A high-efficiency hydraulic cutting method for caving the suspended top coal at the end of the top coal caving working face

Abstract

The present invention discloses a method for hydraulically cutting and efficiently caving the suspended top coal at the end of a top coal caving face. The method utilizes hydraulic cutting to weaken the top coal at the end of a fully-mechanized caving face to precisely control the maximum suspended length of the suspended top coal at the end of the top coal caving face. Modeling and numerical simulation are first performed based on the basic mechanical parameter data of the coal body and surrounding rock of the target fully-mechanized caving face coal seam and its goaf. After obtaining the optimal hydraulic cutting and weakening top coal technical parameters that meet the target maximum suspended length requirements, hydraulic cutting operations are then performed on-site at the target fully-mechanized caving face in the mine. The present invention is safe and reliable, cost-effective, and has a good weakening effect. It can achieve precise control while effectively weakening the mechanical strength of the top coal and controlling its maximum suspended length. It is particularly suitable for weakening and caving the suspended top coal at the end of a top coal caving face.

Description

Technical Field

[0001] The present invention relates to a method for weakening and collapsing the suspended top coal at the end of a top coal caving face, specifically an efficient collapsing method for weakening and collapsing the suspended top coal at the end of a fully mechanized caving face using hydraulic cutting technology, and belongs to the technical field of safe mining in coal mines. Background Art

[0002] Top-coal caving is a mining technique developed specifically for thick and extra-thick coal seams. When using this method, a mining face with a mining height of 2 to 3 meters is located along the floor of the coal seam or within a certain thickness range. Mining is carried out using a comprehensive mechanized method. Using mine pressure or supplemented by loosening blasting, the top coal is released through "coal windows" behind or on the supports and transported out of the face by a scraper conveyor. This method offers many significant advantages, including the ability to mine the entire height of coal seams 5 to 20 meters thick in one go, allowing for the simultaneous extraction of coal that would have previously required multiple layers in thicker seams. However, if the top coal above the mining face is relatively hard, part of the top coal, especially the top coal at the end of the working face, will be difficult to collapse in time and form a suspended roof. When the suspended length of the top coal at the end is large, this part of the top coal is prone to accumulate a large amount of elastic energy. If it suddenly breaks under the disturbance of the mining site, it may induce a roof accident. At the same time, the existence of suspended top coal will also lead to gas accumulation and air leakage in the goaf, inducing gas disaster risks and coal natural hazards. Therefore, the suspended length of the top coal at the end of the top coal caving working face should not be too long, and technical means should be used to ensure that the suspended top coal at the end of the working face collapses in time.

[0003] The conventional method of forced top coal caving in the suspended top coal working face mainly weakens the suspended coal body in advance to shorten the suspended length required for the natural fall of the top coal. Explosive blasting, hydraulic fracturing, carbon dioxide pre-cracking and other means are usually used, but they all have certain shortcomings: explosive blasting has a good weakening effect, but the high energy release generated can easily induce gas explosions, coal dust and other accidents, posing a major safety hazard, and the acquisition and storage of explosives are both very difficult; hydraulic fracturing is pollution-free and safe, but the fracturing effect in the coal seam is weak, and the controllability of the crack propagation direction and length is poor, making it difficult to achieve precise weakening; carbon dioxide pre-cracking technology is relatively new, the cost of a single fracturing is high, and it is currently difficult to promote widely. Summary of the Invention

[0004] In response to the problems existing in the above-mentioned prior art, the present invention provides a hydraulic cutting and efficient caving method for the suspended top coal at the end of a top coal caving working face, which has the characteristics of safety, reliability, controllable cost and good weakening effect. It can accurately control the collapse of the suspended top coal at the end of the top coal caving working face under the premise of effectively weakening the mechanical strength of the top coal and controlling the maximum suspended length of the top coal. It is particularly suitable for the weakening and caving treatment of the suspended top coal at the end of the top coal caving working face.

[0005] To achieve the above-mentioned purpose, the present invention provides a method for efficiently caving the suspended top coal at the end of a top coal caving face by hydraulic slotting. The method weakens the top coal at the end of a fully-mechanized top coal caving face by hydraulic slotting to achieve precise control of the maximum suspended length of the suspended top coal at the end of the top coal caving face. The method specifically includes the following steps:

[0006] Step 1: Obtain mine data and basic mechanical parameter data of the coal body and surrounding rock in the target fully mechanized caving working face coal seam and its goaf;

[0007] Step 2: Based on the data from Step 1, a load-damage mathematical model of the coal strata mined at the target fully-mechanized caving working face is constructed, and a numerical simulation of the mining process of the target fully-mechanized caving working face is performed to obtain the stress distribution, deformation characteristics, and cyclical collapse data of the roof and top coal of the target fully-mechanized caving working face and roadway. The numerical simulation model is verified and parameters are optimized using the cyclical fracture and collapse data of the roof and top coal at the mine site, the coal seam mining stress data, and the roadway surrounding rock deformation and separation data, thereby forming a simulation model that conforms to the actual production conditions and monitoring data at the mine site. In the simulation model, simulated hydraulic cutting is performed on the top coal at the working face end to obtain the optimal hydraulic cutting and top coal weakening technical parameters that can meet the target requirements for the maximum overhang length of the top coal.

[0008] When calculating the maximum suspended length of top coal, the maximum bending moment M at the far end of the suspended top coal is m for:

[0009]

[0010] Where: L3 is the suspended length of the top coal in the front-to-back direction, q1 is the load density directly transferred from the top to the suspended top coal, and q2 is the load density generated by the weight of the suspended top coal itself.

[0011] Maximum tensile stress σ on suspended top coal m for:

[0012]

[0013] Where: H1 is the thickness of the top coal above the roadway;

[0014] Tensile strength of top coal σ t for:

[0015]

[0016] Where: k c is the crack coefficient in the coal body, with a value range of 0.3 to 0.9, σ c is the compressive strength of top coal;

[0017] When σ m Reach the tensile strength of top coal σt When the top coal breaks and becomes unstable, the maximum value of the suspended length L3 of the top coal in the front-back direction is obtained;

[0018] The number, width and depth of hydraulic cutting seams meet the following requirements:

[0019] L4cosθ1<L3

[0020] nL R cosθ1+L3tanθ1

[0021] Where: L3 is the suspended length of the top coal in the front-to-back direction, L4 is the depth of the hydraulic cutting in the front-to-back direction, θ1 is the drilling rig elevation angle, L R is the width of the hydraulic cutting seam, n is the number of hydraulic cutting seams, and H1 is the thickness of the top coal above the roadway;

[0022] Step 3, based on the optimal hydraulic cutting and weakening top coal technical parameters obtained in Step 2, a drilling hole is constructed at an angle in the suspended top coal behind the end of the target fully mechanized caving working face of the mine, and a high-pressure water jet is ejected from the jet nozzle (7) at the end of the drill rod (5) and radially ejected along the drill rod (5) to impact and crush the coal body, and a hydraulic cutting seam (7) is formed in the suspended top coal by the retreat movement of the drill rod (5), completing one hydraulic cutting operation; and by analogy, completing the hydraulic cutting operation of all hydraulic cutting seams (7) in the suspended top coal behind the end;

[0023] Step 4: As the working face continues to advance forward and the top coal fractures and collapses after being weakened at the rear, the numerical simulation model and the simulation model are continuously verified and optimized based on the real-time monitoring data at the target fully-mechanized caving working face of the mine, and key parameters are corrected. Hydraulic cutting operations are performed again at the target fully-mechanized caving working face of the mine after the top coal fractures and collapses after being weakened at the rear.

[0024] Furthermore, in Step 2, when simulating hydraulic cutting of the top coal at the end of the working face in the simulation model, drilling is performed near the junction of the suspended top coal and the top beam of the working face end support equipment, and the forward extension range of the hydraulic cutting does not exceed the junction of the suspended top coal and the top beam of the working face end support equipment.

[0025] Furthermore, in Step 2, when simulating hydraulic cutting of the top coal at the working face end in the simulation model, the drilling rig is set on the side close to the coal pillar of the roadway.

[0026] ​Furthermore, in Step 3, when the hydraulic cutting extends forward to the junction of the suspended top coal and the top beam of the working face end support equipment, and the suspended top coal does not fall as expected, the hydraulic cutting operation is stopped. According to the real-time monitoring data of the weakened top coal at the target fully mechanized caving working face of the mine, the drill rod elevation angle θ1, the drill rod deflection angle θ2 in the front-to-back direction, and the distance L1 between the drill rig and the working face end are adjusted, and Step 2 is repeated to re-perform the hydraulic cutting operation in the suspended top coal behind the working face end.

[0027] Furthermore, after obtaining the stress distribution, deformation characteristics and periodic collapse data of the target fully mechanized caving working face and roadway in Step 2, the drilling position, drill rod elevation angle θ1, drill rod deflection angle θ2 along the front and back direction, hydraulic cutting width L R , the depth dimension L4 of the hydraulic cutting along the front-back direction is grouped for numerical simulation, and the maximum suspended length L3 of the top coal at the end of the working face under different hydraulic cutting parameters is obtained. The main controlling factors are obtained to form the optimal hydraulic cutting top coal weakening technical parameter range that can meet the requirements of the top coal suspended length.

[0028] Furthermore, after obtaining the stress distribution, deformation characteristics, and periodic collapse data of the target fully mechanized caving working face and roadway in Step 2, group numerical simulations are performed based on the stress changes of the on-site working face end support equipment and roadway support and the mine pressure manifestation records to determine the optimal hydraulic cutting top coal weakening technical parameter range that can meet the target requirements for the maximum suspended length of the top coal under the influence of different periodic pressure, support and mining disturbance coupling.

[0029] Furthermore, when obtaining the basic mechanical parameter data of the coal body and surrounding rock of the target fully-mechanized caving working face coal seam and its goaf in Step 1, coal body and surrounding rock samples are selected on-site at the target fully-mechanized caving working face and its goaf in the coal mine and brought to the ground, standard samples are prepared in the laboratory, and the basic mechanical parameter data of the standard samples are tested and obtained.

[0030] Compared with the existing technology, the hydraulic cutting and efficient caving method of the suspended top coal at the end of the top coal caving working face uses hydraulic cutting to weaken the top coal at the end of the fully-mechanized caving working face to achieve precise control of the maximum suspended length of the suspended top coal at the end of the top coal caving working face, which can significantly weaken the mechanical strength of the suspended top coal and greatly shorten the maximum length of the suspended top, with significant effect; at the same time, the construction process of the hydraulic cutting and efficient caving method of the suspended top coal at the end of the top coal caving working face is relatively refined, the engineering amount is small, and the water jet coal breaking technology itself is relatively cost-effective. The method is mature and has low construction difficulty. In addition, the hydraulic cutting and efficient caving method of the suspended top coal at the end of the top coal caving working face can significantly reduce the safety hazards such as gas accumulation and air leakage in the corner of the end, rock burst, gas disasters and spontaneous combustion of residual coal that are easily induced during the production process of the working face by controlling the length of the suspended top. In addition, the water jet coal breaking process can also promote the initiation and expansion of cracks inside the coal body, and water has a softening effect on the coal body, which can further increase the degree of crushing and expansion of the top coal after breaking and caving, thereby improving the top coal caving rate and the overall coal mining rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural diagram of the equipment arrangement and hydraulic cutting operation at the end of the fully mechanized caving working face;

[0032] Figure 2 yes Figure 1 lateral view of;

[0033] Figure 3 yes Figure 1 A top-down rotation view of .

[0034] Figure: 1. Target coal seam, 2. Roadway space in front of the working face, 3. High-pressure water pump, 4. Drilling rig, 5. Drill rod, 6. Support equipment at the working face end, 7. Hydraulic slotting, 8. Space in the fully mechanized caving working face, 9. Overhanging top coal at the working face end, 10. Goaf behind the working face, 11. Coal pillar.

[0035] H1 is the thickness of the top coal above the roadway, H2 is the height of the roadway, H3 is the height of the drilling rig, L1 is the distance between the drilling rig and the end of the working face, L2 is the width of the working face in the front-to-back direction; L3 is the suspended length of the top coal in the front-to-back direction, L4 is the depth of the hydraulic cutting in the front-to-back direction, L5 is the upper width of the roadway, L6 is the lower width of the roadway, L R is the width of the hydraulic cutting, θ1 is the drill pipe elevation angle, and θ2 is the drill pipe deflection angle along the front-back direction. DETAILED DESCRIPTION

[0036] The present invention will be further described below by taking a comprehensive top coal caving mining face of a coal mine as an example with reference to the accompanying drawings.

[0037] This method for efficiently caving the suspended top coal at the end of a top coal caving face by hydraulic slotting uses hydraulic slotting to weaken the top coal at the end of a fully-mechanized top coal caving face, thereby accurately controlling the maximum suspended length of the suspended top coal at the end of the top coal caving face. Specifically, it includes the following steps:

[0038] Step 1: First, obtain the mine data including the geological conditions and mining conditions of the target fully-mechanized caving working face coal seam and the basic mechanical parameter data of the coal body and surrounding rock of the target fully-mechanized caving working face coal seam and its goaf:

[0039] The average burial depth of the comprehensive top coal caving mining face in this coal mine is 400m, the average coal seam inclination is 40°, and the average coal seam thickness is 8m. Key information such as the layout of the target comprehensive top coal caving working face and the surrounding goaf, the roadway support method, and coal mining parameters are determined based on a comprehensive histogram of the coal and rock strata overlying the coal seam (including parameters such as thickness and lithology). The target comprehensive top coal caving working face has a mining height of 2.8m, a coal caving height of 4.2m, a top coal thickness H1 above the roadway of 3.4m, a roadway height H2 of 3.6m, a mining rate of 3.2m / day, an upper roadway width L5 of 4.8m, a lower roadway width L6 of 5.8m, a working face width L2 in the front-to-back direction of 8m, and a working face end support device 6 using an end hydraulic support.

[0040] In order to accurately obtain the basic mechanical parameter data of the coal body and surrounding rock of the target fully-mechanized caving working face and its goaf, relatively complete large-scale block samples of coal body, gangue and rock were selected from the target fully-mechanized caving working face and its goaf in the coal mine. They were brought to the surface, and standard samples were prepared in the laboratory. The actual basic mechanical parameters such as compressive strength, tensile strength, Poisson's ratio, etc. of the standard samples were tested and obtained. The details are as follows:

[0041] The block sample selected underground should be approximately cubic in shape and have a volume of no less than 0.1m 3 In the laboratory, the block samples were processed into cylindrical standard samples of different standard sizes, such as Ф50×100mm and Ф50×250mm. After the samples were grouped, the basic mechanical parameters of the standard samples were obtained using an MTS triaxial loading tester. The compressive strength of the raw coal standard sample was 12.9MPa, the tensile strength was 0.8MPa, the Poisson's ratio was 0.28, and the elastic modulus was 0.9GPa. 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%.

[0042] Step 2: Based on the geological conditions and mining conditions of the target fully-mechanized caving working face coal seam, and on the basis of the mechanical parameters of the coal and rock mass obtained experimentally, a load-damage mathematical model of the target fully-mechanized caving working face coal and rock strata is constructed. A numerical simulation is then performed on the hydraulic cutting of the end top coal and the collapse of the end top coal during the working face mining process. The optimal hydraulic cutting and weakening top coal technical parameters that can meet the target maximum overhang length of the top coal are obtained:

[0043] Firstly, the RFPA engineering version software was used to construct a load-damage mathematical model of the coal strata mined in the target fully-mechanized caving working face. The mine data including the geological conditions and mining conditions of the coal seam of the target fully-mechanized caving working face and the basic mechanical parameter data of the coal body and surrounding rock of the coal seam and its goaf in the target fully-mechanized caving working face were imported into the model to perform numerical simulation of the mining process of the target fully-mechanized caving working face. The stress distribution, deformation characteristics and cyclic collapse data of the roof and top coal of the target fully-mechanized caving working face and the roadway were obtained. The numerical simulation model was verified and the parameters were optimized using the cyclic fracture and collapse data of the roof and top coal, the coal seam mining stress data, the roadway surrounding rock deformation and delamination data and other data at the mine site. The simulation model was optimized to meet the actual production conditions and monitoring data of the mine site.

[0044] When calculating the maximum suspended length of top coal, the maximum bending moment M at the far end of the suspended top coal is m for:

[0045]

[0046] Where: L3 is the length of the suspended top coal, q1 is the load density directly transferred by the top coal to the suspended top coal, and q2 is the load density generated by the weight of the suspended top coal itself;

[0047] Maximum tensile stress σ on suspended top coal m for:

[0048]

[0049] Where: H1 is the thickness of the top coal above the roadway;

[0050] Tensile strength of top coal σ t for:

[0051]

[0052] Where: k c is the crack coefficient in the coal body, with a value range of 0.3 to 0.9, σ c is the compressive strength of top coal;

[0053] When σ m Reach the tensile strength of top coal σ tWhen the top coal breaks and becomes unstable, the maximum overhanging length L3 of the top coal in the front-to-back direction is obtained.

[0054] Secondly, the hydraulic cutting of the top coal at the end of the working face in the simulation model was simulated to analyze the maximum length required for the suspended top coal to fracture and collapse during the forward advancement of the working face. By changing the initial position of the hydraulic cutting 7, the drill rod elevation angle θ1, the drill rod deflection angle θ2 along the front-back direction, the number of hydraulic cutting slits 7, and the width size L of the hydraulic cutting slit, the maximum length required for the suspended top coal to fracture and collapse during the forward advancement of the working face was analyzed. R The changing pattern of the maximum length of the suspended top coal at the end of the working face is analyzed based on parameters such as the depth dimension L4 of the hydraulic cutting along the front and rear directions, the height dimension H3 of the drilling rig, and the distance dimension L1 between the drilling rig and the end of the working face. The changing pattern of the maximum length of the suspended top coal at the end of the working face is analyzed under the coupling effect of strengthened tunnel support, periodic pressure changes and working face advancement, and the model is verified and optimized in combination with the on-site observation results of the mine.

[0055] When analyzing the maximum length required for the suspended top coal to fracture and collapse during the forward advancement of the working face, the overburden stress and its own gravity were applied to the simulation model, and the mechanical strength of the hydraulic cutting was applied to the suspended part of the top coal. As the working face continued to advance forward in the simulation, the suspended length of the top coal continued to increase. Under the action of the overburden stress and its own gravity, the damage to the suspended part of the top coal continued to intensify until fracture and instability occurred. The maximum suspended length L3 of the top coal at the end of the working face was recorded at this time.

[0056] When analyzing the variation law of the maximum length of the hanging top at the end of the working face, the different drilling positions, drill rod elevation angle θ1, drill rod deflection angle θ2 along the front and back direction, and hydraulic cutting width L are analyzed. R , the depth dimension L4 of the hydraulic cutting along the front-back direction, the height dimension H3 of the drilling rig, the distance dimension L1 between the drilling rig and the end of the working face and other parameters are grouped for numerical simulation, and the maximum overhanging length L3 of the top coal at the end of the working face under different hydraulic cutting parameters is obtained. The main controlling factors are obtained, and the optimal hydraulic cutting weakening top coal technical parameter range that can meet the requirements of the top coal overhang length is formed.

[0057] When analyzing the changing law of the maximum length of the suspended top coal at the end under the coupling effects of enhanced tunnel support conditions, cyclic pressure changes, and working face advancement, the enhanced support data (such as the enhanced support data obtained after increasing the number of support anchors, increasing the support resistance of the bracket, etc.) and additional cyclic pressure data were applied on the basis of the simulation model to perform grouped numerical simulation. The maximum value of the suspended length L3 of the top coal at the working face end under different enhanced support data and additional cyclic pressure data conditions was obtained, forming the optimal hydraulic slotting weakening top coal technical parameter range that can meet the requirements of the top coal suspended length.

[0058] The number, width and depth of the hydraulic cutting seams 7 should meet the following requirements:

[0059] L4 cosθ1<L3

[0060] nL R cosθ1+L3 tanθ1

[0061] Where: L3 is the suspended length of the top coal in the front-to-back direction, L4 is the depth of the hydraulic cutting in the front-to-back direction, θ1 is the drilling rig elevation angle, L R is the width of the hydraulic cutting seam, n is the number of hydraulic cutting seams, and H1 is the thickness of the top coal above the roadway.

[0062] Considering the layout of electromechanical equipment in the tunnel space 2 in front of the working face, the remaining space in the tunnel, the dimensions of the drilling rig 4 and the high-pressure water pump 3, and combining the mine site construction conditions, the optimal technical parameters for weakening the top coal by hydraulic cutting in the target fully mechanized caving working face at the mine site are obtained. According to the simulation results, Figures 1 to 3 As shown in the figure, the drilling rig 4 is set on the side of the coal pillar 11 in the roadway. When the maximum allowable length L3 of the coal hanging above the working face end is 4m and the height dimension H3 of the drilling rig is 1.8m, the distance dimension L1 between the drilling rig and the working face end can be determined to be 15m, the drill rod elevation angle θ1 is 10°, the drill rod deflection angle θ2 in the front-back direction is 3°, and the width dimension L of the hydraulic cutting is 1.8m. R The hydraulic cutting slot is 1 m, the depth dimension L4 of the hydraulic cutting slot in the front-to-back direction is 3.5 m, and the inclined length between the starting position of the hydraulic cutting slot 7 and the drilling of the drilling rig 4 is 23.4 m.

[0063] Step 3, based on the optimal technical parameters for weakening the top coal by hydraulic cutting obtained in Step 2, hydraulic cutting construction is carried out on site at the target fully mechanized caving working face of the mine, and hydraulic cutting equipment such as a high-pressure water pump 3 and a drilling rig 4 are arranged in the tunnel space 2 in front of the working face. A hole is drilled obliquely into the suspended top coal behind the end head. After the hole is drilled, high-pressure water is transported by the high-pressure water pump 3 through the drill rod 5, and a high-pressure water jet is ejected radially along the drill rod 5 through the jet nozzle on the drill rod 5. The coal body is crushed by the impact of the high-pressure water jet, and a hydraulic cutting 7 is formed in the suspended top coal by the retreat movement of the drill rod 5. The crushed coal particles and water flow out of the annular space between the drill rod 5 and the borehole in a mixed state; and the hydraulic cutting operation of all hydraulic cutting 7 in the suspended top coal behind the end head is completed by analogy. After the hydraulic cutting is completed, the hydraulic cutting equipment is removed.

[0064] ​As the working face continues to advance, the suspended length of the top coal gradually increases, and under the action of the top coal's own weight and the roof pressure, it breaks and collapses in advance. In order to effectively control the safety hazards of the suspended top coal, the maximum suspended length of the weakened top coal should be less than the target control length. Taking into account the complexity of the on-site conditions, combined with the numerical simulation and field application results, the above technical parameters are optimized and adjusted again. Under the actual on-site conditions, the hydraulic cutting technical parameters required to ensure that the length of the suspended top coal is not greater than the expected target length are determined. The results show that when the distance L1 between the drilling rig and the end of the working face is 12m, the drill rod elevation angle θ1 is 10°, the drill rod deflection angle θ2 along the front and rear direction is 4°, and the width dimension L of the hydraulic cutting is R When the hydraulic cutting depth L4 is 1m, the depth dimension L4 of the hydraulic cutting along the front and rear direction is 4m, and the number of hydraulic cutting seams 7 is 3, the average suspended length L3 of the top coal at the end of the on-site working face is 3.4m, and the maximum value is 3.8m, which is lower than the target value of 4m, meeting the technical requirements of the suspended roof weakening and efficient collapse.

[0065] In order to ensure the coal breaking effect, drilling should be carried out at least from the junction of the suspended top coal and the top beam of the working face end support equipment 6; as the drill rod 5 gradually retreats forward, the range of the hydraulic cutting 7 continues to extend forward, and the forward extension range of the hydraulic cutting 7 shall not exceed the junction of the suspended top coal and the top beam of the working face end support equipment 6, so as to control the impact of the hydraulic cutting on the surrounding rock support of the working face.

[0066] When the hydraulic cutting 7 extends forward to the junction of the suspended top coal and the top beam of the working face end support equipment 6, and the suspended top coal has not fallen as expected, the hydraulic cutting operation should be stopped immediately, the drill rod elevation angle θ1 of the drilling rig 4, the drill rod deflection angle θ2 in the front-to-back direction, and the distance L1 between the drilling rig and the working face end should be adjusted, and the hydraulic cutting operation should be carried out again in the suspended top coal behind the working face end to further weaken the mechanical strength of the top coal and make the suspended top coal collapse in time.

[0067] Step 4: As the working face continues to advance, multiple hydraulic slotting operations are carried out from back to front at the target fully mechanized caving working face in the mine. The effects of different periodic pressure conditions and different roadway support schemes on the maximum suspended length of the top coal are analyzed, and the process parameters of drilling construction and jet coal breaking are optimized to develop a technical method for efficient caving of the suspended top coal at the end of the top coal caving working face that is suitable for different operating conditions. Specifically:

[0068] Multiple hydraulic slotting operations were carried out from back to front at the target fully mechanized caving working face in the mine, and real-time monitoring was performed. The numerical simulation model and the simulation model were continuously verified and optimized, and key parameters were corrected. The drill rod elevation angle θ1, the drill rod deflection angle θ2 in the front-back direction, the drilling position, and the width L of the hydraulic slot were analyzed. R, the influence of the depth dimension L4 of the hydraulic cutting in the front-to-back direction on the maximum length of the suspended length L3 of the top coal at the end of the working face, and the optimal technical parameters for weakening the top coal by using hydraulic cutting in the target fully mechanized caving working face at the mine site are obtained.

[0069] The support measures of the working face can be strengthened by increasing the number of anchor bolts and anchor cables, increasing the initial support force of the working face and tunnel supports, etc.; the changing pattern of periodic pressure can be analyzed by recording the stress changes of the on-site working face supports and tunnel supports and the mine pressure manifestation; the influence of the periodic pressure changes and the support scheme changes on the control of the hanging top of the working face end is analyzed, and the technical scheme for weakening the top coal of the working face end under the influence of different periodic pressures, support and mining disturbance coupling is determined.

[0070] By changing the initial conditions such as coal seam burial depth, inclination and coal thickness, mechanical strength of coal rock mass, working face and tunnel layout and substituting them into the revised simulation model, the technical schemes and process parameters of drilling construction and jet coal breaking that can effectively control the length of suspended top coal under different on-site geological conditions and coal mining conditions can be studied; considering the construction volume and construction difficulty, based on the hydraulic cutting method, a technical scheme for efficient collapse of suspended top coal at the end of the top coal caving working face that is suitable for different complex conditions is formed.

Claims

1. A high-efficiency hydraulic caving method for the suspended top coal at the end of a top coal caving working face, characterized in that: Hydraulic slotting is used to weaken the top coal at the end of the fully-mechanized caving working face to accurately control the maximum hanging length of the top coal at the end of the top coal caving working face. The specific steps include: Step 1: Obtain mine data and basic mechanical parameter data of the coal body and surrounding rock in the target fully mechanized caving working face coal seam and its goaf; Step 2: Based on the data from Step 1, a load-damage mathematical model of the coal strata mined at the target fully-mechanized caving working face is constructed, and a numerical simulation of the mining process of the target fully-mechanized caving working face is performed to obtain the stress distribution, deformation characteristics, and cyclical collapse data of the roof and top coal of the target fully-mechanized caving working face and roadway. The numerical simulation results are verified and parameters are optimized using the cyclical fracture and collapse data of the roof and top coal at the mine site, the coal seam mining stress data, and the roadway surrounding rock deformation and separation data, thereby forming a simulation model that conforms to the actual production conditions and monitoring data at the mine site. In the simulation model, simulated hydraulic cutting is performed on the top coal at the working face end to obtain the optimal hydraulic cutting and top coal weakening technical parameters that can meet the target requirements for the maximum overhang length of the top coal. When calculating the maximum suspended length of top coal, the maximum bending moment M at the far end of the suspended top coal is m for: Where: L3 is the suspended length of the top coal in the front-to-back direction, q1 is the load density directly transferred from the top to the suspended top coal, and q2 is the load density generated by the weight of the suspended top coal itself. Maximum tensile stress σ on suspended top coal m for: Where: H1 is the thickness of the top coal above the roadway; Tensile strength of top coal σ t for: Where: k c is the crack coefficient in the coal body, with a value range of 0.3 to 0.9, σ c is the compressive strength of top coal; When σ m Reach the tensile strength of top coal σ t When the top coal breaks and becomes unstable, the maximum value of the suspended length L3 of the top coal in the front-back direction is obtained; The number, width and depth of the hydraulic cutting seams (7) meet the following requirements: L4cosθ1<L3 nL R cosθ1+L3tanθ1<H1 Where: L3 is the suspended length of the top coal in the front-to-back direction, L4 is the depth of the hydraulic cutting in the front-to-back direction, θ1 is the drilling rig elevation angle, L R is the width of the hydraulic cutting seam, n is the number of hydraulic cutting seams, and H1 is the thickness of the top coal above the roadway; Step 3, based on the optimal hydraulic cutting and weakening top coal technical parameters obtained in Step 2, drilling holes are constructed obliquely in the suspended top coal behind the end of the target fully mechanized caving working face of the mine, and a high-pressure water jet is ejected from the jet nozzle at the end of the drill rod (5) and radially ejected along the drill rod (5) to impact and crush the coal body, and a hydraulic cutting seam (7) is formed in the suspended top coal by the retreat movement of the drill rod (5), completing one hydraulic cutting operation; and by analogy, completing the hydraulic cutting operation of all hydraulic cutting seams (7) in the suspended top coal behind the end; Step 4: As the working face continues to advance forward and the top coal fractures and collapses after being weakened at the rear, the numerical simulation model and the simulation model are continuously verified and optimized based on the real-time monitoring data at the target fully-mechanized caving working face of the mine, and key parameters are corrected. Hydraulic cutting operations are performed again at the target fully-mechanized caving working face of the mine after the top coal fractures and collapses after being weakened at the rear.

2. The method for high-efficiency hydraulic caving of suspended top coal at the end of a top coal caving working face according to claim 1 is characterized in that: Step 2: When simulating hydraulic cutting of the top coal at the end of the working face in the simulation model, drilling is carried out from the vicinity of the junction of the suspended top coal and the top beam of the working face end support equipment (6), and the forward extension range of the hydraulic cutting (7) does not exceed the junction of the suspended top coal and the top beam of the working face end support equipment (6).

3. The high-efficiency hydraulic caving method for the suspended top coal at the end of the top coal caving working face according to claim 1 is characterized in that: In step 2, when simulating hydraulic cutting of the top coal at the working face end in the simulation model, the drilling machine (4) is set on a side close to the coal pillar (11) in the roadway.

4. The method for high-efficiency hydraulic caving of suspended top coal at the end of a top coal caving working face according to claim 1 is characterized in that: In Step 3, when the hydraulic cutting (7) extends forward to the junction of the suspended top coal and the top beam of the working face end support equipment (6), and the suspended top coal does not fall as expected, the hydraulic cutting operation is stopped. According to the real-time monitoring data of the weakened top coal at the target fully mechanized caving working face of the mine, the drill rod elevation angle θ1 of the drilling rig (4), the drill rod deflection angle θ2 in the front-back direction, and the distance L1 between the drilling rig and the working face end are adjusted, and Step 2 is repeated to re-perform the hydraulic cutting operation in the suspended top coal behind the working face end.

5. The method for high-efficiency hydraulic caving of suspended top coal at the end of a top coal caving working face according to claim 1 is characterized in that: After obtaining the stress distribution, deformation characteristics and periodic collapse data of the target fully mechanized caving working face and roadway in Step 2, the drilling position, drill rod elevation angle θ1, drill rod deflection angle θ2 along the front and back direction, hydraulic cutting width L are tested. R , the depth dimension L4 of the hydraulic cutting along the front-back direction is grouped for numerical simulation, and the maximum suspended length L3 of the top coal at the end of the working face under different hydraulic cutting parameters is obtained. The main controlling factors are obtained to form the optimal hydraulic cutting top coal weakening technical parameter range that can meet the requirements of the top coal suspended length.

6. The method for high-efficiency hydraulic caving of suspended top coal at the end of a top coal caving working face according to claim 1 is characterized in that: After obtaining the stress distribution, deformation characteristics and periodic collapse data of the target fully mechanized caving working face and roadway in Step 2, a group numerical simulation is performed based on the stress changes of the on-site working face end support equipment (6) and roadway support and the mine pressure manifestation records to determine the optimal hydraulic cutting and weakening top coal technical parameter range that can meet the target requirements for the maximum suspended length of the top coal under the influence of different periodic pressure, support and mining disturbance coupling.

7. The method for high-efficiency hydraulic caving of suspended top coal at the end of a top coal caving working face according to claim 1 is characterized in that: Step 1: When obtaining the basic mechanical parameter data of the coal body and surrounding rock of the target fully-mechanized caving working face coal seam and its goaf, coal body and surrounding rock samples are selected on-site at the target fully-mechanized caving working face and its goaf in the coal mine and brought to the ground, standard samples are prepared in the laboratory, and the basic mechanical parameter data of the standard samples are tested and obtained.

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