A method for preventing scour in isolated working face roadways

Abstract

This invention discloses a method for preventing rockburst in isolated working faces. It employs a combined approach: multi-layer hydraulic fracturing in the roof of the isolated working face roadway and hydraulic cavity creation in the coal pillars adjacent to the roadway. The hydraulic fracturing increases the fracturing degree of the hard roof, reducing its strength and causing stress to transfer to deeper rock, while simultaneously increasing energy dissipation during far-field dynamic load propagation. The hydraulic cavity creation weakens the mechanical strength of the coal pillars near the roadway, causing roof subsidence and reducing the elastic energy accumulated in the roof near the roadway due to the goaf, thus transferring stress to the coal pillars on the goaf side and preventing the dynamic load generated by roof fracture from propagating through the coal pillars into the roadway. This invention can reduce the energy that can induce rockburst disasters from both dynamic and static load perspectives, lowering the surrounding rock load value of the isolated working face roadway below the rockburst induction threshold, significantly reducing the possibility of rockburst disasters in isolated working face roadways and greatly improving the rockburst prevention effect.

Description

Technical Field

[0001] This invention relates to a method for preventing scour in isolated working faces, specifically a method for improving the scour resistance of isolated working faces by using a combination of hydraulic cavity making and hydraulic slotting to weaken the superimposed dynamic and static loads on the surrounding rock of the roadway. This method belongs to the field of coal mine safety mining technology. Background Technology

[0002] Coal mining in my country is primarily underground. With the increasing depletion of shallow resources, coal mining is gradually extending to deeper underground areas. This leads to increased in-situ stress in coal seams, enhanced mining disturbance, and aggravated rockburst manifestations in coal mine production. Extensive research, both domestically and internationally, has been conducted on the manifestation patterns and disaster mechanisms of rockburst in hard roofs. Rockburst is an instability phenomenon induced when the energy released by the coal-rock system exceeds the energy consumed. Rockburst will not occur when the stress on the coal-rock mass does not exceed its ultimate strength, nor when the rate of elastic energy release in the coal-rock system is less than the rate of energy dissipation during crack propagation. However, mining activities cause a readjustment of stress and energy in the surrounding rock of the mining space. When the static load on the surrounding rock and the dynamic load caused by external dynamic loads exceed the critical load for coal-rock rockburst failure, the coal-rock system becomes unstable and fails, thus inducing rockburst.

[0003] Isolated mining, also known as isolated working face mining, refers to a working face where the surrounding area is a goaf, or where adjacent goafs exist on both sides of the working face roadway. When the overhanging roof above the adjacent goafs is too long, a large amount of elastic energy tends to accumulate. Once it breaks, it will generate a high-energy dynamic load that propagates towards the roadway of the isolated working face. When the surrounding rock of the roadway itself bears a large static load, and the dynamic load propagating to the roadway in the far field is also large, if the superimposed load of the static and dynamic loads approaches the critical value for the occurrence of rockburst, a rockburst disaster may occur.

[0004] Existing technologies for preventing rockbursts mainly fall into four categories: optimizing roadway layout, strengthening support, backfilling for rockburst prevention, and weakening the hard roof. Optimizing roadway layout effectively utilizes the stress-reducing zone of the goaf to reduce the static load on the roadway. Strengthening support, using high-prestressed rock bolts, can effectively control the deformation of the surrounding rock. However, neither of these methods fundamentally solves the high-stress zone in the roof caused by the superposition of dynamic and static loads. While backfilling for rockburst prevention can effectively solve the problem of suspended roofs, it is costly. Therefore, current measures for preventing rockbursts primarily focus on weakening the strength of the hard roof. Traditional roof weakening methods include water injection to weaken the roof, borehole decompression, hydraulic fracturing, and borehole blasting pre-fracturing. Water injection to weaken the roof has significant limitations and is not effective for rock masses with low porosity, low water absorption, and incomplete fracture development. Drilling can reduce the stress concentration of the surrounding coal and rock mass, but the influence range of a single borehole is limited. Hydraulic fracturing cannot effectively evaluate the fracturing effect for roofs with complex structures and lithologies. Drilling and blasting pre-fracturing has a large stress relief range, but the operation is difficult and the dynamic load generated may induce shock pressure. Due to safety and environmental protection restrictions, it is difficult to apply it on a large scale. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preventing rockburst in isolated working face roadways. This method can reduce the energy that can induce rockburst disasters by both dynamic and static loads, thereby reducing the load borne by the isolated working face roadway below the critical value that can induce rockburst disasters, thus improving the rockburst prevention capability of the isolated working face roadway.

[0006] To achieve the above objectives, this method for preventing rock erosion in isolated working face roadways adopts a combined approach: multi-layer hydraulic slit cutting in the roof of the isolated working face roadway and hydraulic cavity creation in the coal pillars of adjacent isolated working face roadways. The specific steps include:

[0007] Step 1: Obtain mine data and conduct on-site sampling, prepare standard samples for experiments, and obtain basic mechanical parameter data, internal porosity data, fracture distribution data, and optimal hydraulic rock breaking technology parameters of the coal seam and surrounding rock of the target fully mechanized longwall face and its goaf.

[0008] Step 2: Based on the mine data from Step 1, construct a finite element model of the load-deformation structure of the adjacent working face goaf-coal pillar-roadway-coal seam to be mined in this working face, and conduct numerical simulation of the target working face mining process. Utilize the mine production data on periodic fracture and collapse of the roof and top coal, coal seam mining stress data, and mine data on roadway surrounding rock deformation and delamination to verify and optimize the parameters of the load-deformation finite element model, forming a simulation model that conforms to the actual production conditions and monitoring data of the mine site. Based on the simulation model, conduct numerical simulation of the working face mining in the subsequent mining plan, calculate the roadway areas with high static load and large stress concentration coefficient, and the roof fracture areas of adjacent goaf areas, and identify the dangerous roadway areas with the risk of rockburst.

[0009] Step 3: Based on the coordinates of the dangerous area of ​​the roadway obtained in Step 2 and the coordinates of the far-field dynamic load source obtained from on-site microseismic monitoring, set up hydraulic cutting and cavity creation combined weakening anti-scour conditions that can meet the roadway anti-scour requirements.

[0010] The diameter, depth, and distribution of hydraulically created cavities satisfy the following conditions:

[0011]

[0012]

[0013] In the formula: L f ,L b These are the depths of the front and rear faces of the cavity, respectively; L R H0 is the hydraulic rock-breaking radius; H2 is the height of the drilling rig; θ1 is the drill rod elevation angle during hydraulic cavity creation; p is the jet pressure; R is the nozzle radius. τ is the internal friction angle of the roof rock; c is the shear strength of the roof rock;

[0014] The number of hydraulic kerfs, kerf diameter, and depth must satisfy the following conditions:

[0015] GF1:L D1 sinθ2-L R cosθ2>H1

[0016]

[0017] In the formula: GF1 is the first hydraulic cut; GF n For the final hydraulic cut; L D1 L is the drill pipe depth for the first hydraulic slotting. Dn θ2 is the drill pipe depth when performing the final hydraulic cut; θ2 is the drill pipe elevation angle when performing the hydraulic cut; L RH1 is the hydraulic rock-breaking radius; H2 is the coal seam thickness; H3 is the roof thickness; m is the width of the coal pillar.

[0018] After the coal pillar is weakened, when the immediate roof settlement height is ΔH, the roof pressure in the slotted area satisfies the following condition:

[0019] F = -(64E3L) Dn cosθH3 3 )ΔH+4qL R 4 / 7L R 3

[0020] In the formula: F is the roof pressure in the slotted area; E3 is the elastic modulus of the immediate roof; H3 is the height of the immediate roof; ΔH is the settlement height of the immediate roof; q is the pressure of the immediate roof on the coal pillar.

[0021] After the combined operation of hydraulic slotting and cavity creation, the energy of the incident and transmitted waves of the dynamic stress wave after encountering the cavity and slots satisfy the following conditions:

[0022]

[0023] In the formula: W I W T These represent the total energy of the incident wave and the transmitted wave under dynamic load, respectively; K is the attenuation rate of the stress wave after passing through the hole. These represent the energies of the incident longitudinal and transverse waves, respectively. The energy of the transmitted longitudinal and transverse waves are represented respectively; A is the area of ​​the unit measuring point; x1 is the distance between the side closer to the source and the source; x2 is the distance between the side farther from the source and the source; ρ is the rock density in the cut region; c P c is the longitudinal wave velocity; s σ1 and τ1 are the normal force and tangential stress of the incident surface, respectively; σ2 and τ2 are the normal force and tangential stress of the transmission surface, respectively.

[0024] Step 4: Based on the simulation model of Step 2 and the combined weakening and anti-scour conditions of hydraulic slotting and cavity creation in Step 3, firstly, in the simulation model, hydraulic slotting is simulated to form multi-layer slots in the roof of the roadway in the dangerous area of ​​the roadway, and hydraulic cavity creation is simulated to form cavities in the coal pillar of the adjacent dangerous area of ​​the roadway. Then, the dynamic load generated by roof failure is simulated at the far-field dynamic load source location, and the numerical simulation of the working face mining of the subsequent mining plan is carried out to obtain the optimal hydraulic slotting and cavity creation combined anti-scour technology parameters that can weaken the dynamic load and reduce the static load.

[0025] Step 5: Based on the optimized hydraulic slotting and cavity-creating combined anti-scouring technology parameters obtained in Step 4, drilling rigs are deployed in the roadway of the target working face of the mine. Drilling is carried out into the roadway roof in the dangerous area of ​​the roadway and the coal pillar in the adjacent dangerous area of ​​the roadway. High-pressure water jets are sprayed out from the jet nozzle at the end of the drill rod and sprayed radially along the drill rod to impact and break the roof rock and coal body. Through the rotation and retraction of the drill rod, multi-layer slots are formed in the roadway roof in the dangerous area of ​​the roadway and columnar cavities are formed in the coal pillar in the adjacent dangerous area of ​​the roadway. This process is repeated to complete the opening of all multi-layer slots and cavities.

[0026] Step 6: Based on the regional and real-time monitoring results of the surrounding rock of the target roadway in the on-site monitoring area, determine the risk of rockburst in the surrounding rock of the target roadway before and after hydraulic cutting and cavity creation. Evaluate and verify the anti-scour effect of hydraulic cutting and cavity creation. For areas where the anti-scour effect does not meet the combined weakening anti-scour condition of hydraulic cutting and cavity creation in Step 3, repeat Step 4 and adjust the optimized hydraulic cutting and cavity creation combined anti-scour technology parameters obtained in Step 4. Based on the adjusted and optimized optimized hydraulic cutting and cavity creation combined anti-scour technology parameters, perform the hydraulic cavity creation operation in Step 5 again until the anti-scour effect meets the combined weakening anti-scour condition of hydraulic cutting and cavity creation in Step 3.

[0027] Furthermore, in Step 2, when performing numerical simulation of the target longwall face mining process, the following steps are taken: First, mine data including the geological conditions and mining conditions of the coal seam in the target longwall face, as well as the basic mechanical parameters, internal porosity data, and fracture distribution data of the coal body and surrounding rock of the target longwall face and its goaf are imported into the load-deformation finite element model. Then, the vertical stress distribution is calculated to obtain the areas with high roof elastic energy density. The mesh is then refined in the areas with high roof elastic energy density. Finally, numerical simulation of the target longwall face mining process is performed to obtain the stress distribution, deformation characteristics, and periodic collapse data of the roof and top coal in the target longwall face and roadway.

[0028] Furthermore, in Step 4, when simulating hydraulic cutting of the roadway roof in the dangerous area of ​​the roadway and simulating hydraulic cavity making of the coal pillar in the adjacent dangerous area of ​​the roadway in the simulation model, the dynamic load weakening zone of the cavity and the multi-layer slot structure is located on the line connecting the far-field dynamic load source and the dangerous area of ​​the roadway.

[0029] Furthermore, in Step 4, when simulating hydraulic cutting of the roadway roof in the dangerous area of ​​the roadway, drilling is carried out near the junction of the roof coal and the coal pillar, and hydraulic cutting is performed. The downward extension range of the first layer of hydraulic cutting does not exceed the junction of the coal pillar and the immediate roof. The coverage range of the multi-layer slots does not exceed the width range of the coal pillar in the adjacent dangerous area of ​​the roadway. The upward extension range of the last layer of hydraulic cutting does not exceed the thickness range of the immediate roof.

[0030] Furthermore, in Step 4, when simulating hydraulic cutting of the roadway roof in the hazardous area, the drill rod elevation angle θ2 during hydraulic cutting satisfies the following condition:

[0031] θ2=arctan[(H1-h0) / l0]

[0032] In the formula: H1 is the coal seam thickness; h0 is the height of the drilling rig; l0 is the distance between the drilling rig and the coal pillar.

[0033] Furthermore, in Step 4, when simulating hydraulic cavity creation for coal pillars in dangerous areas adjacent to roadways, the upward extension range of the cavity does not exceed the interface between the coal pillar and the immediate roof, and the downward extension range of the cavity does not exceed the interface between the coal pillar and the floor.

[0034] Furthermore, in Step 4, when simulating hydraulic cavity creation for coal pillars in dangerous areas adjacent to the roadway, the drill rod elevation angle θ1 during hydraulic cavity creation satisfies the following condition:

[0035] θ1 = arctan(H1m + l0)

[0036] In the formula: H1 is the coal seam thickness; m is the width of the coal pillar; l0 is the distance between the drilling rig and the coal pillar.

[0037] Furthermore, in Step 4, when obtaining the optimal hydraulic slotting and cavity-forming combined anti-scour technology parameters that can weaken dynamic load and reduce static load, the dynamic load attenuation rate, roadway surrounding rock stress-strain change characteristics, and coal pillar area stress transfer characteristics under different parameter conditions are obtained by grouping and numerically simulating different parameters of multi-layer slots and cavities. The main control parameters of hydraulic slotting and cavity-forming combined anti-scour technology parameters are then determined and obtained, forming the optimal hydraulic slotting and cavity-forming combined anti-scour technology parameters.

[0038] Furthermore, in Step 6, when evaluating and verifying the anti-scouring effect of hydraulic slotting and cavity creation, the deformation of the surrounding rock in the roadway is first measured, the deformation of the surrounding rock in the slotted area and the unslotted area is compared, the settlement of the coal pillar roof is measured, the pressure on the coal pillar roof after hydraulic cavity creation is calculated, and the stress concentration level of the surrounding rock is measured by the drill cuttings method. Then, the measured data, theoretical model calculations and numerical simulation calculations are compared and verified.

[0039] Compared with existing technologies, this method for preventing rockburst in isolated working face roadways adopts a combined approach: multi-layer hydraulic cutting in the roof of the isolated working face roadway and hydraulic cavity creation in the coal pillars of adjacent isolated working face roadways. This approach addresses both dynamic and static load aspects of the dynamic-static load superposition induced rockburst theory. Hydraulic cutting increases the degree of fracture in the hard roof of the roadway, reducing its strength and causing stress to transfer to deeper rock, while simultaneously increasing energy dissipation during far-field dynamic load propagation. Hydraulic cavity creation weakens the mechanical strength of the coal pillars near the roadway, causing roof subsidence and reducing the elastic energy accumulated in the roof near the roadway due to the goaf. This transfers stress to the coal pillars on the goaf side, reducing the static load level of the roadway. Simultaneously, the cavities in the coal pillars effectively block the propagation of dynamic loads generated by roof fracture through the coal pillars into the roadway. It can reduce the energy that can induce rockburst disasters from both dynamic and static load aspects, reduce the surrounding rock load value of isolated working face roadways to below the rockburst induction threshold, significantly reduce the possibility of rockburst disasters in isolated working face roadways, and greatly improve the rockburst prevention effect. At the same time, the construction process of hydraulic slotting and hydraulic cavity making is relatively refined and the amount of engineering work is small. The water jet rock breaking technology itself is relatively mature, the process is safe and green and pollution-free, and the construction difficulty is low. It is particularly suitable for improving the rockburst prevention capacity of isolated working face roadways. Attached Figure Description

[0040] Figure 1 This is a top view of the hydraulic cavity-making construction method of the present invention;

[0041] Figure 2 yes Figure 1 A-axis rotated view. Detailed Implementation

[0042] The anti-scour method for the isolated working face roadway adopts a combined anti-scour scheme, which involves multi-layer hydraulic slotting in the roof of the isolated working face roadway and hydraulic cavity creation in the coal pillar of the adjacent isolated working face roadway. The hydraulic cavity creation technology can weaken the coal pillar, settle the roof of the coal pillar, release the elastic energy and static load accumulated in the roof, and at the same time prevent the dynamic load of roof failure from propagating to the roadway through the coal pillar. The hydraulic slotting technology can create a dynamic load attenuation zone between the dynamic load source and the roadway, reduce the dynamic load, increase the degree of roof fragmentation, and at the same time weaken the roof strength so that the stress of the roadway roof is transferred to the deeper rock, thereby reducing the static load level.

[0043] The invention will be further explained below using an isolated working face roadway in a coal mine as an example, in conjunction with the accompanying drawings.

[0044] The anti-scour method for the working face roadway of this isolated island includes the following steps:

[0045] Step 1: Obtain mine data and conduct on-site sampling, prepare standard samples for experiments, and obtain basic mechanical parameter data, internal porosity data, fracture distribution data, and optimal hydraulic rock breaking technology parameters of the coal seam and surrounding rock of the target fully mechanized longwall face and its goaf.

[0046] The average burial depth of the integrated top-coal caving longwall face in this coal mine is 450m, the average coal seam dip angle is 6°, the average coal seam thickness is 7m, the immediate roof thickness is 15.5m, and it is separated from the goaf by a 15m wide coal pillar. The return airway of the longwall face is excavated along the coal floor, with a rectangular cross-section, a height h1 of 3.0m, and a width l1 of 5.0m. The support methods for the return airway are full anchor cable support and single hydraulic prop support. According to the monitoring data analysis, the length of the goaf roof overhang during the target longwall face mining period is between 15 and 35m, and the periodic pressure step distance of the longwall face is 20m.

[0047] To accurately obtain basic mechanical parameters, internal porosity data, and fracture distribution data of the coal seam and surrounding rock in the target fully mechanized longwall face and its goaf, samples of coal body, roof rock, and floor rock were drilled from the working face where the target roadway is located underground in the coal mine. These samples were then transported to a surface laboratory and prepared into standard samples for mechanical testing to obtain the mechanical parameters of the rock numerical model, such as compressive strength, tensile strength, and Poisson's ratio. Specifically, long rock cylinders with a diameter of 50 mm were drilled from the working face to be mined, the roadway roof, the roadway floor, and the coal pillar. These were then processed in the surface laboratory into standard cylindrical samples of different standard sizes, such as Ф50×100 mm and Ф50×250 mm. After grouping the samples, the basic mechanical parameters of the standard samples were obtained using an MTS triaxial loading tester. The porosity and fracture distribution inside the standard samples were tested using a mercury porosimeter and a rock CT scanner, respectively. After testing, the compressive strength of the raw coal standard sample was 14.1 MPa, the tensile strength was 1.0 MPa, the Poisson's ratio was 0.31, and the elastic modulus was 1.1 GPa. The porosity of the raw coal standard sample was 7.8%, the average fracture aperture was 90.1 μm, and the average fracture volume was 2.1 × 10⁻⁶. 7 um 3 The porosity is 0.83%.

[0048] To determine the technical parameters for hydraulic rock breaking, roof and floor rock samples were drilled from the working face of the target roadway in the coal mine and transported to a surface laboratory for water jet slotting experiments. The experiments aimed to determine the technical parameters for hydraulic rock breaking under different lithologies and slotting depth requirements. Specifically, approximately cubic block samples with a volume of not less than 0.1 m³ were selected underground. 3 In the laboratory, the block sample was processed into a cube with a side length of 20cm, and experiments were conducted with different abrasive concentrations, jet pressures, nozzle radii and cutting times to obtain the optimal hydraulic rock breaking technology parameters.

[0049] Step 2: Based on the mine data from Step 1, a finite element model of the load-deformation structure of the adjacent working face goaf-coal pillar-roadway-coal seam to be mined in this working face is constructed using Abaqus. Numerical simulation of the target working face mining process is then performed. The load-deformation finite element model is verified and its parameters are optimized using mine data such as roof and top coal periodic fracture and collapse data, coal seam mining stress data, and roadway surrounding rock deformation and delamination data. This forms a simulation model that conforms to the actual production conditions and monitoring data of the mine site. Based on the simulation model, numerical simulation of the working face mining in the subsequent mining plan is performed. The roadway areas with high static load and high stress concentration coefficient and the roof fracture areas of adjacent goaf areas are calculated, and the dangerous roadway areas with the risk of rockburst are identified.

[0050] When conducting numerical simulation of the target longwall face mining process, the following steps are taken: First, mine data including the geological conditions and mining conditions of the coal seam in the target longwall face, as well as the basic mechanical parameters, internal porosity data, and fracture distribution data of the coal body and surrounding rock in the target longwall face and its goaf are imported into the load-deformation finite element model. Then, the vertical stress distribution of the structure is calculated according to the theory of mechanics of materials to obtain the region with high elastic energy density of the hard roof. The mesh is then refined in the region with high elastic energy density of the roof. Finally, numerical simulation of the target longwall face mining process is conducted to obtain the stress distribution, deformation characteristics, and periodic collapse data of the roof and top coal in the target longwall face and roadway.

[0051] Step 3: Based on the coordinates of the dangerous area of ​​the roadway obtained in Step 2 and the coordinates of the far-field dynamic load source obtained from on-site microseismic monitoring, set up hydraulic cutting and cavity creation combined weakening anti-scour conditions that can meet the roadway anti-scour requirements.

[0052] The diameter, depth, and distribution of hydraulically created cavities satisfy the following conditions:

[0053]

[0054] In the formula: L f ,L b These are the depths of the front and rear faces of the cavity, respectively; L R H0 is the hydraulic rock-breaking radius; h0 is the height of the drilling rig; H1 is the coal seam thickness; θ1 is the drill rod elevation angle during hydraulic cavity creation; p is the jet pressure; R is the nozzle radius. τ is the internal friction angle of the roof; τ is the shear strength of the roof rock; c is the cohesion of the roof rock.

[0055] The number of hydraulic kerfs, kerf diameter, and depth must satisfy the following conditions:

[0056] GF1:L D1 sinθ2-LR cosθ2>H1

[0057]

[0058] In the formula: GF1 is the first hydraulic cut; GF n For the final hydraulic cut; L D1 L is the drill pipe depth for the first hydraulic slotting. Dn θ2 is the drill pipe depth when performing the final hydraulic cut; θ2 is the drill pipe elevation angle when performing the hydraulic cut; L R H1 is the hydraulic rock-breaking radius; H2 is the coal seam thickness; H3 is the roof thickness; m is the width of the coal pillar.

[0059] After the coal pillar is weakened, when the immediate roof settlement height is ΔH, the roof pressure in the slotted area satisfies the following condition:

[0060] F = -(64E3L) Dn cosθH3 3 )ΔH+4qL R 4 / 7L R 3

[0061] In the formula: F is the roof pressure in the slotted area; E3 is the elastic modulus of the direct roof; H3 is the height of the direct roof; ΔH is the settlement height of the direct roof; q is the pressure of the direct roof on the coal pillar.

[0062] After the combined operation of hydraulic slotting and cavity creation, the energy of the incident and transmitted waves of the dynamic stress wave after encountering the cavity and slots satisfy the following conditions:

[0063]

[0064] In the formula: W I W T These represent the total energy of the incident wave and the transmitted wave under dynamic load, respectively; K is the attenuation rate of the stress wave after passing through the hole. These represent the energies of the incident longitudinal and transverse waves, respectively. The energy of the transmitted longitudinal and transverse waves are represented respectively; A is the area of ​​the unit measuring point; x1 is the distance between the side closer to the source and the source; x2 is the distance between the side farther from the source and the source; ρ is the rock density in the cut region; c P For longitudinal wave velocity; c s σ1 represents the transverse wave velocity; σ1 and τ1 represent the normal force and tangential stress of the incident surface, respectively; σ2 and τ2 represent the normal force and tangential stress of the transmission surface, respectively.

[0065] Step 4, based on the simulation model of Step 2 and the combined weakening of scour prevention conditions by hydraulic slotting and cavity creation in Step 3, such as... Figure 1, Figure 2 As shown, firstly, in the simulation model, hydraulic cutting is simulated to form multi-layered slots in the roof of the roadway in the dangerous area, and hydraulic cavitation is simulated to form cavities in the coal pillars of the adjacent dangerous area. Then, the dynamic load generated by roof failure is simulated at the far-field dynamic load source location, and the working face mining of the subsequent mining plan is numerically simulated to obtain the optimal hydraulic cutting and cavitation combined anti-scour technology parameters that can weaken the dynamic load and reduce the static load. The hydraulic cutting and cavitation combined anti-scour technology parameters include hydraulic cavity technology parameters including the orientation, distance, size and quantity of hydraulic cavity, and hydraulic cutting technology parameters including the orientation, distance, size and quantity of hydraulic cutting.

[0066] like Figure 1 , Figure 2 As shown, the dynamic load weakening zone of the cavity and multi-layer slot structure needs to be located on the line connecting the far-field dynamic load source and the dangerous area of ​​the roadway, so that the dynamic load stress wave passes perpendicularly through the multi-layer hydraulic cuts and cavities, thus maximizing the isolation of the dynamic load's influence on the roadway.

[0067] When simulating hydraulic fracturing of the roadway roof in hazardous areas, drilling and hydraulic fracturing should begin near the interface between the roof coal and the immediate roof. The first layer of hydraulic fracturing (GF1) should extend downwards beyond the interface between the coal pillar and the immediate roof. The coverage of multiple layers of fracturing should not exceed the width of the coal pillar adjacent to the hazardous area of ​​the roadway. The last layer of hydraulic fracturing (GF...) n The upward extension range does not exceed the thickness range of the direct top.

[0068] When performing simulated hydraulic cutting on the roof of a hazardous area in a roadway, the drill rod elevation angle θ2 during hydraulic cutting must satisfy the following condition:

[0069] θ2=arctan[(H1-h0) / l0]

[0070] In the formula: H1 is the coal seam thickness; h0 is the height of the drilling rig; l0 is the distance between the drilling rig and the coal pillar.

[0071] When simulating hydraulic cavity creation for coal pillars in dangerous areas adjacent to roadways, the upward extension range of the cavity shall not exceed the interface between the coal pillar and the immediate roof, and the downward extension range of the cavity shall not exceed the interface between the coal pillar and the floor.

[0072] When simulating hydraulic cavity creation for coal pillars in dangerous areas adjacent to roadways, the drill rod elevation angle θ1 during hydraulic cavity creation must satisfy the following condition:

[0073] θ1 = arctan(H1m + l0)

[0074] In the formula: H1 is the coal seam thickness; m is the width of the coal pillar; l0 is the distance between the drilling rig and the coal pillar.

[0075] When obtaining the optimal hydraulic slotting and cavity-based combined scour control technology parameters that can reduce dynamic load and decrease static load, the different locations and cavity depths of the multi-layer slots and cavities are considered. Drill pipe elevation angles θ1, θ2, and hydraulic cut depth L Dn Numerical simulations were performed in groups using parameters such as the slot spacing d, borehole spacing D, drilling rig height h0, and distance l0 between the drilling rig and the coal pillar. The dynamic load attenuation rate, stress-strain variation characteristics of the roadway surrounding rock, and stress transfer characteristics of the coal pillar area were obtained under different parameter conditions. The main control parameters of hydraulic slotting and cavity creation combined with scour prevention that affect the dynamic load attenuation rate, stress-strain variation characteristics of the roadway surrounding rock, and stress transfer characteristics of the coal pillar area were determined, and an optimal scheme that can meet the requirements of blocking the propagation of dynamic load and reducing the static load of the roadway surrounding rock was formed.

[0076] Step 5: Based on the optimized hydraulic slotting and cavity-creating combined anti-scouring technology parameters obtained in Step 4, drilling rigs are deployed in the target working face roadway of the mine. Holes are drilled into the roadway roof in the dangerous area and the coal pillar in the adjacent dangerous area. High-pressure water jets, sprayed radially along the drill rod through the jet nozzle at the end of the drill rod, impact and break the roof rock and coal body. Through the rotation and retraction of the drill rod, multi-layer slots are formed in the roadway roof in the dangerous area and columnar cavities are formed in the coal pillar in the adjacent dangerous area. This process is repeated to complete the creation of all multi-layer slots and cavities.

[0077] Step 6: Based on the regional and real-time monitoring results of the surrounding rock of the target roadway in the on-site monitoring area, determine the risk of rockburst in the surrounding rock of the target roadway before and after hydraulic cutting and cavity creation. Evaluate and verify the anti-scour effect of hydraulic cutting and cavity creation. For areas where the anti-scour effect does not meet the combined weakening anti-scour condition of hydraulic cutting and cavity creation in Step 3, repeat Step 4 and adjust the optimized hydraulic cutting and cavity creation combined anti-scour technology parameters obtained in Step 4. Based on the adjusted and optimized optimized hydraulic cutting and cavity creation combined anti-scour technology parameters, perform the hydraulic cavity creation operation in Step 5 again until the anti-scour effect meets the combined weakening anti-scour condition of hydraulic cutting and cavity creation in Step 3.

[0078] When evaluating and verifying the anti-scouring effect of hydraulic slotting and cavity creation, the deformation of the surrounding rock in the roadway is first measured, the deformation of the surrounding rock in the slotted area and the unslotted area is compared, the settlement of the coal pillar roof is measured, the pressure of the coal pillar roof after hydraulic cavity creation is calculated, and the stress concentration level of the surrounding rock is measured by the drill cuttings method. Then, the measured data, theoretical model calculations and numerical simulation calculations are compared and verified.

[0079] This method for preventing rockburst in isolated working faces adopts a combined approach: multi-layer hydraulic fracturing in the roof of the isolated working face roadway and hydraulic cavity creation in the coal pillars of adjacent isolated working face roadways. This approach addresses both dynamic and static load aspects of the dynamic-static load superposition theory for preventing rockburst: hydraulic fracturing increases the degree of fracture in the hard roof of the roadway, reducing roof strength and causing stress to transfer to deeper rock, while simultaneously increasing energy dissipation during far-field dynamic load propagation; hydraulic cavity creation weakens the mechanical strength of the coal pillars near the roadway, causing roof subsidence and reducing the elastic energy accumulated in the roof near the roadway due to the goaf, thus transferring stress to the coal pillars on the goaf side and reducing the static load level of the roadway. Simultaneously, the cavities in the coal pillars effectively block the propagation of dynamic loads generated by roof fracture through the coal pillars into the roadway. It can reduce the energy that can induce rockburst disasters from both dynamic and static load aspects, reduce the surrounding rock load value of isolated working face roadways to below the rockburst induction threshold, significantly reduce the possibility of rockburst disasters in isolated working face roadways, and greatly improve the rockburst prevention effect. At the same time, the construction process of hydraulic slotting and hydraulic cavity making is relatively refined and the amount of engineering work is small. The water jet rock breaking technology itself is relatively mature, the process is safe and green and pollution-free, and the construction difficulty is low. It is particularly suitable for improving the rockburst prevention capacity of isolated working face roadways.

Claims

1. A method for preventing scour in isolated working face roadways, characterized in that, A combined anti-scouring scheme is adopted, which involves multi-layer hydraulic slit cutting in the roof of the isolated working face roadway and hydraulic cavity creation in the coal pillar of the adjacent isolated working face roadway. The specific steps are as follows: Step 1: Obtain mine data and conduct on-site sampling, prepare standard samples for experiments, and obtain basic mechanical parameter data, internal porosity data, fracture distribution data, and optimal hydraulic rock breaking technology parameters of the coal seam and surrounding rock of the target fully mechanized longwall face and its goaf. Step 2: Based on the mine data from Step 1, construct a finite element model of the load-deformation structure of the adjacent working face goaf-coal pillar-roadway-coal seam to be mined in this working face, and conduct numerical simulation of the target working face mining process. Utilize the mine production data on periodic fracture and collapse of the roof and top coal, coal seam mining stress data, and mine data on roadway surrounding rock deformation and delamination to verify and optimize the parameters of the load-deformation finite element model, forming a simulation model that conforms to the actual production conditions and monitoring data of the mine site. Based on the simulation model, conduct numerical simulation of the working face mining in the subsequent mining plan, calculate the roadway areas with high static load and large stress concentration coefficient, and the roof fracture areas of adjacent goaf areas, and identify the dangerous roadway areas with the risk of rockburst. Step 3: Based on the coordinates of the dangerous area of ​​the roadway obtained in Step 2 and the coordinates of the far-field dynamic load source obtained from on-site microseismic monitoring, set up hydraulic cutting and cavity creation combined weakening anti-scour conditions that can meet the roadway anti-scour requirements. The diameter, depth, and distribution of hydraulically created cavities satisfy the following conditions: In the formula: L f ,L b These are the depths of the front and rear faces of the cavity, respectively; L R H0 is the hydraulic rock-breaking radius; h0 is the height of the drilling rig; H1 is the coal seam thickness; θ1 is the drill rod elevation angle during hydraulic cavity creation; p is the jet pressure; R is the nozzle radius. τ is the internal friction angle of the roof rock; c is the shear strength of the roof rock; The number of hydraulic kerfs, kerf diameter, and depth must satisfy the following conditions: GF1:L D1 sinθ2-L R cosθ2>H1 In the formula: GF1 is the first hydraulic cut; GF n For the final hydraulic cut; L D1 L is the drill pipe depth for the first hydraulic slotting. Dn θ2 is the drill pipe depth when performing the final hydraulic cut; θ2 is the drill pipe elevation angle when performing the hydraulic cut; L R H1 is the hydraulic rock-breaking radius; H2 is the coal seam thickness; H3 is the roof thickness; m is the width of the coal pillar. After the coal pillar is weakened, when the immediate roof settlement height is ΔH, the roof pressure in the slotted area satisfies the following condition: F=-(64E3L Dn cosθH3 3 )ΔH+4qL R 4 / 7L R 3 In the formula: F is the roof pressure in the slotted area; E3 is the elastic modulus of the immediate roof; H3 is the height of the immediate roof; ΔH is the settlement height of the immediate roof; q is the pressure of the immediate roof on the coal pillar. After the combined operation of hydraulic slotting and cavity creation, the energy of the incident and transmitted waves of the dynamic stress wave after encountering the cavity and slots satisfy the following conditions: In the formula: W I W T These represent the total energy of the incident wave and the transmitted wave under dynamic load, respectively; K is the attenuation rate of the stress wave after passing through the hole. These represent the energies of the incident longitudinal and transverse waves, respectively. The energy of the transmitted longitudinal and transverse waves are represented respectively; A is the area of ​​the unit measuring point; x1 is the distance between the side closer to the source and the source; x2 is the distance between the side farther from the source and the source; ρ is the rock density in the cut region; c P For longitudinal wave velocity; c s σ1 and τ1 are the normal force and tangential stress of the incident surface, respectively; σ2 and τ2 are the normal force and tangential stress of the transmission surface, respectively. Step 4: Based on the simulation model of Step 2 and the combined weakening and anti-scour conditions of hydraulic slotting and cavity creation in Step 3, firstly, in the simulation model, hydraulic slotting is simulated to form multi-layer slots in the roof of the roadway in the dangerous area of ​​the roadway, and hydraulic cavity creation is simulated to form cavities in the coal pillar of the adjacent dangerous area of ​​the roadway. Then, the dynamic load generated by roof failure is simulated at the far-field dynamic load source location, and the numerical simulation of the working face mining of the subsequent mining plan is carried out to obtain the optimal hydraulic slotting and cavity creation combined anti-scour technology parameters that can weaken the dynamic load and reduce the static load. Step 5: Based on the optimized hydraulic slotting and cavity-creating combined anti-scouring technology parameters obtained in Step 4, drilling rigs are deployed in the roadway of the target working face of the mine. Drilling is carried out into the roadway roof in the dangerous area of ​​the roadway and the coal pillar in the adjacent dangerous area of ​​the roadway. High-pressure water jets are sprayed out from the jet nozzle at the end of the drill rod and sprayed radially along the drill rod to impact and break the roof rock and coal body. Through the rotation and retraction of the drill rod, multi-layer slots are formed in the roadway roof in the dangerous area of ​​the roadway and columnar cavities are formed in the coal pillar in the adjacent dangerous area of ​​the roadway. This process is repeated to complete the opening of all multi-layer slots and cavities. Step 6: Based on the regional and real-time monitoring results of the surrounding rock of the target roadway in the on-site monitoring area, determine the risk of rockburst in the surrounding rock of the target roadway before and after hydraulic cutting and cavity creation. Evaluate and verify the anti-scour effect of hydraulic cutting and cavity creation. For areas where the anti-scour effect does not meet the combined weakening anti-scour condition of hydraulic cutting and cavity creation in Step 3, repeat Step 4 and adjust the optimized hydraulic cutting and cavity creation combined anti-scour technology parameters obtained in Step 4. Based on the adjusted and optimized optimized hydraulic cutting and cavity creation combined anti-scour technology parameters, perform the hydraulic cavity creation operation in Step 5 again until the anti-scour effect meets the combined weakening anti-scour condition of hydraulic cutting and cavity creation in Step 3.

2. The method for preventing scour in isolated working face roadways according to claim 1, characterized in that, In Step 2, when performing numerical simulation of the target longwall face mining process, the following steps are taken: First, mine data including the geological conditions and mining conditions of the coal seam in the target longwall face, as well as the basic mechanical parameters, internal porosity data, and fracture distribution data of the coal body and surrounding rock of the target longwall face and its goaf are imported into the load-deformation finite element model. Then, the vertical stress distribution is calculated to obtain the areas with high roof elastic energy density. The mesh is then refined in the areas with high roof elastic energy density. Finally, numerical simulation of the target longwall face mining process is performed to obtain the stress distribution, deformation characteristics, and periodic collapse data of the roof and top coal in the target longwall face and roadway.

3. The method for preventing scour in isolated working face roadways according to claim 1, characterized in that, In Step 4, when simulating hydraulic cutting of the roadway roof in the dangerous area of ​​the roadway and simulating hydraulic cavity making of the coal pillar in the adjacent dangerous area of ​​the roadway in the simulation model, the dynamic load weakening zone of the cavity and the multi-layer slot structure is located on the line connecting the far-field dynamic load source and the dangerous area of ​​the roadway.

4. The method for preventing scour in isolated working face roadways according to claim 3, characterized in that, In Step 4, when simulating hydraulic cutting of the roof in the dangerous area of ​​the roadway, drilling is carried out near the junction of the roof coal and the coal pillar. The first layer of hydraulic cutting extends downwards without exceeding the junction of the coal pillar and the immediate roof. The coverage of multiple layers of slots does not exceed the width of the coal pillar in the adjacent dangerous area of ​​the roadway. The last layer of hydraulic cutting extends upwards without exceeding the thickness of the immediate roof.

5. The method for preventing scour in isolated working face roadways according to claim 3, characterized in that, In Step 4, when simulating hydraulic cutting of the tunnel roof in the hazardous area of ​​the tunnel, the drill rod elevation angle θ2 must satisfy the following condition: θ2=arctan[(H1-h0) / l0] In the formula: H1 is the coal seam thickness; h0 is the height of the drilling rig; l0 is the distance between the drilling rig and the coal pillar.

6. The method for preventing scour in isolated working face roadways according to claim 3, characterized in that, In Step 4, when simulating hydraulic cavity creation for coal pillars in dangerous areas adjacent to roadways, the upward extension range of the cavity shall not exceed the interface between the coal pillar and the immediate roof, and the downward extension range of the cavity shall not exceed the interface between the coal pillar and the floor.

7. The method for preventing scour in isolated working face roadways according to claim 3, characterized in that, In Step 4, when simulating hydraulic cavity creation for coal pillars in dangerous areas adjacent to roadways, the drill rod elevation angle θ1 must satisfy the following condition: θ1 = arctan(H1 / m + l0) In the formula: H1 is the coal seam thickness; m is the width of the coal pillar; l0 is the distance between the drilling rig and the coal pillar.

8. The method for preventing scour in isolated working face roadways according to claim 1, characterized in that, In Step 4, when obtaining the optimal hydraulic slotting and cavity-forming combined anti-scour technology parameters that can weaken dynamic load and reduce static load, the different parameters of multi-layer slots and cavities are grouped and numerically simulated to obtain the dynamic load attenuation rate, roadway surrounding rock stress-strain change characteristics and coal pillar area stress transfer characteristics under different parameter conditions. The main control parameters of hydraulic slotting and cavity-forming combined anti-scour technology parameters are determined and obtained, and the optimal hydraulic slotting and cavity-forming combined anti-scour technology parameters are formed.

9. The method for preventing scour in isolated working face roadways according to claim 1, characterized in that, In Step 6, when evaluating and verifying the anti-scouring effect of hydraulic slotting and cavity creation, the deformation of the surrounding rock in the roadway is first measured, the deformation of the surrounding rock in the slotted area and the unslotted area is compared, the settlement of the coal pillar roof is measured, the pressure of the coal pillar roof after hydraulic cavity creation is calculated, and the stress concentration level of the surrounding rock is measured by the drill cuttings method. Then, the measured data, theoretical model calculations and numerical simulation calculations are compared and verified.

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