Construction technology for large deformation of tunnel soft rock

Abstract

The application discloses a construction technology for tunnel soft rock large deformation construction, and the construction technology comprises the following steps: in the design range of the arch part of the working face, an advanced grouting middle pipe shed is constructed, the surrounding rock in front of the excavation is pre-reinforced, and an advanced bearing arch structure is formed; a bench method is used for layered excavation, according to the crushing degree of the surrounding rock, the water seepage amount and the self-stability capacity, a two-bench annular core soil method or a three-bench method is selected, the layered excavation is carried out in a mechanical non-explosive mode, after the residue is excavated out of each bench, initial concrete spraying is carried out in time to close the rock surface and the working face. Through the synergistic effect of the multiple support systems of the advanced grouting middle pipe shed pre-reinforcement, the passive bearing of the double-layer type steel arch and the active constraint of the prestressed hollow anchor rod, the triaxial stress state of the surrounding rock is optimized, and the deformation development rate and the cumulative deformation amount are double-controlled, so that the problems of the initial support invading the limit, the steel arch distortion and deformation and the large-area arch replacement diseases are effectively avoided, and the construction safety and the long-term stability of the soft rock large deformation tunnel are improved.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering construction technology, specifically to a construction process for tunnels with large deformation in soft rock. Background Technology

[0002] Tunnel projects in the western plateau regions of my country often traverse soft rock strata such as metamorphic sandstone, slate, and phyllite. These areas have complex geological structures, high levels of in-situ stress, highly developed rock joints and fissures, and are prone to softening upon contact with water, resulting in poor self-stabilizing capacity of the surrounding rock. After tunnel excavation and unloading, severe large deformation disasters are likely to occur, characterized by rapid deformation rates, large cumulative deformation, long deformation duration, and asymmetrical spatial distribution. This often leads to problems such as initial support cracking, steel arch frame twisting and deformation, structural encroachment, invert arch heave, and even secondary lining cracking. The cumulative deformation of some tunnels can reach more than 2 meters, requiring frequent arch replacement, which seriously threatens construction safety, slows down project progress, and significantly increases construction costs.

[0003] However, existing construction techniques for tunneling in soft rock with large deformation have the following drawbacks: First, the passive support mode of ordinary system anchor bolts combined with single-layer steel arch frames cannot actively constrain the deformation of the surrounding rock. In soft rock with high ground stress, the deformation control effect is limited and it is difficult to curb the development of large deformation. Second, the prestressed anchor cable active reinforcement scheme has a complex construction process, long single-ring operation time, low construction efficiency, and long anchor cables have high requirements for working space. It is difficult to construct within the limited cross-section of the bench method, has poor mechanization adaptability, and has a high overall cost. Third, the conventional "anchor first, support later" anchor bolt installation method results in large prestress loss in weak and fractured surrounding rock, and the active support effect is difficult to fully realize. Summary of the Invention

[0004] The purpose of this invention is to provide a construction process for tunnel construction with large deformation in soft rock, so as to solve the problems of insufficient deformation control capability, low construction efficiency, high cost and poor adaptability of existing support systems for large deformation tunnels in soft rock.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: it includes the following steps: S1. Advanced pre-support: Construct an advanced grouting pipe roof within the design range of the arch section of the working face to pre-reinforce the surrounding rock in front of the excavation and form an advanced load-bearing arch structure. S2. Step-by-step excavation: Based on the degree of rock fragmentation, water seepage and self-stabilizing capacity, select the two-step ring-shaped core soil method or the three-step method, and use mechanical non-explosive method for layered excavation. After the slag is removed from each step, spray concrete is promptly used to seal the rock surface and the working face. S3. First layer of initial support construction: After excavation, the first layer of steel arch frame is erected in sequence, steel mesh is laid, and anchor pipes for locking foot grouting are installed. Then, C30 early high-strength concrete is sprayed to form the first layer of initial support structure. S4. Construction of prestressed hollow anchor rods: The "support first, anchor later" process is adopted. Prestressed hollow anchor rods are installed on the first layer of initial support according to the design spacing. The hole cleaning, anchoring agent installation, mixing and anchoring, tensioning and locking and grouting of non-anchored sections are completed in sequence to apply active compressive stress to the surrounding rock. S5. Second layer initial support construction: 3-5m behind the first layer initial support face, erect the second layer of steel arch frame, lay steel mesh and spray concrete to form a double-layer steel arch frame joint support system. S6. Construction of the lower step and the inverted arch closure: The lower step is excavated in a staggered manner on the left and right and the initial support of the side wall is completed simultaneously. The inverted arch is constructed closely after the lower step so that the support structure can be closed into a ring as soon as possible. S7. Secondary Lining Construction: After the initial support deformation has stabilized, the secondary lining concrete is poured using an integral formwork trolley to form a permanent load-bearing structure.

[0006] Preferably, in step S1, the pipe roof for the advanced grouting uses φ76×4mm seamless steel pipes, with a single length of 6-12m, a circumferential spacing of 40cm, an external insertion angle of 5°~12°, and a layout range of 102° of the arch. The pipe roof wall is provided with plum blossom-shaped grout outlet holes with a diameter of 10mm and a longitudinal and transverse spacing of 15cm. A 1m long non-drilled grout stop section is provided at the tail. After drilling, cement grout is injected to achieve pre-reinforcement of the surrounding rock. By drilling φ76×4mm seamless steel pipes with plum blossom-shaped grout outlet holes along the excavation outline within the 102° range of the arch at the working face, with an external insertion angle of 5°~12°, and injecting cement grout, the grout diffuses and cements along the grout outlet holes of the pipe wall to the surrounding rock fissures, bonding the broken surrounding rock particles into a whole, forming a continuous cylindrical advanced bearing arch structure outside the excavation outline. The 1m grout stop section at the tail can prevent the grout from flowing to the hole opening, ensuring the grouting pressure and diffusion effect. This improves the overall integrity and self-stabilizing strength of the surrounding rock in advance, prevents the surrounding rock from loosening and falling into the tunnel after excavation, reduces the impact of ground stress unloading on the tunnel face, and creates a safe working space for subsequent bench excavation and initial support construction.

[0007] Preferably, in step S2, when the surrounding rock has good self-stabilizing ability, a two-step ring-shaped core soil method is adopted: the upper step height is 7.16m, the lower step height is 3.45m, and the perimeter of the core soil is not less than 2m from the excavation outline; the excavation advance of the upper step is the spacing of 1 to 2 arch frames, and the excavation advance of the lower step is the spacing of 2 arch frames; the initial shotcrete sealing of the working face is completed within 1 hour after the excavation and slag removal, and the thickness of the initial shotcrete is 5 to 10cm; when the surrounding rock is broken, has a large seepage volume, and poor self-stabilizing ability, a three-step method is adopted: the upper step height is 4.9m, the middle step height is 2.8m, and the lower step... The tunnel has a height of 3.45m; the upper step is no more than 5m long, the middle step is no more than 15m long, and the longitudinal spacing between the left and right middle steps is no less than 3m; the upper step is excavated at a distance of 1 arch frame per advance, and the middle and lower steps at a distance of 1-2 arch frames per advance; by dividing the large tunnel cross-section into multiple smaller cross-sections for layered and step-by-step excavation, the area of ​​the free face and the range of surrounding rock unloading disturbance in a single excavation are significantly reduced; the ring-shaped reserved core soil can form a reverse support for the tunnel face, inhibiting the extrusion deformation of the tunnel face; the middle and lower steps are excavated at a staggered pace to avoid unilateral instability caused by continuous unloading of the surrounding rock on the same side. Combined with short advance excavation and rapid initial shotcreting within 1 hour after muck removal, the exposure time of the surrounding rock is minimized, blocking the weathering and softening path. The two-stage method has fewer steps and higher efficiency, and is suitable for surrounding rock with good self-stabilizing ability; the three-stage method has more detailed steps and less disturbance, and is suitable for extremely broken, water-rich, and weak surrounding rock. In this way, while ensuring excavation safety, it also takes into account the construction efficiency under different geological conditions.

[0008] Preferably, in steps S3 and S5, the steel arch frame is an HW200×200 steel arch frame with a longitudinal spacing of 0.6 to 0.8 m, and I16 I-beams are used as longitudinal connecting bars between the arch frames; the steel mesh is made of φ8mm steel bars with a mesh size of 20×20cm; the first layer of shotcrete is C30 early high-strength concrete with a thickness of 26cm, and the second layer of shotcrete is 24cm thick; the anchor pipes are φ76×4mm grouting steel pipes with a single length of 4.5m, and multiple sets of anchor pipes are set for each arch frame. The system employs a double-layered HW200×200 steel arch frame to provide high-rigidity radial resistance, sharing the surrounding rock compression load and preventing overload and torsional deformation of a single-layer arch frame. I16 longitudinal connecting bars connect the independent individual arch frames into a unified spatial force-bearing system, enhancing the longitudinal stability of the support structure. φ8mm steel mesh is embedded in the shotcrete to constrain concrete shrinkage cracking, distribute load evenly, and improve the overall integrity and impact resistance of the shotcrete. C30 early-strength concrete reaches its design strength quickly, rapidly adhering to the rock surface and transferring surrounding rock pressure. Combined with grouting anchor pipes that penetrate deep into the surrounding rock to anchor the arch feet, the system restricts arch frame settlement and lateral displacement, thus forming a high-strength, highly integrated passive load-bearing structure to resist the continuous compression of soft rock under large deformation.

[0009] Preferably, in step S4, the prestressed hollow anchor rod is a φ32×8mm hollow anchor rod, with a single length of 6m, a circumferential spacing of 1.0m, and a longitudinal spacing consistent with the arch frame spacing; the anchor rod is anchored at the end with resin anchoring agent, with an anchoring length of not less than 1.8m, and a designed tension force of 160~220kN, which can be dynamically adjusted according to the strength of the surrounding rock; the non-anchored section is filled with cement grout pressure injection, with an injection pressure of 0.5~1.0MPa; the anchor rod end is firmly bonded to the relatively stable surrounding rock in the deep layer through resin anchoring agent to form a reliable anchoring end; after tensioning, the anchor rod applies active radial compressive stress to the shallow fractured surrounding rock to offset the tensile strain of the surrounding rock generated by excavation unloading, so that the surrounding rock changes from a uniaxial stress state to a triaxial compression state, actively improving the bearing capacity of the surrounding rock itself and constraining the inward shrinkage deformation of the surrounding rock. An anchoring length of 1.8m ensures that the pull-out resistance at the anchoring end meets the tensioning requirements. The tension force is dynamically adjusted according to the strength of the surrounding rock, which can prevent the anchor rod from being pulled out and failing in weak surrounding rock. Pressure grouting in the non-anchoring section can fill the gap between the anchor rod cavity and the hole wall, cement the surrounding fractured rock mass, and at the same time form anti-corrosion protection for the anchor rod body. This achieves the synergistic effect of active and passive support, significantly improving the control effect on large deformations in soft rock.

[0010] Preferably, the specific construction process of step S4 is as follows: Drilling: Use an integrated arch-anchor machine with a φ54mm drill bit to drill along the initial support normal direction, with the hole depth adapted to the anchor bolt design length (m); use high-pressure air combined with a small amount of high-pressure water to remove slag during drilling; Hole cleaning and material loading: After drilling is completed, use high-pressure air to clean the water and rock cuttings in the hole, then fill in the resin anchoring agent and push it to the bottom of the hole; Mixing and anchoring: Insert the hollow anchor rod, use a drilling rig to drive the anchor rod to rotate and mix the anchoring agent for no less than 40 seconds to ensure that the anchoring agent is fully mixed, and let it stand until it solidifies; Tensioning and locking: After the anchoring agent has cured, use a calibrated hydraulic jack to tension the material according to the design tension force. The tensioning rate is slow and controllable. After tensioning to the required level, tighten the anchoring nut to lock it in place. Grouting and Filling: After locking, connect the grouting pipe to the end of the anchor rod and inject neat cement slurry into the gap between the anchor rod cavity and the hole wall. After filling, seal the grouting port. Drill holes precisely along the initial support normal direction using an integrated arch-anchor machine to ensure that the force direction of the anchor rod is consistent with the deformation direction of the surrounding rock, maximizing the restraint effectiveness of the prestress. High-pressure air combined with a small amount of water is used to remove slag, which not only prevents water accumulation in the hole from softening the surrounding rock and weakening the anchoring force, but also suppresses construction dust. Thoroughly clean the hole to remove rock debris and accumulated water, ensuring that the resin anchoring agent is in close contact with the surrounding rock of the hole wall. Stir at a uniform speed for no less than 40 seconds to ensure that the resin A and B components are fully mixed and reacted, ensuring the end anchoring strength. Gradual tensioning can avoid instantaneous loss of prestress caused by impact loads, ensuring that the tension force is precise and controllable. Finally, grouting fills all gaps to replenish the bonding force and isolate corrosive media. In this way, the quality is controlled throughout the entire process from hole formation, anchoring to tensioning and grouting, ensuring that the prestress of each anchor rod is effectively transferred and fully exerts its active support function.

[0011] In step S6, the single excavation length of the invert arch should not exceed 3m. After excavation, the foundation should be cleaned in time and the initial support of the invert arch should be constructed. The distance between the invert arch and the working face should not exceed 30m. In step S7, the thickness of the secondary lining should not be less than 60cm. C35 reinforced concrete should be used, with a permeability grade not lower than P10. The distance between the secondary lining and the working face should not exceed 50m and should not exceed 70m. By controlling the single excavation length of the invert arch to not exceed 3m, the exposure range and unloading disturbance of the foundation surrounding rock are reduced, and the invert arch excavation is avoided from causing instability of the arch foot. The invert arch is constructed closely after the working face, which can quickly change the initial support from an open structure to a closed ring structure. The overall stiffness and deformation resistance of the ring bearing structure are much higher than those of the open structure, which can effectively constrain the circumferential inward deformation of the surrounding rock and the invert arch heave. A thick C35 reinforced concrete secondary lining serves as a permanent safety reserve, bearing the later-stage creep load of the surrounding rock. Its P10 impermeability grade meets the tunnel's waterproofing requirements. Strict control of the distance between the invert arch, secondary lining, and tunnel face prevents unrestrained deformation of the surrounding rock over extended periods. This achieves "rapid excavation, rapid support, and rapid ring formation," curbing the continuous accumulation of creep deformation in soft rock.

[0012] Preferably, the entire construction process is equipped with monitoring and measurement, as well as advanced geological forecasting. By monitoring the deformation rate of the surrounding rock, the cumulative deformation, and the stress on the support structure, support parameters, excavation progress, and allowance for deformation are dynamically adjusted, achieving information-based dynamic construction. Advanced geological forecasting reveals the properties of the surrounding rock ahead of the tunnel face, the development of fissures, and the water content, allowing for early prediction of the risk level of large deformation and providing a basis for adjusting construction methods and support parameters. During construction, the deformation rate of the surrounding rock, the cumulative deformation, and the internal forces of the support structure are continuously monitored to grasp the development trend of surrounding rock deformation and the stress state of the support in real time. The monitoring data is fed back to the construction stage to dynamically adjust the excavation progress, arch spacing, anchor tension, and allowance for deformation. When the surrounding rock deteriorates, the support is strengthened; when the surrounding rock improves, the parameters are optimized. This achieves closed-loop management of "measurement-feedback-adjustment," ensuring support is provided as needed, avoiding both the risk of encroachment and collapse due to insufficient support and the waste of project resources caused by blindly strengthening the support.

[0013] Preferably, the entire construction process employs mechanized operations: excavation is carried out using a tunnel-specific hydraulic breaker excavator for non-explosive excavation; steel arch frame installation, pre-support, and anchor bolt drilling are performed using an integrated arch-anchor machine; shotcrete is applied using a wet-spraying trolley; and secondary lining is poured using an intelligent integrated formwork trolley. The use of a tunnel-specific hydraulic breaker excavator for non-explosive excavation avoids disturbance and damage to the fractured soft rock caused by blasting vibrations, reducing surrounding rock loosening and deformation. The integrated arch-anchor machine integrates multiple processes such as steel arch frame installation, pre-support drilling, and anchor bolt installation, enabling continuous operation and significantly reducing waiting time between processes. Furthermore, the hole-forming accuracy and efficiency are far superior to manual labor. The wet-spraying trolley ensures dense and uniform shotcrete, improving the quality of the initial support and construction efficiency. The intelligent integrated formwork trolley ensures the accuracy of the secondary lining formation and the quality of the pouring. This reduces the safety risks of high-intensity manual labor, improves construction efficiency and standardization, and meets the needs of rapid and safe construction of tunnels in high-altitude soft rock with large deformation.

[0014] Preferably, the support structure is configured with tiered pre-deformation allowances: 20-40cm for the outer layer, 30-50cm for the inner layer, and a total pre-deformation allowance of 10cm for the entire excavation. During construction, the pre-deformation allowances are dynamically adjusted based on monitoring data, with a total pre-deformation allowance of no less than 60cm for sections with poor surrounding rock stability. By setting tiered pre-deformation allowances, reasonable release space is provided for the gradual large deformation of soft rock: the 20-40cm outer layer accommodates the rapid deformation stage of the surrounding rock in the initial excavation phase, the 30-50cm inner layer accommodates the slow creep stage after the support structure is closed, and the 10cm pre-deformation allowance offsets construction errors and initial deformation. Moderate deformation of the surrounding rock is allowed to release some ground stress, preventing the support structure from cracking or twisting due to excessive internal stress caused by restricted deformation. Simultaneously, the pre-deformation values ​​are dynamically adjusted based on monitoring data, with a total pre-deformation allowance of no less than 60cm for weak surrounding rock sections, ensuring that the support structure does not intrude into the construction clearance after deformation release. This achieves a balance between "pressure relief and shape control," fully utilizing the self-bearing capacity of the surrounding rock and optimizing the stress state of the support while controlling deformation without exceeding limits.

[0015] This invention has the following beneficial effects: through the synergistic effect of multiple support systems, including pre-reinforcement of the pipe roof during advanced grouting, passive bearing of the double-layer steel arch frame, and active constraint of the prestressed hollow anchor rod, the triaxial stress state of the surrounding rock is optimized, and the deformation development rate and cumulative deformation are both controlled. This effectively avoids the initial support encroachment, steel arch frame torsion deformation, and large-area arch replacement defects, thereby improving the construction safety and long-term structural stability of soft rock large deformation tunnels.

[0016] By using the "support first, anchor later" construction technique in conjunction with the integrated arch and anchor machine, the drilling, installation, and tensioning processes can be mechanized and continuously operated. This effectively reduces the construction time of a single ring anchor and significantly shortens the gaps between processes, thus adapting to the limited working space of the step method construction, ensuring a rapid tunnel excavation pace, and improving overall construction efficiency.

[0017] By using φ32 hollow prestressed anchor rods to replace traditional prestressed anchor cables as the core active reinforcement component, the cost of support materials per linear meter is reduced. This, combined with the shortened construction period due to improved construction efficiency, reduces the overall project cost and achieves good technical and economic benefits.

[0018] By actively applying compressive stress to the surrounding rock through prestressed anchor rods and evenly distributing the load of the surrounding rock through double-layer steel arch frames, the combined force mode achieves the effect of balanced force on the inner and outer support structures and a more reasonable load distribution in the secondary lining. This reduces the risk of local stress concentration and cracking in the secondary lining and ensures the long-term service performance of the support structure.

[0019] Through parametric design that allows for flexible switching between two-stage and three-stage construction methods and dynamic adjustment of anchor tension and reserved deformation with the surrounding rock, a precise adaptation effect can be achieved for soft rock strata with different degrees of fracturing and different water seepage conditions. This covers construction scenarios with large deformation in soft rock of multiple levels, and is especially suitable for complex geological conditions of tunnels in high-altitude, high-stress, fractured soft rock. Attached Figure Description

[0020] Figure 1 This is a flowchart of the steps of the present invention.

[0021] Figure 2 This is a flowchart of the overall construction process of the present invention.

[0022] Figure 3 This is a schematic cross-sectional view of the double-layer arch frame + prestressed anchor support structure of the present invention.

[0023] Figure 4 This is the advanced support design drawing for the large deformation test section at the entrance of the Shenzuo Tunnel of this invention.

[0024] Figure 5 This is a flowchart of the prestressed anchor construction process of the present invention.

[0025] Figure 6 This is a schematic diagram of the prestressed hollow anchor structure of the present invention. Detailed Implementation

[0026] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0027] See Figures 1-6 As shown, the technical solution adopted in this specific embodiment is: Example 1: Two-stage construction method (moderately fractured surrounding rock) This embodiment targets the Class V surrounding rock section of a high-stress soft rock tunnel in a plateau region with large deformation. The lithology consists of alternating layers of metamorphic sandstone and slate, with well-developed joints and fissures, and fractured rock mass, posing a strong risk of large deformation. The two-stage ring-shaped reserved core soil method is adopted for construction.

[0028] The first step is to construct an advanced pre-support: within a 102° range of the arch at the working face, construct φ76×4mm advanced grouting pipe roofs, each 6m long, with a circumferential spacing of 40cm and an outward insertion angle of 8°. One round is constructed every 2 to 4 arch frames, with an overlap length of not less than 2.8m. Drill φ10mm plum blossom-shaped grout outlet holes in the pipe roof wall, with a 1m stop grouting section at the tail end. After drilling, inject cement grout to pre-reinforce the surrounding rock in front, forming an advanced load-bearing arch.

[0029] The second step involves two-stage, layered excavation: A tunnel boring machine (TBM) is used for non-blasting excavation, employing a two-stage, ring-shaped core soil method. The upper stage is 7.16m high, and the lower stage is 3.45m high. The core soil perimeter is at least 2m from the excavation outline to ensure sufficient space for machinery operation. The upper stage excavation advance is 0.6m per pass (spacing between one arch frame), and the lower stage excavation advance is 1.2–1.6m per pass (spacing between two arch frames). Excavated muck is transported using a loader and dump trucks, with the muck removal process completed within 2 hours. Within 1 hour of muck removal, C30 concrete is initially sprayed to seal the working face, with an initial thickness of 8cm, to quickly stabilize the surrounding rock.

[0030] The third step is the construction of the first layer of initial support: After the upper step is excavated, the first layer of HW200×200 steel arch frames is erected using an integrated arch-anchor machine, with a longitudinal spacing of 0.6 to 0.8m. The arch frames are connected longitudinally using I16 I-beams. φ8mm steel mesh is laid with a mesh size of 20×20cm. Six sets of φ76×4mm anchor pipes are installed at the arch foot of each arch frame, with a single length of 4.5m. Grouting is used to reinforce the arch foot foundation. Then, C30 high-strength concrete is sprayed to a thickness of 26cm to form the first layer of initial support structure.

[0031] The fourth step is the construction of prestressed hollow anchor bolts: the "support first, anchor later" process is adopted, and φ32×8mm hollow prestressed anchor bolts are installed on the first layer of initial support. The single bolt is 6m long and the circumferential spacing is 1.0m. Each arch frame corresponds to one ring of anchor bolts. The specific process is as follows: Using an integrated arch-anchor drilling machine with a φ54mm drill bit, drill holes along the initial support normal direction. Drilling a single hole takes approximately 4 minutes. High-pressure air and a small amount of high-pressure water are used for slag removal during drilling to prevent water accumulation and softening of the surrounding rock. After cleaning the hole with high-pressure air, insert three φ35×800mm medium-speed resin anchoring agents and push them to the bottom of the hole. Insert hollow anchor rods and use a YT28 drilling rig to rotate and stir the anchor rods for 40 seconds. Let them stand for 10 minutes to allow the anchoring agent to solidify. Use a calibrated hydraulic jack to gently tension the anchor rods with a tensioning force of 200kN. Once in place, tighten the anchoring nut to lock it in place. Finally, weld the grouting valve, inject a cement grout with a water-cement ratio of 0.5, and inject at a grouting pressure of 0.6MPa. After filling the gap between the anchor rod cavity and the hole wall, seal the grouting port.

[0032] Step 5, second layer initial support construction: 3-5m behind the first layer of the working face, erect the second layer of HW200×200 steel arch frame. The arch frame spacing is the same as the first layer. The two layers of arch frames are at the same pile number. After laying the steel mesh, spray 24cm thick C30 early high-strength concrete to form a double-layer arch frame support system. The support structure is designed with an outer layer reserved for deformation of 20-40cm and an inner layer reserved for deformation of 30-50cm. The total reserved deformation is adapted to the large deformation requirements.

[0033] Step 6: Construction of the lower step and inverted arch closure: The lower step is excavated in a staggered manner on the left and right, and the double-layer initial support of the sidewall is completed simultaneously; the inverted arch follows the lower step, with a single excavation length of 3m. After timely cleaning of the foundation, the initial support of the inverted arch and the inverted arch filling are carried out to close the structure into a ring; the distance between the inverted arch and the working face is controlled within 25m.

[0034] Step 7, secondary lining construction: After the deformation rate of the initial support is less than 0.5 mm / d for 7 consecutive days, a C35 reinforced concrete secondary lining of not less than 60 cm thick is poured using a fully hydraulic integral formwork trolley. The main reinforcement of the secondary lining is double-layered φ25 threaded steel with a longitudinal spacing of 15 cm. The concrete impermeability grade is P10. The distance between the secondary lining and the working face is controlled within 45 m.

[0035] Throughout the construction process, monitoring and measurement, as well as advanced geological forecasting, are carried out. Support parameters, excavation depth, and allowance for deformation are dynamically adjusted based on the surrounding rock deformation monitoring data, thereby achieving information-based dynamic construction.

[0036] Example 2: Three-stage construction method (surrounding rock extremely fractured section).

[0037] This embodiment addresses a large deformation section of strong soft rock with extremely fractured surrounding rock, high seepage, and poor self-stabilization. The difference from Embodiment 1 lies in the excavation method: a three-stage non-blasting method is used, with the upper stage height being 4.9m, the middle stage 2.8m, and the lower stage 3.45m; the upper stage length is 5m, the middle stage length is 15m, and the left and right middle stages are longitudinally staggered by 3m; the upper stage advances at a single interval of one arch frame, while the middle and lower stages advance at a single interval of 1-2 arch frames. The support construction rhythm is adjusted as follows: after the first layer of initial support and anchor bolt construction is completed on the upper stage, the middle stage is excavated with staggered left and right sections and the first layer of sidewall support is constructed; after the sides of the middle stage are bottomed out, the second layer of arch frames is constructed uniformly; the lower stage follows synchronously to ensure the continuous stability of the support structure. The anchor bolt tension is 160-180kN to avoid anchor bolt pull-out or localized damage to the surrounding rock during tensioning, ensuring the effectiveness of the anchoring. The distance between the invert arch and the working face should be controlled within 30m to accelerate the formation of the ring structure and curb the continuous development of surrounding rock deformation.

[0038] The remaining construction techniques and material parameters are the same as in Example 1.

[0039] Working principle of the invention: Step 1: Pre-support construction.

[0040] Measurement and layout: Within a 102° range of the arch of the working face, mark the pipe roof drilling points at circumferential intervals of 40cm. Set an external insertion angle of 5° to 12° according to the dip angle of the surrounding rock to ensure that the pipe roof is laid out outside the excavation outline.

[0041] Drilling: The arch-anchor integrated machine with matching drill bit is used for drilling, with a single hole designed to a depth of 6.2m. During the drilling process, high-pressure air is used in combination with a small amount of high-pressure water to remove slag, which not only avoids water accumulation in the hole and softens the surrounding rock, but also suppresses construction dust. After the hole is formed, the hole depth, hole diameter and deviation are checked, and the hole depth error is controlled within 100mm.

[0042] Pipe shed installation: Push φ76×4mm seamless steel pipes into the hole one by one, with an effective length of 6m for each pipe; drill φ10mm grout outlet holes in advance on the pipe wall, arranged in a quincunx pattern, with a longitudinal and transverse spacing of 15cm, and leave a 1m un-drilled grout stop section at the end facing the hole opening.

[0043] Grouting reinforcement: Install a grout stop plug at the pipe opening and connect it to the grouting pipeline. Inject cement slurry with a water-cement ratio of 0.45 to 0.5 and control the grouting pressure at 0.5 to 1.0 MPa. After the grouting pressure rises steadily and the slurry returns evenly at the hole opening, continue to stabilize the pressure for 3 to 5 minutes and stop grouting to complete the pre-reinforcement of the surrounding rock in front and form an advanced load-bearing arch structure.

[0044] Step 2: Step-by-step excavation Method selection and determination: On-site investigation of the degree of fracture, seepage volume, and self-stabilizing capacity of the surrounding rock at the working face. When the surrounding rock is moderately fractured and has good self-stabilizing capacity, the two-stage ring-shaped pre-reserved core soil method is selected; when the surrounding rock is extremely fractured, has a large seepage volume, and poor self-stabilizing capacity, the three-stage method is selected.

[0045] Two-stage excavation: First, excavate the annular outline of the upper stage, retaining the central core soil, with the edge of the core soil at least 2m from the excavation outline surface; the excavation height of the upper stage is 7.16m, with each excavation advance corresponding to the spacing of 1-2 arch frames. After the initial support of the upper stage is completed, excavate the lower stage simultaneously, with a height of 3.45m, and each excavation advance corresponding to the spacing of 2 arch frames.

[0046] The three-stage excavation method involves excavating the upper, middle, and lower stages sequentially. The upper stage is 4.9m high and no more than 5m long longitudinally; the middle stage is 2.8m high and no more than 15m long longitudinally; and the lower stage is 3.45m high. The middle and lower stages are excavated with staggered left and right sides, with a longitudinal stagger distance of no less than 3m, to avoid continuous excavation on the same side causing instability of the surrounding rock. The upper stage is advanced at a single advance of one arch frame spacing, while the middle and lower stages are advanced at a single advance of 1 to 2 arch frame spacings.

[0047] Slag Removal and Rapid Sealing: A loader combined with dump trucks is used to transport the tunnel slag, with a single-cycle slag removal time controlled within 2 hours; within 1 hour after slag removal, a 5-10cm thick layer of concrete is sprayed to completely seal the tunnel face and exposed rock surface, blocking the path of weathering and water absorption softening of the surrounding rock. Step 3: Construction of the first layer of initial support Steel arch frame erection: HW200×200 type steel arch frames are hoisted and precisely positioned using an integrated arch-anchor machine, and arranged at longitudinal intervals of 0.6 to 0.8m as designed; the arch frame joints are fastened with high-strength bolts, and I16 I-beams are set between the arch frames as longitudinal connecting bars, evenly distributed in the circumferential direction to ensure the overall rigidity of the support.

[0048] Reinforcing mesh installation: Lay φ8mm welded reinforcing mesh inside the arch frame. The mesh size is 20cm×20cm. The overlap length of adjacent mesh pieces is not less than one mesh width. The reinforcing mesh is fixed to the steel arch frame by spot welding to prevent displacement during shotcreting.

[0049] Construction of anchor pipes for locking feet: φ76×4mm grouting anchor pipes are installed at the arch foot position of each arch frame, with a single length of 4.5m. Multiple sets of anchor pipes are set for each arch frame. After drilling, cement grout is injected to strengthen the anchoring force of the arch foot and suppress the subsidence and horizontal displacement of the arch foot.

[0050] Shotcrete: C30 early high-strength concrete is sprayed in layers using a wet spraying trolley. After initial spraying for leveling, it is re-sprayed to the designed thickness of 26cm. The spraying operation is carried out sequentially from the arch foot to the arch crown to ensure that the concrete is dense, the surface is smooth, and it adheres closely to the rock surface without voids.

[0051] Step 4: Construction of prestressed hollow anchor bolts (support first, anchor later process) Hole location marking: On the surface of the first layer of initial support, mark the anchor bolt drilling points with red paint according to the standard of 1.0m circumferential spacing and the same longitudinal spacing as the arch frame spacing. The drilling direction is laid out along the normal direction of the initial support.

[0052] Drilling and cleaning: The arch-anchor integrated machine is equipped with a φ54mm drill bit for drilling. The depth of a single hole is adapted to the length of the anchor rod, and the drilling time for a single hole is about 4 to 5 minutes. After the hole is formed, high-pressure air is used to blow from the bottom of the hole to the opening to thoroughly clean the water, rock powder and debris inside the hole, ensuring that the hole wall is dry and clean, so as to avoid affecting the anchoring effect.

[0053] Anchoring agent filling: Insert three tubes of medium-speed resin anchoring agent with a specification of φ35×800mm into the hole in sequence, and use a special pusher to push the anchoring agent smoothly to the bottom of the hole; after filling, immediately insert the anchor rod to prevent hole collapse and premature curing of the anchoring agent.

[0054] Mixing and anchoring: Insert the φ32×8mm hollow anchor rod into the bottom of the hole at a uniform speed. Connect the end of the anchor rod to the YT28 drilling rig special connector. While pushing the rod forward, rotate and mix at a uniform speed for no less than 40 seconds to ensure that the A and B components of the resin anchoring agent are fully mixed. The mixing process should be completed in one go, and it is forbidden to stop or mix repeatedly. After mixing, let it stand for 10 minutes to allow the anchoring agent to cure.

[0055] Tensioning and Locking: After the anchoring agent has cured, install the 25cm×25cm×16mm steel anchor plate and anchor in sequence, and use a calibrated hydraulic jack for tensioning; the tension force is dynamically adjusted according to the strength of the surrounding rock and controlled within the range of 160~220kN. The tensioning rate is slow and uniform. After tensioning to the design value, tighten the anchoring nut immediately to lock, and then slowly remove the jack.

[0056] Grouting of non-anchored sections: After locking, weld a grouting valve to the exposed end of the anchor rod, connect the grouting pipeline and inject cement grout with a water-cement ratio of 0.45 to 0.5. Control the grouting pressure at 0.5 to 1.0 MPa. After the grout fills the gap between the hollow cavity of the anchor rod and the hole wall and the hole opening continues to overflow, stop grouting and seal the grouting port to complete the construction of a single anchor rod.

[0057] Step 5: Construction of the second layer of initial support Install the second layer of HW200×200 steel arch frames 3 to 5 meters behind the working face of the first layer of initial support, following the same erection process as the first layer of arch frames. The spacing between the arch frames should be aligned with that of the first layer.

[0058] φ8mm steel mesh was laid and spot-welded to the second layer of arch frame. 24cm thick C30 early high-strength concrete was sprayed using a wet spraying trolley to form a combined support system of "double-layer steel arch frame + double-layer shotcrete".

[0059] The support structure is designed with graded allowances for deformation: the outer arch frame is allowed 20-40cm of deformation, the inner arch frame is allowed 30-50cm of deformation, and the total allowance for deformation is adapted to the large deformation characteristics of soft rock. The total allowance for deformation in sections with poor surrounding rock stability is not less than 60cm.

[0060] Step 6: Construction of the invert arch and structural closure to form a loop After the lower step is excavated to the designed foundation elevation, the double-layer initial support construction of the sidewall is completed simultaneously to ensure that the sidewall support and the arch support are seamlessly connected.

[0061] The length of a single excavation of the invert arch shall not exceed 3m. After the excavation is completed, the loose debris, water and loose rock at the base shall be cleaned manually, and the bearing capacity of the base shall be inspected.

[0062] The inverted arch steel frame was erected in a timely manner and firmly connected with the side wall arch frames. Shotcrete was sprayed to complete the initial support of the inverted arch, and then the inverted arch filling concrete was poured to form a closed ring-shaped load-bearing structure in the entire support section.

[0063] Strictly control the connection time of the process, and the distance between the invert arch and the working face should not exceed 30m, so as to realize the rapid closure of the support structure into a ring and curb the continuous deformation of the surrounding rock.

[0064] Step 7: Secondary Lining Construction The stability of the initial support is determined by monitoring and measuring data. When the deformation rate of the surrounding rock is ≤0.5mm / d for 7 consecutive days, it is determined that the deformation of the initial support tends to be stable, and the secondary lining construction is started.

[0065] The process of base surface treatment, waterproofing membrane laying, and rebar binding is completed in sequence. A fully hydraulic integrated formwork trolley is used for precise positioning, and C35 reinforced concrete with a thickness of not less than 60cm is poured. The secondary lining main reinforcement uses double-layer φ25 threaded steel bars with a longitudinal spacing of 15cm, and the concrete impermeability grade is not lower than P10.

[0066] After the concrete reaches the demolding strength, it should be demolded and cured. The distance between the secondary lining and the working face should be controlled within 50m, and the maximum should not exceed 70m, to form the final permanent load-bearing structure.

[0067] Step 8: Dynamic Information Management Throughout the entire construction process, monitoring and measurement, as well as advanced geological forecasting, are carried out simultaneously. Data such as clearance convergence, arch settlement, and support internal forces are collected daily. Based on the monitoring results, the excavation advance, support parameters, anchor tension, and reserved deformation are dynamically adjusted to achieve closed-loop management of "measurement feedback - parameter adjustment - dynamic construction," ensuring the effectiveness of large deformation control and construction safety.

[0068] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction technique for tunneling in soft rock with large deformation, characterized in that: Includes the following steps: S1. Advanced pre-support: Construct an advanced grouting pipe roof within the design range of the arch section of the working face to pre-reinforce the surrounding rock in front of the excavation and form an advanced load-bearing arch structure. S2. Step-by-step excavation: Based on the degree of rock fragmentation, seepage volume and self-stabilizing capacity, select the two-step ring-shaped core soil method or the three-step method, and use mechanical non-explosive methods for layered excavation. After the slag is removed from each step, spray concrete is promptly used to seal the rock surface and the working face. S3. First layer of initial support construction: After excavation, the first layer of steel arch frame is erected in sequence, steel mesh is laid, and anchor pipes for locking foot grouting are installed. Then, high-strength concrete is sprayed to form the first layer of initial support structure. S4. Construction of prestressed hollow anchor rods: The "support first, anchor later" process is adopted. Prestressed hollow anchor rods are installed on the first layer of initial support according to the design spacing. The hole cleaning, anchoring agent installation, mixing and anchoring, tensioning and locking and grouting of non-anchored sections are completed in sequence to apply active compressive stress to the surrounding rock. S5. Second layer initial support construction: 3-5m later than the first layer initial support face, erect the second layer of steel arch frame, lay steel mesh and spray concrete to form a double-layer steel arch frame joint support system. S6. Construction of the lower step and the inverted arch closure: The lower step is excavated in a staggered manner on the left and right and the initial support of the side wall is completed simultaneously. The inverted arch is constructed closely after the lower step so that the support structure can be closed into a ring as soon as possible. S7. Secondary Lining Construction: After the initial support deformation has stabilized, the secondary lining concrete is poured using an integral formwork trolley to form a permanent load-bearing structure.

2. The construction technology for tunneling in soft rock with large deformation, as described in claim 1, is characterized in that: In step S1, the pre-grouting pipe roof uses φ76×4mm seamless steel pipes, with a single length of 6m, a circumferential spacing of 40cm, an external insertion angle of 5°~12°, and a layout range of 102° for the arch; the pipe roof wall is provided with plum blossom-shaped grout outlet holes with a diameter of 10mm, a longitudinal and transverse spacing of 15cm, and a 1m long non-drilled grout stop section at the tail; after drilling, cement grout is injected to achieve pre-reinforcement of the surrounding rock.

3. The construction technology for tunneling in soft rock with large deformation, as described in claim 1, is characterized in that: In step S2, when the surrounding rock has good self-stabilizing ability, a two-step ring-shaped core soil method is adopted: the upper step is 7.16m high, the lower step is 3.45m high, and the perimeter of the core soil is not less than 2m from the excavation outline; the excavation advance of the upper step is 1-2 arch frame spacings, and the excavation advance of the lower step is 2 arch frame spacings; the initial shotcrete sealing of the working face is completed within 1 hour after the excavation and slag removal, and the initial shotcrete thickness is 5-10cm; when the surrounding rock is broken, has a large seepage volume, and poor self-stabilizing ability, a three-step method is adopted: the upper step is 4.9m high, the middle step is 2.8m high, and the lower step is 3.45m high. The length of the upper step shall not exceed 5m, the length of the middle step shall not exceed 15m, and the longitudinal spacing between the left and right middle steps shall not be less than 3m; the upper step shall be advanced by a single arch frame spacing, and the middle and lower steps shall be advanced by a single arch frame spacing of 1 to 2 arch frames.

4. The construction technology for tunneling in soft rock with large deformation, as described in claim 1, is characterized in that: In steps S3 and S5, the steel arch frame is an HW200×200 steel arch frame with a longitudinal spacing of 0.6 to 0.8 m. I16 I-beams are used as longitudinal connecting bars between the arch frames. The steel mesh is made of φ8mm steel bars with a mesh size of 20×20cm. The first layer of shotcrete is C30 early high-strength concrete with a thickness of 26cm, and the second layer of shotcrete has a thickness of 24cm. The anchor pipes are φ76×4mm grouting steel pipes with a single length of 4.5m. Multiple sets of anchor pipes are set for each arch frame according to the deformation of the surrounding rock.

5. The construction technology for tunneling in soft rock with large deformation, as described in claim 1, is characterized in that: In step S4, the prestressed hollow anchor rod is a φ32×8mm hollow anchor rod with a single length of 6-12m, a circumferential spacing of 1.0m, and a longitudinal spacing consistent with the arch frame spacing. The anchor bolts are anchored at the ends with resin anchoring agent, with an anchoring length of not less than 1.8m and a design tension of 160-220kN, which can be dynamically adjusted according to the strength of the surrounding rock. The non-anchored sections are filled with cement slurry pressure grouting, with a grouting pressure of 0.5-1.0MPa.

6. A construction technology for tunneling in soft rock with large deformation, as described in claim 5, is characterized in that: The specific construction process for step S4 is as follows: Drilling: An integrated arch-anchor drilling machine with a φ54mm drill bit was used to drill along the initial support normal direction, with a hole depth of 6.2m; high-pressure air was used in conjunction with a small amount of high-pressure water to remove slag during drilling; Hole cleaning and material loading: After drilling is completed, use high-pressure air to clean the water and rock cuttings in the hole, then fill in the resin anchoring agent and push it to the bottom of the hole; Mixing and anchoring: Insert the hollow anchor rod, use a drilling rig to drive the anchor rod to rotate and mix the anchoring agent for no less than 40 seconds to ensure that the anchoring agent is fully mixed, and let it stand until it solidifies; Tensioning and locking: After the anchoring agent has cured, use a calibrated hydraulic jack to tension the material according to the design tension force. The tensioning rate is slow and controllable. After tensioning to the required level, tighten the anchoring nut to lock it in place. Grouting: After locking, connect the grouting pipe to the end of the anchor rod and inject neat cement grout into the gap between the anchor rod cavity and the hole wall. After filling, seal the grouting port.

7. A construction technology for tunneling in soft rock with large deformation, as described in claim 1, is characterized in that: In step S6, the length of a single excavation of the invert arch shall not exceed 3m. After excavation, the foundation shall be cleaned in time and the initial support of the invert arch shall be constructed. The distance between the invert arch and the working face shall not exceed 30m. In step S7, the thickness of the secondary lining shall be 60cm, using C35 reinforced concrete with a permeability grade not lower than P10. The distance between the secondary lining and the working face shall not exceed 50m and shall not exceed 70m at most.

8. The construction technology for tunneling in soft rock with large deformation as described in claim 1, characterized in that: The entire construction process is equipped with monitoring and measurement and advanced geological forecasting. By monitoring the deformation rate of the surrounding rock, the cumulative deformation, and the stress on the support structure, the support parameters, excavation progress, and reserved deformation amount are dynamically adjusted to achieve information-based dynamic construction.

9. A construction technology for tunneling in soft rock with large deformation, as described in claim 1, is characterized in that: The entire construction process adopts mechanized operations: excavation is carried out using a tunnel-specific hydraulic breaker excavator for non-explosive excavation; steel arch frame installation, advanced support, and anchor bolt drilling are carried out using an integrated arch and anchor machine; shotcrete is carried out using a wet spraying trolley; and secondary lining is poured using an intelligent integrated formwork trolley.

10. A construction technology for tunneling in soft rock with large deformation, as described in claim 1, characterized in that: The support structure is designed with graded allowances for deformation: 20-40cm for the outer layer, 30-50cm for the inner layer, and 10cm for the total excavation allowance. During construction, the allowances are dynamically adjusted based on monitoring data. The total allowance for deformation in sections with poor surrounding rock stability should not be less than 60cm.

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