Semicircular roadway roof deformation control supporting method under three-soft and half-coal rock condition

Abstract

The invention discloses a semicircular roadway roof deformation control supporting method under the three-soft and half-coal-rock condition, and belongs to the technical field of mine roadway supporting. The method comprises the following steps: carrying out roadway tunneling by adopting a straight-wall semicircular arch-shaped section; immediately implementing temporary support; a high-strength active supporting system is constructed, and horizontal channel steel combined anchor cables are additionally arranged at the base line position of a coal pillar side arch; anchor cable bundles are additionally arranged in the key area at intervals; lagging grouting is conducted on the broken surrounding rock, and a grouting reinforcing ring is formed; and spraying concrete, sealing and arranging a dynamic monitoring system. Through section optimization, active support, surrounding rock modification and dynamic regulation and control integrated cooperative control, the technical problems that the three-soft half coal rock roadway roof is large in deformation and prone to instability are solved, and the method has the advantages of being reliable in support, high in adaptability, good in economical efficiency and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of mine tunnel engineering and underground geotechnical engineering. More specifically, it relates to complex and difficult tunnels in coal mines with soft roof, soft coal seam, and soft floor geological conditions, and which simultaneously contain coal seams and rock strata in the tunnel cross section. In particular, it relates to a method for deformation control and stable support of the semi-circular cross-section roof in such tunnels. Background Technology

[0002] In coal mining, with increasing mining depth and expansion into coalfields with complex geological conditions, the challenge of supporting "three-soft" coal roadways—soft roof strata, soft coal seams, and soft floor strata—is commonly encountered. When such roadways simultaneously traverse coal seams and rock strata with vastly different strengths, they constitute "semi-coal-rock" conditions, making surrounding rock control particularly difficult. This is mainly manifested in: extremely low surrounding rock strength and short self-stabilization time; easy softening, mudification, and expansion upon contact with water; and, under the superposition of tunneling and mining stresses, rapid and large-scale roadway deformation, especially floor heave and roof subsidence, which are prolonged and prone to asymmetric failure.

[0003] Currently, the industry mainly uses the following methods or combinations thereof for the support of such roadways: (1) High-strength anchor bolt and cable mesh support: This is the current mainstream active support technology. It attempts to control the surrounding rock by increasing the strength of the bolts, increasing the preload, and optimizing the spacing between rows. However, under the conditions of "three softnesses" (softness, softness, and softness), the anchoring foundation of the anchor bolts and cables (i.e., the surrounding rock itself) is extremely fragile. It often leads to loss of preload and failure of the anchor body due to the fragmentation and rheology of the surrounding rock, resulting in a situation where the rock becomes looser the more it is pulled. Simple parameter strengthening is difficult to fundamentally improve the mechanical properties of the surrounding rock.

[0004] (2) Passive support using steel profiles (such as U-shaped steel): This serves as a supplementary or primary load-bearing structure. As a passive support, it requires the surrounding rock to deform before it can bear load, and cannot suppress early delamination; the erection process is complex, affecting tunneling efficiency; the contact with the surrounding rock is not tight, which can easily generate point loads leading to instability; the cost is high and the reuse rate is low. On-site problems such as "poor coupling effect between anchor mesh cable active support and U-shaped shed passive support" and "two separate systems" exist, resulting in low overall efficiency of the support system.

[0005] (3) Grouting reinforcement technology: This technology is an effective means of modifying surrounding rock by cementing fractured rock masses with grout, thereby improving their overall strength and stability. However, existing applications are mostly used as post-event remedial measures or carried out in local fractured areas, lacking a systematic collaborative design with high-strength active support systems in terms of timing, space, and mechanics. The interaction mechanism between grouting timing, parameters, and anchor bolt and cable support is unclear, failing to form a closed loop of "active support providing initial stability, and grouting reinforcement providing a long-term load-bearing foundation".

[0006] (4) Combined support: In practice, the combination of "anchor mesh + scaffolding" or "anchor injection" is often used. However, it is often just a simple superposition of technologies rather than an organic integration. For example, the project applicant's existing support scheme adopts a double-layer support of "anchor mesh + scaffolding", but due to component mismatch, such as the anchor cable tray being a U-shaped steel cut piece with line contact, and construction process defects, such as incomplete filling behind the U-shaped scaffolding wall, it failed to achieve the effect of "1+1>2". Instead, the complexity of the process restricted production efficiency. Specifically, this manifests as: some anchor rods and anchor cable trays turning outward, and the pressure on the support structure becoming obvious; some anchor rod nuts stripping and falling off; active support and passive support being two separate systems; and anchor rods being internally anchored.

[0007] In summary, existing technologies for supporting roadways in soft and semi-soft coal and rock conditions either focus on improving the strength of individual components while neglecting system matching, or adopt passive pressure yielding, thus losing the initiative in support, or perform local reinforcement without overall modification, or mechanically pile up multiple technologies without forming a synergistic mechanism. The fundamental reason lies in the failure to construct a comprehensive, integrated, and collaborative control system encompassing the entire process, from optimizing the surrounding rock stress environment to modifying the surrounding rock's own properties, from high-strength active support to ensuring the safety of key components, and from construction implementation to dynamic regulation. Therefore, developing a comprehensive support method that is highly systematic, targeted, and capable of achieving long-term synergistic stability between the surrounding rock and the support has become an urgent need to solve this technical challenge. Summary of the Invention

[0008] To address the aforementioned technical problems, the purpose of this application is to provide a method for controlling roof deformation and supporting semi-circular roadways under conditions of soft and semi-soft coal and rock. This method effectively controls early roof deformation and long-term stability through an integrated technical system that includes surrounding rock stress optimization, active collaborative support, key component reinforcement, surrounding rock modification and reinforcement, and dynamic information feedback, thereby forming a reliable load-bearing structure.

[0009] This invention provides a method for controlling roof deformation and providing support in semi-circular roadways under conditions of soft and semi-soft coal and rock, comprising the following steps: Step 1, tunnel cross-section optimization and shaping: The tunnel is excavated using a straight wall semi-circular arch cross-section; based on numerical simulation analysis and on-site engineering conditions, the tunnel net width B and net height H are determined, where the radius of the semi-circular arch R = B / 2, and the height of the straight wall h = H - R; Step 2, Initial Roof Protection and Temporary Support: After one cycle of tunnel excavation, temporary support is immediately implemented. A high-strength diamond-shaped metal mesh is laid in the tunnel arch, and a machine-mounted hydraulic forward beam or a single hydraulic prop is used in conjunction with a steel beam to effectively support the exposed roof and ensure construction safety. Step 3, Construction of the high-strength active support system: In the construction of the high-strength active support system, the support parameters follow the collaborative design principle, defining the axial direction of the roadway as the row spacing direction, and the cross-sectional direction perpendicular to the axial direction of the roadway as the spacing direction; let the basic row spacing of the support system be D; Step 3.1, High Pre-tightening Anchor Bolt Support for the Top Slab: On the arch outline, drill and install high-strength threaded steel anchor bolts according to the anchor bolt spacing A1 and row spacing D; the length of the anchor bolt is L1, ensuring penetration into the weak and fractured area of ​​the top slab; use resin anchoring agent for full-length anchoring; after installation, apply a pre-tightening torque of not less than T1 and a pre-tightening force of not less than P1; Step 3.2, Deep Anchor Cable Suspension Support of Top Slab: Multiple rows of prestressed anchor cables are arranged in the top slab according to the spacing A2, row spacing D or n×D, where n is a positive integer; the anchor cable length L2 ensures that its inner anchoring section is located in the deep stable rock layer; each hole is anchored with multiple rolls of resin anchoring agent, and a preload of not less than P2 is applied after installation; all anchor cables are connected by high-strength ladder beams or W-shaped steel strips and equipped with disc-shaped large support plates; Step 3.3, Side Anchor Bolt Support and Coal Pillar Shoulder Reinforcement: Anchor bolts are installed on both sides of the roadway, with a focus on reinforcing the upper part of both sides of the roadway near the arch baseline. The side anchor bolts are arranged at a spacing of A3 and a row spacing of D, with a length of L3. The installation pre-tightening torque is not less than T3, and the pre-tightening force is not less than P3. At the coal pillar arch baseline position on the high-stress side, a horizontal channel steel composite anchor cable is added as a shoulder reinforcement structure. The channel steel composite anchor cable includes a channel steel beam and at least one anchor cable, with an anchor cable length of L4 and a pre-tightening force not less than F2, to stabilize the arch foot that supports the arch. Step 4, reinforced support in key areas: In areas of stress concentration in the roadway roof or affected by geological structures, add a set of anchor cable bundles at intervals of N rows of conventional support; the anchor cable bundles consist of high-strength external anchor bearing components and multiple prestressed anchor cables of different lengths to achieve tiered anchoring and concentrated load-bearing. Step 5, Grouting Modification and Reinforcement of Surrounding Rock: After the active support system in Step 3 takes effect and the deformation of the surrounding rock is initially stabilized, delayed grouting reinforcement is carried out on the broken surrounding rock of the roadway roof and upper sidewalls; the grouting holes are arranged between the anchor bolts and anchor cables, and the grout penetrates and consolidates the broken rock mass to form a grouting reinforcement ring; Step 6, full-section closure and dynamic monitoring: spray a layer of concrete onto the surface of the roadway after the support is completed to form a closed support body; install surface displacement, deep displacement and support body stress monitoring systems in typical roadway sections, dynamically evaluate the support effect based on the monitoring data and guide whether reinforcement measures are needed.

[0010] Furthermore, in step 1, the net width B of the straight wall semi-circular arched section is 4.5~5.5m, and the net height H is 3.8~4.5m.

[0011] Furthermore, in step 3, the top plate anchor bolts, top plate anchor cables, and side anchor bolts adopt a uniform foundation spacing D, which is 800~900mm.

[0012] Further, in step 31, the anchor rod is a Φ20~Φ22mm left-hand threaded steel anchor rod without longitudinal reinforcement, L1 is 2.3~2.7m, the spacing A1 is 800~900mm, the pre-tightening torque T1 is not less than 180N·m, and the pre-tightening force P1 is not less than 120 kN; two resin anchoring agents are used for full-length anchoring.

[0013] Furthermore, in step 32, the anchor cable is a high-strength steel strand with a diameter of Φ17.8~Φ21.8mm, a length of L2 of 8.5~9.0m, a spacing of A2 of 800~950mm, and a preload force P2 of not less than 180kN; each hole is anchored with three resin anchoring agents.

[0014] Further, in step 33, the side anchor bolt is a Φ20~Φ22mm threaded steel anchor bolt, L3 is 2.3~2.7m, the spacing A3 is 800~900mm, the pre-tightening torque T3 is not less than 180N·m, and the pre-tightening force P3 is not less than 120 kN; the anchor cable in the coal pillar side channel steel combined anchor cable is a Φ17.8~Φ21.8mm steel strand, L4 is 4.0~5.0m, and the pre-tightening force P3 is not less than 150kN; the channel steel is 14# or 16# channel steel, and the length is not less than 1.8m.

[0015] Further, in step 4, the anchor cable bundle is a disc anchor cable bundle or a linear anchor cable bundle; the disc anchor cable bundle includes a large square support plate on which two first anchor cables of length L2 and two second anchor cables of longer than L2 are arranged diagonally; the linear anchor cable bundle includes a long channel steel or U-shaped steel beam, on which one first anchor cable and two longer second anchor cables are arranged sequentially along its length direction.

[0016] Furthermore, in step 5, the grouting reinforcement uses chemical grout or ultrafine cement grout; the grouting hole depth is 3~5m, the spacing between rows is 1.5~2.0m, the final grouting pressure is 2.0~3.0 MPa, forming a uniform grouting reinforcement ring with a thickness of 3~4m.

[0017] Furthermore, in step 6, the dynamic monitoring includes monitoring of roadway surface displacement, deep roof displacement, and support stress, and setting a warning threshold for roof subsidence speed.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a straight-wall semi-circular arch cross-section combined with a unified foundation spacing, enabling a grid-like and coordinated arrangement of support components. This design optimizes surrounding rock stress, reduces stress concentration, and promotes the superposition and fusion of prestressed fields in various components, forming a continuous composite bearing arch in the shallow section, significantly improving the overall stiffness and early bearing capacity of the system. The roof anchor bolts utilize high preload torque for full-length anchoring, instantly compressing weak roof slabs and suppressing delamination. The roof anchor cables are suspended deep with high preload torque, working in conjunction with the anchor bolts to construct a shallow arch-deep suspension composite structure. Horizontal channel steel composite anchor cables are added to the coal pillar shoulder sockets to strengthen the arch foot, effectively controlling asymmetric deformation at large dip angles. Delayed grouting is implemented after active support, using grout penetration to cement and break the surrounding rock, forming a reinforced ring, improving the mechanical properties of the surrounding rock, transforming it from a load into a bearing body, enhancing the strength and integrity of the surrounding rock itself, providing a reliable foundation for the anchoring system, and ensuring long-term stability. Anchor cable bundles are added in key areas, providing safety redundancy for high-level delamination and shear deformation through tiered anchoring and concentrated bearing. By combining shotcrete sealing with dynamic monitoring of displacement and stress, real-time evaluation and early warning of the effects are achieved, enabling the scheme to have information feedback and adaptive capabilities. The process flow is clear and coherent, highly operable, effectively controls the section shrinkage rate, significantly reduces rework and maintenance costs, improves tunneling efficiency, and yields significant technical and economic benefits. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the cross-section of a semi-circular tunnel support structure provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the disc anchor cable bundle in an embodiment of the present invention; Figure 3 This is a schematic diagram of the linear anchor cable bundle in an embodiment of the present invention; Figure 4 This is a schematic diagram showing the layer relationship between the return air roadway and the transport roadway in an embodiment of the present invention; Figure 5 This is a cloud map showing the vertical stress diffusion for different anchor bolt lengths in an embodiment of the present invention; Figure 6 This is a vertical stress diffusion cloud map of different anchor bolt spacings in an embodiment of the present invention; Figure 7 This is a vertical stress diffusion cloud map of different anchor bolt preload moments in an embodiment of the present invention; Figure 8 This is a vertical stress diffusion cloud map for different anchor cable lengths in an embodiment of the present invention; Figure 9 This is a vertical stress diffusion cloud map of different anchor cable spacings in an embodiment of the present invention; Figure 10 This is a vertical stress diffusion cloud diagram for different anchor cable preloads in an embodiment of the present invention; Figure 11 This is a cloud diagram showing the horizontal stress distribution of different anchor bolt lengths in an embodiment of the present invention; Figure 12 This is a cloud diagram showing the horizontal stress distribution at different anchor bolt spacings in an embodiment of the present invention; Figure 13 This is a cloud map showing the horizontal stress distribution of different preloads on the anchor bolts in an embodiment of the present invention. Figure 14 This is a diagram illustrating the construction scheme for linear anchor cable bundle support according to an embodiment of the present invention; Figure 15 This is a diagram illustrating the construction scheme for disc-type anchor cable bundle support according to an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0022] Example 1 The following detailed description of the invention is based on an engineering example of the return air roadway of the 1179 working face in the Yuka Mine. This roadway is approximately 450m deep, with a roof consisting of 4-6m thick broken coal seam (Protodyakonov coefficient f≈0.68) and sandy mudstone, while the sidewalls and floor are composed of weak mudstone. The coal seam dips at 18-34°, representing typical "three-soft-semi-coal-rock" conditions.

[0023] The following section explains the roof deformation control and support method for semi-circular roadways under soft and semi-coal rock conditions provided in this application, from the perspectives of the reasons for the improved design and the implementation process.

[0024] I. Reasons for the Design Improvement (I) Analysis of the failure mechanism and causes of anchor cable mesh support components 1. Modes and causes of anchor bolt support failure Anchor bolt support structures consist of various components such as bolts, brackets, nuts, washers, and anchoring agents. Therefore, many factors affect the effectiveness of anchor bolt support. Among them, the mechanical properties and compatibility of each component, as well as the stress state of the anchor bolt, are the key factors that determine whether the anchor bolt support capacity can be fully utilized and whether the anchor bolt fails or breaks.

[0025] (1) Anchor nut failure. The failure of anchor nut is mainly manifested by the flattening of the internal thread of the nut or the external thread of the anchor under shear stress. This is mainly due to the poor matching between the thread strength, stiffness and size of the nut and the external thread of the anchor, which leads to the nut being pulled out and failing.

[0026] (2) Anchor plate failure. The main forms of anchor plate failure are the lifting of the four corners of the anchor plate, local tearing and enlargement of the orifice, and the pad being sucked into the surrounding rock, which eventually reduces the load-bearing capacity of the anchor plate or causes structural damage and failure.

[0027] (3) Soft shear failure of the free section of the anchor bolt. For end anchoring and extended anchoring, one of the most likely locations for failure of the free section of the resin anchor bolt is the interface between the anchored and non-anchored sections. Significant bending and shear deformation generally occurs near this location, causing the bolt to break due to tension, bending, shear, torsion, and their combinations. Obvious radial reduction often appears near the fracture surface. Another location prone to failure is the intersection of the bolt and the surrounding rock structure. Due to the displacement of the structure, the bolt at this location experiences significant tension, shear, and their combinations. The complex stress state of the bolt, subjected to tension, bending, shear, torsion, and their combinations, is the main reason for failure in the middle section of the bolt.

[0028] (4) Bonding failure of the inner anchoring section of the anchor rod. ① Shear failure and sliding occur at the interface between the anchoring agent and the anchor rod body; ② Shear failure occurs at the interface between the anchoring agent and the surrounding rock of the borehole; ③ During the installation of resin anchor rods, factors such as the shape of the rod body, the matching of the three diameters, and the operating level of the construction personnel may affect the uneven mixing of the anchoring agent, poor bonding effect, and even the "candy gourd phenomenon", which seriously affects the internal anchoring force; ④ Under conditions such as incomplete borehole flushing, softening of the surrounding rock of the anchoring section by water, and water spraying into the borehole, the anchoring force of the resin anchoring agent is seriously reduced or even fails.

[0029] 2. Failure modes and causes of anchor cable support (1) The failure of the inner anchor of the anchor cable is widespread, and the reasons include the following aspects: ① The rock mass in the inner anchor section is loose and severely fractured, the quality of the anchor hole is poor, and during the installation of the anchor cable, the resin putty is squeezed into the surrounding rock fissures around the borehole, resulting in the inner anchor not being dense. ② Inadequate borehole flushing, especially when the surrounding rock is mudstone, causes rock powder to mix with water to form mud, which adheres to the borehole wall, preventing the anchoring agent from effectively bonding with the surrounding rock during the mixing process; ③ The mismatch between the three diameters of the anchor cable, the borehole, and the anchoring agent causes the resin anchoring agent to fail to be pushed to the bottom of the hole, resulting in false anchoring; ④ If there are intervals or stops in the mixing process of the resin anchoring agent, the reaction chain of the curing agent that has already begun to set will be destroyed, resulting in anchoring failure. ⑤ The smooth cable structure itself prevents the resin putty and curing agent from being fully mixed evenly.

[0030] (2) Soft shear failure of anchor cables in the free section or hard shear failure of the outer anchor end occurs frequently. Due to the extremely complex movement and deformation patterns of the surrounding rock in the roadway, not only is there vertical delamination, but also horizontal shear displacement, which causes soft shear failure of anchor cables in the free section; the surface of the surrounding rock in the roadway in the geological anomaly zone is uneven, poorly formed, or the drilling is not perpendicular to the roadway surface, which causes hard shear failure of anchor cables at the outer anchor end (near the upper surface of the lock).

[0031] (3) Anchor cable failure is common. Mismatch in hardness and diameter between the locking device and the anchor cable can cause the locking device clips to loosen from the anchor cable, resulting in the locking device slipping out and causing the prestressed anchor cable support system to fail.

[0032] 3. Failure modes of composite components For anchor cable support composite components, the current main materials used in anchor cable composite beams are 14#b hot-pressed ordinary channel steel (with a small amount of 16# and 18#a), T-shaped steel strips, and 11# mining I-beams. If the steel strips are not compatible with the engineering geological conditions, resulting in lower strength and stiffness, the composite component will yield or deform and fail when the anchor cable support force is far below its rated support force. This will directly lead to the unloading of surrounding rock pressure into the unsupported space after failure, preventing the high support strength of the anchor cables from being fully utilized, reducing the efficiency of anchor cable support, and even causing support failure.

[0033] II. Implementation Process of the Plan (a) Optimization and shaping of tunnel cross-section 1. Underground roadway conditions: The return air roadway of working face 1179 is 5m wide and 4m high. The roadway is designed to be excavated along the floor of coal seam M7, with a horizontal distance of 20m from the transport roadway of working face 1177 (the transport roadway of working face 1177 is excavated along the roof of coal seam M7). The stratigraphic relationship between the return air roadway of working face 1179 and the transport roadway of working face 1177 is shown in [reference needed]. Figure 5 As shown.

[0034] Based on the relevant geological data of the return air roadway of the 1179 working face and considering the calculation requirements, three numerical calculation models were determined for comparative analysis: a rectangular cross-section (5m width, 3.5m height), a straight-wall micro-arched cross-section (5m width, 3.5m height, 1m radius of the left and right shoulder depressions), and a straight-wall semi-circular arched cross-section (5m width, 4m height, 2.5m radius of the arch, 1.5m straight wall). During the establishment of the mechanical model, the influence of boundary effects during model calculation was considered, ensuring that the main study area was outside the range of boundary effect influence to achieve calculation results closer to reality.

[0035] Based on the comparative analysis results of UDEC numerical simulations of rectangular, micro-arched, and straight-wall semi-circular arched cross sections, the straight-wall semi-circular arched tunnel was ultimately selected.

[0036] (II) Initial support and temporary support Using a roadheader, after each cycle of excavation 800mm, a 5500mm×1000mm galvanized diamond-shaped metal mesh (No. 8) with 60mm×60mm mesh size is immediately laid on the arch. Simultaneously, the roadheader's onboard double-telescopic hydraulic forward support beam is used for temporary support. The forward support beam is tightly attached to the metal mesh, with an initial support force of no less than 50kN to ensure safety during unsupported work.

[0037] (III) Construction of High-Strength Active Support System 1. High pre-tightening anchor bolt support for the roof slab (1) Specific implementation steps A ladder beam, 4480mm long, made of welded Φ12mm steel bars, is hung on the arch. Holes are drilled through the ladder beam using an anchor drilling machine (equipped with a Φ30mm drill bit) to a depth of 2400mm. Φ22mm×2500mm left-hand threaded steel anchors without longitudinal reinforcement are installed, with a length of 2.5m. Two tubes of Z2560 resin anchoring agent are inserted into each hole. The anchoring agent is pushed to the bottom of the hole using an anchor drilling machine and stirred for 25-30 seconds. After waiting 10 minutes for the resin to initially set, the anchor nuts are tightened a second time using a torque wrench to ensure a pre-tightening torque of 220 Nm. The anchor spacing A1=850mm, the row spacing D=800mm, and 7 anchors are arranged in each row in a "4-3" alternating pattern. The support plate is a δ10×150×150mm disc-shaped support plate (parameters are detailed in Table 1).

[0038] (2) Optimization of parameters for top slab anchor bolt support 1) Determining the length of the top slab anchor bolts Vertical stress diffusion cloud diagrams of the surrounding rock in the roadway under different anchor bolt lengths, with a roof anchor bolt spacing of 850mm and an anchor bolt preload torque of 200N.m (see attached diagram). Figure 5As shown in the figure, when anchor bolt support is only applied at the top, the maximum vertical stress appears at the tail of the anchor bolt, and the stress is transmitted to the surrounding rock in a ripple pattern. The anchor bolt support area of ​​the roadway roof is subjected to stress superposition, which diffuses and merges into a whole area of ​​approximately rectangular effective compressive stress. The compressive stress gradually decreases during the diffusion process, forming an ear-shaped compressive stress zone in the horizontal direction. In the vertical direction, the stress decreases to zero near the end of the anchor bolt, and then converts into tensile stress, forming an elliptical tensile stress zone at the end of each anchor bolt. Under the same top anchor bolt spacing and preload, within a certain range, the range of the compressive stress zone will increase with the increase of the anchor bolt length, and the range of the load-bearing structure will also increase. When the anchor bolt length increases further, the compressive stress value in the middle of the anchor bolt will gradually decrease due to the increase of the prestress diffusion distance, resulting in stress field separation between the upper and lower parts of a single anchor bolt. When the length of the top anchor bolt is 2.3m, 2.5m, and 2.7m, the effective compressive stress zone formed by the anchor bolt continuously expands, increasing the area of ​​the effective bearing zone of the roof. However, when the length of the top anchor bolt is further increased to 2.7m, the compressive stress zones formed by the upper and lower parts of the anchor bolt gradually separate, leading to insufficient stability of the resulting bearing structure. Uneven stress on the surrounding rock of the roof results in a lack of stability. Therefore, a critical length needs to be selected, which increases the area of ​​the effective bearing zone of the anchor bolt without causing the compressive stress zone in the middle of the anchor bolt to separate. Therefore, the length of the top anchor bolt is chosen to be 2.5m.

[0039] 2) Determination of the spacing of the top slab anchor bolts The vertical stress distribution cloud map of the surrounding rock in the roadway under different anchor bolt spacing conditions is shown in the attached diagram when the roof anchor bolt length is 2.5m and the anchor bolt preload is 200N.m. Figure 6 As shown in the figure, with the same top anchor bolt length, when the anchor bolt spacing is small, the range and continuity of the compressive stress zone formed by the superposition of stresses from the anchor bolts are good. As the anchor bolt spacing increases, the influence range and distribution trend of the additional stress field formed by the stress distribution of the support components remain roughly unchanged, but the stress fields formed by the anchor bolts tend to be independent, and the area of ​​the stress superposition region gradually decreases. When the top anchor bolt spacing is 750mm and 850mm, an approximately rectangular effective compressive stress zone is formed in the upper part of the roof, with sufficient stress distribution and mutual superposition. When the top anchor bolt spacing is 950mm, the area of ​​the effective compressive stress zone in the upper part of the roof gradually decreases. Due to the increased spacing, the compressive stress cannot be superimposed and connected into a continuous area. The compressive stress value in the middle of two adjacent anchor bolts is too small, which will greatly reduce the active support effect of the anchor bolts, and the range of the compressive stress zone and the load-bearing structure will decrease accordingly. Therefore, it is necessary to reasonably select the anchor bolt spacing to give full play to the support effect of the anchor bolts. Since there is a thin layer of top coal, installing anchor bolts too densely will damage the integrity of the coal seam, resulting in a reduction in the effective anchoring range. Therefore, the spacing of the top slab anchor bolts is selected as 850mm.

[0040] 3) Determination of the pre-tightening moment of the top slab anchor bolts Vertical stress distribution cloud map of the surrounding rock in the roadway under different preload torques when the roof anchor bolt length is 2.5m and the anchor bolt spacing is 850mm (see attached map). Figure 7 As shown in the figure, under the same anchor spacing and length, within a certain range, the range of the compressive stress zone increases with the increase of the anchor preload torque, and the range of the load-bearing structure also increases. When the anchor preload torque further increases, the compressive stress value in the middle of the anchor gradually decreases due to the increase in the preload distribution distance, leading to stress field separation between the upper and lower parts of a single anchor. When the anchor preload torque is 180 N·m, 200 N·m, and 220 N·m, the effective compressive stress zone formed by the anchor continues to expand, increasing the area of ​​the effective load-bearing zone of the roof. However, when the anchor preload torque further increases to 220 N·m, the compressive stress zone formed between the upper and lower parts of the anchor gradually separates, resulting in an unstable load-bearing structure and uneven stress on the surrounding rock of the roof, leading to a lack of stability. Therefore, a critical length needs to be selected, which increases the area of ​​the effective load-bearing zone of the anchor without causing separation of the compressive stress zone in the middle of the anchor. Therefore, the preload torque of the roof anchor is selected as 200 N·m.

[0041] 2. Deep anchor cable suspension support for the roof slab (1) Specific implementation steps On the installed ladder beam, anchor cable holes are constructed at the designed positions. The anchor cable holes are constructed using an anchor cable drilling rig (equipped with a Φ32mm drill bit), with a hole depth of 8600mm. High-strength, low-relaxation steel strand anchor cables (Φ21.8mm×8800mm with breaking force ≥583kN) are installed. To improve the anchoring effect in weak coal seams, a rubber retaining ring with an outer diameter of 26.4 mm and an inner diameter of 21.4 mm is pre-installed 1800 mm from the bottom of the anchor cable. Three tubes of Z2560 resin anchoring agent are sequentially inserted into each hole, stirred with an anchor cable machine, and pushed to the bottom of the hole. After waiting for 30 minutes, the anchor cable is tensioned using a tensioning jack to achieve a preload of 200 kN and then locked. The anchor cable spacing A2 = 850 mm. The anchor cable support plate is made of δ16×300×300 mm disc-shaped steel plate, and adjacent anchor cables are connected into a whole by a ladder beam. The anchor cable row spacing D is the same as that of the anchor rod, which is 800 mm. 3-4 anchor cables are arranged in each row. The anchor cables near the shoulder sockets of both sides must ensure construction quality (see Table 1 for parameters).

[0042] (2) Optimization of parameters for top slab anchor bolt support 1) Determination of the length of the top slab anchor cable Vertical stress distribution cloud map of the surrounding rock of the roadway under different anchor cable lengths when the roof anchor cable spacing is 850mm and the anchor bolt preload torque is 180N.m (see attached map). Figure 8As shown in the figure, the stress field distribution pattern formed by a single anchor cable at the top spreads outward from the anchor cable, first forming an elliptical high-stress distribution area. Then, the stress further weakens towards both sides of the anchor cable, eventually forming a heart-shaped compressive stress area at the top of the tunnel and an elliptical tensile stress area at the ends. With the increase in the number of anchor cables, the compressive stress fields at the top of the tunnel superimpose to form a larger compressive stress area, gradually covering the tunnel top area, with a fan-shaped low-compressive stress area forming at each of the two corners.

[0043] Under the same top anchor spacing and preload torque, within a certain range, the range of the compressive stress zone increases with the increase of anchor length, and the bearing capacity also increases accordingly. When the anchor length further increases, the compressive stress value in the middle of the anchor gradually decreases due to the increased preload distribution distance, leading to stress field separation between the upper and lower parts of a single anchor. When the top anchor length is 8.5m, 8.8m, and 9m, the effective compressive stress zone formed by the anchor continues to expand, increasing the area of ​​the effective bearing capacity of the roof. However, when the anchor length further increases to 9m, the compressive stress zones formed by the upper and lower parts of the anchor gradually separate, resulting in an unstable bearing structure and uneven stress on the surrounding rock of the roof, leading to compromised stability. Therefore, a critical length needs to be selected, which increases the area of ​​the effective bearing capacity of the anchor without causing separation of the compressive stress zone in the middle of the anchor. Therefore, the length of the top anchor is chosen to be 8.8m.

[0044] 2) Determination of the spacing of the top slab anchor cables The vertical stress distribution cloud map of the surrounding rock of the roadway under different anchor cable spacing conditions is shown in the attached diagram when the roof anchor cable length is 8.8m and the anchor cable preload is 180kN. Figure 9 Under the same preload and length conditions, when the anchor cable spacing is small, the compressive stress areas formed by each anchor cable overlap, and the effects of the anchor cables are interconnected. When the anchor cable spacing increases, the effects of the anchor cables become independent, and the stress triangle area on the roadway surface unprotected by the anchor cables is larger, making the roof surface prone to collapse and hindering roof control. Therefore, it is necessary to select an appropriate anchor cable spacing to form an integrated load-bearing structure, which is beneficial for the effective use of anchor cable support. However, the anchor cable spacing cannot be too small; excessively increasing the support density will lead to increased roadway support costs, reduced tunneling speed, and negatively impact the roadway's economic efficiency. Therefore, the roof anchor cable spacing is determined to be 850mm. In summary, the roof anchor cable support spacing is determined to be 850mm, and the anchor cable length is determined to be 8.8m, which can effectively control the roof while meeting the mine's safe and efficient production requirements.

[0045] 3) Determination of the preload of the top slab anchor cables Vertical stress distribution cloud map of the surrounding rock of the roadway under different anchor cable preload conditions when the roof anchor cable length is 8.8m and the anchor cable spacing is 850mm (see attached map). Figure 10As the preload of the anchor cables increases, the stress values ​​at both ends of the anchor cables also increase, as does the compressive stress in the middle of the anchor cables. This shows that increasing the preload can reduce the development of surrounding rock fissures and the occurrence of delamination. Increasing the preload causes the compressive stress areas between the anchor cables to overlap, forming a stable load-bearing structure, which significantly plays a role in fully utilizing the anchor cable support function and controlling the deformation of the surrounding rock in the tunnel. When the anchor cable preload is large, the compressive stress areas formed by each row of anchor cables overlap, and the effects of each row of anchor cables are interconnected, forming an integrated load-bearing structure. Conversely, when the preload is small, each row of anchor cables is independent. When the preload is 180 kN, an integrated load-bearing structure is formed. Furthermore, to match the anchor cable preload, reduce support costs, and accelerate the tunneling speed, the anchor cable support preload was determined to be 180 kN.

[0046] 3. Anchor bolt support on both sides and reinforcement of coal pillar shoulder socket (1) Specific implementation steps Both sides are covered with 3000mm×1000mm diamond-shaped metal mesh, and vertical steel ladder beams are hung. The anchor rods for the sides are Φ22mm×2500mm fully threaded or left-hand threaded steel anchor rods, with an anchor rod spacing A3=850mm and a row spacing D=800mm, and 3 anchor rods are arranged for each side (up to 4 anchor rods can be arranged if the side spalling is severe). One tube of Z2560 anchoring agent is used for each hole, and the installation pre-tightening torque reaches 180 Nm. δ10×150×150mm disc-shaped support plate (parameters are detailed in Table 1).

[0047] Key reinforcement: On the high-stress side of the coal pillar, in this case, near the 1177 goaf, at the arch baseline position, a row of horizontal channel steel composite anchor cables is constructed as a shoulder reinforcement structure. A composite beam with a length of 2000mm is made of 14# channel steel, with three anchor cable holes arranged on it. The anchor cable specifications are Φ21.8mm×4300mm, and two Z2560 anchoring agents are used in each hole. The pre-tensioning force is 150 kN. This set of anchor cables can be constructed a certain distance behind the face, but not exceeding 50m (parameters are detailed in Table 1).

[0048] Explanation of the relationship between preload torque and preload force: The preload force of the anchor bolt is achieved by applying a preload torque. For a Φ22mm threaded steel anchor bolt, the conversion relationship between the preload torque T and the generated preload force P is approximately: P≈T / K, where K is the torque coefficient, with a value range of 0.15~0.25. In this embodiment, the preload torque of 220 Nm for the top plate anchor bolt corresponds to a preload force of approximately 110~147 kN, and the preload torque of 180 Nm for the side anchor bolt corresponds to a preload force of approximately 90~120 kN. The on-site construction shall be based on the measurement value of a torque wrench.

[0049] (2) Optimization of side support parameters 1) Determining the length of the side plate anchor bolt The horizontal stress distribution cloud map of the surrounding rock in the roadway under different anchor bolt lengths is shown in the attached diagram when the spacing between the sidewall anchor bolts is 850mm and the preload torque is 180N.m. Figure 11 With the same anchor bolt spacing, the area of ​​the bearing compressive stress zone increases with the increase of anchor bolt length. However, the stress distribution effect weakens with the increase of distribution distance. When the anchor bolt length is too large, the compressive stress value in the middle of the anchor bolt will be too small, resulting in discontinuous stress distribution and affecting the support effect. The stress distribution law of the side rib is similar to that of the roof. The critical anchor bolt length that ensures sufficient stress distribution and prevents the compressive stress zone from separating in the middle of the anchor bolt is 2.5m. The effective stress superposition forms a larger bearing structure, enabling active support for a larger area of ​​soft coal seam in the side rib. Therefore, the side anchor bolt length is selected as 2.5m.

[0050] 2) Determination of the spacing between the side anchor bolts The horizontal stress distribution cloud map of the surrounding rock in the roadway under different anchor bolt spacing conditions is shown in the attached diagram when the length of the side anchor bolt is 2.5m and the preload torque is 180N.m. Figure 12 Under the same anchor bolt length, the area of ​​the effective compressive stress zone formed by the superposition of anchor bolt stress decreases with the increase of anchor bolt spacing. Furthermore, the decrease in the superimposed stress zone begins at the middle of adjacent anchor bolts and expands outwards. This means that when the anchor bolt spacing is too large, the side anchor bolts cannot form an effective support compressive stress field. When the spacing increases to more than 950mm, the compressive stress value in the middle of two adjacent anchor bolts is too small to form an effective stress-bearing zone, significantly reducing the active support effect of the anchor bolts. Therefore, the spacing of side anchor bolts should be less than 950mm. While a spacing of 750mm reduces the spacing without changing the number of anchor bolts, the effective compressive stress field range formed is not significantly different from that at 850mm. Moreover, since the sides are coal seams, the coal is relatively soft and contains intercalation, resulting in lower strength compared to rock strata. Densely installing anchor bolts would damage the integrity of the coal seam and affect the support effect. Therefore, a side anchor bolt spacing of 850mm is chosen.

[0051] 3) Determination of preload of anchor bolts in the side section The horizontal stress distribution cloud map of the surrounding rock in the roadway under different preload conditions is shown in the attached diagram when the length of the anchor bolts is 2.5m and the anchor bolt spacing is 850mm. Figure 13Under the same anchor spacing and length, within a certain range, as the anchor preload increases, the area of ​​the compressive stress zone increases, and the load-bearing structure also expands. When the anchor preload further increases, the compressive stress value in the middle of the anchor gradually decreases with the increase in preload distribution distance, leading to stress field separation between the upper and lower parts of a single anchor. When the top anchor preload is 160 N·m, 180 N·m, and 200 N·m, the effective compressive stress zone formed by the anchor continues to expand, increasing the area of ​​the effective load-bearing zone of the roof. However, when the top anchor preload further increases to 200 N·m, the compressive stress zones formed between the upper and lower parts of the anchor gradually separate, leading to insufficient stability of the load-bearing structure and uneven stress on the surrounding rock of the roof, resulting in compromised stability. Therefore, a critical length needs to be selected, which increases the area of ​​the effective load-bearing zone of the anchor without causing separation of the compressive stress zone in the middle of the anchor. Therefore, a top anchor preload of 180 N·m is recommended.

[0052] Table 1. Overview of Anchor Bolt (Cable) Support Parameters (iv) Strengthen support in key areas 1. Specific implementation steps In the normal support section of the roadway, every three rows, or 2.4m, a set of disc-type anchor cable bundles is installed in the middle of the roof as a safety guarantee to cope with potential high-level delamination and shear deformation of the roof. The anchor cable bundle includes a 500mm×500mm×18mm high-strength square support plate, on which two Φ21.8mm×8800mm anchor cables and two Φ21.8mm×9800mm anchor cables are arranged diagonally. The anchor cable bundle is constructed 80~100m behind the face. During installation, the four anchor cables are tensioned simultaneously, and the preload is not less than 200 kN.

[0053] 2. Anchor cable bundle structure design and support mechanism analysis This application proposes "disc-type anchor cable bundles" and "linear anchor cable bundles", which involve arranging 3 to 5 anchor cables on the same high-strength outer anchor component and using anchor cables of different lengths to achieve tiered anchoring with other anchor cables, thereby avoiding stress concentration in the inner anchor section at the same rock stratum. At the same time, one hollow grouting anchor cable is used to achieve full-length anchoring of all anchor cables in the anchor cable bundle, thereby avoiding breakage caused by individual anchor cables being broken.

[0054] The anchor cable bundle support mechanism is as follows: See the disc anchor cable bundle design. Figure 2 Linear anchor cable bundle design (see...) Figure 3 .

[0055] (1) Anchors of different lengths are used to achieve stepped anchoring with other conventional anchors to avoid stress concentration in the inner anchor section at the same rock stratum. (2) Three to five anchor cables are arranged in a concentrated manner to increase the number of anchor cables per unit area, so as to jointly resist the horizontal deformation of the surrounding rock and avoid the individual breakage of the anchor cables; (3) The high-strength hollow grouting anchors arranged on the anchor cable bundle are used to achieve full-length anchoring of all anchors in the anchor cable bundle, thereby further improving the shear resistance. (4) By increasing the stiffness of the outer anchor components, the shear failure of the anchor cable orifice caused by insufficient stiffness of the outer anchor end can be avoided; (5) By increasing the strength of the external anchor and lengthening the anchor cable, a mechanical connection is established between the shallow damaged surrounding rock and the deep stable rock in the roadway.

[0056] 3. Construction plan and process for linear anchor cable bundle support The specific construction plan and process are as follows: Construction plan for linear anchor cable bundle support (details attached) Figure 14 ) 1) The tunnel is constructed using the step method, with the height of the upper step not less than 2.5m and not more than 2.8m.

[0057] 2) When the tunnel boring machine is working, it can cut 0.8 / 0.9m at a time and the maximum distance between the top and the bottom should not exceed 0.9 / 1.0m.

[0058] 3) After the roadheader has excavated one row of anchor bolts, immediately install a 5500×1000mm (8# galvanized iron wire diamond mesh) top net and support the top ladder beam (4480mm long). At the same time, drive two single props under the ladder beam as temporary support. The single props should be driven 1 to 1.5 meters to the left and right in the roadway (avoiding the anchor bolt holes of the ladder beam). The initial support force should not be less than 50KN. If the roof at the face is broken, advance anchor bolts must be installed for reinforcement before excavation can proceed.

[0059] 4) When drilling anchor bolt holes, the sides and top must be checked first. The 7 Φ22×2500mm left-hand threaded steel anchor bolts for the tunnel arch support should be closely followed at the face. The length of the upper step should be controlled to 2-4 rows before the kiln is cut.

[0060] 5) The arch anchor cables are installed in a “3-4” pattern, with one set of linear anchor cable bundles arranged alternately every 3 rows. The single arch anchor cable and the central positioning anchor cable (Φ21.8×8800mm) should lag behind the face by no more than 3 rows. The extended anchor cables (Φ21.8×9800mm) on both sides of the central positioning anchor cable can be installed behind the face, but the maximum lag distance should not exceed 80m.

[0061] 6) The overlap length of the top and side mesh is 100-200mm. It is tied with double-strand 16# iron wire with a wire spacing of 200mm. It is tied tightly with a network hook. The overlap of adjacent top and side meshes is overlapped with ladder beams.

[0062] 7) Anchor bolt (cable) spacing: 850×800 / 900mm. For the first 50m of the test, the anchor bolt spacing is 800mm; after 50m of anchor bolt support test, after on-site verification and project team demonstration, the anchor bolt spacing can be adjusted to 900mm.

[0063] 8) The side wall is supported by one Φ12×60×3630mm steel ladder beam + one Φ12×60×4480mm steel ladder beam, one 3000×1000mm No. 8 diamond metal mesh on each side, and three or four Φ22×2500mm left-hand threaded steel anchors or fully threaded anchors + one Φ21.8×4300mm anchor cable for the coal pillar side (considering factors such as roadway side spalling, the side wall can be supported by fully threaded anchors. If the roadway is too wide or has spalling, the number of side wall anchors may be increased to four).

[0064] 9) The ladder beams of the side wall and the ladder beams of the arch are overlapped. The distance between the 1-2 anchor bolts of the upper side wall and the facing should not exceed 2 rows. After the anchor bolts of the upper side wall are supported, the ladder beams of the side wall can be rolled up. After the lower step of the facing is cleared, the rolled-up ladder beams of the side wall should be restored to their original state. The anchor bolts of the lower side wall should not lag behind the lower step by more than 2 rows.

[0065] 10) Without affecting the installation of the conveyor belt, the construction of the horizontal channel steel combined anchor cable of the first row of coal pillars can be delayed at the face, but the delay distance should not exceed 50m.

[0066] 11) Anchor bolt (cable) hole diameter Φ30 / 32mm. Two tubes of Z2560 resin anchoring agent are used for each anchor bolt hole in the arch crown, and three tubes of Z2560 resin anchoring agent are used for each anchor cable hole in the arch crown. The pre-tightening torque of the anchor bolts in the arch crown shall not be less than 200Nm, and the pre-tightening force of the anchor cables in the arch crown shall not be less than 180KN. One tube of Z2560 resin anchoring agent is used for each anchor bolt hole in the roadway side, and two tubes of Z2560 resin anchoring agent are used for each anchor cable hole in the coal pillar side. The pre-tightening torque of the anchor bolts in the roadway side shall not be less than 180Nm, and the pre-tightening force of the anchor cables in the roadway side shall not be less than 150KN. If the anchor bolt pre-tightening torque does not meet the design requirements, the anchor bolts can be manually tightened a second time using long-handled tools, an anchor bolting machine, or a pneumatic wrench.

[0067] 12) Due to the initial testing of anchor cable net support in the mine, a set of U-shaped sheds (3 frames) was installed every 10m for the first 50m of the test, and then gradually removed.

[0068] 4. Construction plan and process for disc-type anchor cable bundle support To compare the support effects of linear anchor bundles and disc anchor bundles, the linear anchor bundle construction scheme was modified to a disc anchor bundle. The disc anchor bundle consists of one 500×500×18mm flat support plate, two Φ21.8×8800mm anchor cables, and two Φ21.8×9800mm anchor cables, with the same specifications of anchor cables arranged diagonally on the support plate. For the disc anchor bundle support section, the initial row spacing for the anchor bolt support test was designed to be 900m, while other support parameters and processes remained unchanged. Tests were conducted for 100m each for both linear and disc anchor bundles (details attached). Figure 15 ).

[0069] (v) Grouting modification and reinforcement of surrounding rock After approximately 50m of initial anchor and cable support was completed in the tunnel excavation, delayed grouting began on the roof and upper sides of the supported section. Grouting holes were arranged between the anchor bolts and cables, with a depth of 4.0m and a spacing of 1.6m x 1.6m, forming a five-hole pattern. Modified urea-formaldehyde resin chemical grout was used, and a dedicated grouting pump was employed for grouting. Grouting proceeded row by row from one end of the tunnel to the other, with an initial grouting pressure of 0.5~1.0MPa. After the grout had fully penetrated, the pressure was gradually increased to 2.5 MPa and maintained for 10 minutes. After grouting, the fractured coal and rock mass was cemented into a unified whole, forming a uniform grouting reinforcement ring approximately 3~4m thick. The bearing capacity of the surrounding rock was significantly improved, providing a reliable foundation for the anchor bolts and cables.

[0070] (vi) Full-section closure and dynamic monitoring 1. Specific implementation steps After the grouting reinforcement is completed and the grout has completely solidified, C20 concrete is sprayed onto the entire cross-section of the roadway with a thickness of 100mm, completely covering the metal mesh, ladder beams, etc., to form a complete sprayed concrete layer 8, which plays a role in sealing, preventing weathering, fire prevention and improving the overall support.

[0071] Within the test section, a comprehensive monitoring station was set up every 30m: this included monitoring surface displacement using a cross-point method, installing multi-point displacement gauges to monitor delamination at depths of 3m, 6m, and 9m within the roof, and installing anchor bolt and cable force gauges to monitor the stress on the support structure. The warning threshold for roof subsidence rate was set at 5mm / day. Monitoring data showed that after adopting this method, roof subsidence during tunnel excavation was controlled within 200mm, and the deformation rate quickly stabilized. When monitoring data was abnormal, anchor cables were promptly installed or local re-grouting was performed in the corresponding areas, achieving dynamic control.

[0072] 2. Anchor bolt (cable) construction technology and construction quality inspection (1) Construction process of anchor bolts and anchor cables 1) Construction process of arch crown anchor bolts The tunnel cross-section was constructed according to the design requirements, and temporary support was provided, including the laying of metal mesh and the installation of ladder beams.

[0073] Drilling roof anchor bolt holes: Use a single anchor bolt drilling machine to drill anchor bolt holes according to the ladder beam hole positions. The anchor bolt holes are drilled from the top of the roadway outwards to both sides. The roadway roof anchor bolts are 2500mm long. Use a drill bit with a diameter of Φ32mm and a drill rod of the same length as the anchor bolt to drill the holes. The anchor bolt hole depth is 2450mm.

[0074] Sending resin cartridges: Insert two Z2560 resin cartridges through the ladder beam holes into the anchor bolt holes, and slowly push the resin cartridges to the bottom of the holes using the assembled anchor bolts.

[0075] Mixing the resin: Connect the drilling rig to the anchor pin (plug) nut using the mixing connector, then raise the drilling rig and push the anchor rod. When it reaches 300-500mm from the top rock surface, start mixing. Slowly raise the drilling rig and keep mixing for 25-35 seconds before stopping.

[0076] Tightening the anchor bolts: After 10 minutes, restart the drilling rig while rotating the nut and advancing the bolts. The support plate quickly presses against the top rock surface, giving the anchor bolts a large pre-tension force. Finally, at the tunneling face, manually increase the pre-tightening torque to over 200 N.m.

[0077] 2) Coal Mine Anchor Bolt Construction Technology Drill roadway side anchor bolt holes according to the design location: use a pneumatic coal drill to drill the holes. The side anchor bolt is 2500mm long. Use a drill bit with a diameter of Φ32mm and a drill rod of the same length as the anchor bolt to drill the holes. The anchor bolt hole is 2450mm deep.

[0078] Sending resin cartridges: Insert one Z2560 resin cartridge through the ladder beam eye into the anchor bolt hole, and slowly push the resin cartridge into the bottom of the hole using the assembled anchor bolt. Stirring the resin: Connect the pneumatic coal drill to the anchor nut using the connecting sleeve, and push the resin cartridge into the bottom of the hole using the anchor rod. Then start the drill and stir while pushing forward, keep for 25~35 seconds and stop after pushing into the bottom of the hole. Tightening the anchor bolts: After 10 minutes, restart the pneumatic coal drill while rotating the nut and advancing the bolt. The support plate quickly presses against the coal face, giving the anchor bolts a large pre-tension force. Finally, at the tunneling face, manually increase the pre-tightening torque to over 180 N.m.

[0079] 3) Anchor cable construction process Drilling: Use a Φ32mm diameter drill bit and extended drill rods to drill holes (1m to 1.5m per rod). Install according to the designed hole positions and angles. The hole depth of the arch anchor cable is 8 / 9m, and the hole depth of the side anchor cable is 4m.

[0080] Resin cartridge delivery: After the anchor cable drilling is completed, immediately load 3 / 2 rolls of Z2560 resin cartridges into the hole (3 rolls of Z2560 resin cartridges for the arch anchor cable), and slowly push the resin cartridges to the bottom of the hole using steel strand. Connect the single anchor drilling rig to the steel strand using a mixing joint, then raise the drilling rig and push the steel strand forward while mixing, until it reaches the bottom of the hole. Stop raising the drilling rig and mixing for 25-35 seconds, then stop the machine.

[0081] Tensioning the steel strands: After half an hour, tension the steel strands using tensioning jacks. The pre-tensioning force of the arch anchor cable should not be less than 180kN, and the pre-tensioning force of the side anchor cable should not be less than 150kN.

[0082] (2) Anchor bolt (cable) construction quality inspection 1) Monitoring requirements The construction quality of anchor bolt (cable) support should be tested in a timely manner according to the design requirements. If the test results do not meet the design requirements, construction should be stopped and rectification should be carried out. If the construction quality is substandard, remedial measures should be taken promptly.

[0083] 2) Anchor bolt anchoring force testing The anchoring force of anchor bolts should be tested using an anchor bolt pull-out test.

[0084] The sampling rate for anchor bolt anchoring force testing is 3%, with one group (9 bolts in total) sampled from every 300 top and side anchor bolts. If there are fewer than 300 bolts, they are considered as one sampling group of 300 bolts. The anchoring force of the arch top anchor bolts shall not be less than 150KN, and the anchoring force of the coal side anchor bolts shall not be less than 120KN.

[0085] 3) Anchor bolt installation geometric parameter detection The geometric parameters to be checked during anchor bolt installation include anchor bolt spacing, row spacing, and anchor bolt installation angle.

[0086] The detection range for the geometric parameters of the anchor bolt installation shall be no less than 15m, and the number of detection points shall be no less than 3.

[0087] The spacing and row spacing of the anchor bolts were measured using a steel tape measure, showing the distance between four anchor bolts arranged in a quadrilateral.

[0088] The installation angle of the anchor bolts is measured using a semicircular measuring instrument.

[0089] 4) Anchor bolt preload torque detection The sampling rate for anchor bolt preload torque testing is 5%. One group (15 bolts in total) is sampled from every 300 top and side anchor bolts for testing. If there are fewer than 300 bolts, they are considered as 300 bolts as a sampling group.

[0090] The pre-tightening torque of the anchor bolts is checked using a torque wrench. The pre-tightening torque of the anchor bolts at the arch top shall not be less than 200 N·m, and the pre-tightening torque of the anchor bolts at the coal ribs shall not be less than 180 N·m.

[0091] 5) Anchor bolt bracket installation quality inspection The inspection range for anchor bolt tray installation quality shall be no less than 15m, with no fewer than 3 inspection points. Each inspection point shall be inspected in groups of one row of anchor bolts.

[0092] The quality inspection of anchor bolt tray installation is carried out by visual observation. During the inspection, the tray is tapped with a hammer to observe whether it is in close contact with the connected components.

[0093] 6) Anchor cable preload test The sampling rate for anchor cable preload testing is 5%. One group (15 cables in total) is sampled from every 300 arch and side anchor cables for testing. If there are fewer than 300 cables, they are considered as 300 cables as one sampling group.

[0094] The preload of the anchor cables is tested using a tensioning jack. The preload of the anchor cables at the arch crown shall not be less than 180 kN, and the preload of the anchor cables at the coal rib shall not be less than 150 kN.

[0095] The methods and implementations provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are merely for the purpose of helping to understand the methods and core ideas of this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for roof deformation control support of a semicircular roadway under the condition of three-soft and half-coal rock, characterized in that, The specific steps are as follows: Step 1, roadway section optimization forming: adopt straight wall semicircular arch section for roadway excavation; according to numerical simulation analysis and field engineering conditions, determine the roadway net width B and net height H, wherein the radius R of semicircular arch is B / 2, and the straight wall height h = H - R; Step 2, initial surface protection and temporary support: after one cycle of roadway excavation, immediately implement temporary support, lay high-strength diamond-shaped metal mesh on the arch of the roadway, and use airborne hydraulic front jib or single hydraulic prop to cooperate with steel beam to effectively support the exposed roof, ensuring construction safety; Step 3, construction of high-strength active support system: in the construction of the high-strength active support system, the support parameters follow the principle of collaborative design, defining the axial direction of the roadway as the row spacing direction and the cross-sectional direction perpendicular to the axial direction of the roadway as the spacing direction; let the basic row spacing of the support system be D; Step 3.1, roof high pre-tightening force anchor rod support: on the arch contour line, drill and install high-strength threaded steel anchor rods according to the anchor rod spacing A1 and row spacing D; the length of the anchor rod is L1, ensuring that it penetrates through the weak and broken zone of the roof; full-length anchoring is achieved using resin anchoring agent; after installation, the pre-tightening torque is not less than T1, and the pre-tightening force is not less than P1; Step 3.2, roof deep anchor cable suspension support: multiple rows of pre-stressed anchor cables are arranged on the roof, according to the spacing A2 and row spacing D or n×D, wherein n is a positive integer; The length L2 of the anchor cable ensures that its inner anchoring segment is located in the deep stable rock layer; each hole is anchored using multiple coils of resin anchoring agent, and after installation, a pre-tightening force of not less than P2 is applied; all anchor cables are connected through high-strength ladder beams or W-shaped steel belts, and are equipped with disc-shaped large brackets; Step 3.3, two-side anchor rod support and coal pillar shoulder nest reinforcement: anchor rods are constructed on both sides of the roadway, with a focus on strengthening the support at the upper part of both sides of the roadway near the arch baseline; the side anchor rod is arranged according to the spacing A3 and row spacing D, and the length of the side anchor rod is L3; the pre-tightening torque after installation is not less than T3, and the pre-tightening force is not less than P3; at the arch baseline position of the coal pillar on the high stress side, a horizontally directed channel steel combined anchor cable is added as a shoulder nest reinforcement structure, which includes a channel steel beam and at least one anchor cable, wherein the length of the anchor cable is L4, and the pre-tightening force is not less than F2, to stabilize the arch foot of the bearing arch; Step 4, key area reinforcement support: in the stress concentration area of the roof of the roadway or the area affected by geological structure, interval N rows of conventional support are added, and a group of anchor cable bundles are added; the anchor cable bundle is composed of a high-strength outer anchor bearing member and multiple pre-stressed anchor cables of different lengths, achieving step-by-step anchoring and concentrated bearing; Step 5, surrounding rock grouting modification and reinforcement: after the active support system in step 3 is in operation and the deformation of the surrounding rock is preliminarily stabilized, the broken surrounding rock on the roof and upper part of the roadway is reinforced by lag grouting; the grouting holes are arranged between the anchor rods and anchor cables, and the grout penetrates and consolidates the broken rock mass, forming a grouting reinforced ring; Step 6, full-face closure and dynamic monitoring: spray a layer of concrete on the surface of the completed roadway support to form a closed support body; surface displacement, deep displacement and support body stress monitoring systems are arranged in typical roadway sections, and the monitoring data are used to dynamically evaluate the support effect and guide whether reinforcement measures need to be taken.

2. The method of supporting of claim 1, wherein, In step 1, the net width B of the straight wall semi-circular arched section is 4.5-5.5 m, and the net height H is 3.8-4.5 m.

3. The method of supporting of claim 1, wherein, In step 3, the roof anchor rod, roof anchor cable and the help anchor rod adopt a unified basic row spacing D, and the basic row spacing D is 800-900 mm.

4. The method of supporting of claim 3, wherein, In step 31, the anchor rod is a left-handed non-longitudinal reinforcement threaded steel anchor rod with a diameter of Φ20-Φ22 mm, L1 is 2.3-2.7 m, the spacing A1 is 800-900 mm, the pre-tightening torque T1 is not less than 180 N·m, the pre-tightening force P1 is not less than 120 kN; two branches of resin anchoring agent are used for full-length anchoring.

5. The method of supporting of claim 3, wherein, In step 32, the anchor cable is a high-strength steel strand with a diameter of Φ17.8-Φ21.8 mm, L2 is 8.5-9.0 m, the spacing A2 is 800-950 mm, and the pre-tightening force P2 is not less than 180 kN; three branches of resin anchoring agent are used for anchoring per hole.

6. The method of supporting of claim 3, wherein, In step 33, the help anchor rod is a threaded steel anchor rod with a diameter of Φ20-Φ22 mm, L3 is 2.3-2.7 m, the spacing A3 is 800-900 mm, the pre-tightening torque T3 is not less than 180 N·m, and the pre-tightening force P3 is not less than 120 kN; the anchor cable in the coal pillar help channel steel combined anchor cable is a steel strand with a diameter of Φ17.8-Φ21.8 mm, L4 is 4.0-5.0 m, and the pre-tightening force P3 is not less than 150 kN; the channel steel is a 14# or 16# channel steel with a length not less than 1.8 m.

7. The method of supporting of claim 1, wherein, In step 4, the anchor cable bundle is a disc type anchor cable bundle or a line type anchor cable bundle; the disc type anchor cable bundle includes a square large backing plate, two first anchor cables with a length of L2 and two second anchor cables with a length greater than L2 are arranged diagonally on the square large backing plate; the line type anchor cable bundle includes a long channel steel or U-shaped steel beam, a first anchor cable and two longer second anchor cables are arranged in sequence along the length direction of the long channel steel or U-shaped steel beam.

8. The method of supporting of claim 1, wherein, In step 5, the grouting reinforcement adopts chemical slurry or ultra-fine cement slurry; the grouting hole depth is 3-5 m, the interval row spacing is 1.5-2.0 m, the grouting final pressure is 2.0-3.0 MPa, and a uniform grouting reinforcement ring with a thickness of 3-4 m is formed.

9. The method of supporting of claim 1, wherein, In step 6, the dynamic monitoring includes roadway surface displacement, roof deep displacement and support body stress monitoring, and a roof subsidence speed early warning threshold is set.

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