Construction method for preventing slip collapse and controlling damage when large-deformation tunnel passes through contact pressure-bearing belt

Abstract

The invention discloses a construction method for preventing slip collapse and controlling damage when a large-deformation tunnel penetrates through a contact pressure-bearing zone. The construction method comprises the steps that loose surrounding rock is pre-reinforced through 8 m half-section curtain grouting outside an arch wall; implementing a double-row phi 42 mm advanced small guide pipe combined double-layer HW200 steel frame supporting system; two-step staggered excavation (the upper step is 13-15m / the lower step is 5-8m) is matched with an I18 I-steel temporary inverted arch to control deformation; a locking anchor pipe with the diameter being 89 mm is arranged on an arch foot, and a self-propelled anchor rod with the diameter being 32 mm is adopted for reinforcing the surrounding rock; micro piles with the diameter of 146 mm are constructed at the bottom of the tunnel and connected with a raft inverted arch with the thickness of 40 cm to restrain upwelling; the reinforced secondary lining is made of double-limb reinforcing steel bars with the diameter of phi 25 mm and C40 concrete, and the stress of the embedded component is monitored in real time; the method can effectively solve the key construction problems that under the adverse working conditions that the tunnel penetrates through the contact pressure-bearing belt, the tunnel face is prone to slipping and slump, water bursts suddenly, deformation control is difficult, the structure is potentially damaged, and the construction progress is slow; the method has the advantages of improving the field operation environment, increasing the intensive utilization rate of resources, strengthening the durability of the structure, remarkably improving the engineering safety quality, shortening the construction period and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction methods, and in particular to a construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact pressure zone. Background Art

[0002] In recent years, the scale of transportation tunnel projects in mountainous areas of my country has continued to expand, with a large number of tunnels required to traverse geological zones characterized by rock contact pressure zones under high geostress. These areas are commonly characterized by the development of weak interlayers and interlayer slip surfaces, as well as water-rich and pressure-bearing structural fissures. These conditions can easily lead to a series of problems during construction, including face water inrush and collapse, large deformation intrusion into the initial support, arch uplift, and secondary lining cracking. Traditional construction methods, when dealing with the coupled effects of high geostress and pressure water, often face significant safety risks and delays due to inadequate surrounding rock reinforcement, insufficient support structure resistance, and inadequate process control.

[0003] Current conventional technical means have obvious limitations: first, the scope of advance pre-grouting is insufficient and the consolidation effect of weak areas is poor, which cannot effectively suppress the expansion of the loose zone of the loose surrounding rock; second, the support system is single (such as single-layer steel frame, conventional locking anchor rods), which is difficult to resist the compressive shear deformation caused by high ground stress, and the arch foot settlement and steel frame distortion occur frequently; third, the anti-uplift measures of the inverted arch are missing, and the inverted arch filling layer and the base reinforcement lack a coordinated force design, which cannot reduce the pressure of pressurized water seepage and the accumulation of deformation energy; fourth, the safe step distance control only focuses on spatial distance, ignores the cumulative deformation effect in the time dimension, and accelerates potential damage to the structure.

[0004] There is an urgent need to develop a construction method that integrates active surrounding rock reinforcement, support system enhancement, and full-process deformation control. This method can systematically address the issues of preventing tunnel collapse in high-stress contact zones, improving support structure stability, and optimizing construction efficiency. Key technical bottlenecks must be overcome, including deep consolidation of loose surrounding rock, multi-dimensional support reinforcement, anti-uplift design of inverted arches, and dual-control safety step distances, to achieve the goal of safe, efficient, and low-loss tunnel construction. Summary of the Invention

[0005] In response to the above technical problems in the related art, the present invention proposes a construction method for preventing collapse and controlling damage in a large deformation tunnel passing through a contact pressure zone, which can overcome the above shortcomings of the existing technology.

[0006] To achieve the above technical objectives, the technical solution of the present invention is implemented as follows: A construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact pressure zone; The construction method for preventing collapse and controlling damage of a large deformation tunnel crossing a contact pressure zone includes the following steps: S1. Build a grouting wall close to the upper step of the tunnel face, using a combination of steel and wooden formwork. Pour concrete in three stages. Pre-embed the opening pipes for the curtain holes and seal them. Install two rows of anchor steel bars around the perimeter for initial support. Grouting reinforcement is provided at the bottom using four rows of steel pipes at the interface with the lower step to resist the pressure of the curtain grouting. S2. Use a down-the-hole drill to drill curtain holes within 8m of the arch wall excavation outline. Eight rings of holes are arranged in an umbrella-shaped radial pattern, with the outer rings drilled first and the inner rings later. Curtain grouting is performed in 25m longitudinal sections. After 20m of excavation, a 5m stop rock plate is reserved. Reinforcement is achieved using a combination of forward segmented grouting and backward clustered sleeve valve pipe grouting. S3. Install two rows of Φ42mm advanced small ducts along the upper step, with an effective overlap length of ≥1m. The tail end is welded to the HW200 steel frame and grouting is used to form a stable shell. S4. Divide the section into upper and lower steps for excavation. The upper step accounts for 3 / 5 of the height and is 13m to 15m long, while the lower step accounts for 2 / 5 of the height and is 5m to 8m long, with a 2m offset between the two sides. Use an excavator's hammer to expand the excavation in a circular pattern from top to bottom and adjust the contours. S5. Install a double-layer HW200 steel frame, with the second layer lagging 3m to 5m behind the first. Construct a temporary inverted arch and weld it to the HW200 steel frame, sealing it with sprayed C30 concrete. Install Φ89mm locking anchor pipes at the arch foot to prevent displacement. S6. Use Φ32mm self-propelled anchors to reinforce the surrounding rock of the arch wall to form a bearing ring, and use Φ76mm orifice pipes to compensate for grouting in the blind area behind the HW200 steel frame flange plate; S7. Conduct dual control of time and span for the safe step distance of primary support, invert and secondary lining; S8. Add 146mm micropiles for grouting reinforcement at the initial support tunnel bottom. Install a raft slab within 40cm of the inverted arch leveling layer and connect it to the exposed reinforcement tendons of the micropiles. S9. Strengthen the secondary lining structure, adjust the main reinforcement to double-leg reinforcement, increase the concrete grade to C40, and embed components to monitor the stress in real time.

[0007] Furthermore, the slurry stop wall is 2m thick at the top and 3m thick at the bottom, with a chest slope of 1:0.2, and is cast with C25 concrete; the embedded orifice pipes are wrapped and tied with geotextiles, and the anchor steel bars are Φ25mm, 1m long, and buried 0.5m deep; the four rows of Φ42mm steel pipes at the bottom are 3.5m long, arranged at a spacing of 2m×1m, and the two rows of steel flower pipes in the middle extend 50cm into the slurry stop wall.

[0008] Furthermore, the curtain drilling hole has a diameter of Φ127mm, and a 1m long Φ108mm orifice pipe is buried at the port; the vertical distance between the bottom row of drilled holes and the lower step is 0.6m; the forward segmented grouting in the curtain grouting is 4m to 6m long, the backward sleeve valve pipe grouting section is 8m to 10m long, the grouting pressure is 5MPa to 8MPa, and the cement slurry with a water-cement ratio of 0.7:1 to 1:1 is used.

[0009] Furthermore, the double rows of Φ42mm advanced small ducts are 4m long, the inner row has an external insertion angle of 5° to 10°, the outer row has an external insertion angle of 30° to 35°, the circumferential spacing is 40cm, the two rows of holes are staggered and the overlap length is ≥1m.

[0010] Furthermore, the HW200 steel frame unit joints are staggered by more than 50 cm, and joints are prohibited on the main arch top; the temporary inverted arch uses I18 I-beams with a center rise of 1.5 m; Φ89mm locking foot anchor pipes are installed on each side of each steel frame, two each, 6 m long, with an angle of 20° to 40° horizontally and downwardly, 10 cm away from the arch foot joint, and welded to the steel frame through L-shaped steel bars.

[0011] Furthermore, the Φ32mm self-propelled anchor arch is 6m long, the side wall is 10m long, and the spacing is 0.8m×1.2m; the grouting pressure is 1.0MPa to 1.5MPa, and the slurry with a water-cement ratio of 0.8:1 to 1:1 is used; the Φ76mm orifice pipe is 1m long and is arranged with a circumferential spacing of 1.5m along the 20cm range on both sides of each steel frame. The gap is sealed with an anchor agent before grouting.

[0012] Furthermore, the dual control of safety step distance meets the following requirements: initial support step distance ≤ 25m and closure time ≤ 25 days, invert arch step distance ≤ 70m and pouring time ≤ 60 days, secondary lining step distance ≤ 110m and pouring time ≤ 85 days.

[0013] Furthermore, the secondary lining main reinforcement is double-legged Φ25mm with a longitudinal spacing of 20cm; the distribution reinforcement is Φ14mm with a circumferential spacing of 25cm; the stirrups are Φ10mm with a spacing of 20cm×25cm; after the initial setting of the arch crown, RPC mold grouting is carried out using slightly expansive cement mortar.

[0014] Furthermore, the Φ146mm micropiles are positioned by pre-buried Φ180mm PVC pipes; the steel bar bundle consists of 4 Φ25mm steel bars, each 20m long, and mechanically connected in vertical segments; the spacing is 1.2m×1.8m in a plum blossom shape, and a Φ42mm steel pipe is used as a fixing ring every 1m; the top is located 5.5cm below the inverted arch filling surface, and a Φ20mm polyethylene grouting pipe is built in and injected with M35 cement mortar; the longitudinal and transverse steel bars of the raft slab are all Φ20mm threaded steel bars with a spacing of 25cm, and the stirrups are Φ8mm round steel bars with a layer spacing of 28.8cm; the connection with the micropiles is reinforced with a Φ25mm stirrup cage and poured with C35 concrete.

[0015] Furthermore, the components are set up at 5 monitoring points along the second lining of each plate every 12m, and a pressure box and 2 concrete strain gauges are buried at each point; the sensor cables are exposed in a 50cm×50cm fixed box reserved within 1m above the side ditch cover.

[0016] The beneficial effects of the present invention are as follows: the semi-section curtain grouting technology is used to consolidate the loose surrounding rock into a stress-bearing whole, thereby effectively suppressing water burst and collapse and the expansion of the loose circle; the double-row small guide tubes and double-layer HW200 steel frames are combined with large-diameter locking anchor pipes to significantly improve the multi-dimensional bearing capacity of the initial support to resist high-ground stress deformation and prevent structural intrusion; the micro-pile-raft combined structure and the secondary lining reinforcement design are used to block the energy transfer path of the inverted arch and reduce the risk of lining cracking; the two-step mechanized excavation and time-space dual-control safety step distance management are used to take into account both construction safety and excavation efficiency, thereby achieving the beneficial effects of solving face diseases, controlling structural damage, improving project quality and effectively shortening the construction period. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 This is a schematic diagram of a longitudinal section arrangement of curtain drilling for a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 2 This is a front view diagram of the curtain drilling arrangement of a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the front arrangement of a grouting wall in a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the side arrangement of a grouting wall in a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 5 Schematic diagram of the longitudinal section layout of a tunnel according to a construction method for preventing collapse and controlling damage in a large deformation tunnel passing through a contact bearing zone according to an embodiment of the present invention; Figure 6 Schematic diagram of tunnel cross-section layout according to a construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact bearing zone according to an embodiment of the present invention; Figure 72. A schematic diagram of the front arrangement of micropiles according to a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 8 Schematic diagram of the micro-pile layout in a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 9 Schematic diagram of a micropile reinforcement cage structure according to a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 10 3. A schematic diagram of raft reinforcement arrangement for a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 11 This is a schematic diagram of the front arrangement of components monitoring for a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure 12 This is a schematic diagram of the component monitoring cross-section arrangement of a construction method for preventing collapse and controlling damage in a large deformation tunnel crossing a contact bearing zone according to an embodiment of the present invention; Figure: 1. Upper step; 2. Stop wall; 3. Primary support; 4. Lower step; 5. Curtain drilling; 6. Curtain grouting; 7. Double row of φ42mm advanced small guide tubes; 8. HW200 steel frame; 9. Temporary invert; 10. φ89mm large diameter locking foot anchor pipe; 11. φ32mm self-propelled anchor rod; 12. φ76mm orifice pipe; 13. Invert; 14. Secondary lining; 15. φ146 mm micro pile; 16. raft; 17. components; 18. working platform; 19. center line of section; 20. φ25mm anchor steel bar; 21. φ42mm steel pipe; 22. construction trestle; 23. φ25mm main reinforcement; 24. ditch side wall; 25. reserved box; 26. measuring point one; 27. measuring point two; 28. measuring point three; 29. ​​measuring point four; 30. measuring point five; 31. surrounding rock. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0020] It should be understood that in the description of the embodiments of the present invention, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the embodiments of the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the embodiments of the present invention, the meaning of "several" is two or more, unless otherwise clearly and specifically defined.

[0021] like Figure 1-12 As shown, according to an embodiment of the present invention, a construction method for preventing landslide and controlling damage in a large deformation tunnel crossing a contact pressure zone includes the following key control technical measures: half-section curtain high-pressure grouting, two-step plus temporary invert mechanical excavation, double-row advance small guide tubes, increased initial support strength, dual-control safety step distance, tunnel bottom micro-reinforcement piles, filling layer raft slabs, secondary lining structure reinforcement, and component stress monitoring.

[0022] In order to facilitate understanding of the above technical solutions of the present invention, the above technical solutions of the present invention are described in detail below through specific steps.

[0023] In specific use, according to the construction method of the present invention for preventing collapse and controlling damage of a large deformation tunnel crossing a contact bearing zone, the specific construction process is as follows: Step 1: Build the mortar stop wall 2 close to the step 1 on the face of the tunnel. Use a combination of steel and wooden formwork for support. Set restraining reinforcement inside and outside. Use a ground pump to pump C25 concrete in three times. The pouring order is: foundation - wall body - wall body to the top. The top thickness of the mortar stop wall 2 is 2m, the bottom thickness is 3m, and the chest slope is 1:0.2. According to the designed curtain drilling holes, 5 holes are pre-embedded with φ108mm orifice pipes in advance. Wrap the pipe mouth with geotextile and tie it with wire for a meter to prevent concrete from pouring in. A row of φ25mm steel bars is anchored to the initial support 3, with a single length of 1m, a length of 0.5m for the embedded steel bar, a depth of 0.5m in the grouting wall 2, and a circumferential spacing of 1m; the bottom is reinforced with grouting at the interface with the lower step 4 using 4 rows of φ42mm steel pipes, with a length of 3.5m and a spacing of 2m horizontally and 1m vertically. The two rows of steel flower pipes in the middle extend 50cm into the grouting wall 2 to ensure that the curtain grouting 6 can resist the grouting pressure and prevent the grouting wall 2 from being squeezed back.

[0024] Step 2: The down-the-hole drill rig carries out curtain drilling 5 construction. The area is 8m outside the arch wall excavation outline. Each cycle of curtain drilling 5 is carried out for a total of 8 rings, which are a combination of long and short and arranged in an umbrella-shaped radial shape. The drilling order is first the outer ring and then the inner ring. The holes in the same ring are constructed at intervals, and the interval distance shall not be less than 5 hole spacings. The opening diameter of the curtain drilling 5 is φ127mm, and a 1m long φ108mm orifice pipe is buried at the port. The effective diffusion radius of a single hole is considered to be 2m. In view of the cross-sectional height of the upper step 1, slag is required to be used for platform filling during the construction process. The vertical distance between the bottom row of curtain drilling holes 5 and the lower step 4 is 0.6m. The horizontal projection length of the first ring is 8m, the horizontal projection length of the second ring is 12.5m, the horizontal projection length of the third ring is 18m, and the horizontal projection length of the fourth to eighth rings is 25m. During drilling, the falling, collapse, blockage, drilling speed, etc. are checked. Detailed records are kept, especially accurate records of the water output; the curtain grouting 6 single-cycle longitudinal grouting section is 25m long, with an excavation of 20m, and a 5m overlapping grouting rock plate is reserved. The outer circle hole is very prone to hole formation, drill sticking, and difficulty in pulling out the drill during the early drilling process. 4-6m forward segmented grouting is adopted, and the slurry gradually penetrates and fills from the outside to the inside, and the broken rock mass is consolidated and improved. The middle hole and the inner circle hole adopt the 8m-10m backward sleeve valve pipe grouting process. The grouting material is mainly cement slurry. Cement slurry-water glass double liquid slurry is used in water-rich areas, with a water-cement ratio of 0.7:1 to 1:1. The control method combining quantitative and constant pressure is followed, and the grouting pressure is controlled at 5-8MPa. The grouting end standard is judged according to the combination of single hole and full section to ensure that the rock mass within the reinforcement circle of step 1 on the weak part is effectively consolidated, effectively suppressing the deformation around the hole caused by excavation.

[0025] Step three: implement double rows of φ42mm advance small guide tubes 7 along the upper step 1, and use anchor drills to drill holes. The steel pipe length is 4m, the inner row external insertion angle is 5°~10°, the outer row external insertion angle is 30°~35°, the circumferential arrangement spacing is 40cm, the two rows of cross-circular construction holes are staggered by 20cm, the effective overlap length is not less than 1m, and the drilling is strictly carried out according to the designed hole position angle to prevent cross obstruction. The tail of the double row of φ42mm advance small guide tubes 7 is welded to the flange plate of the HW200 steel frame 8, and a stable shell is further formed by grouting.

[0026] Step 4: The excavation section is divided into two steps. The height of the upper step 1 accounts for 3 / 5, and the length is controlled at 13-15m, providing working space for mechanized supporting construction. A certain slope is reserved for the free surface of the face rock mass, with a slope ratio of 1:0.3-1:0.5, and it is strictly forbidden to hang upside down at the bottom; the height of the lower step 4 accounts for 2 / 5, and the length is controlled at 5-8m, with a staggered distance of 2m on both sides. A climbing ramp is reserved for about 1 / 2 of the width in the middle of the lower step 4. Considering the performance of mechanical vehicles, the slope shall not be greater than 10%. The excavator breaker hammer is used to expand the excavation section layer by layer from top to bottom and in a circular order, and finally the contour line is trimmed. During the crushing process, at least one stream of water is guaranteed to cover the crushing hammer head. During the slag discharge process, water is manually sprinkled on the rock slag, and people are sent to sprinkle water to moisten the road surface to prevent dry dust.

[0027] Step 5: The arch frame installation machine installs the double-layer HW200 steel frame 8. The installation distance of the second layer lags behind the first layer by about 3 to 5 meters. The joints of each layer are staggered by more than 50 cm to facilitate the smooth connection of the joint position to ensure verticality. At the same time, the installation positions of the first layer HW200 steel frame 8 and the second layer HW200 steel frame 8 should be back-to-back and overlapped, which significantly improves the strength against deformation. It is strictly forbidden to set joints at the top of the arch. The temporary inverted arch 9 lags behind the second layer HW200 steel frame 8 by about 2 meters. I18 I-beam is used with a center rise of 1.5 meters. The arch foot is sprayed with concrete and chiseled out to separate it from the HW200. The steel frame 8 is welded firmly and sealed with C30 shotcrete. The middle arc section is backfilled with slag to ensure normal passage of engineering vehicles. A three-arm rock drilling rig is used to install φ89mm large-diameter locking foot anchor pipes 10 at the arch foot of the HW200 steel frame 8. Two are set on each side of each HW200 steel frame 8 on each floor. The length of each pipe is 6m. The installation angle is 20°~40° horizontally and downwardly. The installation height is 10cm from the arch foot joint. L-shaped short steel bars are used to weld the HW200 steel frame 8 to prevent the arch foot from sinking and sudden convergence displacement after the temporary inverted arch 9 is removed during the construction of the lower step 4.

[0028] Step 6: Use a three-arm drilling rig to implement φ32mm self-propelled anchor rods 11 in the arch wall range, with an arch length of 6m, a side wall length of 10m, a spacing of 0.8m circumferentially and 1.2m longitudinally. Ordinary cement single-liquid slurry is mainly used. When groundwater is developed, cement-water glass double-liquid slurry is used with a water-cement ratio of 0.8:1 to 1:1 and a grouting pressure of 1.0MPa to 1.5MPa. Put the arch pad on the exposed part of the anchor rod, install the nut and tighten it with a wrench after it is in close contact with the surface of the primary support spray anchor, and then tighten the four sides of the tunnel. The surrounding rock is squeezed and bonded to reinforce it, forming a bearing ring with high rock strength; φ76mm orifice pipes 12, 1m long, are drilled within 20cm on both sides of each HW200 steel frame 8, with a circumferential spacing of 1.5m. Anchoring agents are used to seal the gap between the orifice pipes and the sprayed concrete to prevent leakage during the grouting process. The grouting material is pure cement slurry, with a grouting pressure of 2.0MPa to 3.0MPa. Compensatory grouting is performed on the blind area of ​​the sprayed concrete behind the flange plate of the HW200 steel frame 8.

[0029] Step seven: Double control the safe step distances of the initial support 3, invert arch 13, and secondary lining 14 in terms of time and span. The safe step distance of the initial support 3 is controlled at 25m, and the closure time is no more than 25 days; the safe step distance of the invert arch 13 is controlled at 70m, and the pouring time is no more than 60 days; the safe step distance of the secondary lining 14 is controlled at 110m, and the pouring time is no more than 85 days. The deformation development potential is controlled, the ability to resist potential risks is strengthened, and the excavation of the face is suspended if necessary.

[0030] Step 8: Initial support 3 tunnel bottom is reinforced with 15 φ146mm micro piles by grouting. A down-the-hole drill is used to drill holes quickly. When pouring the filling layer of the inverted arch 13, a φ180mm PVC pipe is embedded for positioning to avoid damage to the primary support steel frame and lining steel bars during drilling. The steel bar bundle consists of 4 φ25mm steel bars, each 20m long. The vertical steel bars are mechanically connected in 9m sections. The percentage of joint area in the same connection section should not be greater than 50%. The spacing is 1.2m×1.8m (circular×longitudinal), and the arrangement is in a plum blossom shape. A 5cm long φ42mm steel pipe is used as a fixed ring connection every 1m. The top of the steel bar bundle is located 5.5cm below the filling surface of the inverted arch 13. During installation, a φ20mm polyethylene grouting pipe is installed inside, and a circular concrete positioning block is set. The grouting material is M35 cement mortar.

[0031] Step 9: A raft slab 16 reinforcement layer is set within 40 cm of the leveling layer of the inverted arch 13. The longitudinal reinforcement is φ20 mm threaded steel with a spacing of 25 cm. The transverse reinforcement is φ20 mm threaded steel with a spacing of 25 cm. The stirrups are φ8 mm round steel with a layer spacing of 28.8 cm. The thickness of the steel bar protective layer is not less than 35 mm. The exposed steel bar bundle at the top of the φ146 mm micropile 15 is reinforced with a φ25 mm stirrup cage. C35 concrete is poured. A small vibrator is used to fully vibrate and compact the densely reinforced area to prevent the inverted arch 13 from rising due to the action of groundwater and deformation accumulation energy.

[0032] Step 10: Strengthen the strength of the secondary lining 14 structure. The inner and outer layers of the designed main reinforcement φ25mm are adjusted to double-legged φ25mm to ensure the width and depth of welding, the longitudinal spacing is 20cm, the distribution reinforcement φ14mm is circumferentially spaced 25cm, the stirrup φ10mm is spaced 20cm*25cm, the thickness of the steel bar protective layer is not less than 55mm, and the number of protective layer pads is not less than 4 per 1m2. The lining concrete grade is adjusted from C35 to C40 for pouring to enhance the overall stress of the secondary lining. After the initial setting of the arch concrete, RPC formwork grouting is started, using slightly expansive cement mortar, and the grouting is completed when the thick slurry flows out of the exhaust hole.

[0033] Step 11: Components 17 are buried before the secondary lining 14 is closed. Five monitoring points are arranged along the middle of the secondary lining 14 for every 12m of the plate. A pressure box is buried at each point, buried in the contact base between the secondary lining 14 and the initial support 3. Two concrete strain gauges are buried between the inner and outer layers of the secondary lining 14. A 50cm*50cm fixed box is reserved for the sensor cable to be exposed within 1m of the upper and lower reaches of the side trench cover. The monitoring frequency is once a day within 0-15 days, twice a week within 16-30 days, and once a month after 1 month, to monitor the structural health status in real time.

[0034] In summary, with the help of the above-mentioned technical scheme of the present invention, the semi-section curtain grouting technology is used to consolidate the loose surrounding rock into a stress-bearing whole, thereby effectively suppressing water burst and collapse and the expansion of the loose circle; the double-row small guide tubes and double-layer HW200 steel frames are combined with large-diameter locking anchor pipes to significantly improve the multi-dimensional bearing capacity of the initial support to resist high-ground stress deformation and prevent structural intrusion; the micro-pile-raft combined structure and the secondary lining reinforcement design are used to block the energy transfer path of the uplift of the inverted arch and reduce the risk of lining cracking; the two-step mechanized excavation and time-space dual-control safety step distance management are used to take into account both construction safety and excavation efficiency, thereby achieving the beneficial effects of solving face diseases, controlling structural damage, improving project quality and effectively shortening the construction period.

[0035] 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 in the scope of protection of the present invention.

Claims

1. A construction method for preventing collapse and controlling damage in a large deformation tunnel passing through a contact pressure zone, characterized in that: The following steps are involved: S1. Build a grouting wall (2) close to the step (1) on the face of the tunnel, using a combination of steel and wooden formwork for support, pouring concrete in three steps, pre-embed the opening pipe of the curtain drilling (5) and seal the pipe opening; apply two rows of anchor steel bars around the perimeter and fix them to the initial support (3), and use four rows of steel pipes at the bottom to reinforce the interface with the lower step (4) by grouting to resist the pressure of the curtain grouting (6); S2. Use a down-the-hole drill to construct curtain holes (5) within 8m outside the arch wall excavation contour line, with a total of eight rings of long and short holes arranged in an umbrella-shaped radial pattern, drilling in the order of outer ring first and inner ring later; perform curtain grouting (6) on a 25m longitudinal section, reserve a 5m stop rock plate after 20m of excavation, and use forward segmented grouting and backward cluster sleeve valve pipe grouting for reinforcement; S3. Implement a double row of Φ42mm leading small ducts (7) along the upper step (1), with an effective overlap length ≥1m, the tail end is welded to the HW200 steel frame (8), and grouting is performed to form a stable shell; S4. Divide the section into an upper step (1) and a lower step (4) for excavation; the upper step (1) accounts for 3 / 5 of the height and is 13m to 15m long, while the lower step (4) accounts for 2 / 5 of the height and is 5m to 8m long, with a 2m offset on both sides; use an excavator hammer to expand the excavation in a circular manner from top to bottom and trim the contour line; S5 installation of double-layer HW200 steel frame (8), the second layer lags behind the first layer 3m to 5m; temporary arch (9) and welded with HW200 steel frame (8), sprayed C30 concrete closed; Φ89mm lock foot anchor pipe (10) is set at the arch foot to prevent displacement of the arch foot; S6. Use Φ32mm self-propelled anchor rods (11) to reinforce the surrounding rock of the arch wall to form a bearing ring, and use Φ76mm orifice tubes (12) to compensate for the blind area behind the flange plate of the HW200 steel frame (8); S7. Dual control of time and span for the safety step distance of the initial support (3), the invert (13) and the secondary lining (14); S8. Add Φ146mm micro piles (15) for grouting reinforcement at the bottom of the initial support (3), set a raft (16) within 40cm of the leveling layer of the inverted arch (13), and connect it with the exposed steel bar of the micro pile (15); S9. Strengthen the structural strength of the secondary lining (14), adjust the main reinforcement to double-leg reinforcement, increase the concrete grade to C40, and embed components (17) to monitor the stress in real time.

2. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact pressure zone according to claim 1 is characterized in that: The mortar stop wall (2) has a top thickness of 2m and a bottom thickness of 3m, a chest slope of 1:0.2, and is cast with C25 concrete; the pre-buried orifice pipe is wrapped and tied with geotextile, and the anchor steel bar is Φ25mm, 1m long, and buried 0.5m deep; the four rows of Φ42mm steel pipes at the bottom are 3.5m long and arranged at a spacing of 2m×1m, and the two rows of steel flower pipes in the middle extend 50cm into the mortar stop wall (2).

3. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact bearing zone according to claim 1 is characterized in that: The curtain drilling (5) has an opening diameter of Φ127mm, and a 1m long Φ108mm orifice pipe is buried at the end; the vertical distance between the bottom row of drilling holes and the lower step (4) is 0.6m; the forward segmented grouting in the curtain grouting (6) is 4m to 6m long, the backward sleeve valve pipe grouting section is 8m to 10m long, the grouting pressure is 5MPa to 8MPa, and the cement slurry is 0.7:1 to 1:1 in water-cement ratio.

4. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact bearing zone according to claim 1 is characterized in that: The double-row Φ42mm leading small conduits (7) are 4m long, with an inner row external insertion angle of 5° to 10° and an outer row external insertion angle of 30° to 35°, a circumferential spacing of 40cm, and two rows of holes staggered and an overlap length of ≥1m.

5. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact pressure zone according to claim 1 is characterized in that: The HW200 steel frame (8) unit joints are staggered by more than 50 cm, and joints are prohibited on the main arch top; the temporary inverted arch (9) uses I18 I-beams with a center rise of 1.5 m; Φ89 mm locking foot anchor pipes (10) are set on each side of each steel frame, two each, 6 m long, with an angle of 20° to 40° horizontally and downwardly, 10 cm away from the arch foot joint, and welded to the steel frame through L-shaped steel bars.

6. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact bearing zone according to claim 1 is characterized in that: The Φ32mm self-propelled anchor rod (11) has an arch length of 6m and a side wall length of 10m, with a spacing of 0.8m×1.2m; the grouting pressure is 1.0MPa to 1.5MPa, and a slurry with a water-cement ratio of 0.8:1 to 1:1 is used; the Φ76mm orifice pipe (12) is 1m long and is arranged along the 20cm range on both sides of each steel frame with a circumferential spacing of 1.5m. The gap is sealed with an anchoring agent before grouting.

7. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact bearing zone according to claim 1 is characterized in that: The dual control of safety step distance satisfies: the initial support (3) step distance ≤ 25m and the closure time ≤ 25 days, the invert (13) step distance ≤ 70m and the pouring time ≤ 60 days, and the secondary lining (14) step distance ≤ 110m and the pouring time ≤ 85 days.

8. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact pressure zone according to claim 1 is characterized in that: The main reinforcement of the second lining (14) is double-legged Φ25mm, with a longitudinal spacing of 20cm; the distribution reinforcement is Φ14mm, with a circumferential spacing of 25cm; the stirrups are Φ10mm, with a spacing of 20cm×25cm; after the initial setting of the vault, RPC mold grouting is carried out, using slightly expansive cement mortar.

9. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact bearing zone according to claim 1, characterized in that: The Φ146mm micro pile (15) is positioned by pre-buried Φ180mm PVC pipe; the steel bar bundle consists of 4 Φ25mm steel bars, each 20m long, and vertically segmented mechanically connected; the spacing is 1.2m×1.8m in a plum blossom shape, and a Φ42mm steel pipe is used as a fixing ring every 1m; the top is located 5.5cm below the inverted arch filling surface, and a Φ20mm polyethylene grouting pipe is built in and injected with M35 cement mortar; the longitudinal and transverse steel bars of the raft (16) are Φ20mm threaded steel bars with a spacing of 25cm, and the stirrups are Φ8mm round steel bars with a layer spacing of 28.8cm; the connection with the micro pile (15) is reinforced with a Φ25mm stirrup cage and poured with C35 concrete.

10. The construction method for preventing collapse and controlling damage of a large deformation tunnel passing through a contact bearing zone according to claim 1 is characterized in that: The components (17) are arranged at 5 monitoring points along the second lining (14) of each plate every 12m, with a pressure box and 2 concrete strain gauges buried at each point; the sensor cables are exposed in a 50cm×50cm fixed box reserved within 1m above the side ditch cover.

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