Island working face roadway scour prevention method

Abstract

The invention discloses an islanding working face roadway scour prevention method, which adopts a combined scour prevention scheme of carrying out multilayer hydraulic slotting in an islanding working face roadway roof and carrying out hydraulic caving in a coal pillar adjacent to an islanding working face roadway. The strength of the top plate is reduced, so that stress is transferred to deep rocks, and meanwhile, energy dissipation during far-field dynamic load propagation is increased; hydraulic caving is utilized to weaken the mechanical strength of coal pillars near the roadway, so that coal pillar roofs are settled, the elastic energy of the roofs near the roadway accumulated due to goaf top suspension is reduced, stress is transferred to the coal pillars on the goaf side, and dynamic loads generated by roof breakage are prevented from being transmitted to the roadway through the coal pillars. According to the method, the energy capable of inducing the rock burst disaster can be reduced in the two aspects of dynamic load and static load, the load value of the surrounding rock of the island working face roadway is reduced and is lower than the impact inducing critical value, the possibility of the rock burst disaster of the island working face roadway can be remarkably reduced, and the impact prevention effect is greatly improved.

Description

Technical Field

[0001] The present invention relates to an anti-scouring method for a tunnel of an isolated working face, specifically an anti-scouring method for a tunnel of an isolated working face, which utilizes the combined operation of hydraulic cavitation and hydraulic cutting to weaken the dynamic and static superimposed loads borne by the tunnel surrounding rock to improve the anti-scouring capability of the tunnel, and belongs to the technical field of safe mining of coal mines. Background Art

[0002] Coal mining in my country is mainly carried out in underground mining. With the increasing depletion of shallow resources, coal mining has gradually expanded to deep underground, which has led to increased stress in the coal seams, increased mining disturbance, and intensified strong mine pressure faced by coal mine production. A large number of studies have been conducted at home and abroad on the manifestation law of hard roof mine pressure and its disaster-causing mechanism. Rock burst is an instability phenomenon induced when the energy released by the coal-rock system is greater than the energy consumed. Rock burst will not occur when the stress on the coal-rock mass does not exceed the ultimate strength, and when the rate of elastic energy release in the coal-rock system is less than the rate of energy dissipation during crack expansion. However, mining engineering activities will lead to the readjustment of the stress and energy of the surrounding rock in the mining space. When the static load of the surrounding rock and the dynamic load caused by the external dynamic load are superimposed and exceed the critical load of coal-rock impact failure, the coal-rock system will be unstable and damaged, and rock burst will be induced.

[0003] Isolated coal mining is also called isolated working face mining. An isolated working face refers to a working face that is surrounded by goafs or has adjacent goafs in the tunnels on both sides of the working face. When the suspended ceiling above the adjacent goaf is too long, a large amount of elastic energy will often accumulate. Once it breaks, a high-energy dynamic load will be generated and propagated toward the tunnel of the isolated working face. When the surrounding rock of the tunnel itself is subjected to a large static load, and the dynamic load transmitted from the far field to the tunnel is also large, if the superimposed load of the dynamic and static loads is close to the critical value of rock burst, rock burst disasters may occur.

[0004] In the prior art, the preventive measures against impact mining pressure are mainly divided into four solutions, namely, optimizing tunnel layout, strengthening support, filling and anti-impact, and weakening the hard roof. Among them, in terms of optimizing tunnel layout, the stress reduction zone in the goaf can be effectively utilized to weaken the static load effect on the tunnel; in terms of strengthening support, the deformation of the tunnel surrounding rock can be effectively controlled by using high prestressed anchor rods. However, neither of these two methods can fundamentally solve the high stress area of ​​the roof caused by the superposition of dynamic and static loads. Although filling and anti-impact can effectively solve the problem of suspended roof, the cost is high. Therefore, the current preventive measures against impact mining pressure mainly focus on weakening the strength of the hard roof. Traditional roof weakening methods include water injection to weaken the roof, drilling pressure relief, hydraulic fracturing, drilling and blasting pre-cracking and other means. Among them, water injection to weaken the roof has great limitations, and is not effective for rock masses with small porosity, weak water absorption and incomplete fracture development; drilling unloading can reduce the stress concentration of the surrounding coal rock mass, but the impact 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-cracking has a large unloading range, but the operation is difficult, and the dynamic load generated may induce impact mine pressure. It is difficult to apply on a large scale due to restrictions on safe operations and environmental protection. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for preventing impact of isolated working face tunnels, which can reduce the energy that can induce impact mine pressure disasters in terms of both dynamic loads and static loads, thereby making the load borne by the isolated working face tunnels lower than the critical value that can induce impact mine pressure disasters, thereby improving the anti-impact ability of the isolated working face tunnels.

[0006] To achieve the above purpose, the anti-bumping method of the isolated working face roadway adopts a combined anti-bumping scheme of multi-layer hydraulic cutting in the roof of the isolated working face roadway and hydraulic cavitation in the coal pillar adjacent to the isolated working face roadway, which specifically includes the following steps:

[0007] Step 1: Obtain mine data, 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 technical parameters of the target fully mechanized caving working face coal seam and its goaf.

[0008] Step 2, based on the mine data in Step 1, construct a load-deformation finite element model of the adjacent working face goaf-coal pillar-tunnel-coal seam structure to be mined in the current working face, and perform numerical simulation of the target working face mining process. Use the periodic fracture and collapse data of the roof and top coal during mine production, the coal seam mining stress data, and the tunnel surrounding rock deformation and separation mine data to verify and optimize the load-deformation finite element model, and form a simulation model that meets the actual production conditions and monitoring data of the mine site. Based on the simulation model, perform numerical simulation of the working face mining in the subsequent mining plan, calculate the tunnel area with high static load and large stress concentration coefficient and the roof fracture area of ​​the adjacent goaf, and identify the dangerous area of ​​the tunnel with the risk of impact mine pressure;

[0009] Step 3: According to the coordinates of the dangerous area of ​​the tunnel obtained in Step 2 and the coordinates of the far-field dynamic load source obtained by on-site microseismic monitoring, the hydraulic cutting and cavitation combined weakening anti-scouring conditions that can meet the anti-scouring requirements of the tunnel are set;

[0010] The diameter, depth and distribution of hydraulic cavitation meet the following conditions:

[0011]

[0012]

[0013] Where: L f ,L b L are the depth of the front and rear surfaces of the cavity respectively; R is the hydraulic rock breaking radius; h0 is the height of the drilling rig; H2 is the coal seam thickness; θ1 is the drill rod elevation angle during hydraulic cavitation; p is the jet pressure; R is the nozzle radius; 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;

[0014] The number of slits, slit diameter and depth of hydraulic slits shall meet the following conditions:

[0015] GF1:L D1 sinθ2-L R cosθ2>H1

[0016]

[0017] Where: GF1 is the first layer of hydraulic cutting; GF n For the last layer of hydraulic cutting; L D1 L is the drill pipe depth for the first hydraulic cutting. Dn is the drill pipe depth when the last layer of hydraulic slotting is performed; θ2 is the drill pipe elevation angle when hydraulic slotting is performed; L Ris the hydraulic rock breaking radius; H1 is the coal seam thickness; H2 is the roof thickness; m is the coal pillar width;

[0018] After the coal pillar is weakened, when the direct roof settlement height is ΔH, the roof pressure in the cutting area meets the following conditions:

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

[0020] Where: F is the roof pressure in the cut 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;

[0021] After the combined operation of hydraulic slotting and cavitation, the energy of the incident wave and the transmitted wave of the dynamic load stress wave after encountering the cavity and the slot meets the following conditions:

[0022]

[0023] Where: W I , W T They represent the total energy of the incident wave and the transmitted wave under dynamic loading respectively; K is the attenuation rate of the stress wave after passing through the cavity; represent the energy of longitudinal and transverse waves on the incident side, respectively; They represent the energy of longitudinal and shear waves on the transmission side, respectively; A is the area of ​​the unit measuring point; x1 is the distance between the side close to the source and the source; x2 is the distance between the side far from the source and the source; ρ is the rock density in the cut area; c P is the longitudinal wave velocity; c s is the shear wave velocity; σ1 and τ1 are the normal stress and tangential stress of the incident surface, respectively; σ2 and τ2 are the normal stress and tangential stress of the transmission surface, respectively;

[0024] Step 4, based on the simulation model of Step 2 and the hydraulic cutting and cavitation combined weakening anti-bumping conditions of Step 3, firstly, in the simulation model, simulate hydraulic cutting to form multi-layer slots for the tunnel roof in the dangerous area of ​​the tunnel, and simulate hydraulic cavitation to form cavities for the coal pillars in the adjacent dangerous area of ​​the tunnel, then simulate the dynamic load generated by the roof breakage at the far-field dynamic load source position, and simultaneously perform numerical simulation of the working face recovery of the subsequent mining plan, so as to obtain the optimal hydraulic cutting and cavitation combined anti-bumping technical parameters that can weaken the dynamic load and reduce the static load;

[0025] Step 5, according to the optimal hydraulic slotting and cavitation combined anti-bumping technical parameters obtained in Step 4, a drilling rig is arranged in the tunnel of the target working face of the mine, and holes are drilled into the tunnel roof in the dangerous area of ​​the tunnel and the coal pillars adjacent to the dangerous area of ​​the tunnel respectively, and the high-pressure water jet ejected from the jet nozzle at the end of the drill rod and sprayed along the radial direction of the drill rod is used to impact and crush the roof rock and coal body, and through the rotation and retreat of the drill rod, multi-layer slots are formed in the tunnel roof in the dangerous area of ​​the tunnel, and columnar holes are formed in the coal pillars adjacent to the dangerous area of ​​the tunnel, and so on, to complete the opening of all multi-layer slots and holes;

[0026] Step 6. According to the regional and real-time monitoring results of the tunnel surrounding rock in the target area monitored on site, determine the impact mine pressure hazard of the target tunnel surrounding rock before and after hydraulic cutting and cavitation, evaluate and verify the anti-collision effect of hydraulic cutting and cavitation, and repeat Step 4 for the areas where the anti-collision effect does not meet the combined weakened anti-collision condition of hydraulic cutting and cavitation in Step 3, adjust the optimal hydraulic cutting and cavitation combined anti-collision technical parameters obtained in Step 4, and perform the hydraulic cavitation construction operation of Step 5 again based on the adjusted and optimized optimal hydraulic cutting and cavitation combined anti-collision technical parameters until the anti-collision effect meets the combined weakened anti-collision condition of hydraulic cutting and cavitation in Step 3.

[0027] Furthermore, when numerically simulating the mining process of the target working face in Step 2, firstly, the mine data including the geological conditions and mining conditions of the coal seam of the target fully-mechanized caving working face, as well as the basic mechanical parameter data of the coal body and surrounding rock of the coal seam and its goaf of the target fully-mechanized caving working face, the internal porosity data and the fracture distribution data are imported into the load-deformation finite element model; then, the vertical stress distribution is calculated to obtain the area with high elastic energy density of the roof; the grid of the area with high elastic energy density of the roof is encrypted; finally, the numerical simulation of the mining process of the target fully-mechanized caving working face is carried out to obtain the stress distribution, deformation characteristics and periodic collapse data of the roof and top coal of the target fully-mechanized caving working face and roadway.

[0028] Furthermore, in Step 4, when simulating hydraulic cutting of the tunnel roof in the dangerous area of ​​the tunnel and simulating hydraulic cavitation of the coal pillars adjacent to the dangerous area of ​​the tunnel in the simulation model, the dynamic load weakening area of ​​the cavity and the multi-layer seam structure is on the line connecting the far-field dynamic load source and the dangerous area of ​​the tunnel.

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

[0030] Furthermore, when simulating hydraulic cutting of the tunnel roof in the dangerous area of ​​the tunnel in Step 4, the drill rod elevation angle θ2 during hydraulic cutting satisfies the following conditions:

[0031] θ2=arctan[(H1-h0) / l0]

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

[0033] Furthermore, when simulating hydraulic cavitation for the coal pillars in the dangerous areas adjacent to the roadways in Step 4, 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, when simulating hydraulic cavitation for the coal pillar in the dangerous area adjacent to the roadway in Step 4, the drill rod elevation angle θ1 during hydraulic cavitation satisfies the following conditions:

[0035] θ1=arctan(H1m+l0)

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

[0037] Furthermore, when obtaining the optimal hydraulic cutting and cavitation combined anti-collision technical parameters that can weaken dynamic loads and reduce static loads in Step 4, the dynamic load attenuation rate, the stress-strain change characteristics of the tunnel surrounding rock, and the stress transfer characteristics of the coal pillar area under different parameter conditions are obtained by grouping numerical simulations of different parameters of the multi-layer seams and cavities, and the main control parameters of the hydraulic cutting and cavitation combined anti-collision are judged and obtained to form the optimal hydraulic cutting and cavitation combined anti-collision technical parameters.

[0038] Furthermore, when evaluating and verifying the anti-impact effect of hydraulic cutting and cavitation in Step 6, first measure the deformation of the surrounding rock of the tunnel, compare the deformation of the surrounding rock in the cutting area and the uncut area, measure the settlement of the coal pillar roof, calculate the pressure of the coal pillar roof after hydraulic cavitation, and measure the stress concentration level of the surrounding rock by the drill cuttings method. Then, compare and verify the measured data, theoretical model calculations and numerical simulation calculations.

[0039] Compared with the existing technology, the anti-impact method of the isolated working face tunnel adopts a combined anti-impact scheme of performing multi-layer hydraulic cutting in the roof of the isolated working face tunnel and performing hydraulic cavitation in the coal pillar of the adjacent isolated working face tunnel, and prevents and controls the impact mine pressure from two aspects: dynamic load and static load in the dynamic and static load superposition induced impact theory: hydraulic cutting is used to increase the degree of crushing of the hard roof of the tunnel, reduce the strength of the roof to transfer stress to deep rocks, and at the same time increase the energy dissipation during the propagation of far-field dynamic loads; hydraulic cavitation is used to weaken the mechanical strength of the coal pillar near the tunnel, cause the roof of the coal pillar to settle, reduce the elastic energy accumulated in the roof near the tunnel due to the suspended roof of the goaf, transfer stress to the coal pillar on the side of the goaf, reduce the static load level of the tunnel, and at the same time, the holes in the coal pillar can effectively block the dynamic load generated by the roof break from propagating to the tunnel through the coal pillar. It can reduce the energy that can induce impact mine pressure disasters in terms of both dynamic load and static load, reduce the surrounding rock load value of the isolated working face tunnel and make it lower than the critical value of inducing impact, significantly reduce the possibility of impact mine pressure disasters in the isolated working face tunnel, and greatly improve the anti-impact effect. At the same time, the construction process of hydraulic cutting and hydraulic cavitation is relatively refined and the engineering volume is small. The water jet rock breaking technology itself is relatively mature, the process is safe, green and pollution-free, and the construction difficulty is low. It is particularly suitable for improving the anti-impact capacity of the isolated working face tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a top view layout diagram of the hydraulic cavitation construction of the present invention;

[0041] Figure 2 yes Figure 1 A-axis rotated view. DETAILED DESCRIPTION

[0042] This anti-bumping method for the isolated working face tunnel adopts a combined anti-bumping scheme of conducting multi-layer hydraulic cutting in the roof of the isolated working face tunnel and conducting hydraulic cavitation in the coal pillar adjacent to the isolated working face tunnel. The hydraulic cavitation technology can weaken the coal pillar, sink the roof of the coal pillar, release the elastic energy and static load accumulated in the roof, and prevent the dynamic load caused by the broken roof from propagating to the tunnel through the coal pillar; the hydraulic cutting technology can construct a dynamic load attenuation zone between the dynamic load source and the tunnel, reduce the dynamic load, increase the degree of roof crushing, and at the same time weaken the roof strength to transfer the stress of the tunnel roof to the deep rock, thereby reducing the static load level.

[0043] The present invention will be further described below by taking an isolated working face tunnel of a coal mine working face as an example in conjunction with the accompanying drawings.

[0044] The anti-collision method of the isolated island working face roadway specifically includes the following steps:

[0045] Step 1: Obtain mine data, 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 technical parameters of the target fully-mechanized caving working face coal seam and its goaf.

[0046] The average burial depth of the comprehensive top coal mining working face of this coal mine is 450m, the average coal seam inclination is 6°, the average coal seam thickness is 7m, the direct roof thickness is 15.5m, and there is a 15m wide coal pillar between the goaf and the working face. The working face return air lane 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 form of the return air lane is full anchor cable support and single hydraulic support. According to the monitoring data analysis, the length of the goaf roof during the target working face mining period is between 15 and 35m, and the working face periodic pressure step is 20m.

[0047] In order to accurately obtain the basic mechanical parameter data, internal porosity data and crack distribution data of the coal body and surrounding rock of the target fully-mechanized caving working face coal seam and its goaf, samples of coal body, roof rock, floor rock and other samples were drilled from the working face where the target tunnel was located in the coal mine underground and brought to the ground laboratory to be prepared into standard samples for mechanical testing to obtain the mechanical parameters of the rock numerical model, such as compressive strength, tensile strength, Poisson's ratio, etc. Specifically: long rock cylinders with a diameter of 50 mm were drilled from the underground working face to be mined, the tunnel roof, the tunnel floor and the coal pillar, respectively, and processed and prepared into cylindrical standard samples of different standard sizes such as Ф50×100mm and Ф50×250mm in the ground laboratory. After grouping the samples, the basic mechanical parameters of the standard samples were obtained by using the MTS triaxial loading tester, and the porosity and crack distribution results inside the standard samples were tested by using a mercury intrusion instrument and a rock CT machine. After the test, the compressive strength of the raw coal standard sample was 14.1MPa, the tensile strength was 1.0MPa, the Poisson's ratio was 0.31, and the elastic modulus was 1.1GPa; the porosity of the raw coal standard sample was 7.8%, the average crack opening was 90.1um, and the average crack volume was 2.1×10 7 um 3 , the crack degree is 0.83%.

[0048] In order to determine the technical parameters of hydraulic rock breaking, the top and bottom rock samples were drilled from the working face of the target tunnel in the coal mine and brought to the ground laboratory for water jet cutting experiments to determine the technical parameters of hydraulic rock breaking under different rock properties and different cutting depth requirements. Specifically: select a block sample with a cube shape and a volume of not less than 0.1m 3 In the laboratory, the block samples were processed into cubes with a side length of 20 cm, and experiments with different abrasive concentrations, jet pressures, nozzle radii and cutting times were carried out to obtain the optimal hydraulic rock breaking technical parameters.

[0049] Step 2, based on the mine data in Step 1, use Abaqus to construct a load-deformation finite element model of the adjacent working face goaf-coal pillar-tunnel-coal seam to be mined structure, and perform numerical simulation of the target working face mining process. Use mine data such as roof and top coal periodic fracture and collapse data, coal seam mining stress data, tunnel surrounding rock deformation and delamination during mine production to verify and optimize the load-deformation finite element model, and form a simulation model that meets the actual production conditions and monitoring data of the mine site. Based on the simulation model, perform numerical simulation of working face mining in the subsequent mining plan, calculate the tunnel area with high static load and large stress concentration coefficient and the roof fracture area of ​​the adjacent goaf, and identify the dangerous area of ​​the tunnel with the risk of impact mine pressure.

[0050] When conducting numerical simulation of the mining process of the target working face, firstly, the mine data including the geological conditions and mining conditions of the coal seam of the target fully-mechanized caving working face, as well as the basic mechanical parameter data of the coal body and surrounding rock of the coal seam and its goaf of the target fully-mechanized caving working face, the internal porosity data and the fracture distribution data are imported into the load-deformation finite element model; then, the vertical stress distribution of the structure is calculated according to the material mechanics theory to obtain the area with high elastic energy density of the hard roof; the grid of the area with high elastic energy density of the roof is encrypted; finally, the numerical simulation of the mining process of the target fully-mechanized caving working face is carried out to obtain the stress distribution, deformation characteristics and periodic collapse data of the roof and top coal of the target fully-mechanized caving working face and roadway.

[0051] Step 3: According to the coordinates of the dangerous area in the tunnel obtained in Step 2 and the coordinates of the far-field dynamic load source obtained by on-site microseismic monitoring, the hydraulic cutting and cavitation combined weakening anti-scouring conditions that can meet the requirements of tunnel anti-scouring are set.

[0052] The diameter, depth and distribution of hydraulic cavitation meet the following conditions:

[0053]

[0054] Where: L f ,L b L are the depth of the front and rear surfaces of the cavity respectively; R 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 cavitation; p is the jet pressure; R is the nozzle radius; 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 slits, slit diameter and depth of hydraulic slits shall meet the following conditions:

[0056] GF1:L D1 sinθ2-LR cosθ2>H1

[0057]

[0058] Where: GF1 is the first layer of hydraulic cutting; GF n For the last layer of hydraulic cutting; L D1 L is the drill pipe depth for the first hydraulic cutting. Dn is the drill pipe depth when the last layer of hydraulic slotting is performed; θ2 is the drill pipe elevation angle when hydraulic slotting is performed; L R is the hydraulic rock breaking radius; H1 is the coal seam thickness; H2 is the roof thickness; m is the coal pillar width.

[0059] After the coal pillar is weakened, when the direct roof settlement height is ΔH, the roof pressure in the cutting area meets the following conditions:

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

[0061] Where: F is the roof pressure in the cutting 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 cavitation, the energy of the incident wave and the transmitted wave of the dynamic load stress wave after encountering the cavity and the slot meets the following conditions:

[0063]

[0064] Where: W I , W T They represent the total energy of the incident wave and the transmitted wave under dynamic loading respectively; K is the attenuation rate of the stress wave after passing through the cavity; represent the energy of longitudinal and transverse waves on the incident side, respectively; They represent the energy of longitudinal and shear waves on the transmission side, respectively; A is the area of ​​the unit measuring point; x1 is the distance between the side close to the source and the source; x2 is the distance between the side far from the source and the source; ρ is the rock density in the cut area; c P is the longitudinal wave velocity; c s is the shear wave velocity; σ1 and τ1 are the normal stress and tangential stress of the incident surface, respectively; σ2 and τ2 are the normal stress and tangential stress of the transmission surface, respectively.

[0065] Step 4, based on the simulation model of Step 2 and the hydraulic cutting and cavitation combined with weakening anti-scouring conditions in Step 3, such as Figure 1, Figure 2 As shown, firstly, in the simulation model, hydraulic cutting is simulated to form multi-layer slots for the tunnel roof in the dangerous area of ​​the tunnel, and hydraulic cavitation is simulated to form cavities for the coal pillars in the adjacent dangerous area of ​​the tunnel. Then, the dynamic load generated by the roof breaking is simulated at the far-field dynamic load source position, and the numerical simulation of the working face recovery of the subsequent mining plan is carried out at the same time, so as to obtain the optimal hydraulic cutting and cavitation combined anti-collision technical parameters that can weaken the dynamic load and reduce the static load. The hydraulic cutting and cavitation combined anti-collision technical parameters include hydraulic cavitation technical parameters including hydraulic cavitation orientation, distance, size and number, and hydraulic cutting technical parameters including hydraulic cutting orientation, distance, size and number.

[0066] like Figure 1 , Figure 2 As shown in the figure, the dynamic load weakening zone of the cavity and multi-layer slot structure needs to be on the line connecting the far-field dynamic load source and the dangerous area of ​​the tunnel, so that the dynamic load stress wave passes vertically through the multi-layer hydraulic cutting and cavity, thereby isolating the impact of the dynamic load on the tunnel to the greatest extent.

[0067] When simulating hydraulic cutting of the roadway roof in the dangerous area of ​​the roadway, drilling is carried out near the junction of the roadway roof coal and the coal pillar and hydraulic cutting is carried out. The downward extension range of the first layer of hydraulic cutting (GF1) does not exceed the interface between the coal pillar and the immediate roof. The coverage range of the multi-layer seam grooves does not exceed the width range of the coal pillar adjacent to the dangerous area of ​​the roadway. The last layer of hydraulic cutting (GF n ) The upward extension range does not exceed the thickness range of the immediate top.

[0068] When simulating hydraulic cutting of the tunnel roof in the dangerous area of ​​the tunnel, the drill rod elevation angle θ2 during hydraulic cutting meets the following conditions:

[0069] θ2=arctan[(H1-h0) / l0]

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

[0071] When simulating hydraulic cavitation for coal pillars in dangerous areas adjacent to tunnels, 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.

[0072] When simulating hydraulic cavitation for coal pillars in dangerous areas adjacent to tunnels, the drill rod elevation angle θ1 during hydraulic cavitation meets the following conditions:

[0073] θ1=arctan(H1m+l0)

[0074] Where: H1 is the thickness of the coal seam; 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 cavitation combined anti-scouring technical parameters that can weaken dynamic loads and reduce static loads, the different positions of multi-layer slots and cavities, cavitation depth Drill pipe elevation angle θ1, θ2, hydraulic cutting depth L Dn , cutting slot spacing d, drilling hole spacing D, drilling rig height h0, distance size l0 between drilling rig and coal pillar and other parameters are grouped for numerical simulation, and the dynamic load attenuation rate, stress-strain change characteristics of tunnel surrounding rock and stress transfer characteristics of coal pillar area under different parameter conditions are obtained. The main control parameters of hydraulic cutting slotting and cavitation combined anti-impact that affect the dynamic load attenuation rate, stress-strain change characteristics of tunnel surrounding rock and stress transfer characteristics of coal pillar area are determined, and the optimal scheme that can block the propagation of dynamic load and reduce the static load of tunnel surrounding rock is formed.

[0076] Step 5. Based on the optimal hydraulic cutting and cavitation combined anti-bumping technical parameters obtained in Step 4, a drilling rig is arranged in the tunnel of the target working face of the mine, and holes are drilled into the tunnel roof in the dangerous area of ​​the tunnel and the coal pillars adjacent to the dangerous area of ​​the tunnel respectively. The roof rock and coal body are crushed by the high-pressure water jet ejected from the jet nozzle at the end of the drill rod and sprayed radially along the drill rod. Through the rotation and retreat of the drill rod, multi-layer seams are formed in the tunnel roof in the dangerous area of ​​the tunnel, and columnar cavities are formed in the coal pillars adjacent to the dangerous area of ​​the tunnel. By analogy, all multi-layer seams and cavities are opened.

[0077] Step 6. According to the regional and real-time monitoring results of the tunnel surrounding rock in the target area monitored on site, determine the impact mine pressure hazard of the target tunnel surrounding rock before and after hydraulic cutting and cavitation, evaluate and verify the anti-collision effect of hydraulic cutting and cavitation, and repeat Step 4 for the areas where the anti-collision effect does not meet the combined weakened anti-collision condition of hydraulic cutting and cavitation in Step 3, adjust the optimal hydraulic cutting and cavitation combined anti-collision technical parameters obtained in Step 4, and perform the hydraulic cavitation construction operation of Step 5 again based on the adjusted and optimized optimal hydraulic cutting and cavitation combined anti-collision technical parameters until the anti-collision effect meets the combined weakened anti-collision condition of hydraulic cutting and cavitation in Step 3.

[0078] When evaluating and verifying the anti-impact effect of hydraulic cutting and cavitation, first measure the deformation of the surrounding rock of the tunnel, compare the deformation of the surrounding rock in the cutting area and the uncut area, measure the settlement of the coal pillar roof, calculate the pressure of the coal pillar roof after hydraulic cavitation, and measure the stress concentration level of the surrounding rock by the drill cuttings method. Then, compare and verify the measured data, theoretical model calculations and numerical simulation calculations.

[0079] This anti-bumping method for the isolated working face tunnel adopts a combined anti-bumping scheme of performing multi-layer hydraulic cutting in the roof of the isolated working face tunnel and performing hydraulic cavitation in the coal pillar of the adjacent isolated working face tunnel, and prevents and controls the impact mine pressure from two aspects: dynamic load and static load in the dynamic and static load superposition induced cavitation theory: hydraulic cutting is used to increase the degree of crushing of the hard roof of the tunnel, reduce the strength of the roof to transfer stress to deep rocks, and at the same time increase the energy dissipation during the propagation of far-field dynamic loads; hydraulic cavitation is used to weaken the mechanical strength of the coal pillar near the tunnel, cause the roof of the coal pillar to settle, reduce the elastic energy accumulated in the roof near the tunnel due to the suspended roof of the goaf, transfer stress to the coal pillar on the side of the goaf, reduce the static load level of the tunnel, and at the same time, the cavities in the coal pillar can effectively block the dynamic load generated by the roof break from propagating to the tunnel through the coal pillar. It can reduce the energy that can induce impact mine pressure disasters in terms of both dynamic load and static load, reduce the surrounding rock load value of the isolated working face tunnel and make it lower than the critical value of inducing impact, significantly reduce the possibility of impact mine pressure disasters in the isolated working face tunnel, and greatly improve the anti-impact effect. At the same time, the construction process of hydraulic cutting and hydraulic cavitation is relatively refined and the engineering volume is small. The water jet rock breaking technology itself is relatively mature, the process is safe, green and pollution-free, and the construction difficulty is low. It is particularly suitable for improving the anti-impact capacity of the isolated working face tunnel.

Claims

1. A method for preventing erosion in an isolated working face tunnel, characterized in that: A combined anti-bumping scheme is adopted, which includes multi-layer hydraulic cutting in the roof of the isolated working face roadway and hydraulic cavitation in the coal pillar of the roadway adjacent to the isolated working face, which specifically includes the following steps: Step 1: Obtain mine data, 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 technical parameters of the target fully mechanized caving working face coal seam and its goaf. Step 2, based on the mine data in Step 1, construct a load-deformation finite element model of the adjacent working face goaf-coal pillar-tunnel-coal seam structure to be mined in the current working face, and perform numerical simulation of the target working face mining process. Use the periodic fracture and collapse data of the roof and top coal during mine production, the coal seam mining stress data, and the tunnel surrounding rock deformation and separation mine data to verify and optimize the load-deformation finite element model, and form a simulation model that meets the actual production conditions and monitoring data of the mine site. Based on the simulation model, perform numerical simulation of the working face mining in the subsequent mining plan, calculate the tunnel area with high static load and large stress concentration coefficient and the roof fracture area of ​​the adjacent goaf, and identify the dangerous area of ​​the tunnel with the risk of impact mine pressure; Step 3: According to the coordinates of the dangerous area of ​​the tunnel obtained in Step 2 and the coordinates of the far-field dynamic load source obtained by on-site microseismic monitoring, the hydraulic cutting and cavitation combined weakening anti-scouring conditions that can meet the anti-scouring requirements of the tunnel are set; The diameter, depth and distribution of hydraulic cavitation meet the following conditions: Where: L f ,L b L are the depth of the front and rear surfaces of the cavity respectively; R 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 cavitation; p is the jet pressure; R is the nozzle radius; 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; The number of slits, slit diameter and depth of hydraulic slits shall meet the following conditions: GF1:L D1 sinθ2-L R cosθ2>H1 Where: GF1 is the first layer of hydraulic cutting; GF n For the last layer of hydraulic cutting; L D1 L is the drill pipe depth for the first hydraulic cutting. Dn is the drill pipe depth when the last layer of hydraulic slotting is performed; θ2 is the drill pipe elevation angle when hydraulic slotting is performed; L R is the hydraulic rock breaking radius; H1 is the coal seam thickness; H2 is the roof thickness; m is the coal pillar width; After the coal pillar is weakened, when the direct roof settlement height is ΔH, the roof pressure in the cutting area meets the following conditions: <h2 style=";text-align:left;direction:ltr">F=-(64E3L<h2 style=";text-align:left;direction:ltr"> Dn <h2 style=";text-align:left;direction:ltr"> cosθH3<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> ΔH+4qL)<h2 style=";text-align:left;direction:ltr"> R <h2 style=";text-align:left;direction:ltr"> 4 <h2 style=";text-align:left;direction:ltr"> / 7L<h2 style=";text-align:left;direction:ltr"> R <h2 style=";text-align:left;direction:ltr"> 3 Where: F is the roof pressure in the cut 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; After the combined operation of hydraulic slotting and cavitation, the energy of the incident wave and the transmitted wave of the dynamic load stress wave after encountering the cavity and the slot meets the following conditions: Where: W I , W T They represent the total energy of the incident wave and the transmitted wave under dynamic loading respectively; K is the attenuation rate of the stress wave after passing through the cavity; represent the energy of longitudinal and transverse waves on the incident side, respectively; They represent the energy of longitudinal and shear waves on the transmission side respectively; A is the area of ​​the unit measuring point; x1 is the distance between the side close to the source and the source; x2 is the distance between the side far from the source and the source; ρ is the rock density in the cut area; c P is the longitudinal wave velocity; c s is the shear wave velocity; σ1 and τ1 are the normal stress and tangential stress of the incident surface, respectively; σ2 and τ2 are the normal stress and tangential stress of the transmission surface, respectively; Step 4, based on the simulation model of Step 2 and the hydraulic cutting and cavitation combined weakening anti-bumping conditions of Step 3, firstly, in the simulation model, simulate hydraulic cutting to form multi-layer slots for the tunnel roof in the dangerous area of ​​the tunnel, and simulate hydraulic cavitation to form cavities for the coal pillars in the adjacent dangerous area of ​​the tunnel, then simulate the dynamic load generated by the roof breakage at the far-field dynamic load source position, and simultaneously perform numerical simulation of the working face recovery of the subsequent mining plan, so as to obtain the optimal hydraulic cutting and cavitation combined anti-bumping technical parameters that can weaken the dynamic load and reduce the static load; Step 5, according to the optimal hydraulic slotting and cavitation combined anti-bumping technical parameters obtained in Step 4, a drilling rig is arranged in the tunnel of the target working face of the mine, and holes are drilled into the tunnel roof in the dangerous area of ​​the tunnel and the coal pillars adjacent to the dangerous area of ​​the tunnel respectively, and the high-pressure water jet ejected from the jet nozzle at the end of the drill rod and sprayed along the radial direction of the drill rod is used to impact and crush the roof rock and coal body, and through the rotation and retreat of the drill rod, multi-layer slots are formed in the tunnel roof in the dangerous area of ​​the tunnel, and columnar holes are formed in the coal pillars adjacent to the dangerous area of ​​the tunnel, and so on, to complete the opening of all multi-layer slots and holes; Step 6. According to the regional and real-time monitoring results of the tunnel surrounding rock in the target area monitored on site, determine the impact mine pressure hazard of the target tunnel surrounding rock before and after hydraulic cutting and cavitation, evaluate and verify the anti-collision effect of hydraulic cutting and cavitation, and repeat Step 4 for the areas where the anti-collision effect does not meet the combined weakened anti-collision condition of hydraulic cutting and cavitation in Step 3, adjust the optimal hydraulic cutting and cavitation combined anti-collision technical parameters obtained in Step 4, and perform the hydraulic cavitation construction operation of Step 5 again based on the adjusted and optimized optimal hydraulic cutting and cavitation combined anti-collision technical parameters until the anti-collision effect meets the combined weakened anti-collision condition of hydraulic cutting and cavitation in Step 3.

2. The anti-collision method for isolated working face tunnel according to claim 1 is characterized in that: When numerically simulating the mining process of the target working face in Step 2, firstly, the mine data including the geological conditions and mining conditions of the coal seam of the target fully-mechanized caving working face, as well as the basic mechanical parameter data of the coal body and surrounding rock of the coal seam and its goaf of the target fully-mechanized caving working face, the internal porosity data and the fracture distribution data are imported into the load-deformation finite element model; then, the vertical stress distribution is calculated to obtain the area with high elastic energy density of the roof; the mesh of the area with high elastic energy density of the roof is encrypted; finally, the numerical simulation of the mining process of the target fully-mechanized caving working face is carried out to obtain the stress distribution, deformation characteristics and periodic collapse data of the roof and top coal of the target fully-mechanized caving working face and roadway.

3. The anti-collision method for isolated working face tunnel according to claim 1 is characterized in that: In Step 4, when hydraulic cutting is simulated for the tunnel roof in the dangerous area of ​​the tunnel and hydraulic cavitation is simulated for the coal pillar in the adjacent dangerous area of ​​the tunnel in the simulation model, the dynamic load weakening area of ​​the cavity and the multi-layer seam structure is located on the line connecting the far-field dynamic load source and the dangerous area of ​​the tunnel.

4. The anti-collision method for isolated working face tunnel according to claim 3 is characterized in that: When simulating hydraulic cutting of the tunnel roof in the dangerous area of ​​the tunnel in Step 4, drilling is carried out near the junction of the tunnel roof coal and the coal pillar and hydraulic cutting is carried out. The downward extension range of the first layer of hydraulic cutting does not exceed the interface between the coal pillar and the immediate roof, the coverage range of the multi-layer seam grooves does not exceed the width range of the coal pillar adjacent to the dangerous area of ​​the tunnel, and the upward extension range of the last layer of hydraulic cutting does not exceed the thickness range of the immediate roof.

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

6. The anti-collision method for isolated working face tunnel according to claim 3 is characterized in that: When simulating hydraulic cavitation for coal pillars in dangerous areas adjacent to tunnels in Step 4, 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.

7. The anti-collision method for isolated working face tunnel according to claim 3 is characterized in that: When simulating hydraulic cavitation for coal pillars in dangerous areas adjacent to tunnels in Step 4, the drill rod elevation angle θ1 satisfies the following conditions: θ1=arctan(H1 / m+l0) Where: H1 is the thickness of the coal seam; m is the width of the coal pillar; l0 is the distance between the drilling rig and the coal pillar.

8. The anti-collision method for isolated working face tunnel according to claim 1, characterized in that: When obtaining the optimal hydraulic slotting and cavitation combined anti-scouring technical parameters that can weaken dynamic loads and reduce static loads in Step 4, the dynamic load attenuation rate, the stress-strain change characteristics of the tunnel surrounding rock, and the stress transfer characteristics of the coal pillar area under different parameter conditions are obtained by grouping numerical simulations of different parameters of multi-layer slots and cavities, and the main control parameters of hydraulic slotting and cavitation combined anti-scouring are judged and obtained to form the optimal hydraulic slotting and cavitation combined anti-scouring technical parameters.

9. The anti-collision method for isolated working face tunnel according to claim 1, characterized in that: When evaluating and verifying the anti-impact effect of hydraulic cutting and cavitation in Step 6, first measure the deformation of the surrounding rock of the tunnel, compare the deformation of the surrounding rock in the cutting area and the uncut area, measure the settlement of the coal pillar roof, calculate the pressure of the coal pillar roof after hydraulic cavitation, and measure the stress concentration level of the surrounding rock by the drill cuttings method. Then, compare and verify the measured data, theoretical model calculations and numerical simulation calculations.

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