A hydraulic cavity-forming method for weakening and preventing erosion in the hard roof of an open tunnel.

Abstract

This invention discloses a hydraulic cavity-forming method for weakening and preventing rockbursts in hard roofs of roadways near goaf areas. First, the roadway area at risk of inducing rockbursts is identified, and the dynamic and static load states on the surrounding rock are analyzed when dynamic load phenomena such as roof fractures in adjacent goaf areas occur. Based on the critical conditions for rockburst occurrence, the rockburst prevention requirements for hydraulic weakening are determined. Then, based on the effect of weakening parameters on the weakening effect, a suitable cavity layout scheme is selected, and the construction location, angle, and size of the cavities are determined. Finally, hydraulic cavity-forming is carried out. This invention, on the one hand, utilizes the cavity space to relieve pressure on the surrounding rock and reduce static load from a static load perspective; on the other hand, it utilizes the cavity space to impede the propagation of far-field dynamic loads to the surrounding rock and reduce dynamic loads. This achieves a combined reduction in the energy that could induce rockburst disasters from both dynamic and static load perspectives, lowering the load value of the surrounding rock below the rockburst induction threshold, and significantly reducing the possibility of rockburst disasters in the roadway.

Description

Technical Field

[0001] This invention relates to a hydraulic cavity-forming method for weakening and preventing rockburst in the hard roof of an open roadway. Specifically, it is a method that uses hydraulic cavity-forming technology to weaken the surrounding rock of an open roadway to reduce the energy that can induce rockburst disasters in both dynamic and static load aspects, thereby improving the roadway's rockburst prevention capability. This method belongs to the field of coal mine safety mining technology. Background Art

[0002] Coal mining in my country is primarily underground. With the increasing depletion of shallow resources, coal mining is gradually extending to deeper underground areas. This leads to increased in-situ stress in the coal seam and intensified mining disturbances, making rockbursts a more severe and complex threat to underground coal mine production. Rockbursts are the result of the combined effects of dynamic and static loads during coal mining. Static load factors include the self-weight of the overlying coal and rock strata, geological structures, and pressure generated by mining disturbances. Dynamic load factors include detonation waves generated by blasting operations and seismic activity. When the combined static and dynamic loads accumulate on the surrounding rock of the roadway, exceeding the limit that the surrounding rock can withstand, a rockburst disaster will be induced. Statistics show that 90% of rockburst accidents occur in roadways, especially those near goaf areas (referred to as "goaf roadways"). Local stress concentration is likely to occur in the coal and rock mass surrounding the roadway, and when phenomena such as the fracture of the hard roof overlying the adjacent goaf occur, impact loads can be generated and propagate rapidly towards the roadway in the form of stress waves. Therefore, roadways near the goaf are always under the threat of rockburst disasters.

[0003] Currently, the main methods for preventing rock erosion in roadways include coal seam water injection, borehole pressure relief, and artificial blasting. Among these, coal seam water injection reduces the accumulation of elastic energy by weakening the mechanical strength of the coal, resulting in a relatively simple preventative effect; borehole pressure relief can reduce the stress concentration of the surrounding coal and rock mass, but the impact range of a single borehole is limited; artificial blasting has a large pressure relief range, but its widespread application is limited due to safety and environmental protection restrictions. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a hydraulic cavity-forming method for weakening and preventing rockburst in roadways with hard roofs near the ground. This method can reduce the energy that can induce rockburst disasters by both dynamic and static loads, thereby reducing the load borne by the roadway below the critical value that can induce rockburst disasters, thus improving the roadway's rockburst prevention capability. It is particularly suitable for rockburst prevention in roadways with grounds near the ground.

[0005] To achieve the above objectives, the hydraulic cavity-forming method for weakening and preventing scour in the hard roof of the tunnel includes the following steps:

[0006] Step 1: Obtain mine data and conduct on-site sampling, prepare standard samples for experiments, and obtain basic mechanical parameter data of coal and surrounding rock in different areas of roadways, as well as optimal hydraulic rock breaking technology parameters.

[0007] Step 2: Based on the data from Step 1, construct a three-dimensional numerical model of the load deformation of the longwall face, roadway, coal pillar, and adjacent goaf to simulate the surrounding rock stress values ​​of different areas of the roadway during the longwall face mining process. Verify and optimize the simulation results obtained from the numerical model using monitoring data on roof periodic fracture and collapse and coal seam mining-induced stress at the mine site. Utilize the optimized numerical simulation to calculate roadway areas with high static load and large stress concentration coefficients, as well as roof fracture areas in adjacent goafs, to identify roadway sections with rockburst hazards and determine the target roadway areas.

[0008] 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, and set hydraulic cavity creation weakening anti-scour conditions that can meet the anti-scour requirements of the roadway.

[0009] Hydraulic cavity creation must meet the following conditions:

[0010]

[0011] In the formula: U t σ represents the total energy of the surrounding rock of the roadway under the combined action of static and dynamic loads; E represents the elastic modulus of the surrounding rock of the roadway; σ represents the total energy of the surrounding rock of the roadway under the combined action of static and dynamic loads. s and σ d These are the static and dynamic loads acting on the surrounding rock of the roadway, respectively; σ l The dynamic and static load critical values ​​that enable rockburst in the roadway;

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

[0013]

[0014] Where: H n ρ represents the vertical height of coal and rock strata at different burial depths. n denoted as density of different coal and rock strata; g is the acceleration due to gravity; M is the mass of the collapsing rock strata; v is the collapse velocity of the rock strata; A is the impact area; λ is the Lamé constant of the rock strata; w is the stress wave frequency of the impact load.

[0015] in:

[0016]

[0017] In the formula: c is the vertical damping coefficient of the rock stratum; k is the vertical spring coefficient of the rock stratum; G is the shear modulus of the rock stratum; u is the Poisson's ratio of the rock stratum; 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 With dynamic load σ d All will experience different degrees of decay, and the decayed values ​​will satisfy the following conditions:

[0019]

[0020] In the formula: r0 is the radius of the hole; r x denoted as , where is the distance between the surrounding rock location and the cavity center; C is the stress wave attenuation coefficient; x0 is the distance between the cavity and the dynamic source; x is the distance between the surrounding rock and the dynamic source.

[0021] The weakened dynamic and static loads should be less than the critical stress σ required for rockburst to occur. l Critical stress σ l It is expressed as follows:

[0022]

[0023] In the formula: K is the impact energy index, determined by the stress-strain curve of uniaxial compression of the coal and rock sample; σ c p0 represents the uniaxial compressive strength of the sample; p0 represents the support strength of the surrounding rock of the roadway.

[0024] The propagation speed v of the stress wave 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 cavity creation weakening anti-scour conditions in Step 3, simulate hydraulic cavity creation to form cavities in the target area roadway in the numerical model, and determine the hydraulic cavity creation technical parameters, including the orientation, distance, size and quantity of hydraulic cavity creation, that can meet the anti-scour requirements of the roadway.

[0027] Step 5: Based on the hydraulic cavity-making technical parameters obtained in Step 4, drill rigs are deployed in the tunnel space of the target area to drill holes. High-pressure water jets are sprayed from the nozzle at the end of the drill rod and sprayed radially along the drill rod to impact and break the rock at the bottom of the hole, forming a columnar cavity. This process is repeated to complete the hydraulic cavity-making of all cavities.

[0028] Step 6: Based on the regional and real-time monitoring results of the surrounding rock of the target roadway in the field monitoring area, determine the rockburst risk of the surrounding rock of the target roadway before and after hydraulic cavity creation, evaluate and verify the anti-scour effect of hydraulic cavity creation, and for areas where the anti-scour effect does not meet the anti-scour weakening condition of hydraulic cavity creation in Step 3, repeat Step 4, adjust the hydraulic cavity creation technical parameters obtained in Step 4, and carry out the hydraulic cavity creation construction operation in Step 5 again based on the adjusted and optimized hydraulic cavity creation technical parameters until the anti-scour effect meets the anti-scour weakening condition of hydraulic cavity creation in Step 3.

[0029] Furthermore, in Step 2, when constructing the three-dimensional numerical model of the loading and deformation of the longwall face, roadway, coal pillar, and adjacent goaf, the basic mechanical parameter data of the surrounding rock of the longwall face, roadway, 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 roadway is selected, and the distribution of 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, and the mesh is densified in the area with high elastic energy density and the mesh density of key areas is optimized. Then, appropriate loading conditions and boundary conditions are set to conduct numerical simulation of the longwall mining process of the target fully mechanized longwall face. Finally, the numerical simulation analysis results are compared and verified with the field monitoring results. The numerical simulation model is verified and the parameters are optimized using the roof fracture and collapse data and mining-induced stress data from the mine site. The calculation parameters are continuously iterated and adjusted to correct and optimize the model, and finally, a simulation model that conforms to the actual production conditions and monitoring data of the mine site is formed.

[0030] Furthermore, in Step 4, when simulating hydraulic cavity creation, during the process of simulating drilling and hydraulic cavity creation from near the junction of the roadway roof and coal pillar into the surrounding rock, the forward extension of the cavity does not exceed the junction of the immediate roof and the main roof, and the backward extension does not exceed the junction of the top coal and the immediate roof.

[0031] Furthermore, during the simulated hydraulic cavity creation in Step 4, the cavity is located in the direction of stress wave propagation from the dynamic source into the tunnel.

[0032] Furthermore, the axial direction of the cavity corresponds to the direction in which the stress wave propagates from the dynamic source into the roadway.

[0033] Furthermore, during the simulated hydraulic cavity creation in Step 4, boreholes are drilled into the roof and floor of adjacent goaf areas, with the drilling direction of the drill rod at 90° to the direction of the roadway. The drill rod elevation angle θ1 and depression angle θ2 respectively satisfy the following:

[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 roadway.

[0036] Furthermore, during the simulated hydraulic cavity creation in Step 4, the cavity radius r0 of the hydraulic cavity creation satisfies the following condition:

[0037]

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

[0039] Furthermore, in Step 6, when adjusting the hydraulic cavity-forming technology parameters obtained in Step 4, group experiments are conducted for different parameters to obtain the main control parameters for hydraulic cavity-forming anti-scour. The measured data, theoretical model calculations and numerical simulations are compared and verified, and the main control parameters that do not meet the expectations are corrected.

[0040] Compared with existing technologies, this hydraulic cavity-making weakening and anti-rockburst method for hard roofs in goaf-prone roadways first identifies roadway areas with a risk of inducing rockbursts and analyzes the dynamic and static load states on the surrounding rock of the roadway when dynamic load phenomena such as roof fractures in adjacent goaf areas occur. Based on the critical conditions for rockburst occurrence, the anti-rockburst requirements for hydraulic weakening are determined. Then, based on the effect of weakening parameters on the weakening effect, a suitable cavity layout scheme is selected, determining the construction location, angle, and size of the cavities. Finally, hydraulic cavity-making is carried out. On the one hand, from a static load perspective, the cavity space can be used to relieve pressure on the surrounding rock of the roadway and reduce static load; on the other hand, the cavity space can be used to impede far-field forces. The propagation of dynamic loads to the surrounding rock of the roadway and the reduction of dynamic loads can reduce the energy that can induce rockburst disasters from both dynamic and static load aspects, reduce the load value of the surrounding rock of the roadway to below the critical value for inducing rockburst, significantly reduce the possibility of rockburst disasters in the roadway, and greatly improve the rockburst prevention effect. At the same time, the construction process of this hydraulic cavity-making method for weakening rockburst prevention in the hard roof of the roadway is relatively refined and the amount of engineering work is small. The water jet rock breaking technology itself is relatively mature, the process is safe and green and pollution-free. The single cavity has a large rockburst prevention area and good engineering benefits. It can actively and efficiently prevent and control the risk of rockburst disasters in the roadway, and is particularly suitable for rockburst prevention in roadways with open spaces. Attached Figure Description

[0041] Figure 1 This is a top view of the hydraulic cavity-making construction method of the present invention;

[0042] Figure 2 This is a side view of the hydraulic cavity-making construction method of the present invention;

[0043] Figure 3These are diagrams illustrating the effects of hydraulic cavity creation on static and dynamic loads according to the present invention, wherein (a) is a diagram illustrating the effects of hydraulic cavity creation on static loads and (b) is a diagram illustrating the effects of hydraulic cavity creation on dynamic loads.

[0044] In the diagram: 1. Dynamic load source; 2. Adjacent goaf; 3. Stress wave propagation path; 4. Coal pillar; 5. Void; 6. Roadway; 7. Area in the roadway with the risk of rockburst; 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 Implementation

[0045] Hydraulic cavity creation technology is a safe, green, and efficient method. It involves drilling conventional boreholes into the surrounding rock (coal seam and roof) of a roadway, and then using a high-pressure water jet to create a cavity of a certain diameter within the coal and rock strata through radial rotation and impact. This technology is safe to operate, uses water as the jet fluid, causes no environmental pollution, and creates a cavity with a much larger impact range than pressure-relief boreholes. This invention utilizes hydraulic cavity creation technology to reduce the energy that could induce rockburst disasters from both dynamic and static load perspectives.

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

[0047] This hydraulic cavity-forming method for weakening and preventing rockburst in tunnels with hard roofs utilizes hydraulic cavity-forming to create cavities through jet impact on the surrounding rock, reducing the stress concentration of the surrounding rock under static load, and hindering the propagation of far-field dynamic loads towards the tunnel, increasing the energy dissipation of dynamic loads along the propagation path. This achieves efficient prevention and control of rockburst disasters in tunnels. Specifically, it includes the following steps:

[0048] Step 1 involves conducting on-site investigations, collecting geological data, historical rockburst event records, and mining parameters for the target mine, and analyzing the implementation of on-site coal seam mining sequence, coal pillar placement, and mining methods. On-site sampling and testing are conducted to obtain data on the surrounding rock characteristics and basic mechanical parameters of the coal and rock mass. Analysis of the mining area's geological structure, coal and rock strata mechanical properties, coal and rock strata stress state, roof periodic fracture and collapse monitoring results, and coal seam mining-induced stress monitoring results are performed to obtain the impact of different factors on rockbursts. Rockburst tendency identification and rockburst hazard assessment are conducted for different roadway areas.

[0049] When obtaining data on the surrounding rock characteristics and basic mechanical parameters of coal and rock masses, coal body samples, roof surrounding rock samples, and floor surrounding rock samples can be selected from the target area roadway 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 testing machine to obtain data such as the elastic modulus, compressive / tensile strength, Poisson's ratio, and internal friction angle of the surrounding rock samples; for samples with a volume not less than 0.1m³... 3Approximately cubic raw coal and roof rock block samples were prepared into cubes with a side length of 20 cm. Water jet impact crushing tests were conducted with different abrasive concentrations, jet pressures, nozzle radii, and cutting times to obtain the optimal jet pressure p, nozzle radius R, and rock-breaking radius L. R Parameters for hydraulic rock breaking technology.

[0050] Step 2: Based on the data from Step 1, a three-dimensional numerical model of the load deformation of the longwall face, roadway, coal pillar, and adjacent goaf is constructed using RFPA software to simulate the surrounding rock stress (static load) values ​​of different areas of the roadway during the longwall face mining process. The simulation results calculated by the numerical model are verified and the parameters are optimized using data monitoring results such as roof periodic fracture collapse and coal seam mining stress at the mine site. The optimized numerical simulation is used to calculate the roadway areas with high static load and large stress concentration coefficient, as well as the roof fracture areas of adjacent goaf (location of far-field dynamic load sources), and the roadway sections with rockburst risk are identified to determine the target area roadway.

[0051] When constructing a three-dimensional numerical model of the load-deformation of the longwall face, roadway, coal pillar, and adjacent goaf, the REPF software is used to establish a three-dimensional numerical model based on the field survey and experimental test results of the target mine's mining area. The basic mechanical parameter data of the surrounding rock of the longwall face, roadway, and goaf are imported into the model to determine the boundary conditions and initial conditions. Then, an appropriate material model is selected, and the material parameters are checked to ensure they conform to the actual situation. The distribution of vertical stress in the structure is analyzed based on the theory of mechanics of materials to identify areas with high elastic energy density in the roof. The model is then rationally meshed, with mesh densification in areas of high elastic energy density and optimization of mesh density in key areas to ensure the simulation is accurate. The accuracy of the results met the requirements. Then, appropriate loading and boundary conditions were set, and a suitable numerical solution method was selected to conduct numerical simulation of the target fully mechanized longwall mining process. During this process, the convergence and stability of the calculation process were monitored to ensure that the calculation could complete the expected steps. Finally, the numerical simulation analysis results were compared and verified with the field monitoring results. Data such as roof fracture and collapse data and mining-induced stress data from the mine site were used to verify and optimize the numerical simulation model. The calculation parameters were continuously iterated and adjusted to correct and optimize the model, so that the calculation results conformed to the actual field conditions. Finally, a simulation model that conformed to the actual production conditions and monitoring data of the mine site was optimized.

[0052] Step 3: Based on the monitoring results such as micro-seismic activity on site, obtain the far-field dynamic load values ​​and the location of the dynamic load source generated by roof fracture and manual blasting in adjacent goaf areas. Based on the location of the far-field dynamic load source, set hydraulic cavity creation weakening anti-scour conditions that can meet the anti-scour requirements of the roadway.

[0053] Hydraulic cavity creation must meet the following conditions:

[0054]

[0055] In the formula: U t σ represents the total energy of the surrounding rock of the roadway under the combined action of static and dynamic loads; E represents the elastic modulus of the surrounding rock of the roadway; σ represents the total energy of the surrounding rock of the roadway under the combined action of static and dynamic loads. s and σ d These are the static and dynamic loads acting on the surrounding rock of the roadway, respectively; σ l The dynamic and static load critical values ​​that enable the roadway to experience rockburst.

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

[0057]

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

[0059] in:

[0060]

[0061] In the formula: c is the vertical damping coefficient of the rock stratum; k is the vertical spring coefficient of the rock stratum; G is the shear modulus of the rock stratum; u is the Poisson's ratio of the rock stratum; 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 With dynamic load σ d All will experience different decays, and the decayed values ​​satisfy the following:

[0063]

[0064] In the formula: r0 is the radius of the hole; r x denoted as , where is the distance between the surrounding rock location and the cavity center; C is the stress wave attenuation coefficient; x0 is the distance between the cavity and the dynamic load source; and x is the distance between the surrounding rock and the dynamic load source.

[0065] The weakened dynamic and static loads should be less than the critical stress σ required for rockburst to occur. l :

[0066]

[0067] In the formula: K is the impact energy index, determined by the stress-strain curve of uniaxial compression of the coal and rock sample; σ cp0 represents the uniaxial compressive strength of the sample; p0 represents the support strength of the surrounding rock of the roadway.

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

[0069] v w =[(λ+2G) / ρ] 1 / 2

[0070] Step 4: Based on the three-dimensional numerical model of load deformation in Step 2 and the hydraulic cavity creation weakening anti-scour conditions in Step 3, simulate hydraulic cavity creation to form cavities in the target area roadway in the numerical model, and determine the hydraulic cavity creation technical parameters, including the orientation, distance, size and quantity of hydraulic cavity creation, that can meet the anti-scour requirements of the roadway.

[0071] When simulating hydraulic cavity creation, such as Figure 1 , Figure 2 As shown, simulated drilling and hydraulic cavity creation are performed from near the junction of the roadway roof and coal pillar into the surrounding rock. The cavity extends forward no more than the junction of the immediate roof and the main roof, and extends backward no more than the junction of the top coal and the immediate roof. To achieve better anti-scour effect, the cavity can be located in the direction of stress wave propagation from the dynamic load source into the roadway, and the axial direction of the cavity corresponds to the direction of stress wave propagation from the dynamic load source into the roadway. For dynamic loads of roof fracture and roof collapse impacting the floor of the goaf, drilling can be carried out at an angle along the coal pillar side towards the roadway roof area, and hydraulic cavity creation can be completed. Then, a corresponding hydraulic cavity creation operation is performed on the floor to form a hydraulic cavity protection surface against dynamic loads of roof fracture and roof collapse impacting the floor of the goaf.

[0072] During simulated drilling, boreholes are drilled into the roof and floor of adjacent goaf areas, with the drilling direction of the drill rod at 90° to the direction of the roadway. The drill rod elevation angle θ1 and depression angle θ2 respectively satisfy the following:

[0073]

[0074] 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 roadway.

[0075] The cavity radius r0 of hydraulic cavity creation cannot increase indefinitely; it is constrained by jet pressure, nozzle radius, and the basic mechanical parameters of the surrounding rock, and must satisfy the following conditions:

[0076]

[0077] In the formula: p is the jet pressure; r m The nozzle radius; τ is the internal friction angle of the surrounding rock; τ is the shear strength of the surrounding rock; c c It represents the cohesion of the surrounding rock.

[0078] Step 5: Based on the technical parameters obtained in Step 4, such as the orientation, distance, size, and quantity of hydraulic cavity creation that meet the requirements for roadway erosion prevention, a drilling rig is deployed in the roadway space of the target area. The drilling is carried out at an angle along the coal pillar towards the surrounding rock (coal seam roof) area of ​​the roadway. At the bottom of the borehole, a high-pressure water jet is sprayed radially along the drill rod through the jet nozzle at the end of the drill rod to impact and break the roof rock. Through the rotation and retraction of the drill rod, a cylindrical cavity is formed in the hard roof, completing one hydraulic rock breaking cavity creation operation. The formed cavity meets the expected requirements for orientation, angle, distance, and size. This process is repeated to complete the hydraulic cavity creation of all cavities.

[0079] When conducting hydraulic cavity creation operations on-site, the construction plan is first optimized based on the coal seam occurrence conditions, geological structure, and roof and floor lithology of the mining area. Then, the drilling rig, high-pressure water pump, and water curtain support equipment are connected and powered on for performance testing to ensure stable and reliable performance during construction. Next, the location, orientation, and angle of the borehole are determined in the surrounding rock of the roadway according to the established hydraulic cavity creation plan. The drilling rig is then used to perform drilling operations, and the drilling progress and water pressure are controlled to ensure drilling quality. Then, the emulsification pump operator is notified through the underground dedicated communication system to turn on the high-pressure pump switch. Once water flows into the high-pressure water pipe, the emulsification pump pressure is adjusted according to the previously designed water pressure parameters, and the drilling rig is started. The drill rod reciprocates, cutting and flushing continuously using rotating high-pressure water. Each cycle is 1 meter long, and the flushing continues until the set time is reached. The advance and retreat of the high-pressure drill rod is controlled based on the borehole slag discharge and the actual slag volume until the hydraulic cavity creation operation of the target cavity is completed.

[0080] like Figure 3 As shown, the cavity space is used to relieve pressure on the surrounding rock, reducing the stress concentration factor of the static load. Simultaneously, when far-field impact loads such as hard roof fractures occur in adjacent goaf areas, the cavity space weakens the stress waves propagating from the dynamic load source into the roadway, reducing the magnitude of the dynamic load received by the roadway's surrounding rock. This reduces the likelihood of rockburst disasters in the roadway's surrounding rock from both dynamic and static load perspectives.

[0081] Step 6: Based on the regional and real-time monitoring results of the surrounding rock of the target roadway in the field (such as ground stress, drill cuttings volume, microseismic monitoring, electromagnetic radiation monitoring, etc.), determine the rockburst risk of the surrounding rock of the target roadway before and after hydraulic cavity creation, evaluate and verify the anti-scour effect of hydraulic cavity creation, and repeat Step 4 for areas where the anti-scour effect does not meet expectations (i.e., the conditions for weakening anti-scour effect by hydraulic cavity creation in Step 3 are not met). Adjust the hydraulic cavity creation technical parameters obtained in Step 4 to optimize the hydraulic cavity creation anti-scour technology scheme, and carry out the hydraulic cavity creation construction operation in Step 5 again until the anti-scour effect reaches expectations.

[0082] When evaluating and verifying the anti-scouring effect of hydraulic cavity creation, taking microseismic monitoring as an example, as the working face advances, the surrounding rock properties and stress-strain conditions of the target roadway will change due to mining and cavity creation operations. Using microseismic detection points near the roadway, the energy of the mine seismic event is detected and the location of the mine seismic event is determined. The microseismic data after cavity creation is compared with the historical microseismic data before cavity creation to obtain the attenuation coefficient of the cavity to the stress wave. At the same time, the dynamic load attenuation rate is obtained by theoretical calculation based on the measured stress-strain-time data of the surrounding rock of the roadway. Then, the measured attenuation rate, the theoretically calculated attenuation rate, and the numerically simulated attenuation rate are compared, and the technical parameters of the cavity creation operation are corrected for those attenuation rates that do not meet expectations.

[0083] When adjusting the hydraulic cavity-making technical parameters obtained in Step 4, adjustments can be made to the location, depth, drill pipe elevation angle θ, and radius L of the hydraulic rock-breaking cavity. R The parameters of hydraulic cavity-making technology were adjusted by conducting group tests on parameters such as the height of the drilling rig (h0) and the distance between the drilling rig and the working face (l0). The main control parameters for hydraulic cavity-making and scour prevention were obtained. The measured data, theoretical model calculations and numerical simulations were compared and verified to optimize the hydraulic cavity-making and scour prevention technology scheme.

[0084] This hydraulic cavity-forming method for weakening and preventing rockburst in hard roof tunnels near air gaps can, on the one hand, utilize the cavity space to relieve pressure on the surrounding rock and reduce static load from a static load perspective; on the other hand, it can use the cavity space to block the propagation of far-field dynamic loads to the surrounding rock and reduce dynamic loads. This achieves a combined reduction in the energy that can induce rockburst disasters from both dynamic and static load perspectives, lowering the load value of the surrounding rock below the rockburst induction threshold. This can significantly reduce the possibility of rockburst disasters in tunnels and greatly improve the rockburst prevention effect. At the same time, the construction process of this hydraulic cavity-forming method for weakening and preventing rockburst in hard roof tunnels near air gaps is relatively streamlined and the amount of engineering work is small. The water jet rock breaking technology itself is relatively mature, the process is safe and green and pollution-free. The single cavity has a large rockburst prevention area and good engineering benefits, making it particularly suitable for rockburst prevention in tunnels near air gaps.

Claims

1. A method for hydraulically creating cavitation holes to weaken and prevent erosion in a tunnel with an open roadway, characterized in that, Specifically, the following steps are included: Step 1: Obtain mine data and conduct on-site sampling, prepare standard samples for experiments, and obtain basic mechanical parameter data of coal and surrounding rock in different areas of roadways, as well as optimal hydraulic rock breaking technology parameters. Step 2: Based on the data from Step 1, construct a three-dimensional numerical model of the load deformation of the longwall face, roadway, coal pillar, and adjacent goaf to simulate the surrounding rock stress values ​​of different areas of the roadway during the longwall face mining process. The simulation results obtained from the numerical model were verified and the parameters were optimized by using the monitoring results of periodic roof fracture and collapse and coal seam mining stress data at the mine site. The optimized numerical simulation was used to obtain the roof fracture areas of roadways with high static load and high stress concentration coefficient and adjacent goaf areas, and the roadway sections with rockburst risk were identified to determine the target area roadways. 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, and set hydraulic cavity creation weakening anti-scour conditions that can meet the anti-scour requirements of the roadway. Hydraulic cavity creation must meet the following conditions: In the formula: U t σ represents the total energy of the surrounding rock of the roadway under the combined action of static and dynamic loads; E represents the elastic modulus of the surrounding rock of the roadway; σ represents the total energy of the surrounding rock of the roadway under the combined action of static and dynamic loads. s and σ d These are the static and dynamic loads acting on the surrounding rock of the roadway, respectively; σ l The dynamic and static load critical values ​​that enable rockburst in the roadway; Initial static load σ of the surrounding rock of the tunnel 0s With dynamic load σ 0d The following conditions must be met: In the formula: H n ρ represents the vertical height of coal and rock strata at different burial depths. n denoted as density of different coal and rock strata; g is the acceleration due to gravity; M is the mass of the collapsing rock strata; v is the collapse velocity of the rock strata; A is the impact area; λ is the Lamé constant of the rock strata; w is the stress wave frequency of the impact load. in: In the formula: c is the vertical damping coefficient of the rock stratum; k is the vertical spring coefficient of the rock stratum; G is the shear modulus of the rock stratum; u is the Poisson's ratio of the rock stratum; 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 With dynamic load σ d All will experience different degrees of decay, and the decayed values ​​will satisfy the following conditions: In the formula: r0 is the radius of the hole; r x denoted as , where is the distance between the surrounding rock location and the cavity center; C is the stress wave attenuation coefficient; x0 is the distance between the cavity and the dynamic source; x is the distance between the surrounding rock and the dynamic source. The weakened dynamic and static loads should be less than the critical stress σ required for rockburst to occur. l Critical stress σ l It is expressed as follows: In the formula: K is the impact energy index, determined by the stress-strain curve of uniaxial compression of the coal and rock sample; σ c p0 represents the uniaxial compressive strength of the sample; p0 represents the support strength of the surrounding rock of the roadway. The propagation speed v of the stress wave 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 cavity creation weakening anti-scour conditions in Step 3, simulate hydraulic cavity creation to form cavities in the target area roadway in the numerical model, and determine the hydraulic cavity creation technical parameters, including the orientation, distance, size and quantity of hydraulic cavity creation, that can meet the anti-scour requirements of the roadway. Step 5: Based on the hydraulic cavity-making technical parameters obtained in Step 4, drill rigs are deployed in the tunnel space of the target area to drill holes. High-pressure water jets are sprayed from the nozzle at the end of the drill rod and sprayed radially along the drill rod to impact and break the rock at the bottom of the hole, forming a columnar cavity. This process is repeated to complete the hydraulic cavity-making of all cavities. Step 6: Based on the regional and real-time monitoring results of the surrounding rock of the target roadway in the on-site monitoring area, determine the rockburst risk of the surrounding rock of the target roadway before and after hydraulic cavity creation, evaluate and verify the anti-scour effect of hydraulic cavity creation, and for areas where the anti-scour effect does not meet the anti-scour weakening conditions of hydraulic cavity creation in Step 3, repeat Step 4, adjust the hydraulic cavity creation technical parameters obtained in Step 4, and carry out the hydraulic cavity creation construction operation in Step 5 again based on the adjusted and optimized hydraulic cavity creation technical parameters until the anti-scour effect meets the anti-scour weakening conditions of hydraulic cavity creation in Step 3.

2. The method for hydraulically creating cavitation to weaken and prevent erosion in the hard roof of an open roadway according to claim 1, characterized in that, In Step 2, when constructing the three-dimensional numerical model of the loading and deformation of the longwall face, roadway, coal pillar, and adjacent goaf, the basic mechanical parameter data of the surrounding rock of the longwall face, roadway, 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 roadway is selected, and the distribution of 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, and the mesh density is refined in the area with high elastic energy density and the mesh density of key areas is optimized. Then, appropriate loading conditions and boundary conditions are set to conduct numerical simulation of the longwall mining process of the target fully mechanized longwall face. Finally, the numerical simulation analysis results are compared and verified with the field monitoring results. The numerical simulation model is verified and the parameters are optimized using the roof fracture and collapse data and mining-induced stress data from the mine site. The calculation parameters are continuously iterated and adjusted to correct and optimize the model, and finally, a simulation model that conforms to the actual production conditions and monitoring data of the mine site is formed.

3. The method for hydraulically creating cavitation to weaken and prevent erosion in the hard roof of an open roadway according to claim 1, characterized in that, In Step 4, when simulating hydraulic cavity creation, during the process of simulating drilling and hydraulic cavity creation from near the junction of the roadway roof and coal pillar into the surrounding rock, the forward extension of the cavity does not exceed the junction of the immediate roof and the main roof, and the backward extension does not exceed the junction of the top coal and the immediate roof.

4. The method for hydraulically creating cavitation to weaken and prevent erosion in the hard roof of an open roadway according to claim 1, characterized in that, When simulating hydraulic cavity creation in Step 4, the cavity is located in the direction of stress wave propagation from the dynamic load source into the tunnel.

5. The method for hydraulically creating cavitation to weaken and prevent erosion in the hard roof of an open roadway according to claim 4, characterized in that, The axial direction of the cavity corresponds to the direction in which the stress wave propagates from the dynamic load source into the roadway.

6. The method for hydraulically creating cavitation to weaken and prevent erosion in the hard roof of an open roadway according to claim 1, characterized in that, In Step 4, during the simulated hydraulic cavity creation, boreholes are drilled into the roof and floor of the adjacent goaf, with the drilling direction of the drill rod at 90° to the direction of the roadway. The drill rod elevation angle θ1 and depression angle θ2 respectively satisfy the following: 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 roadway.

7. The method for hydraulically creating cavitation to weaken and prevent erosion in the hard roof of an open roadway according to claim 1, characterized in that, When simulating hydraulic cavity creation in Step 4, the cavity radius r0 of the hydraulic cavity creation satisfies the following condition: In the formula: p is the jet pressure; r m The nozzle radius; τ is the internal friction angle of the surrounding rock; τ is the shear strength of the surrounding rock; c c It represents the cohesion of the surrounding rock.

8. The method for hydraulically creating cavitation to weaken and prevent erosion in the hard roof of an open roadway according to claim 1, characterized in that, In Step 6, when adjusting the hydraulic cavity-forming technology parameters obtained in Step 4, group experiments are conducted for different parameters to obtain the main control parameters for hydraulic cavity-forming anti-scour. The measured data, theoretical model calculations and numerical simulations are compared and verified, and the main control parameters that do not meet the expectations are corrected.

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