阅读说明：本技术 一种综采放顶煤工作面堆喷混凝土沿空留巷方法 (Gob-side entry retaining method for fully-mechanized top coal caving face pile-spraying concrete ) 是由 郝兵元 任兴云 李宪军 张涛 刘建彪 乔安 于 2021-09-23 设计创作，主要内容包括：一种综采放顶煤工作面堆喷混凝土沿空留巷方法,属于煤炭行业无煤柱开采领域,可解决现有沿空留巷技术存在的巷旁墙体接顶和支撑性能差、巷道围岩支护结构维护困难、所留巷道采空区漏风、留巷成本高等问题,本发明中锚索高预应力支护,可防止巷道顶板离层,保持沿空留巷顶板岩层的整体性。巷道顶板、墙体、底板一体化设计,内置横向拉筋和纵向拉筋,沿空留巷的围岩结构稳定。堆喷形成的巷旁墙体强度上升速度快,及时支撑不让压,强力切断采空侧顶板,减小沿空留巷的围岩应力,临时支护时间短。巷旁墙体微膨胀,接顶密实不漏风,有效隔绝采空区。采煤与沿空留巷互不干扰,堆喷构筑巷旁墙体紧跟采煤工作面,可实现高产高效。(A gob-side entry retaining method for fully mechanized top coal caving face pile-spraying concrete belongs to the field of coal-pillar-free mining in the coal industry, and can solve the problems of poor top-contacting and supporting performance of a roadside wall body, difficulty in maintaining a supporting structure of surrounding rocks of a roadway, air leakage of a reserved roadway goaf, high entry retaining cost and the like in the existing gob-side entry retaining technology. The roadway roof, the wall body and the bottom plate are integrally designed, transverse tie bars and longitudinal tie bars are arranged in the roadway roof, the wall body and the bottom plate, and the surrounding rock structure of the gob-side entry retaining is stable. The roadside wall body formed by the pile-spraying has high strength rising speed, is supported in time without yielding pressure, strongly cuts off the mining side top plate, reduces the surrounding rock stress of the gob-side entry retaining, and has short temporary supporting time. The roadside wall body expands slightly, is tightly connected with the roof and does not leak air, and effectively isolates a gob. Coal mining and gob-side entry retaining are not interfered with each other, and high yield and high efficiency can be realized by constructing a wall body beside a roadway by pile spraying to closely follow a coal mining working face.)

1. A fully mechanized top coal caving working face pile-spraying concrete gob-side entry retaining method is characterized in that: the method comprises the following steps:

the first step, anchor rope high prestressing force is strutted, prevents the tunnel roof absciss layer, keeps the wholeness of roof stratum:

respectively punching holes in the center line position of a roadway top plate and the middle position of a roadside wall body in advance of a stope face, mounting strong anchor cables, applying mounting pretightening force, and forming high-prestress support for the roadway top plate; the anchor cable is anchored in a stable top plate rock stratum, and when the distance between the stable rock stratum and a roadway top plate exceeds 10m, the length of the anchor cable is determined according to 2m which exceeds the height of a natural balance arch;

secondly, temporarily sealing the goaf at the goaf side at the rear of the hydraulic support:

following the coal face, keeping the working face recovery cycle progress consistent, supporting a U-shaped steel pillar at the edge of the goaf side of the roadway, hanging a layer of gangue blocking reinforcing mesh on the side of the U-shaped steel pillar close to the roadway, laying a layer of flame-retardant and anti-static fiber cloth on the side of the gangue blocking reinforcing mesh close to the roadway, temporarily blocking gangue and sealing the goaf;

thirdly, designing a roadside wall structure:

the mine pressure is related to the ground stress of the coal bed, the greater the ground stress is, the greater the mine pressure is, the higher the required bearing capacity is, and the thicker the designed roadside wall body is;

when the coal seam has a low stress level of 0-10 MPa, the thickness of the roadside wall body is designed to be 0.6 m; when the local stress is in a medium stress level of 10-18 MPa, the thickness of the roadside wall body is designed to be 0.8 m; when the local stress is at a high stress level of 18-30 MPa, the thickness of the roadside wall body is designed to be 1.0 m;

fourthly, integrally designing a structure of a roadway top plate, a roadway-side wall body and a bottom plate to stabilize the gob-side entry retaining surrounding rock structure:

excavating a foundation pit at a roadway bottom plate wall building position, arranging a plurality of bottom plate anchor rods at the middle position of the bottom of the foundation pit, laying a layer of reinforcing mesh sheet at the bottom of the foundation pit, wherein the reinforcing mesh sheet is paved at the bottom of the foundation pit, and the exposed parts of the top plate anchor cables and the exposed parts of the bottom plate anchor rods which are installed at the middle position of the roadside wall body enter the roadside wall body, so that an integrated structure design is formed for a roadway top plate, the roadside wall body and a bottom plate, and the stability of the surrounding rock structure of the top plate, the bottom plate and the roadside wall body of the gob-side entry is enhanced;

fifthly, reinforcing bars are arranged in the roadside wall body to enhance tensile and shear resistance:

arranging a layer of reinforcing mesh on each of two sides of a roadway-side wall, enabling the reinforcing mesh to be connected with the top and touch the bottom, erecting a plurality of round-rod transverse lacing wires with hooks at two ends along the height direction of the roadway-side wall, firmly binding the hooks of the transverse lacing wires with the reinforcing mesh by binding wires, erecting a plurality of round-rod longitudinal lacing wires with hooks at two ends along the direction of the roadway-side wall, and firmly binding the hooks of the longitudinal lacing wires with the transverse lacing wires by the binding wires;

sixthly, the strength of the pile-spraying concrete wall body rises quickly, the pile-spraying concrete wall body is supported in time without yielding, the mining side top plate is cut off by force, and only 7 days of temporary support are needed for gob-side entry retaining:

the strength of the roadside wall body constructed by the pile-spraying is high in rising speed, the uniaxial compressive strength of 3 days can reach 22MPa, the uniaxial compressive strength of 7 days can reach 26MPa, the uniaxial compressive strength of 28 days can reach 40MPa, the later strength is not lost, a roadway roof can be timely supported, the roof of a gob-side entry retaining can be prevented from sinking and deforming, the roof of one side of a gob-side can be powerfully cut off, the pressure of surrounding rocks of the entry retaining can be reduced, the surrounding rock structure can be kept stable under the high-strength supporting effect of the roadside wall body of the gob-side entry retaining, and only a single support of 7 days is needed to temporarily support in the gob-side entry retaining;

seventhly, slightly expanding the wall, tightly contacting the roof without air leakage, and isolating the goaf:

the stacking and spraying construction process can enable concrete to be rapidly formed, a roadside wall body is formed in a layer-by-layer stacking and accumulating mode, the concrete material at the outlet of the injection pipe of the stacking and spraying equipment has a certain injection speed, is tightly connected with the top, and can completely isolate a gob; meanwhile, the roadside wall has the micro-expansion characteristic, does not generate shrinkage cracks, is dense and does not leak air;

and eighthly, coal mining and gob-side entry retaining are not interfered with each other, and high yield and high efficiency can be realized by stacking and spraying a wall body beside a roadway to closely follow a coal mining working face:

the method comprises the steps of utilizing a mine car to feed into an underground temporary stock ground, enabling the distance between the temporary stock ground and a coal face to be 200m, laying a conveying pipeline with the outer diameter of 60mm along the axial direction of a roadway, mixing and spraying dry materials in the stock ground according to the proportion required by a stacking and spraying process, utilizing compressed air to convey dry mixed materials to the position, behind the coal face, of a constructed roadway-side wall body in the stock ground through a pipeline by stacking and spraying equipment, closely following an end support of the coal face, and forming the roadway-side wall body through stacking and spraying to achieve gob-side entry retaining.

2. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: in the first step, the diameter of the strong anchor cable is phi 21.8mm, the breaking load is 580kN, a high-strength self-aligning metal tray with the thickness of 300mm multiplied by 16mm and a lockset are matched for use, the anchoring length is 2.0m, and the applied installation pretightening force is 300 kN.

3. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: in the first step, the exposed length of a roof anchor cable arranged in the middle of the roadside wall body is 0.5m, and the anchoring length is 2.0 m; the exposed length of a top plate anchor cable arranged at the center line position of the roadway top plate is 0.2m, and the anchoring length is 2.0 m.

4. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: in the second step, the row spacing of the U-shaped steel struts is 0.5m, the diameter of the waste rock blocking reinforcing steel mesh is 6mm, and the size of the grid is 0.1m multiplied by 0.1 m.

5. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: and in the fourth step, the depth of the foundation pit is 0.5m, and the width of the foundation pit is consistent with the thickness of the roadside wall body designed in the third step.

6. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: in the fourth step, the distance between the bottom plate anchor rods is 0.5m, the specification is phi 20mm multiplied by 2000mm, the left-handed thread steel anchor rod is made of MG335 material, the yield load is 105kN, the anchoring length of the bottom plate anchor rod is 1.0m, and the exposed length is 1.0 m.

7. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: in the fourth step, the diameter of the reinforcing mesh is 6mm, and the size of the grid is 0.1m multiplied by 0.1 m.

8. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: in the fifth step, the diameter of the reinforcing mesh is 6mm, and the size of the grid is 0.1m multiplied by 0.1 m; the space between the transverse tie bars is 1.0m, the row spacing is 0.6m, the diameter of the transverse tie bars is 20mm, and the length of the transverse tie bars is consistent with the thickness of the wall body beside the roadway; the distance between the longitudinal tie bars is 0.3m, each layer comprises 2 longitudinal tie bars, the diameter of each longitudinal tie bar is 20mm, and the length of each longitudinal tie bar is 1.2 m.

9. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: the eighth step, the piling and spraying equipment is a concrete sprayer used in coal mines, the spraying and conveying distance is 200m, and the spraying capacity is 7-8 m³/h。

10. The fully mechanized top coal caving face pile-spraying concrete gob-side entry retaining method according to claim 1, characterized in that: and in the eighth step, the stacking-spraying mixture is prepared from sand, pebbles, 425# ordinary portland cement and a JCT-1 spraying concrete additive according to the required proportion of a stacking-spraying process.

Technical Field

The invention belongs to the technical field of coal-pillar-free mining in the coal industry, and particularly relates to a gob-side entry retaining method for fully-mechanized top coal caving face pile-spraying concrete.

Background

With the reduction of non-renewable coal resources and the construction of a resource-saving society, the improvement of the recovery rate of a coal face is imperative. Under the technical support of theoretical research, gob-side entry retaining coal pillar-free mining is a development trend of the coal industry, and engineering technicians are always exploring gob-side entry retaining methods which are adaptive to the occurrence conditions and the production process of a coal seam to be mined.

The gob-side entry retaining is a space surrounded by a coal wall, a wall body beside the roadway and a roof rock layer above the roadway, and the key of successful entry retaining lies in keeping the stability of the surrounding rock structure. The coal-based rock stratum is a brittle material, and fracture damage can occur when the separation layer or sinking deformation of the roadway top plate exceeds a certain range. The gob-side entry retaining surrounding rock is supported by an in-lane anchor net support and a roadside wall together, and the roadside anchor net support capacity is limited, so that the roadside wall must be required to form a high-strength support for a top plate as early as possible, the separation and sinking deformation of the entry retaining top plate are prevented, the effect similar to a top-cutting column can be exerted, a cantilever top plate on the gob-side is cut off, and the basic top rock layer of the gob-side entry retaining is broken on the gob-side.

Therefore, the key of the successful entry retaining is that the wall body beside the roadway can provide enough supporting force for the top plate as soon as possible, so that the separation layer or brittle fracture of the top plate above the gob-side roadway is avoided, meanwhile, a cantilever top plate with a certain thickness at the goaf side can be cut off, and the bearing pressure borne by the gob-side roadway is reduced.

The currently available gob-side entry retaining technology comprises a flexible membrane bag high-water material method, a rigid template pump concrete injection method and a roof cutting pressure relief gangue supporting method. The defects of the gob-side entry retaining technology can be summarized as follows: the wall body on the goaf side can not be completely connected with the roof, the supporting performance is poor, the sinking and bottom bulging deformation of the top plate of the entry retaining are large, the maintenance of the surrounding rock structure of the entry retaining is difficult, the air leakage of the goaf is caused, the number of the single pillars used for temporary support is large, the time is long, the cost is high, and the like. The detention time of the single prop in the retained roadway far exceeds the range of temporary support, and the single prop becomes permanent support, which causes great difficulty for temporary support of gob-side retained roadway. Therefore, field engineering technicians always search for a safe, quick, efficient and low-cost gob-side entry retaining technical method.

The pile-spraying process is a new method for building concrete wall (CN 201810566315.0 is a method for quickly building concrete wall by pile-spraying underground coal mine), and is characterized by that the sand and stone material, cement and JCT-1 sprayed concrete additive are uniformly mixed according to a certain proportion in the wet (or dry) state, then fed into a sprayer, the mixture is conveyed to the sprayer position along the pipeline by means of compressed air and mixed with water, and sprayed at high speed to the working surface to form spray layer or build wall body.

The concrete wall or spray layer constructed by the pile-spraying process has the following characteristics: firstly, the thickness of a primary sprayed layer is large, the wall body is quickly formed, and the construction does not need formwork support and maintenance; secondly, the sprayed layer has high adhesiveness, dust fall and water seal are achieved, and the rebound rate is less than 5%; thirdly, the concrete is early strengthened without losing the final strength, the final strength exceeds C30, and the tensile and shear resistance is stronger by matching with the reinforcement in the concrete; fourthly, the roof connecting effect is good, and the sprayed layer and the rock stratum bear load together; the wall body has the characteristics of high density, high strength and micro-expansion, and is dense and does not leak air; the construction equipment has small volume, is quick, flexible and convenient, saves investment and labor and has high construction efficiency.

The construction speed of the pile-spraying process for constructing the concrete wall is high, the operation is convenient, the concrete strength is not lost, the cost is low, and the safety production requirement of the underground coal mine is met. The speed of the wall building of the heap spraying process is mainly related to the spraying capacity of the spraying machine, and under the condition that the spraying capacity of the spraying machine meets the requirement, the wall building speed of the heap spraying process can reach 7-8 m³And h, the method has important significance for improving the wall building speed, reducing the labor intensity of workers, synchronizing the working face mining and the gob-side entry retaining wall building and promoting the safe and efficient production of the coal mine.

Disclosure of Invention

The invention aims at the problems of poor top connection and support performance of the roadside wall, large sinking and bottom bulging deformation of the top plate of the retained roadway, difficult maintenance of a supporting structure of surrounding rock of the roadway, air leakage of a gob of the retained roadway, large quantity and long time of single pillars used for temporary supporting, high cost of retained roadway and the like in the existing gob-side retained roadway technology, in particular to the problems of a fully mechanized caving face. A gob-side entry retaining method for fully mechanized top coal caving face pile-spraying concrete is provided by utilizing the high strength characteristic and safe, rapid and efficient pile-spraying construction process of concrete materials.

The invention adopts the following technical scheme:

a fully mechanized top coal caving working face pile-spraying concrete gob-side entry retaining method comprises the following steps:

the first step, anchor rope high prestressing force is strutted, prevents the tunnel roof absciss layer, keeps the wholeness of roof stratum:

respectively punching holes in the center line position of a roadway top plate and the middle position of a roadside wall body in advance of a stope face, mounting strong anchor cables, applying mounting pretightening force, and forming high-prestress support for the roadway top plate; the anchor cable is anchored in a stable top plate rock stratum, and when the distance between the stable rock stratum and a roadway top plate exceeds 10m, the length of the anchor cable is determined according to 2m which exceeds the height of a natural balance arch;

secondly, temporarily sealing the goaf at the goaf side at the rear of the hydraulic support:

following the coal face, keeping the working face recovery cycle progress consistent, supporting a U-shaped steel pillar at the edge of the goaf side of the roadway, hanging a layer of gangue blocking reinforcing mesh on the side of the U-shaped steel pillar close to the roadway, laying a layer of flame-retardant and anti-static fiber cloth on the side of the gangue blocking reinforcing mesh close to the roadway, temporarily blocking gangue and sealing the goaf;

thirdly, designing a roadside wall structure:

the mine pressure is related to the ground stress of the coal bed, the greater the ground stress is, the greater the mine pressure is, the higher the required bearing capacity is, and the thicker the designed roadside wall body is. When the coal seam has a low stress level of 0-10 MPa, the thickness of the roadside wall body is designed to be 0.6 m; when the local stress is in a medium stress level of 10-18 MPa, the thickness of the roadside wall body is designed to be 0.8 m; when the local stress is at a high stress level of 18-30 MPa, the thickness of the roadside wall body is designed to be 1.0 m;

fourthly, integrally designing a structure of a roadway top plate, a roadway-side wall body and a bottom plate to stabilize the gob-side entry retaining surrounding rock structure:

excavating a foundation pit at a roadway bottom plate wall building position, arranging a plurality of bottom plate anchor rods at the middle position of the bottom of the foundation pit, laying a layer of reinforcing mesh sheet at the bottom of the foundation pit, wherein the reinforcing mesh sheet is paved at the bottom of the foundation pit, and the exposed parts of the top plate anchor cables and the exposed parts of the bottom plate anchor rods which are installed at the middle position of the roadside wall body enter the roadside wall body, so that an integrated structure design is formed for a roadway top plate, the roadside wall body and a bottom plate, and the stability of the surrounding rock structure of the top plate, the bottom plate and the roadside wall body of the gob-side entry is enhanced;

fifthly, reinforcing bars are arranged in the roadside wall body to enhance tensile and shear resistance:

arranging a layer of reinforcing mesh on each of two sides of a roadway-side wall, enabling the reinforcing mesh to be connected with the top and touch the bottom, erecting a plurality of round-rod transverse lacing wires with hooks at two ends along the height direction of the roadway-side wall, firmly binding the hooks of the transverse lacing wires with the reinforcing mesh by binding wires, erecting a plurality of round-rod longitudinal lacing wires with hooks at two ends along the direction of the roadway-side wall, and firmly binding the hooks of the longitudinal lacing wires with the transverse lacing wires by the binding wires;

sixthly, the strength of the pile-spraying concrete wall body rises quickly, the pile-spraying concrete wall body is supported in time without yielding, the mining side top plate is cut off by force, and only 7 days of temporary support are needed for gob-side entry retaining:

the strength of the roadside wall body constructed by the pile-spraying is high in rising speed, the uniaxial compressive strength of 3 days can reach 22MPa, the uniaxial compressive strength of 7 days can reach 26MPa, the uniaxial compressive strength of 28 days can reach 40MPa, the later strength is not lost, a roadway roof can be timely supported, the roof of a gob-side entry retaining can be prevented from sinking and deforming, the roof of one side of a gob-side can be powerfully cut off, the pressure of surrounding rocks of the entry retaining can be reduced, the surrounding rock structure can be kept stable under the high-strength supporting effect of the roadside wall body of the gob-side entry retaining, and only a single support of 7 days is needed to temporarily support in the gob-side entry retaining;

seventhly, slightly expanding the wall, tightly contacting the roof without air leakage, and isolating the goaf:

the stacking and spraying construction process can enable concrete to be rapidly formed, a roadside wall body is formed in a layer-by-layer stacking and accumulating mode, the concrete material at the outlet of the injection pipe of the stacking and spraying equipment has a certain injection speed, is tightly connected with the top, and can completely isolate a gob; meanwhile, the roadside wall has the micro-expansion characteristic, does not generate shrinkage cracks, is dense and does not leak air;

and eighthly, coal mining and gob-side entry retaining are not interfered with each other, and high yield and high efficiency can be realized by stacking and spraying a wall body beside a roadway to closely follow a coal mining working face:

the method comprises the steps of utilizing a mine car to feed into an underground temporary stock ground, enabling the distance between the temporary stock ground and a coal face to be 200m, laying a conveying pipeline with the outer diameter of 60mm along the axial direction of a roadway, mixing and spraying dry materials in the stock ground according to the proportion required by a stacking and spraying process, utilizing compressed air to convey dry mixed materials to the position, behind the coal face, of a constructed roadway-side wall body in the stock ground through a pipeline by stacking and spraying equipment, closely following an end support of the coal face, and forming the roadway-side wall body through stacking and spraying to achieve gob-side entry retaining.

Furthermore, in the first step, the diameter of the strong anchor cable is phi 21.8mm, the breaking load is 580kN, a high-strength self-aligning metal tray with the thickness of 300mm multiplied by 16mm and a lock are matched for use, the anchoring length is 2.0m, and the applied installation pretightening force is 300 kN.

Furthermore, in the first step, the exposed length of a roof anchor cable arranged in the middle of the roadside wall body is 0.5m, and the anchoring length is 2.0 m; the exposed length of a top plate anchor cable arranged at the center line position of the roadway top plate is 0.2m, and the anchoring length is 2.0 m.

Furthermore, in the second step, the row spacing of the U-shaped steel struts is 0.5m, the diameter of the waste rock blocking reinforcing mesh is 6mm, and the size of the grid is 0.1m multiplied by 0.1 m.

Further, the depth of the foundation pit in the fourth step is 0.5m, and the width of the foundation pit is consistent with the thickness of the roadside wall body designed in the third step.

Furthermore, in the fourth step, the distance between the floor anchor rods is 0.5m, the specification is phi 20mm multiplied by 2000mm, the yield load of the left-handed thread steel anchor rod made of MG335 material is 105kN, the anchoring length of the floor anchor rod is 1.0m, and the exposed length is 1.0 m.

Furthermore, the diameter of the reinforcing mesh in the fourth step is 6mm, and the size of the grid is 0.1m multiplied by 0.1 m.

Furthermore, in the fifth step, the diameter of the reinforcing mesh is 6mm, and the size of the grid is 0.1m multiplied by 0.1 m; the space between the transverse tie bars is 1.0m, the row spacing is 0.6m, the diameter of the transverse tie bars is 20mm, and the length of the transverse tie bars is consistent with the thickness of the wall body beside the roadway; the distance between the longitudinal tie bars is 0.3m, each layer comprises 2 longitudinal tie bars, the diameter of each longitudinal tie bar is 20mm, and the length of each longitudinal tie bar is 1.2 m.

Further, the stacking and spraying equipment in the eighth step is a concrete sprayer used in coal mines, the spraying and conveying distance is 200m, and the spraying capacity is 7-8 m³/h。

And furthermore, in the eighth step, the stacking-spraying mixture is sand, gravel, 425# ordinary portland cement and a JCT-1 shotcrete additive, and is prepared according to the required proportion of a stacking-spraying process, and the method is referred to patent No. CN201810566315.0 and is used for rapid wall building of the underground coal mine stacking-spraying concrete.

The JCT-1 shotcrete admixture is an inorganic nano-grade material refined by a mechanical grinding method, is a multi-effect multifunctional admixture integrating acceleration, early strength and water reduction, is in a grey white powder shape, is non-toxic, tasteless and non-combustible, and has the density of 2.1-2.3 g/cm³The particle size is 0.3-0.5 μm, and no adverse effect is caused to human body in the using process. The JCT-1 shotcrete admixture is a shotcrete admixture developed and researched by Shanxi Jichangtai mine engineering technology limited company, and the JCT-1 shotcrete admixture can realize the effects of increasing the cohesive force of a sprayed layer without shrinkage, improving the early strength and the final strength of concrete, reducing the splashing resilience, being fast in forming, increasing the thickness of the sprayed layer, being compact in roof connection and the like.

The invention has the following beneficial effects:

the novel gob-side entry retaining technology provided by the invention is based on the processes of reinforcing bar construction and concrete piling and spraying, and has the technical advantages of safety, rapidness, high efficiency, short temporary supporting time in the gob-side entry retaining, no need of advanced roof cutting, low entry retaining cost and the like compared with the existing method.

According to the technical scheme provided by the invention, the anchor cable high-prestress support can prevent the roof of the roadway from separating, and the integrity of the rock stratum of the roof of the gob-side entry retaining is kept. The integrated structural design of the top plate, the wall body and the bottom plate of the roadway is provided with two reinforcing bars of a transverse tie bar and a longitudinal tie bar in a built-in mode, and the surrounding rock structure of the gob-side entry retaining is stable. The strength of the roadside wall body formed by the pile-spraying is high in rising speed, the roadside wall body is supported in time without yielding pressure, the goaf side top plate is cut off strongly, the surrounding rock stress of the gob-side entry retaining is reduced, and the temporary supporting time is short. The roadside wall body expands slightly, is tightly connected with the roof and does not leak air, and effectively isolates a gob. Coal mining and gob-side entry retaining are not interfered with each other, and high yield and high efficiency can be realized by constructing a wall body beside a roadway by pile spraying to closely follow a coal mining working face. The gob-side entry retaining of the pile-spraying concrete building wall only needs one mining concrete sprayer, the underground temporary stock yard is loaded, the construction process is simple, the construction equipment is flexible and convenient, the operation is simple, the cost investment is low, the pile-spraying concrete gob-side entry retaining method can be suitable for complex engineering conditions such as large mining height, rapid push mining, large ground pressure, large buried depth, spontaneous combustion ignition coal beds and the like, and the adaptability is strong.

Drawings

FIG. 1 is a schematic view of the gob-side entry retaining process of the present invention;

FIG. 2 is a top view of the gob-side entry retaining production system of the present invention;

FIG. 3 is a schematic structural view of gob-side entry retaining surrounding rock of the invention;

FIG. 4 is a schematic diagram of a roadside wall reinforcing bar of the invention;

FIG. 5 is a schematic view of a transverse lacing wire of the present invention;

FIG. 6 is a schematic view of a longitudinal tie bar of the present invention;

FIG. 7 is a schematic view of a rebar grid of the present invention;

wherein: 1-roadside wall; 2-U-shaped steel struts; 3-reinforcing steel bar mesh; 4-a goaf; 5-foundation pits; 6-hydraulic support; 7-coal face; 8-gob-side entry retaining; 9-a material conveying pipeline; 10-a jet machine; 11-stock ground; 12-a coal seam; 13-anchor cable; 14-floor anchor; 15-transverse lacing wire; 16-longitudinal lacing wire.

Detailed Description

The invention content and the implementation steps of a coal face pile-spraying concrete gob-side entry retaining method are as follows:

the first step is as follows: the anchor cable is supported in a high-prestress mode, so that a roadway top plate is prevented from being separated, and the integrity of a top plate rock stratum is kept;

and (3) leading the stope face, punching and installing a strong anchor cable with the specification of phi 21.8mm at the central line position of the roadway roof and the middle position of the roadside wall body, and applying 300kN of installation pretightening force to form a high-prestress support for the roadway roof. The exposed length of a roof anchor cable arranged in the middle of the roadside wall body is 0.5m, and the anchoring length is 2.0 m; the exposed length of the top plate anchor cable arranged at the middle line position of the top plate is 0.2m, and the anchoring length is 2.0 m. The length of the anchor cable is determined according to the condition of the coal rock layer of the top plate of the roadway, and the anchor cable needs to be anchored into the stable top plate rock layer; when the distance between the stable rock stratum and the roadway top plate exceeds 10m, the length of the anchor cable is determined according to 2m which exceeds the height of the natural balance arch.

The second step is that: a goaf is temporarily closed at the goaf side behind the hydraulic support;

following the coal face, keeping the same with the working face extraction circulation progress, and supporting a U-shaped steel support on the edge of the roadway mining side, wherein the row spacing of the U-shaped steel support is 0.5 m; meanwhile, a gangue blocking reinforcing mesh piece with the diameter of 6.0mm and the mesh size of 0.1m multiplied by 0.1m is hung on the side, close to the roadway, of the U-shaped steel strut, a layer of flame-retardant and anti-static fiber cloth is laid on the side, close to the roadway, of the gangue blocking reinforcing mesh piece, gangue is temporarily blocked, and the goaf is closed.

The third step: designing a roadside wall structure;

the mine pressure is related to the ground stress of the coal bed, the greater the ground stress is, the greater the mine pressure is, the higher the required bearing capacity is, and the thicker the designed roadside wall body is. When the coal seam has a low stress level of 0-10 MPa, the thickness of the wall body is designed to be 0.6 m; when the local stress is in a medium stress level of 10-18 MPa, the thickness of the wall body is designed to be 0.8 m; when the local stress is in a high stress level of 18-30 MPa, the thickness of the wall body is designed to be 1.0 m.

The fourth step: the integrated structural design of the top plate, the wall body and the bottom plate of the roadway ensures that the gob-side entry retaining surrounding rock structure is stable;

the thickness of the roadside wall body constructed by the pile-sprayed concrete is determined according to the third step of the invention according to the ground stress level of the coal bed. Excavating a foundation pit with the depth of 0.5m and the width consistent with the thickness of a wall body beside a roadway at the wall building position of a roadway bottom plate, and arranging a row of bottom plate anchor rods with the specification of phi 20mm multiplied by 2000mm at the middle position of the bottom of the foundation pit according to the interval of 0.5m, wherein the anchoring length of the bottom plate anchor rods is 1.0m, and the exposed length of the bottom plate anchor rods is 1.0 m; and a layer of reinforcing mesh with the diameter of 6.0mm and the grid size of 0.1m multiplied by 0.1m is paved at the bottom of the foundation pit, and the reinforcing mesh is paved at the bottom of the foundation pit. Exposed parts of the top plate anchor cables and exposed parts of the bottom plate anchor rods, which are arranged in the middle of the roadway-side wall, enter the roadway-side wall, so that an integrated structural design is formed for the top plate, the wall and the bottom plate of the roadway, and the stability of the surrounding rock structure of the top plate, the bottom plate and the wall of the gob-side entry retaining is enhanced.

The fifth step: the wall body is internally provided with reinforcing bars, so that the tensile and shear resistance is enhanced;

two sides of the wall are respectively provided with a layer of steel bar net with the diameter of 6.0mm and the grid size of 0.1m multiplied by 0.1m, and the steel bar net is connected with the top and touches the bottom. Round bar transverse lacing wires with hooks at two ends and 20mm in diameter and 1.0m in length are erected along the height of the roadside wall body at the interval of 1.0m and the row spacing of 0.6m, and the hooks of the transverse lacing wires are firmly bound with the steel mesh pieces by binding wires. And (3) erecting longitudinal tie bars of round rods with the diameter of 20mm and the length of 1.2m at intervals of 0.3m and 2 round rods on each layer along the direction of the wall, and firmly binding hooks of the longitudinal tie bars and the transverse tie bars by using binding wires.

And a sixth step: the strength of the pile-spraying concrete wall body is increased quickly, the pile-spraying concrete wall body is supported in time without yielding pressure, the mining side top plate is cut off by force, and only 7-day temporary support is needed for gob-side entry retaining;

the strength rising speed of the roadside wall body constructed by the pile-spraying is high, the uniaxial compressive strength in 3 days can reach 22MPa, the uniaxial compressive strength in 7 days can reach 26MPa, the uniaxial compressive strength in 28 days can reach 40MPa, the later strength is not lost, the roadway roof can be timely supported, the roof of the gob-side entry retaining is prevented from sinking and deforming, the roof on one side of the gob can be forcibly cut off, and the pressure of the surrounding rock of the entry retaining is reduced. And under the high-strength supporting action of the roadside wall body, the surrounding rock structure can be kept stable, and only 7-day single-prop temporary support is needed in the gob-side entry retaining.

The seventh step: the wall body expands slightly, the roof is tightly connected, air leakage is avoided, and a goaf is isolated;

the stacking and spraying construction process can enable concrete to be rapidly formed, and the roadside wall body is formed in a layer-by-layer stacking and accumulating mode. The concrete material at the outlet of the jet pipe of the stack spraying equipment has a certain jet speed, is tightly connected with the top and can completely isolate a goaf; meanwhile, the roadside wall has the characteristic of micro-expansion, does not generate shrinkage cracks, and is dense and free of air leakage.

Eighth step: coal mining and gob-side entry retaining are not interfered with each other, and high yield and high efficiency can be realized by constructing a wall body beside a roadway by pile spraying to closely follow a coal mining working face.

The method comprises the steps of utilizing a mine car to feed into an underground temporary stock ground, enabling the distance between the temporary stock ground and a coal face to be 200m, laying a conveying pipeline with the outer diameter of 60mm along the axial direction of a roadway, mixing and spraying dry materials in the stock ground according to the proportion required by a stacking and spraying process, utilizing compressed air to convey dry mixed materials to the position, behind the coal face, of a constructed roadway-side wall body in the stock ground through a pipeline by stacking and spraying equipment, closely following an end support of the coal face, and forming the roadway-side wall body through stacking and spraying to achieve gob-side entry retaining.

The heap spraying equipment is a concrete sprayer used in coal mines, the spraying and conveying distance is 200m, and the spraying capacity is 7-8 m³/h。

The stacking and spraying mixture is prepared from sand, pebbles, 425# common portland cement and a JCT-1 spraying concrete additive according to the required proportion of a stacking and spraying process.

The roof anchor rope is the prestressing force steel strand wires of diameter 21.8mm, and the breaking load is 580kN, and supporting high strength self-aligning metal tray and the tool to lock that use 300mm 16mm, anchor length is 2.0m, and the installation pretightning force is 300 kN.

The floor anchor rod is a left-handed thread steel anchor rod made of MG335 material and having the diameter of 20mm and the length of 2000mm, the yield load is 105kN, and the anchoring length is 1.0 m.

The transverse lacing wire is round steel with the diameter of 20mm, the length of the round steel is consistent with the thickness of the roadside wall body, and hooks are arranged at two ends of the round steel.

The longitudinal lacing wire is a round steel with the diameter of 20mm, the length of 1.2m and hooks at two ends.

The steel bar mesh is a welded steel bar mesh with the diameter of 6mm and the mesh size of 100mm multiplied by 100mm, and the mesh size is manufactured according to the height of the roadway.