A rapid excavation method for coal seam elastic potential energy advance release and coordinated advance support

Abstract

The present invention discloses a method for rapid excavation by pre-release of elastic potential energy of coal seams in coordination with pre-support. The method realizes the pre-release of accumulated stress in front of the excavation working face by constructing pressure relief boreholes in the area where the stress of the facing wall is obvious. The front of the excavation face is anchored before the excavation operation to form a stress pre-frame in the deep part of the coal body, and to form a unloading belt in the process of releasing the elastic potential energy inside the coal body, thereby ensuring the integrity of the coal body in the process of releasing the elastic potential energy. The present invention only needs to construct pressure relief boreholes in the area where the stress of the facing wall is obvious, which simplifies the construction process, reduces the drilling construction during the overall excavation, improves the construction efficiency, and greatly shortens the tunnel excavation cycle. After the pre-precise pressure relief, the tunnel eliminates or reduces the phenomenon of top and side explosion, and creates a good working environment in coordination with the pre-support, laying a foundation for the alternating construction of two excavation working faces to achieve rapid excavation.

Description

Technical Field

[0001] This invention relates to the field of tunneling technology, and in particular to a rapid tunneling method that combines advanced release of elastic potential energy of coal seams with advanced support. Background Technology

[0002] For tunneling faces located in extra-thick coal seams, the immediate roof and main roof lithology are siltstone, fine sandstone, medium-coarse sandstone, and gravelly coarse sandstone, with a Protodyakonov coefficient of 7, indicating relative hardness. The working face cross-section is generally rectangular. Existing tunneling technology employs fully mechanized tunneling construction, with anchor-mesh-cable support. During tunneling, roof and sidewall blasting is prone to occur, resulting in poor roadway roof and sidewall formation, with local sidewall spalling depths exceeding 600mm, further contributing to poor roadway formation. This severely impacts the improvement of safety production standardization standards at the tunneling face. Considering factors such as gas control cycles and personnel production organization, alternating construction of two tunneling faces is chosen. Given the aforementioned drawbacks, achieving efficient and rapid tunneling and matching the tunneling time of the two faces becomes a challenge. To address this, a method for rapid tunneling with pre-release of coal seam elastic potential energy and coordinated pre-support is proposed, ensuring rapid and efficient roadway tunneling under safe conditions. This provides theoretical reference and technical guidance for mining areas with similar geological conditions. Summary of the Invention

[0003] Purpose of the invention: In order to overcome the shortcomings of the existing technology, the present invention provides a method for rapid tunneling by pre-releasing the elastic potential energy of coal seams and coordinating with pre-support. By realizing the pre-releasing of the elastic potential energy of coal seams and selecting a reasonable support scheme, the occurrence of roof and sidewall blasting can be reduced, and rapid and efficient tunneling can be carried out under the premise of safety.

[0004] Technical Solution: To achieve the above objectives, the present invention provides a rapid tunneling method for advanced release of elastic potential energy in coal seams, coordinated with advanced support. This method involves constructing pressure-relief boreholes in areas where stress is evident in the facing wall to achieve advanced release of accumulated stress ahead of the tunneling face. Before tunneling operations, anchor bolts are installed ahead of the facing to form a stress-prevention framework deep within the coal seam. This creates an unloading zone during the release of elastic potential energy within the coal seam, ensuring the integrity of the coal seam during the release of elastic potential energy. The method specifically includes the following steps:

[0005] Step 1, Determining the location of the pre-decompression boreholes: Construct several decompression holes on the facing wall at the locations corresponding to the shoulder and centerline of the roadway cross section, ensuring that the diameter and depth of the several decompression holes are consistent;

[0006] Step II, Design of Pre-Relief Holes: First, boreholes are drilled in the roof of the coal seam. Then, borehole inspection equipment is used to observe the inner wall condition until multiple sections of coal seam failure and multiple sections of intact coal seam are clearly observed. Then, the sections of coal seam that are basically in a stable state are eliminated by stress distribution law. The remaining sections of coal seam are the main accumulation sections of elastic potential energy. Finally, the borehole depth is calculated based on the depth range of the main accumulation sections of elastic potential energy. The borehole dip angle is determined by the pitch angle of the coal seam in the strike direction. The minimum resistance line between boreholes is determined by the hardness and shear strength of the coal seam where the working face is located. The drilling spacing of the pressure relief boreholes is determined by this.

[0007] Step III, Advance Support and Roadway Support: Several advance support anchors are installed symmetrically on both sides of the roadway, within a range of 1 / 2 to 2 / 3 of the roadway width. The advance support anchors extend into the coal seam from the angle between the facing wall and the roof, and the angle between the advance support anchors and the roof is controlled between 20° and 30°.

[0008] At the same time, several anchor bolts are arrayed on both sides of the roadway and the roof. The compressive stress zone of each anchor bolt is close to each other and connected as a whole to form an integral support structure. Two rows of roof anchor cables are symmetrically set on both sides of the roadway centerline.

[0009] Furthermore, on the facing wall at the shoulder of the roadway cross section, four pre-decompression holes are arranged vertically from top to bottom: a1, a2, a3, and a4. The drilling positions of a1, a2, a3, and a4 are arranged at equal intervals, wherein a1 extends at an elevation angle of 15°, and a2, a3, and a4 all extend at an elevation angle of 3°.

[0010] Furthermore, on the facing wall at the center line of the roadway cross section, there are two advance pressure relief holes arranged vertically from top to bottom: a5 and a6, where a5 extends at an elevation angle of 10° and a6 extends perpendicular to the center of the facing wall.

[0011] Furthermore, the two sides of the roadway include the mining side and the coal pillar side. Fiberglass anchor bolts are used on the mining side, while left-handed threaded steel anchor bolts without longitudinal ribs are used on the roof and coal pillar side. The drilling positions of all anchor bolts are evenly distributed in an array on the roof or both sides. The anchor bolts extend into the surrounding rock of the roadway perpendicular to the inner wall of the roadway. In particular, the two rows of anchor bolts located at the shoulder sockets on both sides of the roof are inclined towards the coal pillar side on the same side, and the two rows of anchor bolts located at the upper and lower ends of the coal pillar side are inclined towards the upper and lower sides respectively.

[0012] Furthermore, grouting anchors are interspersed at equal intervals in both rows of top plate anchors, with one grouting anchor between every two top plate anchors, and the grouting anchors are equidistant from the top plate anchors on both sides.

[0013] Furthermore, the grouting anchor cable includes a hollow steel strand, which extends into a pre-drilled grouting hole in the top slab. A grout-stopping plug is provided near the opening of the pre-drilled grouting hole in the top slab, blocking the opening. A tray is provided outside the grout-stopping plug, supporting the top slab wall around the opening of the pre-drilled grouting hole. A locking device is provided outside the tray for anchoring the tray to the top slab. A threaded plug is provided at the outermost end of the hollow steel strand.

[0014] Furthermore, several bidirectional grouting through-cable cables are installed on the coal pillar side. Specifically, the spacing between the grouting anchor cables is determined by calculating the grouting diffusion radius R without considering the mutual influence of multiple pores, wherein:

[0015]

[0016] Furthermore, the bidirectional grouting through-cable also includes hollow steel strands, with an internal grouting pipe inside. The grouting pipe wall has several grout outlets. Both ends of the hollow steel strand are sequentially provided with grout stop plugs, trays, and locks. The hollow steel strands of the bidirectional grouting through-cable pass through the pre-reserved grouting hole in the coal pillar side are passed through. The grout stop plugs at both ends respectively block the two ends of the pre-reserved grouting through hole in the coal pillar side. The trays at both ends are respectively supported on the side wall around the two ends of the pre-reserved grouting through hole in the coal pillar side. The locks are used to anchor the trays to the coal walls on both sides of the coal pillar.

[0017] Furthermore, the installation of the grouting anchor cable includes the following steps: First, drill holes for the anchor cable; then, insert resin cartridges into the hole, use a pneumatic drill to continuously push the anchor cable into the hole, push the anchor cable to the bottom of the hole and stir it; after the through-hole grouting anchor cable passes through the coal pillar, it only needs to be tensioned in both directions; then, push the anchor cable with the grout stop plug to a certain depth in the hole, wrap enough cotton thread behind the grout stop plug and compact it, so that it does not obstruct the entry into the hole when the anchor cable is anchored; then, reset the jack and perform secondary tensioning. During secondary tensioning, the lock and tray are properly installed, and it must be ensured that the jack does not engage with the welded end of the anchor cable; finally, after stirring the grout evenly, open the grouting hole at the rear of the anchor cable, connect the grouting nozzle and start grouting until it is full.

[0018] Beneficial effects: The coal seam elastic potential energy advance release and coordinated advance support rapid tunneling method of the present invention has at least the following advantages:

[0019] (1) During the tunnel excavation, the side anchor cables and some top anchor cables, as well as the pressure relief boreholes on the back side of the tunnel, are no longer constructed. Only the pressure relief boreholes need to be constructed in the area where the stress of the facing wall is obvious. This simplifies the construction process, reduces the drilling construction during the overall tunneling period, improves construction efficiency, greatly shortens the tunnel excavation cycle, reduces labor costs, alleviates the urgency of mine mining and excavation succession, and lays the foundation for the alternation of construction of the two tunneling working faces.

[0020] (2) After the pre-precision pressure relief, the roadway has eliminated or reduced the phenomenon of roof and side explosions, creating a good working environment. During the construction period, the workers no longer panic because of the sound of coal blasting, and at the same time avoid the risk of side collapse and roof falling that could injure people.

[0021] (3) It solves the problem of roof and side blasting during tunneling and deformation and instability during coal pillar mining, which affect tunneling. It can be widely applied to the safe tunneling of all roadways in extra-thick coal seam working faces. At the same time, it provides theoretical reference and technical guidance for mining areas with similar geological conditions, and has certain practicality and innovation. Attached Figure Description

[0022] Appendix Figure 1 This is a block diagram of a rapid tunneling method for early release of elastic potential energy in coal seams and coordinated early support according to the present invention.

[0023] Appendix Figure 2 This is a diagram showing the stress distribution pattern of the surrounding rock in a tunnel in a specific example.

[0024] Appendix Figure 3 A stress analysis diagram showing the positional relationship between the pre-support anchor bolts and the roof slab, and the support mechanism.

[0025] Appendix Figure 4 Schematic diagram of the distribution of compressive stress zone of anchor bolts in optimized cross-section for tunnel support;

[0026] Appendix Figure 5 Design three-view diagrams for pressure relief drilling;

[0027] Appendix Figure 6 Schematic diagram of optimized cross-section for roadway support in alternating construction of two working faces;

[0028] Appendix Figure 7 Schematic diagram of the roof support reinforcement;

[0029] Appendix Figure 8 This is a structural diagram of the grouting anchor cable;

[0030] Appendix Figure 9 This is a structural diagram of a bidirectional grouting through-cable anchor cable;

[0031] Appendix Figure 10 A schematic plan view of a coal pillar support reinforcement example; Detailed Implementation

[0032] The invention will now be further described with reference to the accompanying drawings.

[0033] Within the same coal seam, the alternating construction method of two working faces is an effective way to achieve rapid tunneling by rationally arranging the gas control cycle and personnel production organization. However, it addresses the safety issues caused by the accumulation of internal rock stress during the alternating construction of two working faces, as well as the deformation and instability problems during the coal pillar mining between the two working faces, which prevent the achievement of the expected rapid tunneling effect.

[0034] As attached Figure 1 The aforementioned method for rapid tunneling with coordinated advance support and advance release of coal seam elastic potential energy solves the problem by constructing pressure relief boreholes in areas where stress is evident in the facing wall 1, thereby achieving the advance release of accumulated stress in front of the tunneling face 2. Before tunneling operations, anchor bolt support is first installed in front of the facing to form a stress-advanced skeleton deep within the coal seam. This creates an unloading zone during the release of elastic potential energy within the coal seam, ensuring the integrity of the coal seam during the release of elastic potential energy. Specifically, the method includes the following steps:

[0035] Step 1, Determining the location of the pre-decompression boreholes: Construct several decompression holes on the facing wall 1 at the locations corresponding to the shoulder and centerline of the roadway cross section, ensuring that the diameter and depth of the several decompression holes are consistent;

[0036] In the initial stage of determining the drilling location, through drilling experiments and observations, we attempted to design three pressure relief boreholes within each excavation cycle on the facing wall. The boreholes were located at the lower part of the roadway cross section. Secondly, we drilled one pressure relief borehole at every end on the sidewall of the excavated roadway. After a long period of observation, no changes occurred and the pressure relief effect was not achieved.

[0037] During the actual tunnel excavation, observations revealed that roof and side blasting often occurred in the shoulder pits and the middle of the roof of the tunnel cross-section. This indicates that the shear strength of the coal in this area is far lower than the destructive strength of the elastic potential energy. Based on the above-mentioned borehole test observations, it was determined that this area required pre-decompression drilling. However, the boreholes located at the lower part of the tunnel cross-section could not play the role of pre-decompression. Similarly, since the elastic potential energy had been released due to the excavation, the boreholes located at the side of the tunnel after excavation were also ineffective.

[0038] Therefore, instead of the original decompression drilling in the roadway sidewalls, drilling was carried out only on the facing wall at the locations corresponding to the roadway cross-section shoulder and centerline. This area is where the elastic potential energy is most clearly manifested. After decompression drilling was carried out in this area according to the designed drilling depth, observation was conducted. After 4 hours, the top of the borehole from the opening to the bottom was basically completely cracked. Some boreholes showed obvious decompression effects around them. These boreholes consumed a large amount of elastic potential energy accumulated inside the coal body, making the shear strength of the coal body itself greater than the destructive strength of the elastic potential energy. The phenomena of roof and sidewall blasting and roadway formation were well controlled.

[0039] Step II, Design of Advanced Pressure Relief Holes: First, boreholes are drilled in the top plate 3 of the coal seam. Then, a borehole inspection device is inserted into the borehole to observe the condition of the inner wall until multiple sections of coal seam failure and multiple sections of intact coal seam are clearly observed. Then, the sections of the intact coal seam that are basically in a stable state are eliminated by stress distribution law. The remaining sections of the intact coal seam are the main accumulation sections of elastic potential energy. Finally, the borehole depth is calculated based on the depth range of the main accumulation sections of elastic potential energy. The borehole dip angle is determined by the pitch angle of the coal seam in the strike direction. The minimum resistance line between boreholes is determined by the hardness and shear strength of the coal seam where the working face is located, and the drilling spacing of the pressure relief boreholes is determined accordingly.

[0040] Determining the depth of the pre-decompression borehole is essentially an application of the distribution law of the characteristics of the surrounding rock strata in the roadway. Here is an example: at the 350m and 420m mark of a certain numbered conveyor belt, boreholes were drilled to inspect the roof of the coal seam. The borehole inspection equipment used here is existing technology. Through observation, severe fracture development was found at 2.2-2.5m. It can be clearly observed that there is a long fractured section in the coal body in this section, and the coal body is severely fractured. Therefore, this section is identified as fracture zone A.

[0041] The coal pore surface in the 2.5–8m and 10–15m sections is smooth, the coal body is stable, and the arc surface is rounded. It is not affected by stress, or the shear strength of the coal body in this section can resist the effect of stress failure. Therefore, this section is judged to be plastic. Among them, the 2.5–8m section is the plastic zone B, and the section beyond 10m is the original rock stress zone D.

[0042] Severe fracture development was observed at 9m, and it was clearly observed that the coal body in this section had a short fractured section. The coal body was affected by stress and produced significant tensile cracks. The degree of fracture development gradually weakened further into the hole at 10m. Therefore, this section was identified as elastic zone C.

[0043] Therefore, we can conclude that... Figure 2The stress distribution diagram of the surrounding rock in the roadway shows that the coal body exhibits damage to its integrity in the 0–2.5m and 8–10m ranges, while other sections remain intact. The 10–15m range also shows intact coal body integrity. Furthermore, based on the known distribution patterns of stress in mining engineering ("three zones" and "four areas"), it is proven that the coal body is basically stable in areas greater than 10m. Therefore, elastic potential energy mainly accumulates in the 2.5–8m range. Thus, the effective borehole depth calculation should assume the effective release of elastic potential energy within an 8m range. Additionally, the dip angle of the coal seam in the strike direction should also be considered (different coal seams exhibit different dip angles).

[0044] Furthermore, the accumulation of elastic potential energy within coal is regional. If the accumulated elastic potential energy is not cut off near the roadway outline during tunnel excavation within this area, it can easily lead to roof and side collapses near the roadway outline, significantly impacting roadway formation and severely hindering the improvement of roadway safety standards. Simultaneously, there is a risk of roof and side collapses, posing a hazard to workers.

[0045] Based on the hardness and shear strength of the coal seam where the working face is located (i.e., the on-site geological exploration report of the coal mine), the minimum resistance line between boreholes was determined when drilling holes were arranged in the coal seam, and the drilling spacing of the pressure relief boreholes was determined accordingly.

[0046] In summary, when designing the angle of the pressure relief borehole in the coal roadway excavation face, the elevation angle is designed at +10°, and the horizontal angle of the pressure relief borehole in the sidewall is designed at about 3°. This effectively cuts off the elastic potential energy accumulated in the coal body near the roadway outline, thereby reducing the damage of elastic potential energy to the integrity of the coal body near the roadway outline.

[0047] like Figure 5 As shown, a specific embodiment of an advanced pressure relief borehole is described. In this embodiment, four advanced pressure relief holes, a1, a2, a3, and a4, are arranged vertically from top to bottom at the shoulder of the roadway section on the facing wall 1. The boreholes a1, a2, a3, and a4 are arranged at equal intervals. A1 extends at an elevation angle of 15°, while a2, a3, and a4 all extend at an elevation angle of 3°.

[0048] On the facing wall 1, at the center line of the roadway cross section, there are two advance pressure relief holes arranged vertically from top to bottom: a5 and a6. A5 is set with an elevation angle of 10°, and a6 is set with a vertical extension at the center position of the facing wall 1.

[0049] Among them, a1, a2, a3, a4, a5, and a6 all have an angle of 0° with the tunnel excavation direction.

[0050] Step III, advance support: Several advance support anchor bolts 6-1 are installed symmetrically on both sides of the roadway, within a range of 1 / 2 to 2 / 3 of the roadway width. The advance support anchor bolts 6-1 extend into the coal body from the angle between the facing wall 1 and the roof 3, and the angle between the advance support anchor bolts 6-1 and the roof is controlled between 20° and 30°.

[0051] Regarding the determination of the pre-support anchor placement area: Through the study of the coal seam and stress distribution mechanism during the excavation of double-hard extra-thick coal seams, it was found that when the shear strength of the coal body itself is less than the stress failure effect, the coal body will undergo certain deformation and failure. Within the exposed area of ​​a roadway cross section, the area with more prominent deformation and failure indicates that the shear capacity of the coal body in that area is weaker or that a large amount of failure potential energy has accumulated in that area. Therefore, pre-support anchors need to be placed in that area to provide pre-support reinforcement to the coal body in that area.

[0052] Pre-support involves anchoring the face before tunneling, transforming passive support into active support. Through the transmission of stress within the surrounding rock and the force exerted by the anchors on the coal body and the reaction force of the surrounding rock on the anchors, as the pre-support anchor trays are continuously tightened, axial stress is generated along the anchors within a certain range. This causes the surrounding rock to adhere to the area around the anchors, forming an inverted cone-shaped structure. Further tightening of the pre-support anchor trays, reaching a certain pre-tightening force, causes the coal body to form a compression arch under the combined action of multiple pre-support anchors. Under the action of the compression arch, the coal body is tightly bound together, forming a whole and preventing collapse.

[0053] According to the rock bolt support compression theory, the pre-support rock bolts form a conical force system slightly ahead of the facing wall. The cone head of the conical force system is distributed at the rear of the roadway (i.e., the tray end of the rock bolt), and the cone tail is distributed inside the coal body in front of the facing wall, gradually spreading out towards the roadway outline. Therefore, the pre-support rock bolts can be arranged in the middle of the roadway, which is convenient for supporting the coal body whose integrity in front of the facing wall is damaged, so that it can form a whole in advance.

[0054] like Figure 3 As shown, the angle θ between the pre-support anchor bolt 6-1 and the roof is controlled between 20° and 30°. The main mechanism is that during the construction of the pre-support anchor bolt in front of the tunnel, the anchoring agent acts on the deep coal body and produces a solidification and adhesion effect. The other end of the anchor bolt is the anchor plate. The coal body between the anchor plate and the anchoring section is subjected to compression, generating a horizontal stress that stretches into the depth of the coal body. At the same time, a horizontal stress that stretches into the depth of the coal body is generated, and a component force that causes the coal body to move upward is generated. This plays a positive role in preventing the coal body from overflowing and falling off, thus preventing the coal body from falling off.

[0055] Due to the effect of the pre-decompression borehole, the elastic potential energy severely damages the integrity of the coal body during the release process. Severe fractures develop within the coal body, especially around the borehole, and these fractures continuously merge and expand, forming numerous unloading fractures within the coal body. Within one cycle, an unloading zone is formed, causing a rapid decrease in the shear strength of the coal within this zone, leading to coal fragmentation. As tunneling progresses, unloading deformation occurs within the coal body, tending towards the facing wall. The presence of the pre-support anchor rods restricts the further development and transmission of this unloading deformation, constraining the free deformation of the coal body after excavation and preventing the unloading zone from extending further into the deeper rock mass. This achieves overall stability of the facing wall and roof, ensuring complete support for the fractured coal body and roof, thereby guaranteeing production safety. This synergy between the pre-release of elastic potential energy and pre-support lays the foundation for alternating construction of two tunneling faces.

[0056] Roadway support: While providing advance support, several anchor bolts 6 are arrayed on both sides of the roadway and at the position of the roof 3. The compressive stress zone of each anchor bolt is close to each other and connected as a whole to form an integral support structure. Two rows of roof anchor cables 7 are symmetrically arranged on both sides of the roadway centerline of the roof 3. Among them, the arrangement spacing of the advance support anchor bolts 6-1 is half of the arrangement spacing of the anchor bolts 6, and the advance support anchor bolts 6-1 in the front and rear rows are staggered.

[0057] As attached Figure 4 As shown, regarding the determination of anchor bolt spacing: through research on the theory of arching caused by anchor bolt support and numerical simulation analysis of the anchor bolt support effect, under the condition of a fixed roadway size, as the anchor bolt spacing decreases, the number of anchor bolts increases, and the stress field formed by the anchor bolts in the rock strata also changes continuously. A cone-shaped compressive stress distribution is formed around a single anchor bolt, with the maximum compressive stress near the tail of the anchor bolt, followed by the area near the anchoring initiation point, and smaller stress in the middle section of the free part of the anchor bolt. The end of the anchor bolt is in a state of zero stress or small compressive stress. When the anchor bolt spacing is 1000mm, the anchor bolt pressure field shows obvious separation, and an integral prestressed bearing structure cannot be formed. When the anchor bolt spacing is 900mm, the pressure field shows a small amount of separation. When the anchor bolt spacing is 800mm, the compressive stress areas of each anchor bolt are close to each other and connected to form an integral support structure. When the anchor bolt spacing continues to decrease to 600mm, the compressive stress areas of each anchor bolt overlap, the improvement of the prestress diffusion effect of the anchor bolts becomes insignificant, and the economic cost increases.

[0058] Different anchor bolt densities directly affect the strength of the surrounding rock anchor body itself. Based on the axial and lateral forces of the anchor bolts, the smaller the spacing between anchor bolts, the greater the support density, and the maximum sum of axial and lateral forces in the anchor bolt support system. However, in actual calculations, after the anchor bolt density increases to a certain value, the prestressing superposition effect in the roadway no longer changes significantly. Conversely, if the anchor bolt density is too small, the conical compressive stress areas formed by individual anchor bolts are independent and cannot form an integral support structure. Therefore, the spacing between anchor bolts cannot be too large or too small. Excessive density makes it difficult to form a solid anchor body in the surrounding rock, while insufficient density easily leads to material waste.

[0059] like Figure 6 The diagram shows a schematic of alternating construction of two working faces and a schematic of the optimized roadway cross-section. In the diagram, the coal seam around the right roadway has been mined out, while the coal seam around the left roadway has not yet been mined, so the support structure is still retained. The middle of the two roadways is a coal pillar. Therefore, the two sides of the roadway include the mining side 4 and the coal pillar side 5. The mining side is the side wall on one side of the mining face of the roadway, and the coal pillar side is the side wall on one side of the coal pillar of the roadway. The coal pillar is located between the two tunneling faces. Fiberglass anchors are used on the mining side 4, and left-hand threaded steel anchors without longitudinal ribs are used on the roof 3 and the coal pillar side 5. The drilling positions of all anchors 6 are evenly distributed in an array on the roof 3 or the two sides. The anchors 6 extend into the interior of the roadway surrounding rock perpendicular to the inner wall of the roadway. In particular, the two rows of anchors 6 located at the shoulder sockets on both sides of the roof 3 are inclined towards the same side of the coal pillar, and the two rows of anchors 6 located at the upper and lower ends of the coal pillar side 5 are inclined towards the upper and lower sides respectively.

[0060] The inclination angles of the two rows of anchor bolts 6 located at the shoulder sockets on both sides of the top plate 3 toward the same side of the coal wall, and the inclination angles of the two rows of anchor bolts 6 located at the upper and lower ends of the coal pillar 5 toward the upper and lower sides, shall not exceed 15°.

[0061] like Figure 7 As shown, grouting anchor cables 8 are interspersed at equal intervals in both rows of top plate anchor cables 7, and one grouting anchor cable 8 is provided between every two top plate anchor cables 7. The grouting anchor cables 8 are equidistant from the top plate anchor cables 7 on both sides.

[0062] like Figure 8 As shown, the grouting anchor cable 8 includes a hollow steel strand 10, which extends into the grouting pre-reserved hole in the top plate. A grout stop plug 11 is provided on the hollow steel strand 10 near the opening of the grouting pre-reserved hole in the top plate. The grout stop plug 11 blocks the opening of the grouting pre-reserved hole in the top plate. A tray 12 is provided on the outside of the grout stop plug 11. The tray 12 is supported on the top plate wall around the opening of the grouting pre-reserved hole in the top plate. A lock 13 is provided on the outside of the tray 12. The lock 13 is used to anchor the tray 12 to the top plate 3. A threaded plug 14 is provided at the outermost end of the hollow steel strand 10.

[0063] Several bidirectional grouting through-cable cables 9 are installed on the coal pillar 5. The spacing between the grouting anchor cables is determined by calculating the grouting diffusion radius R without considering the mutual influence of multiple holes.

[0064]

[0065] In formula i, r is the radius of the grouting pipe, k is the permeability parameter, P is the grouting pressure, β is the viscosity ratio of the grout to water, n is the porosity of the coal, and t is the grouting time.

[0066] In one example, r is taken as 0.005m; k is taken as 0.0001m / s under the influence of mining; P is taken as 3MPa; β is taken as 3; n is taken as 0.3; t is taken as 20min; substituting into equation a, the calculated grout diffusion radius of a single grouting anchor cable is R≈1.186m. Therefore, the spacing between grouting anchor cables in coal pillars should not exceed 2400×2400mm. Figure 10 As shown, in a preferred embodiment, the coal pillar height is 3400mm, and two rows of bidirectional grouting through-cable cables are arranged. The upper row of anchor cables is 1000mm from the top, and the lower row of anchor cables is 1200mm from the bottom, with a lateral spacing of 2400mm, forming a three-flower arrangement structure with a row spacing of 1200×2400mm. The diameter of the grouting anchor cables is... The length is L5000mm, and it is equipped with anchor cable locks with matching strength and performance. Considering the tension on both sides of the grouting anchor cable, the pre-tension force on one side is not less than 150KN, which is less than that of conventional anchor cables, to avoid the breakage of the internal grouting pipe of the grouting anchor cable. The grouting anchor cable tray adopts a matching 300×300mm×14mm disc-shaped anchor cable tray. The grouting material is an inorganic single-liquid grouting reinforcement material. Its characteristics are that it is a powdered inorganic mineral material with ultra-fine particle size, non-toxic, non-flammable, non-combustible, anti-static, excellent permeability, high strength, and micro-expansion. When using it, it is mixed with water in proportion and used for single-liquid grouting. In addition, a thin layer of sealing material of the same properties is sprayed on the surface of the tunnel to achieve rapid spray sealing of the tunnel surface, prevent weathering, and prevent gas extraction leakage.

[0067] like Figure 9 As shown, the bidirectional grouting through-anchor cable 9 also includes a hollow steel strand 10. The hollow steel strand 10 has an internal grouting pipe 15. The grouting pipe 15 has several grout outlets 16 on its wall. Both ends of the hollow steel strand 10 are provided with a grout stop plug 11, a tray 12, and a lock 13. The hollow steel strand 10 of the bidirectional grouting through-anchor cable 9 passes through the pre-reserved through hole for grouting in the coal pillar. The grout stop plugs 11 at both ends block the two ends of the pre-reserved through hole for grouting in the coal pillar. The trays 12 at both ends are supported on the side wall around the two ends of the pre-reserved through hole for grouting in the coal pillar. The lock 13 is used to anchor the tray 12 to the coal wall on both sides of the coal pillar. Both ends of the hollow steel strand 10 of the bidirectional grouting through-anchor cable 9 are also provided with a thread plug 14.

[0068] It should be noted that the hollow steel strand 10, grout stopper 11, tray 12, lock 13, and plug 14 mentioned in the structural description of grouting anchor cable 8 and bidirectional grouting through anchor cable 9 are not specific to or shared by the two types of grouting anchor cables, but rather refer to a series of structures indicated by the corresponding designations. Both types of grouting anchor cables are composed of these structures. The use of the same overlapping names and designations in the structural descriptions of the two is to clearly depict their similarities and differences. The main difference between the two is that the grouting anchor cable can only be grouted at one end, while the bidirectional grouting through anchor cable can be grouted at both ends simultaneously. Furthermore, the bidirectional grouting through anchor cable has an internal grouting pipe 15. The difference between the two lies in the structural adjustments applied at different locations.

[0069] The installation of the grouting anchor cable includes the following steps: First, drill holes for the anchor cable, selecting a suitable drill bit based on the diameter of the bird's nest section of the grouting anchor cable; then, insert resin cartridges into the hole, and use a pneumatic drill to continuously push the anchor cable into the hole, pushing it to the bottom of the hole and stirring it. After the through-hole grouting anchor cable passes through the coal pillar, only bidirectional tensioning is required; then, push the anchor cable with its own grout stop plug 11 to a certain depth in the hole, wrap sufficient cotton thread behind the grout stop plug and compact it, ensuring that it does not obstruct the entry into the hole when the anchor cable is anchored; then, reset the jack and perform secondary tensioning. During secondary tensioning, secure the locking device 13 and the tray 12, ensuring that the jack does not engage with the welded end of the anchor cable; finally, after stirring the grout evenly, open the grouting hole at the rear of the anchor cable, connect the grouting nozzle, and begin grouting until the hole is full.

[0070] Anchor cable grouting includes the following steps: First, connect the air and water pipelines at the grouting site, have an electrician connect the power supply, install the grouting pump and mixer, and connect the grouting pipe and grouting nozzle; during grouting, first remove the plug at the end of the anchor cable, connect the grouting device to the internal thread at the end of the anchor cable, slowly tighten the grouting device, and then connect the grouting device to the grouting pump using the grouting pipeline; grouting can only begin after the grouting device (quick connector) and the grouting pipeline are intact and reliably connected.

[0071] Remove debris from the mixing tank to prevent clogging of the grouting pump; calculate the grouting volume based on the number of grouting holes, inject a certain amount of clean water into the mixing tank, start the mixer, and slowly pour in cement and additives according to the ratio until evenly mixed; slowly open the air supply valve of the grouting pump to start grouting, and start with a slow grouting speed to control the grouting pressure; when the pressure reaches 3MPa, first turn off the grouting pump, then close the shut-off valve at the tail of the hollow anchor cable, open the pipeline pressure relief valve to relieve pressure in the pipeline, then remove the grouting device at the tail of the anchor cable and tighten the plug at the tail of the anchor cable.

[0072] During grouting, if localized grout leakage is detected, grouting should be stopped immediately, and the leaks should be sealed with cotton yarn or similar materials. After grouting, wait for the grout to initially set before opening the shut-off ball valve at the tail of the hollow anchor cable. Connect the hollow grouting anchor cable to the grouting pipe through the grouting nozzle, start the grouting pump, and adjust the grouting pressure as needed based on the actual site conditions, ensuring the maximum grouting pressure does not exceed 5 MPa. During grouting, observe the amount of grout absorbed by the anchor cable. If the grout absorption is low, affecting the grout quality and grouting quality, use a three-way diversion device to divert the flow, injecting two anchor cables at a time. After grouting is completed, clean the grouting system with clean water to prevent the cement grout from setting.

[0073] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the above principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for rapid excavation by advance release of coal seam elastic potential energy and coordinated advance support, characterized in that: By constructing a pressure relief borehole in an area where stress on the facing wall (1) is obvious, the accumulated stress in front of the excavation working face (2) is released in advance, and anchor support is first performed in front of the facing wall before the excavation operation to form a stress advance skeleton deep in the coal body, and a load relief belt is formed during the release of the elastic potential energy inside the coal body, thereby ensuring the integrity of the coal body during the release of the elastic potential energy. Specifically, the following steps are included: Step I, determining the position of the advance pressure relief drilling hole: constructing a number of pressure relief holes on the front wall (1) at positions corresponding to the shoulder and center line of the tunnel section, with the diameter and depth of the pressure relief holes being kept consistent; Step II, advance pressure relief drilling design: first, drilling is performed on the roof (3) of the coal seam, and then a drilling peep device is inserted into the hole to observe the inner wall condition until it can be clearly observed that there are multiple coal body damaged sections and multiple coal body intact sections in the segmented coal body, and then the sections in which the coal body is basically in a stable state among the multiple coal body intact sections are excluded according to the stress distribution law, and the remaining sections among the multiple coal body intact sections are the main elastic potential energy accumulation sections, and finally the drilling depth is calculated within the depth range of the main elastic potential energy accumulation section; the drilling inclination angle is determined by the elevation angle of the coal seam in the strike direction; the minimum resistance line between the drilling holes when arranging the drilling holes in the coal seam is determined by the hardness and shear strength of the coal seam where the working face is located, so as to determine the drilling and opening spacing of the pressure relief drilling holes; Step III, advance support and roadway support: a plurality of advance support anchor rods (6-1) are arranged symmetrically on both sides of the roadway within a range of 1 / 2 to 2 / 3 of the roadway width, the advance support anchor rods (6-1) extending into the coal body from the angle between the front wall (1) and the roof (3), and the angle between the advance support anchor rods (6-1) and the roof is controlled at 20° to 30°; At the same time, a plurality of anchor rods (6) are arranged in an array at the two sides of the tunnel and the top plate (3), and the compressive stress zones of each anchor rod (6) are close to each other and connected as a whole to form an integral support structure. The top plate (3) is symmetrically provided with two rows of top plate anchor cables (7) on both sides of the center line of the tunnel; The two sides of the tunnel include a mining side (4) and a coal pillar side (5), the mining side (4) uses glass fiber reinforced plastic anchor rods, the roof (3) and the coal pillar side (5) both use left-handed non-longitudinal rib threaded steel anchor rods, the drilling positions of all anchor rods (6) are evenly distributed in an array on the roof (3) or the two sides, the anchor rods (6) extend into the surrounding rock of the tunnel perpendicular to the inner wall of the tunnel, the two rows of anchor rods (6) located at the shoulder sockets on both sides of the roof (3) are respectively inclined toward the same side of the coal side, and the two rows of anchor rods (6) located at the upper and lower ends of the coal pillar side (5) are respectively inclined toward the upper and lower sides; Grouting anchor cables (8) are evenly spaced and interspersed in the two rows of top plate anchor cables (7), one grouting anchor cable (8) is arranged between every two top plate anchor cables (7), and the grouting anchor cables (8) are evenly spaced from the top plate anchor cables (7) on both sides.

2. The method for rapid excavation by advance release of coal seam elastic potential energy and coordinated advance support according to claim 1 is characterized in that: The grouting anchor cable (8) comprises a hollow steel strand (10), the hollow steel strand (10) extending into a top plate grouting reserved hole, the hollow steel strand (10) being provided with a grouting stopper (11) near the opening of the top plate grouting reserved hole, the grouting stopper (11) blocking the opening of the top plate grouting reserved hole, a tray (12) being provided outside the grouting stopper (11), the tray (12) being supported on the top plate wall around the opening of the top plate grouting reserved hole, a lock (13) being provided outside the tray (12), and a wire plug (14) being provided at the outermost end of the hollow steel strand (10).

3. The method for rapid excavation by advance release of coal seam elastic potential energy and coordinated advance support according to claim 2 is characterized in that: A plurality of bidirectional grouting cross-linking anchor cables (9) are arranged on the coal pillar side (5).

4. A method for rapid excavation by advance release of coal seam elastic potential energy and coordinated advance support according to claim 3, characterized in that: The bidirectional grouting through-anchor cable (9) also comprises a hollow steel strand (10), wherein a built-in grouting pipe (15) is arranged in the hollow steel strand (10), and a plurality of grouting outlets (16) are arranged on the wall of the grouting pipe (15). Both ends of the hollow steel strand (10) are provided with grouting stoppers (11), trays (12) and locks (13) in sequence. The hollow steel strand (10) of the bidirectional grouting through-anchor cable (9) passes through a through hole reserved for grouting in the side of the coal pillar, and the grouting stoppers (11) at both ends respectively block the two ends of the through hole reserved for grouting in the side of the coal pillar, and the trays (12) at both ends are respectively supported on the side wall around the two ends of the through hole reserved for grouting in the side of the coal pillar.

5. The method for rapid excavation by advance release of coal seam elastic potential energy and coordinated advance support according to claim 4 is characterized in that: The installation of grouting anchor cable includes the following steps: First, drill a hole for the anchor cable; then put the resin roll into the hole, use a pneumatic drill to drive the anchor cable to continuously push it into the hole, push the anchor cable to the bottom of the hole and stir it, and after the two-way grouting through the anchor cable (9) passes through the coal pillar, only two-way tensioning is required; then, push the anchor cable's own stop plug (11) to a certain depth in the hole, wrap enough cotton thread behind the stop plug and compact it so that the anchor cable does not block the hole when it is anchored; then reset the jack and perform a second tensioning. During the second tensioning, the lock (13) and the tray (12) are installed and fixed, and it must be ensured that the jack does not bite at the welding point of the anchor cable end; finally, after the slurry is evenly stirred, open the grouting hole at the rear end of the anchor cable, connect the grouting nozzle and start grouting until it is full.

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