Hydrodynamic caving weakening anti-scour method for hard roof of free roadway

Abstract

The invention discloses an open-air roadway hard roof hydraulic caving weakening scour prevention method which comprises the following steps: firstly, judging a roadway area with the risk of inducing rock burst, and analyzing dynamic and static load states on roadway surrounding rocks when dynamic load phenomena such as fracture of adjacent goaf roofs and the like occur; according to the critical condition of rock burst occurrence, the hydraulic weakening scour prevention requirement is determined, then according to the action effect of weakening parameters on the weakening effect, a proper cavity arrangement scheme is selected, and the construction position, angle and size of a cavity are determined; and then hydraulic cave building construction is carried out. On one hand, pressure relief can be performed on roadway surrounding rock by utilizing the cavity space from a static load angle to reduce static load, and on the other hand, transmission of far-field dynamic load to the roadway surrounding rock can be retarded by utilizing the cavity space to reduce dynamic load; the energy capable of inducing the rock burst disaster is reduced in the two aspects of dynamic load and static load, the load value of the surrounding rock of the roadway is reduced and is lower than the impact inducing critical value, and the possibility of the rock burst disaster of the roadway can be remarkably reduced.

Description

Technical Field

[0001] The present invention relates to a method for hydraulically creating holes to weaken and prevent impacts on the hard roof of an empty tunnel, and specifically to a method for hydraulically creating holes to weaken and prevent impacts on the hard roof of an empty tunnel by using hydraulic hole-making technology to reduce the energy that can induce rock burst disasters in terms of both dynamic loads and static loads, thereby improving the anti-impact capacity 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 moved deeper underground, which has led to increased ground stress in coal seams and increased mining disturbances. The threat of rock burst to underground coal mine production has become increasingly severe and complex. Rock burst is the result of the combined action of dynamic and static load factors in the coal mining process. Among them, static load factors include the deadweight of the overlying coal and rock layers and the pressure generated by geological structures and mining disturbances, and dynamic load factors include blast waves and seismic activities generated by blasting operations. When the energy accumulated by the superposition of static loads and dynamic loads on the surrounding rock of the tunnel exceeds the limit that the surrounding rock of the tunnel can bear, rock burst disasters will be induced in the tunnel. According to statistics, 90% of rock burst accidents occur in tunnels, especially tunnels near goafs (referred to as "goaf tunnels"). Local stress concentration is prone to occur in the coal and rock mass around the tunnel, and when the hard roof overlying the adjacent goaf breaks, impact loads can be generated and quickly propagate toward the tunnel in the form of stress waves. Therefore, the goaf tunnel is always under the threat of rock burst disasters.

[0003] At present, the main anti-blowout measures for tunnel surrounding rock include coal seam water injection, drilling pressure relief, artificial blasting, etc. Among them, coal seam water injection weakens the mechanical strength of coal body and thus reduces the accumulation of elastic energy, and the prevention effect is relatively simple; drilling pressure relief can reduce the stress concentration of surrounding coal and rock body, but the influence range of a single drilling hole is limited; artificial blasting has a large pressure relief range, but it is difficult to apply on a large scale due to the restrictions of safe operation and environmental protection. Summary of the invention

[0004] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for hydraulic cavitation weakening and anti-impacting of the hard roof of an empty tunnel, which can reduce the energy that can induce impact ground pressure disasters in terms of both dynamic loads and static loads, and thus make the load borne by the tunnel lower than the critical value that can induce impact mine pressure disasters, thereby improving the anti-impact ability of the tunnel, and is particularly suitable for anti-impacting of empty tunnels.

[0005] To achieve the above purpose, the hydraulic cavitation weakening and anti-scouring method of the hard roof of the air-link tunnel specifically includes the following steps:

[0006] Step 1: Obtain mine data, conduct on-site sampling, prepare standard samples for experiments, and obtain basic mechanical parameter data of coal bodies and surrounding rocks around tunnels in different areas and optimal hydraulic rock breaking technical parameters;

[0007] Step 2: Based on the data from Step 1, a three-dimensional numerical model of the load and deformation of the mining working face-tunnel-coal pillar-adjacent goaf is constructed to simulate the surrounding rock stress values ​​of the tunnels in different areas during the mining process of the working face; the simulation results calculated by the numerical model are verified and the parameters are optimized using the monitoring results of the roof periodic fracture and collapse and coal seam mining stress data at the mine site; the optimized numerical simulation is used to calculate the tunnel area with high static load and large stress concentration coefficient and the roof fracture area of ​​the adjacent goaf, identify the tunnel section with the risk of rock burst, and determine the target area tunnel;

[0008] Step 3: According to the on-site microseismic monitoring results, obtain the far-field dynamic load value and the location of the dynamic load source, and set the hydraulic cavitation weakening anti-scouring conditions that can meet the tunnel anti-scouring requirements;

[0009] The following conditions must be met for hydraulic cavitation:

[0010]

[0011] Where: U t is the total energy of the tunnel surrounding rock under the combined action of dynamic and static loads; E is the elastic modulus of the tunnel surrounding rock; σ s and σ d are the static load and dynamic load acting on the surrounding rock of the tunnel respectively; l It is the critical value of dynamic and static load that can cause rock burst in the tunnel;

[0012] Initial static load of tunnel surrounding rock σ 0s and dynamic load σ 0d The following conditions must be met:

[0013]

[0014] Where: H n is the vertical height of coal strata at different burial depths; ρ n is the density of different coal and rock layers; g is the acceleration of gravity; M is the mass of the collapsed rock layer; v is the collapse velocity of the rock layer; A is the impact area; λ is the Lame constant of the rock layer; w is the stress wave frequency of the impact load;

[0015] in:

[0016]

[0017] Where: c is the vertical damping coefficient of the rock formation; k is the vertical spring coefficient of the rock formation; G is the shear modulus of the rock formation; u is the Poisson's ratio of the rock formation; r is the equivalent radius of the collapsed rock mass;

[0018] When hydraulic cavitation exists in the surrounding rock of the tunnel, the static load σ s and dynamic load σ d Different attenuation will occur, and the attenuated values ​​meet the following conditions:

[0019]

[0020] Where: r0 is the hole radius; r x is the distance between the surrounding rock position and the center of the cavity; C is the stress wave attenuation coefficient; x0 is the distance between the cavity and the dynamic load source; x is the distance between the surrounding rock and the dynamic load source;

[0021] The dynamic and static loads after weakening should be less than the critical stress σ of rock burst l , critical stress σ l It is expressed as follows:

[0022]

[0023] Where: K is the impact energy index, which is determined by the stress-strain curve of the uniaxial compression of the coal rock sample; σ c is the uniaxial compression strength of the sample; p0 is the support strength of the tunnel surrounding rock;

[0024] The propagation speed of stress wave v w The following conditions:

[0025] v w =[(λ+2G) / ρ] 1 / 2 ;

[0026] Step 4: Based on the three-dimensional numerical model of load deformation in Step 2 and the hydraulic cavitation weakening anti-scouring conditions in Step 3, simulate hydraulic cavitation to form cavities in the target area tunnels in the numerical model, and determine the hydraulic cavitation technical parameters including hydraulic cavitation orientation, distance, size and number that can meet the tunnel anti-scouring requirements;

[0027] Step 5: Based on the hydraulic cavitation technical parameters obtained in Step 4, a drilling rig is arranged in the tunnel space of the target area to drill holes, and a high-pressure water jet is ejected from the jet nozzle at the end of the drill pipe and radially ejected along the drill pipe to impact and crush the rock at the bottom of the hole to form a columnar cavity. This process is repeated to complete the hydraulic cavitation of all the cavities.

[0028] 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 rock burst hazard of the target tunnel surrounding rock before and after hydraulic cavitation, evaluate and verify the anti-blasting effect of hydraulic cavitation, and repeat Step 4 for areas where the anti-blasting effect does not meet the weakened anti-blasting conditions of hydraulic cavitation in Step 3, adjust the hydraulic cavitation technical parameters obtained in Step 4, and perform the hydraulic cavitation construction work in Step 5 again based on the adjusted and optimized hydraulic cavitation technical parameters until the anti-blasting effect meets the weakened anti-blasting conditions of hydraulic cavitation in Step 3.

[0029] Furthermore, when constructing the load-deformation three-dimensional numerical model of the mining working face-tunnel-coal pillar-adjacent goaf in Step 2, the basic mechanical parameter data of the surrounding rock of the working face, tunnel and goaf are imported into the model to determine the boundary conditions and initial conditions of the model; then a material model that conforms to the actual surrounding rock of the tunnel is selected, and the distribution of the vertical stress of the structure is analyzed according to the material mechanics theory to obtain the area with high elastic energy density of the roof; then the model is reasonably meshed, the mesh is encrypted in the area with high elastic energy density, and the mesh density of the key area is optimized; then appropriate loading conditions and boundary conditions are set to perform numerical simulation of the mining process of the target fully mechanized caving working face; finally, the numerical simulation analysis results are compared and verified with the on-site monitoring results, and the roof fracture collapse data and mining stress data at the mine site are used to verify and optimize the parameters of the numerical simulation model, and the calculation parameters are continuously iterated to calibrate and optimize the model, and finally the simulation model that conforms to the actual production conditions and monitoring data of the mine site is optimized.

[0030] Furthermore, when simulating hydraulic cavitation in Step 4, in the process of simulating drilling from the vicinity of the junction of the tunnel roof and the coal pillar into the tunnel surrounding rock and simulating hydraulic cavitation to form a cavity, the forward extension range of the cavity does not exceed the junction of the immediate roof and the basic roof, and the backward extension range does not exceed the junction of the top coal and the immediate roof.

[0031] Furthermore, when simulating hydraulic cavitation in Step 4, the cavity is located in the direction of stress wave propagation from the dynamic load source to the tunnel.

[0032] Furthermore, the axial direction of the cavity corresponds to the direction of stress wave propagation from the dynamic load source to the tunnel.

[0033] Furthermore, when simulating hydraulic cavitation in Step 4, drilling holes is constructed into the roof and floor of the adjacent goaf, and the drilling direction of the drill rod is 90° to the direction of the tunnel. The drill rod elevation angle θ1 and depression angle θ2 satisfy the following conditions:

[0034]

[0035] In the formula: h0 is the height of the drilling rig; l0 is the distance between the drilling rig and the coal pillar, and h1 is the height of the tunnel.

[0036] Furthermore, when simulating hydraulic cavitation in Step 4, the cavity radius r0 of hydraulic cavitation satisfies the following conditions:

[0037]

[0038] Where: p is the jet pressure; r m is the nozzle radius; is the internal friction angle of the surrounding rock; τ is the shear strength of the surrounding rock; c c It is the cohesion of surrounding rock.

[0039] Furthermore, in Step 6, when adjusting the hydraulic cavitation technical parameters obtained in Step 4, group tests are carried out for different parameters to obtain the main control parameters of hydraulic cavitation for anti-scouring, and comparative verification is carried out among measured data, theoretical model calculations and numerical simulations, and corrections are made to the main control parameters that do not meet expectations.

[0040] Compared with the existing technology, the hydraulic cavitation weakening and anti-bumping method of the hard roof of the goaf tunnel first determines the tunnel area with the risk of inducing rock burst, and analyzes the dynamic and static load states on the tunnel surrounding rock when dynamic load phenomena such as fracture of the roof of the adjacent goaf occur; the anti-bumping demand of hydraulic weakening is determined according to the critical conditions for the occurrence of rock burst, and then according to the effect of the weakening parameters on the weakening effect, the appropriate cavity arrangement scheme is selected to determine the construction position, angle and size of the cavity; then the hydraulic cavitation construction is carried out. On the one hand, from the static load perspective, the cavity space can be used to relieve the pressure on the tunnel surrounding rock and reduce the static load, and on the other hand, the cavity space can be used to block the far field The transmission of dynamic load to the surrounding rock of the tunnel and the reduction of dynamic load can jointly reduce the energy that can induce impact ground pressure disasters in terms of dynamic load and static load, reduce the load value of the tunnel surrounding rock and be lower than the critical value of induced impact, which can significantly reduce the possibility of impact ground pressure disasters in the tunnel and greatly improve the anti-impact effect. At the same time, the construction process of this hydraulic cavitation weakening and anti-impact method for the hard roof of the air-facing tunnel is relatively refined and the engineering volume is small. The water jet rock breaking technology itself is relatively mature, the process is safe and green and pollution-free. The single cavity has a large anti-impact area and good engineering benefits. It can actively and efficiently prevent and control the risk of impact disasters in the tunnel, and is particularly suitable for anti-impact in air-facing tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a top view layout diagram of the hydraulic cavitation construction of the present invention;

[0042] Figure 2 It is a side view layout diagram of the hydraulic cavitation construction of the present invention;

[0043] Figure 3Graphs showing the effect of hydraulic cavitation on static load and dynamic load according to the present invention, wherein (a) is a graph showing the effect of hydraulic cavitation on static load, and (b) is a graph showing the effect of hydraulic cavitation on dynamic load.

[0044] In the figure: 1. Dynamic load source; 2. Adjacent goaf; 3. Propagation path of stress wave; 4. Coal pillar; 5. Cavity; 6. Roadway; 7. Area in the roadway with the risk of rock burst; 8. Coal seam to be mined in this working face; 9. Goaf in this working face; 10. Coal seam roof; 11. Coal seam floor. DETAILED DESCRIPTION

[0045] Hydraulic cavitation technology is a safe, green and efficient technical means. It constructs conventional holes in the surrounding rock (coal seam and roof) of the tunnel, and uses high-pressure water jets to rotate and impact along the radial direction of the holes, so as to form a cavity space of a certain diameter in the coal rock layer. The technology is safe to operate, the jet fluid is water, there is no environmental pollution, and the cavitation space and the impact range are much larger than the pressure relief borehole. The present invention uses hydraulic cavitation technology to reduce the energy that can induce rock burst disasters in terms of both dynamic load and static load.

[0046] The present invention will be further described below in conjunction with the accompanying drawings.

[0047] The hydraulic cavitation weakening and anti-impact method for the hard roof of the air-linked tunnel uses hydraulic cavitation to jet impact the surrounding rock of the air-linked tunnel to break the rock and create cavities, reduce the stress concentration of the static load of the surrounding rock, and block the propagation of the far-field dynamic load toward the tunnel direction, increase the energy dissipation of the dynamic load on the propagation path, and realize the efficient prevention and control of the rock burst disaster in the tunnel. The specific steps include:

[0048] Step 1, conduct on-site investigation, collect geological data of the target mine, historical rock burst event records, mining parameters and other data, analyze the implementation of on-site coal seam mining sequence, coal pillar retention, mining methods, etc. Conduct on-site sampling and testing, experimentally obtain data such as surrounding rock characteristics and basic mechanical parameters of coal and rock mass, analyze the geological structure of the mining site, mechanical property test of coal and rock strata, stress state of coal and rock strata, monitoring results of periodic fracture and collapse of roof, monitoring results of coal seam mining stress, obtain the influence of different factors on rock burst, and conduct rock burst tendency identification and rock burst hazard evaluation for different tunnel areas.

[0049] When obtaining data on surrounding rock characteristics and basic mechanical parameters of coal and rock mass, coal samples, roof surrounding rock samples, floor surrounding rock samples and other samples can be selected from the target area tunnels in the coal mine and brought to the surface. Standard samples (Φ50×100mm and Φ50×25mm) are prepared in the laboratory and tested using an MTS triaxial loading tester to obtain data on the elastic modulus, compressive / tensile strength, Poisson’s ratio, internal friction angle and other data of the surrounding rock samples. For samples with a volume of not less than 0.1m 3The block samples of raw coal and roof rock in the shape of a cube are processed into cubes with a side length of 20 cm. Water jet impact crushing tests with different abrasive concentrations, jet pressures, nozzle radii and cutting times are carried out to obtain the optimal jet pressure p, nozzle radius R and rock breaking radius L. R And other hydraulic rock breaking technical parameters.

[0050] Step 2. Based on the data from Step 1, a three-dimensional numerical model of load and deformation of the mining face-tunnel-coal pillar-adjacent goaf is constructed using RFPA software to simulate the surrounding rock stress values ​​(static load) of tunnels in different areas during the mining process of the working face; the simulation results calculated by the numerical model are verified and parameters are optimized using the data monitoring results of the roof periodic fracture and collapse, coal seam mining stress, etc. at the mine site; the optimized numerical simulation is used to calculate the tunnel areas with high static loads and large stress concentration coefficients and the roof fracture areas of adjacent goafs (the location of the far-field dynamic load source), identify the tunnel sections with the risk of rock burst, and determine the target area tunnels.

[0051] When constructing the load-deformation three-dimensional numerical model of the mining working face-tunnel-coal pillar-adjacent goaf, the three-dimensional numerical model is established using REPF software based on the on-site investigation and experimental test results of the target mine site, and the basic mechanical parameter data of the surrounding rock of the working face, tunnel and goaf are imported into the model to determine the boundary conditions and initial conditions of the model; then, an appropriate material model is selected, the material parameters are checked to ensure that they conform to the actual situation, the distribution of the vertical stress of the structure is analyzed according to the material mechanics theory, and the area with high elastic energy density of the roof is determined; the model is reasonably meshed, the mesh is encrypted in the area with high elastic energy density, and the mesh density of the key area is optimized to ensure the simulation The accuracy of the results meets the requirements; then set appropriate loading conditions and boundary conditions, select appropriate numerical solutions, and carry out numerical simulation of the mining process of the target fully mechanized caving working face. During the process, monitor the convergence and stability of the calculation process to ensure that the calculation can complete the expected steps; finally, compare and verify the numerical simulation analysis results with the field monitoring results, use the roof fracture and collapse data, mining stress data and other data at the mine site to verify and optimize the parameters of the numerical simulation model, and iterate and adjust the calculation parameters to correct and optimize the model, so that the calculation results are consistent with the actual situation on site, and finally optimize to form a simulation model that meets the actual production conditions and monitoring data of the mine site.

[0052] Step 3, based on the on-site microseismic monitoring results, obtain the far-field dynamic load value and the location of the dynamic load source caused by the roof fracture and artificial blasting in the adjacent goaf, and set the hydraulic cavitation weakening anti-scouring conditions that can meet the tunnel anti-scouring requirements according to the location of the far-field dynamic load source.

[0053] The following conditions must be met for hydraulic cavitation:

[0054]

[0055] Where: U t is the total energy of the tunnel surrounding rock under the combined action of dynamic and static loads; E is the elastic modulus of the tunnel surrounding rock; σ s and σ d are the static load and dynamic load acting on the surrounding rock of the tunnel respectively; l It is the critical value of dynamic and static loads that can cause rock burst in the tunnel.

[0056] Initial static load of tunnel surrounding rock σ 0s and dynamic load σ 0d satisfy:

[0057]

[0058] Where: H n is the vertical height of coal strata at different burial depths; ρ n is the density of different coal and rock formations; g is the acceleration of gravity; M is the mass of the collapsed rock formation; v is the collapse velocity of the rock formation; A is the impact area; λ is the Lame constant of the rock formation; and w is the stress wave frequency of the impact load.

[0059] in:

[0060]

[0061] Where: c is the vertical damping coefficient of the rock formation; k is the vertical spring coefficient of the rock formation; G is the shear modulus of the rock formation; u is the Poisson's ratio of the rock formation; r is the equivalent radius of the collapsed rock mass;

[0062] When hydraulic cavitation exists in the surrounding rock of the tunnel, the static load σ s and dynamic load σ d Different attenuations will occur, and the attenuated values ​​satisfy:

[0063]

[0064] Where: r0 is the hole radius; r x is the distance between the surrounding rock position and the center of the cavity; C is the stress wave attenuation coefficient; x0 is the distance between the cavity and the dynamic load source; x is the distance between the surrounding rock and the dynamic load source.

[0065] The dynamic and static loads after weakening should be less than the critical stress σ of rock burst l :

[0066]

[0067] Where: K is the impact energy index, which is determined by the stress-strain curve of the uniaxial compression of the coal rock sample; σ cis the uniaxial compression strength of the sample; p0 is the support strength of the tunnel surrounding rock.

[0068] The propagation speed of stress wave v w satisfy:

[0069] v w =[(λ+2G) / ρ] 1 / 2 .

[0071] Step 4, based on the load-deformation three-dimensional numerical model of Step 2 and the hydraulic cavitation weakening anti-scouring conditions of Step 3, simulate the hydraulic cavitation to form cavities in the target area tunnels in the numerical model, and determine the hydraulic cavitation technical parameters including hydraulic cavitation orientation, distance, size and number that can meet the tunnel anti-scouring requirements.

[0072] When simulating hydraulic cavitation, Figure 1 , Figure 2 As shown in the figure, simulated drilling and hydraulic cavitation are performed from the junction of the roadway roof and the coal pillar to the surrounding rock of the roadway to form a cavity. The forward extension range of the cavity does not exceed the junction of the direct roof and the basic roof, and the backward extension range does not exceed the junction of the top coal and the direct roof. In order to obtain a better anti-impact effect, the cavity can be located in the direction of stress wave propagation from the dynamic load source to the roadway, and the axial direction of the cavity corresponds to the direction of stress wave propagation from the dynamic load source to the roadway. In response to the dynamic load of the roof breaking and the impact of the roof collapse on the floor of the goaf, drilling can be carried out along the coal pillar side to the roadway roof area, and hydraulic cavitation operations can be completed. Then, a hydraulic cavitation operation is performed on the floor to form a hydraulic cavitation protection surface for the dynamic load of the roof breaking and the impact of the roof collapse on the floor of the goaf.

[0073] When simulating drilling, drilling is performed on the roof and floor of the adjacent goaf, and the drilling direction of the drill rod is 90° to the direction of the tunnel. The drill rod elevation angle θ1 and depression angle θ2 satisfy the following conditions:

[0074]

[0075] In the formula: h0 is the height of the drilling rig; l0 is the distance between the drilling rig and the coal pillar, and h1 is the height of the tunnel.

[0076] The radius r0 of the hydraulic cavitation is not unlimited. It is restricted by the jet pressure, nozzle radius, and basic mechanical parameters of the surrounding rock, and meets the following conditions:

[0077]

[0078] Where: p is the jet pressure; r m is the nozzle radius; is the internal friction angle of the surrounding rock; τ is the shear strength of the surrounding rock; c cIt is the cohesion of surrounding rock.

[0079] Step 5. Based on the technical parameters such as the orientation, distance, size and number of hydraulic cavitation that can meet the requirements of tunnel anti-blowout obtained in Step 4, arrange the drilling rig in the tunnel space of the target area, and construct the borehole obliquely along the coal pillar side to the tunnel surrounding rock (coal seam roof) area. At the bottom of the borehole, use the jet nozzle at the end of the drill pipe and the high-pressure water jet sprayed radially along the drill pipe to impact and crush the roof rock. Through the rotation and retreat of the drill pipe, a cylindrical cavity is formed in the hard roof, completing a hydraulic rock breaking and cavitation construction operation, so that the formed cavity meets the expected requirements of orientation, angle, distance and size. By analogy, complete the hydraulic cavitation of all the cavities.

[0080] When hydraulic cavitation is carried out on site, the construction plan of hydraulic cavitation is first designed and optimized according to the coal seam occurrence conditions, geological structure, top and bottom plate lithology and other characteristics of the mining site; then the drilling rig, high-pressure water pump, water curtain support equipment and other equipment are connected and powered on to carry out performance tests to ensure stable and reliable performance during the construction process; then the position, orientation and angle of the borehole are determined in the surrounding rock of the tunnel according to the determined hydraulic cavitation construction plan, and the drilling rig is used for drilling operations, and the drilling progress and water pressure are controlled to ensure the quality of the drilling; then the emulsification pump driver is notified through the underground dedicated communication system to turn on the high-pressure pump switch, and when water flows into the high-pressure water pipe, the emulsification pump pressure is adjusted according to the water pressure parameters designed in the early stage, and the drilling rig is started, and the drill rod is reciprocated through drilling and retreat, and high-pressure water is used to rotate and continuously cut and flush, with 1m as a circulation unit, and flushing is repeated until the set time, and the advance and retreat of the high-pressure drill rod is controlled according to the drilling slag discharge situation and the actual slag discharge amount until the hydraulic cavitation operation of the target cavity is completed.

[0081] like Figure 3 As shown in the figure, the hole-making space is used to relieve the pressure on the surrounding rock around the hole, reducing the stress concentration coefficient of the static load; at the same time, when the hard roof fracture occurs in the adjacent goaf, the hole-making space is used to weaken the stress wave propagating from the dynamic load source to the tunnel, reducing the size of the dynamic load received by the tunnel surrounding rock. The possibility of rock burst disasters in the tunnel surrounding rock is reduced from both dynamic and static loads.

[0082] Step 6. According to the regional and real-time monitoring results of the tunnel surrounding rock in the target area of ​​on-site monitoring (such as ground stress, drill cuttings, microseismic monitoring, electromagnetic radiation monitoring, etc.), the rock burst hazard of the target tunnel surrounding rock before and after hydraulic cavitation is determined, and the anti-impact effect of hydraulic cavitation is evaluated and verified. For the places where the anti-impact effect does not meet the expectations (i.e., the weakened anti-impact conditions of hydraulic cavitation in Step 3 are not met), Step 4 is repeated, and the hydraulic cavitation technical parameters obtained in Step 4 are adjusted to optimize the hydraulic cavitation anti-impact technical scheme, and the hydraulic cavitation construction operation in Step 5 is performed again until the anti-impact effect reaches the expected effect.

[0083] When evaluating and verifying the anti-blowout effect of hydraulic cavitation, taking microseismic monitoring as an example, as the working face advances, the surrounding rock properties and stress-strain conditions of the target tunnel will change due to mining and cavitation operations. Microseismic detection points near the tunnel are used to detect the mine earthquake energy and locate the mine earthquake position. The microseismic data after cavitation is compared with the historical microseismic data before cavitation to obtain the attenuation coefficient of the cavity to the stress wave; at the same time, the measured tunnel surrounding rock stress-strain-time data is theoretically calculated to obtain the dynamic load attenuation rate; then the measured attenuation rate, theoretically calculated attenuation rate and numerically simulated attenuation rate are compared, and the technical parameters of the cavitation operation whose attenuation rate does not meet expectations are corrected.

[0084] When adjusting the hydraulic cavitation technical parameters obtained in Step 4, the hydraulic cavitation position, cavitation depth, drill rod elevation angle θ, hydraulic cavitation radius L can be adjusted. R The hydraulic cavitation technical parameters are adjusted by group tests based on parameters such as the height dimension h0 of the drilling rig, the distance dimension l0 between the drilling rig and the end of the working face, the main control parameters of the hydraulic cavitation for anti-scouring are obtained, the measured data, theoretical model calculations and numerical simulations are compared and verified, and the hydraulic cavitation for anti-scouring technical scheme is optimized.

[0085] On the one hand, this hydraulic cavitation weakening and anti-impact method for the hard roof of the tunnel near the sky can use the cavity space to relieve the pressure on the tunnel surrounding rock and reduce the static load from the static load perspective. On the other hand, it can use the cavity space to block the propagation of far-field dynamic loads to the tunnel surrounding rock and reduce the dynamic load, thereby achieving the reduction of the energy that can induce rock burst disasters in terms of both dynamic and static loads, reducing the load value of the tunnel surrounding rock and lowering it below the critical value of inducing rock burst, which can significantly reduce the possibility of rock burst disasters in the tunnel and greatly improve the anti-impact effect. At the same time, the construction process of this hydraulic cavitation weakening and anti-impact method for the hard roof of the tunnel near the sky has a relatively refined construction process and a small amount of engineering work. The water jet rock breaking technology itself is relatively mature, the process is safe and green and pollution-free, the single cavity has a large anti-impact area and good engineering benefits, and is particularly suitable for anti-impact in tunnels near the sky.

Claims

1. A method for hydraulically creating holes to weaken and prevent erosion in hard roof of an open tunnel, characterized in that: The specific steps include: Step 1: Obtain mine data, conduct on-site sampling, prepare standard samples for experiments, and obtain basic mechanical parameter data of coal bodies and surrounding rocks around tunnels in different areas and optimal hydraulic rock breaking technical parameters; Step 2: Based on the data from Step 1, a three-dimensional numerical model of the load and deformation of the mining face-tunnel-coal pillar-adjacent goaf is constructed to simulate the surrounding rock stress values ​​of the tunnels in different areas during the mining process of the working face; The simulation results obtained by numerical model calculation are verified and parameters are optimized using the monitoring results of roof periodic fracture and collapse and coal seam mining stress data at the mine site; the optimized numerical simulation is used to calculate the roadway area with high static load and large stress concentration factor and the roof fracture area of ​​the adjacent goaf, identify the roadway section with rock burst danger, and determine the target area roadway; Step 3: According to the on-site microseismic monitoring results, obtain the far-field dynamic load value and the location of the dynamic load source, and set the hydraulic cavitation weakening anti-scouring conditions that can meet the tunnel anti-scouring requirements; The following conditions must be met for hydraulic cavitation: Where: U t is the total energy of the tunnel surrounding rock under the combined action of dynamic and static loads; E is the elastic modulus of the tunnel surrounding rock; σ s and σ d are the static load and dynamic load acting on the surrounding rock of the tunnel respectively; l It is the critical value of dynamic and static load that can cause rock burst in the tunnel; Initial static load of tunnel surrounding rock σ 0s and dynamic load σ 0d The following conditions must be met: Where: H n is the vertical height of coal strata at different burial depths; ρ n is the density of different coal and rock layers; g is the acceleration of gravity; M is the mass of the collapsed rock layer; v is the collapse velocity of the rock layer; A is the impact area; λ is the Lame constant of the rock layer; w is the stress wave frequency of the impact load; in: Where: c is the vertical damping coefficient of the rock formation; k is the vertical spring coefficient of the rock formation; G is the shear modulus of the rock formation; u is the Poisson's ratio of the rock formation; r is the equivalent radius of the collapsed rock mass; When hydraulic cavitation exists in the surrounding rock of the tunnel, the static load σ s and dynamic load σ d Different attenuation will occur, and the attenuated values ​​meet the following conditions: Where: r0 is the hole radius; r x is the distance between the surrounding rock position and the center of the cavity; C is the stress wave attenuation coefficient; x0 is the distance between the cavity and the dynamic load source; x is the distance between the surrounding rock and the dynamic load source; The dynamic and static loads after weakening should be less than the critical stress σ of rock burst l , critical stress σ l It is expressed as follows: Where: K is the impact energy index, which is determined by the stress-strain curve of the uniaxial compression of the coal rock sample; σ c is the uniaxial compression strength of the sample; p0 is the support strength of the tunnel surrounding rock; The propagation speed of stress wave v w The following conditions: v w =[(λ+2G) / ρ] 1 / 2 ; Step 4: Based on the three-dimensional numerical model of load deformation in Step 2 and the hydraulic cavitation weakening anti-scouring conditions in Step 3, simulate hydraulic cavitation to form cavities in the target area tunnels in the numerical model, and determine the hydraulic cavitation technical parameters including hydraulic cavitation orientation, distance, size and number that can meet the tunnel anti-scouring requirements; Step 5: Based on the hydraulic cavitation technical parameters obtained in Step 4, a drilling rig is arranged in the tunnel space of the target area to drill holes, and a high-pressure water jet is ejected from the jet nozzle at the end of the drill pipe and radially ejected along the drill pipe to impact and crush the rock at the bottom of the hole to form a columnar cavity. This process is repeated to complete the hydraulic cavitation of all the cavities. 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 rock burst hazard of the target tunnel surrounding rock before and after hydraulic cavitation, evaluate and verify the anti-blasting effect of hydraulic cavitation, and repeat Step 4 for areas where the anti-blasting effect does not meet the weakened anti-blasting conditions of hydraulic cavitation in Step 3, adjust the hydraulic cavitation technical parameters obtained in Step 4, and perform the hydraulic cavitation construction work in Step 5 again based on the adjusted and optimized hydraulic cavitation technical parameters until the anti-blasting effect meets the weakened anti-blasting conditions of hydraulic cavitation in Step 3.

2. The method for hydraulically creating holes to weaken and prevent impact in hard roof of air-access tunnels according to claim 1 is characterized in that: When constructing the load-deformation three-dimensional numerical model of the mining working face-tunnel-coal pillar-adjacent goaf in Step 2, the basic mechanical parameter data of the surrounding rock of the working face, tunnel and goaf are imported into the model to determine the boundary conditions and initial conditions of the model; then the material model that conforms to the actual surrounding rock of the tunnel is selected, and the distribution of the vertical stress of the structure is analyzed according to the material mechanics theory to obtain the area with high elastic energy density of the roof; then the model is reasonably meshed, the mesh is encrypted in the area with high elastic energy density, and the mesh density of the key area is optimized; then appropriate loading conditions and boundary conditions are set to perform numerical simulation of the mining process of the target fully mechanized caving working face; finally, the numerical simulation analysis results are compared and verified with the on-site monitoring results, and the roof fracture collapse data and mining stress data at the mine site are used to verify and optimize the parameters of the numerical simulation model, and the calculation parameters are adjusted iteratively to calibrate and optimize the model, and finally the simulation model that conforms to the actual production conditions and monitoring data at the mine site is optimized.

3. The method for hydraulically creating holes to weaken and prevent impact in hard roof of air-access tunnels according to claim 1 is characterized in that: When simulating hydraulic cavitation in Step 4, in the process of simulating drilling from the junction of the tunnel roof and the coal pillar into the tunnel surrounding rock and simulating hydraulic cavitation to form a cavity, the forward extension range of the cavity does not exceed the junction of the immediate roof and the basic roof, and the backward extension range does not exceed the junction of the top coal and the immediate roof.

4. The method for hydraulically creating holes to weaken and prevent impact in hard roof of air-access tunnels according to claim 1 is characterized in that: When simulating hydraulic cavitation in Step 4, the cavity is located in the direction of stress wave propagation from the dynamic load source to the tunnel.

5. The method for hydraulically creating holes to weaken and prevent impact in hard roof of air-access tunnels according to claim 4 is characterized in that: The axial direction of the cavity corresponds to the direction of stress wave propagation from the dynamic load source to the tunnel.

6. The method for hydraulically creating holes to weaken and prevent impact in hard roof of air-access tunnels according to claim 1 is characterized in that: When simulating hydraulic cavitation in Step 4, drilling holes is performed on the roof and floor of the adjacent goaf, and the drilling direction of the drill rod is 90° to the direction of the tunnel. The drill rod elevation angle θ1 and depression angle θ2 satisfy the following conditions: In the formula: h0 is the height of the drilling rig; l0 is the distance between the drilling rig and the coal pillar, and h1 is the height of the tunnel.

7. The method for hydraulically creating holes to weaken and prevent impact in hard roof of air-access tunnels according to claim 1 is characterized in that: When simulating hydraulic cavitation in Step 4, the radius of the hydraulic cavitation r0 satisfies the following conditions: Where: p is the jet pressure; r m is the nozzle radius; is the internal friction angle of the surrounding rock; τ is the shear strength of the surrounding rock; c c It is the cohesion of surrounding rock.

8. The method for hydraulically creating holes to weaken and prevent impact in hard roof of air-access tunnels according to claim 1 is characterized in that: In Step 6, when adjusting the hydraulic cavitation technical parameters obtained in Step 4, group tests are carried out for different parameters to obtain the main control parameters of hydraulic cavitation for anti-scouring, and comparative verification is carried out among measured data, theoretical model calculations and numerical simulations, and corrections are made to the main control parameters that do not meet expectations.

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