock to produce an equivalent plastic softening effect, thereby maintaining a local mechanical equilibrium.

[0023] S103 utilizes blasting holes to deflect and guide the stress transmission path. Under unrelieved conditions, the pre-support stress ahead of the working face is smoothly transmitted within the continuous surrounding rock medium. Roof blasting holes and coal blasting holes form a discontinuous physical interface within the surrounding rock. After introducing roof and coal blasting holes, the principal stress transmission path is truncated at the physical interface. Because the free surface of the physical interface cannot transmit normal tensile stress and its shear transmission capacity is reduced, the principal stress path is forced to deflect at the axial edges of the roof and coal blasting holes. The stress intensity at the crack tips around the blasting holes is affected by normal stress and geometric configuration. By guiding the change in stress direction through roof and coal blasting holes, the concentrated stress that originally tended towards the return airway is deflected along a predetermined dip direction towards the deeper parts of the goaf, providing a guiding interface for weakening the energy of subsequent gradient charging blasting.

[0024] S200 performs initial blasting to construct the foundation stress relief zone, specifically including the following steps: S201 Arrange a group of large-diameter boreholes and blasting holes. At the edge of the return air roadway sidewall, arrange large-diameter stress relief holes in the coal seam at 0.9-meter intervals to construct a group of large-diameter boreholes. Coal seam blasting holes and roof blasting holes are arranged around the group of large-diameter boreholes. For the laying of the blasting busbar and the connection of the initiating equipment, those skilled in the art can implement it according to conventional coal mine blasting procedures. The laying of the blasting busbar and the connection of the initiating equipment are well-known technologies in this field and will not be described in detail in this specification.

[0025] S202. Initial blasting is carried out. A small amount of explosive is loaded into the blasting holes in the coal seam. Permitted emulsion explosives for coal mines are used. The blasting holes in the coal seam are then detonated.

[0026] S203 constructs a basic stress relief zone. The detonation of a small amount of explosive generates stress waves and gas expansion forces. These stress waves induce initial fractures within the surface coal and rock mass. The gas expansion forces drive these initial fractures to extend into the geometric cavities provided by the large-diameter stress relief holes in the coal mass. The continuous structure within the surface coal and rock mass is physically weakened by the cutting action of these initial fractures, reducing the equivalent elastic modulus of the surface coal and rock mass. An initial plastic zone forms in the outer area of ​​the two sides of the return airway roadway within the surface coal and rock mass. The walls of the large-diameter stress relief holes deform inwards under pressure, releasing stress. The deformation of the hole walls, combined with the initial fractures, produces a plastic softening effect, forming the basic stress relief zone. This basic stress relief zone reduces the equivalent resistance of the surrounding rock boundary, providing a deformation buffer space for the radial expansion of the plastic zone during intermediate-order blasting.

[0027] S204 determines the spatial offset and temporal sequence of the initial blasting. Based on the advance distance of the longwall face, the implementation space for the initial blasting is set. The initial blasting is carried out in advance outside the advanced influence zone of the return air roadway, using a small amount of explosives inside the coal seam blast holes to create a basic pressure relief zone. The timing of the blasting energy release is controlled through a modification process that progresses from shallow to deep and from weak to strong, thus forming the basic pressure relief process.

[0028] After constructing the basic stress relief zone, the stress field inside the surrounding rock is controlled in multiple stages through gradient charging and staged blasting. The specific implementation of gradient charging and staged blasting is achieved through the following sub-steps: S301 implements gradient charging and delayed initiation for intermediate-order blasting. As the longwall face advances, intermediate-order blasting is carried out inside the coal seam blasting holes. The intermediate-order blasting increases the charge and borehole depth in gradients. The first charge gradient sets the borehole depth at 20 meters and loads 9 kg of explosive per hole. The second charge gradient sets the borehole depth at 25 meters and loads 12 kg of explosive per hole. A decoupled charge structure is used to maintain a gap between the explosive and the borehole wall to adjust the initial impact pressure of the detonation wave on the borehole wall. During the initiation network deployment, coal seam blasting holes with different charge gradients are connected using millisecond delay detonators of different segments to achieve time-phased initiation.

[0029] S302 regulates the spatial stepped distribution of released energy. Through multi-stage detonation and gradient charge design, the total energy released by the blast exhibits a stepped distribution in the three-dimensional space in front of the working face. The energy released by each blast is determined by the product of the charge amount per hole and the detonation heat of the emulsion explosive. By progressively increasing the charge amount and hole depth, a gradual energy release from shallow to deep is achieved.

[0030] S303 drives the staggered expansion of fractures, cutting through key layers. Under the control of stepped blasting energy, the expansion force of explosive gases and the detonation shock wave act alternately on the coal and rock mass surrounding the foundation stress relief zone. The gas expansion force enters the tip of micro-fractures, driving the initial fractures to penetrate deeper into the coal mass. The continuously penetrating fractures intersect and converge within the coal and rock mass, cutting the original continuous roof key layer into discontinuous rock blocks. The friction and slippage between the discontinuous rock blocks consume the geostress potential energy, reduce the peak stress concentration, and complete the radial expansion of the plastic zone.

[0031] S304 determines the spatiotemporal continuity of intermediate-order blasting and promotes the dynamic expansion of the plastic zone boundary in the surrounding rock. As the longwall face advances, intermediate-order blasting is carried out in stress concentration areas close to the longwall face. The surrounding rock is subjected to progressive dynamic disturbances from the initial and intermediate-order blasting, altering its mechanical equilibrium. With the increase in borehole depth and charge per borehole during intermediate-order blasting, the equivalent resistance force applied to the plastic zone boundary decreases. This decrease in equivalent resistance force causes the plastic zone boundary to expand radially from the initial plastic zone radius into the deeper coal and rock mass, completing the depth expansion process.

[0032] S401 employs high-order deep-hole blasting to cut through thick, hard rock strata. When the longwall face advances to an area threatened by the overhanging roof structure of the goaf and the thick, hard rock strata are in a cantilever state, the high-order deep-hole roof-cutting process is initiated. 45 kg of explosive is loaded into each roof blasting hole, with a designed depth of 45 meters. The detonation network detonates the loaded roof blasting holes in a concentrated manner at the same level. The strong shock wave generated by the concentrated detonation propagates along the pre-designed weak surface direction of the roof blasting holes, cutting off the continuous medium between the thick, hard rock strata above the goaf and the coal pillar of the stop line, forcing the cantilevered thick, hard rock strata to fracture vertically.

[0033] S402 Transfer of advance support pressure alters stress distribution. After the thick, hard rock strata fracture, the suspended load originally borne by the coal pillar of the stop-mining line loses its continuous transmission medium. The advance support pressure leaves the return airway area and transfers deeper into the goaf, changing the stress distribution profile in front of the working face. The fracture of the thick, hard rock strata increases the width of the mechanical stress relief zone deep in the goaf. According to the attenuation law of stress transfer, the increase in the width of the mechanical stress relief zone forces the peak value of the remaining support pressure above the coal pillar to shift outward into the deeper goaf and reduce it to within the safe threshold, eliminating the risk of rockburst in the roadway.

[0034] S403 determines the spatiotemporal continuity of high-order deep-hole blasting and constructs a pressure-stabilizing protection zone. When the longwall face advances to the critical caving step distance of the overhanging roof, high-order deep-hole blasting is carried out simultaneously at the edge of the goaf. High-order deep-hole blasting cuts through the thick, hard rock layer above the goaf, completing the key layer roof-cutting process. The peak displacement of the support pressure caused by the initial, intermediate, and high-order deep-hole blasting accumulates, causing the peak position of the advance support pressure to shift outward towards the deeper part away from the return airway wall. The outward shift of the peak position of the advance support pressure forms a stress-relieving area in the space in front of the longwall face and around the return airway, which constitutes the pressure-stabilizing protection zone. The pressure-stabilizing protection zone blocks the transmission path of high mining stress to the return airway, controlling the deformation of the floor and sidewalls of the return airway.

[0035] Alternating blasting procedures are executed along the construction timeline, encompassing initial-order blasting, intermediate-order blasting, and high-order deep-hole blasting. Alternating blasting procedures alter the energy release frequency and the pressure relief properties of the surrounding rock. The specific implementation method for alternating blasting energy release and generating a dynamic pressure relief response is achieved through the following steps: S501 employs alternating blasting to control the frequency of energy release. During the mining advance of the return air roadway, blasting intervals are set along the advance direction of the return air roadway, alternating between three rounds of coal body blasting and two rounds of roof blasting. The alternating construction of three rounds of coal body blasting and two rounds of roof blasting converts the impact kinetic energy into multiple small energy release events. These multiple small energy release events avoid the concentrated dynamic manifestation caused by the instantaneous collapse of the roof over a long distance.

[0036] The total kinetic energy of the target area satisfies the energy dissipation equation:

[0037] In the energy dissipation equation: The total kinetic energy of the target area is expressed in joules. This refers to the total frequency of alternating blasting and kinetic energy release events; The energy of microseismic events induced by a single alternating blast is expressed in joules. The harmless energy safely dissipated by the plastic deformation of the surrounding rock, measured in joules.

[0038] The maximum magnitude intensity index of a microseismic event satisfies the intensity calculation equation:

[0039] In the strength calculation equation: The magnitude index; Assign uniformity coefficients to spatiotemporal frequencies.

[0040] Adjusting the blasting spacing increases the alternation frequency of coal seam blasting and roof blasting, improves the spatiotemporal frequency distribution uniformity coefficient, and reduces the magnitude intensity index. For the installation of microseismic monitoring equipment and the acquisition of microseismic energy data, those skilled in the art can refer to the coal mine dynamic disaster monitoring specifications. The installation of microseismic monitoring equipment and the acquisition of microseismic energy data are well-known technologies in this field and will not be elaborated further in this specification.

[0041] S502 connects microfractures to construct a continuous stress relief zone. Alternating coal blasting and roof blasting generate combined disturbances. These combined disturbances cause the microfractures within the coal and rock mass to repeatedly expand. After the microfractures connect with the large-diameter stress relief pores in the coal mass, structurally weak surfaces are formed within the coal and rock mass. These structurally weak surfaces connect the fractured zones to form a continuous stress relief zone. This continuous stress relief zone blocks the transmission path of impact energy.

[0042] S503 generates structural stress relief response to dissipate impact kinetic energy. The coal and rock mass in the continuous stress relief zone exhibits nonlinear stress relief characteristics. When the surrounding rock is disturbed by mining stress, the micro-cracks within the continuous stress relief zone close, and the structural weak surfaces undergo plastic slippage. The closure of micro-cracks and plastic slippage generate deformation strain, dissipating the mining stress within the continuous stress relief zone.

[0043] The nonlinear constitutive relation of the continuous stress relief zone satisfies the following equation:

[0044] In the nonlinear constitutive relation equation: The dynamic stress borne by the continuous stress relief zone, measured in megapascals (MPa). This represents the initial elastic modulus of the primary coal and rock mass, expressed in megapascals (MPa). This is the equivalent strain caused by microcrack closure and plastic slip; This represents the limiting equivalent strain corresponding to the peak stress. It is the equivalent plastic softening coefficient generated by the superposition of multidimensional drilling and progressive blasting.

[0045] The increase in the equivalent plastic softening coefficient and the expansion of the equivalent strain together reduce the dynamic stress borne by the continuous stress relief zone. The dynamic deformation of the continuous stress relief zone absorbs the impact kinetic energy, maintains the stability of the return air roadway cross-section, and ensures the safe advancement of the longwall face.

[0046] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams, characterized in that, Includes the following steps: S100. Construct pressure relief holes and blasting holes in the cross-section of the return air roadway, construct large-diameter stress relief holes for coal body on both sides of the return air roadway, construct large-diameter pressure relief holes for the bottom plate of the return air roadway, construct roof blasting holes inside the roof plate and coal blasting holes inside the coal body, utilize the large-diameter stress relief holes for coal body and the large-diameter pressure relief holes for the bottom plate to form a pressure relief space, and utilize the roof blasting holes and coal blasting holes as preset weak surfaces to cut off the stress transmission path of the continuous medium; S200. Perform initial blasting to construct the basic pressure relief zone. Explosives are placed inside the blasting holes in the coal body and the blasting holes in the roof to carry out initial blasting, generating initial fractures in the surface coal and rock mass and constructing an initial plastic zone to form the basic pressure relief zone. S300, Perform intermediate-level blasting to expand the range of the plastic zone. As the longwall face advances, increase the hole depth and single-hole charge of the coal body blasting holes. Utilize gas expansion force and detonation shock wave to cause the initial fractures to penetrate and expand into the deeper part of the coal body, reducing the peak value of concentrated stress. S400. Perform high-order deep-hole blasting to cut thick and hard rock layers. When the mining face advances to the area threatened by the goaf roof, the roof blasting holes are blasted in a concentrated manner to cut off the continuous medium between the thick and hard rock layers above the goaf and the coal pillar of the stop mining line, forcing the advance support pressure to transfer to the depth of the goaf. S500: Implement alternating blasting to release energy, spanning the construction timeline from the initial blasting to the high-order deep-hole blasting. Alternately execute multiple rounds of coal body blasting and roof blasting, converting impact energy into multiple small energy release events. This causes micro-fractures to connect with the large-diameter stress release holes in the coal body to form a continuous stress release zone, isolating the direct effect of mining stress on the return air roadway and ensuring the safety of the return air roadway cross-section.

2. The method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 1, characterized in that, The S100, which involves constructing pressure relief holes and blasting holes in the cross-section of the return air roadway, includes: The large-diameter stress relief holes of the coal body, the large-diameter pressure relief holes of the floor, the blasting holes of the roof, and the blasting holes of the coal body are arranged synchronously in the cross-section of the return air roadway. The diameter of the large-diameter stress relief holes in the coal body is set to 150 mm, and they are arranged horizontally or alternately at a downward inclination angle of 0 to 15 degrees along the sidewall of the return air roadway. The diameter of the large-diameter pressure relief hole in the bottom plate is set to 150 mm, and it is arranged perpendicular to the bottom plate of the return air roadway downward or obliquely downward towards the goaf. The depth of the large-diameter pressure relief hole in the bottom plate is set according to the depth of the bottom drum sliding line of the bottom plate. The diameter of the blasting holes in the roof is set at 75 mm and the depth at 45 m, and they are arranged obliquely upwards towards the working face and above the goaf, in the thick and hard rock layer. The diameter of the coal blasting holes is set to 42 mm, and they are arranged between adjacent large-diameter stress relief holes in the coal body.

3. The method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 2, characterized in that, The stress relief space is formed by utilizing the large-diameter stress relief holes in the coal body and the large-diameter pressure relief holes in the bottom plate, and the stress transmission path of the continuous medium is cut off by using the blasting holes in the roof plate and the blasting holes in the coal body as preset weak surfaces, including: When the external load exceeds the strength of the coal and rock mass, the surrounding rock of the large-diameter stress relief hole of the coal mass and the large-diameter pressure relief hole of the bottom plate undergoes shear failure, and the surrounding rock of the hole wall undergoes geometric deformation into the internal hole, generating a local low-stress zone, thereby achieving deformation pressure control of the roadway sides and bottom plate. As the effective residual cross-sectional area of ​​the borehole decreases, volume release occurs around the borehole. The cumulative effect of volume release causes the surrounding rock of the borehole wall to produce an equivalent plastic softening effect, maintaining a local mechanical equilibrium. After the introduction of the roof blast hole and the coal body blast hole, the principal stress transmission path is cut off at the physical interface. Since the free surface of the physical interface cannot transmit normal tensile stress and the shear transmission capacity is reduced, the principal stress path is forced to deflect at the axial edge of the roof blast hole and the coal body blast hole. By guiding the change in stress direction through the blasting holes in the roof and the coal body, the concentrated stress approaching the return air roadway is deflected towards the depth of the goaf along a preset inclined direction.

4. The method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 1, characterized in that, The S200, which involves performing initial blasting to construct a foundation pressure relief zone, includes: At the edge of the return air roadway, a group of large-diameter stress relief holes for the coal body is constructed by arranging them at 0.9-meter intervals. The coal body blasting holes and the roof blasting holes are arranged around the group of large-diameter boreholes. A small amount of explosive is loaded into the blast hole of the coal body, and the blast hole is detonated after loading. The detonation of the small-quantity explosive generates stress waves and gas expansion forces. The stress waves induce initial fractures within the surface coal and rock mass, and the gas expansion forces drive the initial fractures to extend toward the geometric cavity provided by the large-diameter stress relief holes in the coal mass. The continuous structure inside the surface coal and rock mass is physically weakened under the cutting action of the initial fractures, reducing the equivalent elastic modulus of the surface coal and rock mass and forming an initial plastic zone in the outer area of ​​both sides of the return air roadway. The large-diameter stress relief hole in the coal body is subjected to pressure and deforms into the hole to release stress. The deformation of the hole wall and the initial cracks superimpose to produce a plastic softening effect, forming the basic pressure relief zone.

5. The method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 1, characterized in that, The S300, which involves performing intermediate-level blasting to expand the plastic zone, includes: As the longwall face advances, a mid-level blasting process is carried out inside the blasting holes of the coal seam. The mid-level blasting process gradually increases the amount of explosives and the depth of the borehole. The first charging gradient of the intermediate-level blasting process sets the depth of the coal body blasting hole to 20 meters and fills each hole with 9 kg of explosive; the second charging gradient of the intermediate-level blasting process sets the depth of the coal body blasting hole to 25 meters and fills each hole with 12 kg of explosive. The explosive loading adopts a decoupled loading structure, which retains the gap between the explosive and the hole wall. The coal blasting holes with different loading gradients are connected by millisecond delay detonators of different segments to achieve time-based detonation. Through the design of multi-stage detonation and graded charge, the total energy released by the blast is distributed in a stepped manner in the three-dimensional space in front of the working face.

6. The method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 5, characterized in that, Under the control of the stepped distribution state, the expansion force of the explosive gas and the detonation shock wave act alternately on the coal and rock mass outside the basic pressure relief zone in stages; The expansion force of the explosive gas enters the tip of the micro-fracture, driving the initial fracture to penetrate deep into the coal body. The penetrating fractures intersect and converge inside the coal and rock mass, cutting the original continuous roof key layer into discontinuous rock blocks. As the depth of the blasting holes and the amount of explosive charge per hole increase in the intermediate-level blasting process, the equivalent resistance force applied to the boundary of the plastic zone decreases. The decrease in the equivalent resistance force causes the boundary of the plastic zone to expand radially from the initial plastic zone radius to the depth of the coal and rock mass, thus completing the depth expansion process.

7. The method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 1, characterized in that, The S400, which performs high-order deep-hole blasting to cut through thick and hard rock strata, includes: When the longwall face advances to the area threatened by the goaf roof structure, the high-order deep hole roof breaking process is initiated, and 45 kg of explosives are loaded into each of the roof blasting holes. The designed depth of the roof blasting holes is 45 meters. The detonation network detonates the top blast holes in the same segment in a concentrated manner. The strong shock wave generated by the concentrated detonation propagates along the weak surface direction of the top blast holes, cutting off the continuous medium between the thick hard rock layer above the goaf and the coal pillar of the stop mining line, forcing the cantilevered thick hard rock layer to fracture vertically. After the thick, hard rock layer undergoes a vertical fracture, the suspended load borne by the coal pillar of the stop-mining line loses its continuous transmission medium, the advanced support pressure leaves the return air roadway area and transfers to the depth of the goaf, and the width of the mechanical pressure relief zone at the depth of the goaf increases.

8. The method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 7, characterized in that, The S400, which performs high-order deep-hole blasting to cut through thick and hard rock layers, also includes: When the longwall face advances to the critical collapse step distance of the suspended roof, the high-order deep hole blasting is carried out simultaneously at the edge of the goaf. The cumulative displacement of the peak support pressure caused by the execution of primary blasting, intermediate blasting and high-order deep hole blasting causes the position of the peak support pressure to shift outward toward the deeper part of the return air roadway wall. The outward shift of the peak position of the advanced support pressure forms a stress-relieving area in the space in front of the mining face and around the return air roadway. The stress-relieving area constitutes a pressure-stabilizing protection zone, which blocks the transmission path of high mining stress to the return air roadway.

9. The method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 1, characterized in that, The S500, which implements alternating blasting to release energy, includes: During the mining advance of the return air roadway, the blasting interval is set along the advance direction of the return air roadway, and three rounds of coal body blasting and two rounds of roof blasting are carried out alternately. The alternating construction of the three rounds of coal body blasting and the two rounds of roof blasting transforms the impact energy into the multiple small energy release events; Adjusting the blasting spacing increases the alternation frequency of coal body blasting and roof blasting, improves the spatiotemporal frequency distribution uniformity coefficient, and reduces the magnitude intensity index.

10. A method for preventing rockburst in the coal pillar area of ​​the cessation line in layered mining of extra-thick coal seams according to claim 9, characterized in that, The S500, which implements alternating blasting to release energy, also includes: Alternating coal blasting and roof blasting generate combined disturbances, which cause the micro-fractures inside the coal and rock mass to expand repeatedly. After the micro-fractures connect with the large-diameter stress relief holes in the coal mass, they form structural weak surfaces in the coal and rock mass. These structural weak surfaces connect the fractured areas to form the continuous stress relief zone. The coal and rock mass in the continuous stress relief zone has nonlinear pressure relief characteristics. When the surrounding rock is disturbed by mining stress, the micro-cracks inside the continuous stress relief zone close, and the weak surface of the structure undergoes plastic slip. The closure of the micro-cracks and the plastic slip generate deformation strain, which dissipates the mining stress inside the continuous stress relief zone. The increase in the equivalent plastic softening coefficient and the expansion of the equivalent strain together reduce the dynamic stress borne by the continuous stress relief zone. The dynamic deformation of the continuous stress relief zone absorbs the impact energy, maintains the stability of the return air roadway cross section, and ensures the safe advancement of the longwall mining face.

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