Synergistic reinforcement method for shallow-buried unsymmetrical-pressure small-clear-distance tunnel deformation section

Abstract

The invention relates to the technical field of tunnels, and provides a collaborative reinforcement method for a shallow-buried unsymmetrical-pressure small-clear-distance tunnel deformation section, which comprises the following steps of: performing radial grouting reinforcement within the range of the tunnel deformation section to form a radial grouting body in a hole, constructing a grouting support pile, constructing an in-hole backfilling platform body in the hole, and constructing an earth surface collaborative reinforcement structure. And after the three-dimensional integral reinforcing structure is formed, layered excavation is conducted on the in-hole backfilling platform body, an original primary support is dismantled, a new steel arch frame is erected, concrete is sprayed to form a new primary support, a secondary lining is constructed, and reinforcing treatment is conducted on arch annular main ribs of the secondary lining. A three-dimensional overall stress system is formed through cooperative reinforcement inside and outside the hole, the bias load is balanced from the source, construction and operation safety is ensured, and remarkable engineering value is achieved.

Description

Technical Field

[0001] This invention relates to the field of tunnel technology, and in particular to a collaborative reinforcement method for the deformation section of a shallow-buried tunnel with bias pressure and small clearance. Background Technology

[0002] Due to limitations imposed by topographical and geological conditions, as well as the influence of surrounding buildings and the overall alignment, tunnels with small clearances are becoming increasingly common. In mountainous tunnel construction, it is also frequently encountered that the tunnel traverses shallowly buried, biased, and weak surrounding rock sections. Because of the extremely shallow overburden, weak surrounding rock, topographical bias, and the small clearance between the left and right tunnels, the stress redistribution in the surrounding rock after excavation is severe under these complex geological conditions, easily leading to large deformations. The initial support system, which is the core of tunnel stability, especially the steel arches bearing the main structural loads, faces severe challenges. Deformation of the initial support not only reduces the bearing capacity of the support structure itself, but in severe cases, can lead to support encroachment, and even trigger local collapses, roof falls, and other serious safety accidents, seriously threatening the safety of construction personnel and equipment, and significantly delaying the construction period and increasing project costs. Furthermore, if the shallow-buried biased pressure condition of the tunnel is not effectively mitigated, even if construction is safe during the tunnel construction phase, long-term biased loads during tunnel operation can cause lining cracking, deformation, or even damage, resulting in huge costs. This situation frequently occurs during operation.

[0003] For shallow-buried tunnels with eccentric pressure and small clearance, traditional single-method internal reinforcement methods (such as strengthening lining support parameters, grouting reinforcement of surrounding rock, and using sidewall pilot tunnels for temporary support) cannot completely solve the problem of initial support deformation, cannot alleviate the eccentric load at its source, and are difficult to form a permanently effective overall load-bearing system. Therefore, how to promptly and effectively address the deformation problem of the initial support arch in extremely shallow-buried tunnels with eccentric pressure and small clearance, prevent further deterioration of deformation, restore and enhance the stability of the support structure, and ensure the safe and smooth progress of subsequent construction and safe operation of the tunnel has become a key technical problem that urgently needs to be solved in the tunnel engineering field.

[0004] In view of this, it is necessary to propose a collaborative reinforcement method for the deformation section of shallow-buried tunnels with bias pressure and small clearance to solve or at least alleviate the above-mentioned defects. Summary of the Invention

[0005] The main objective of this invention is to provide a collaborative reinforcement method for the deformation section of shallow-buried tunnels with small clearance under bias pressure, in order to solve the problems that the traditional single tunnel reinforcement method in the prior art cannot completely solve the initial support deformation problem, cannot fundamentally alleviate the bias load, and is difficult to form a permanent and effective overall stress system.

[0006] To achieve the above objectives, the present invention provides a method for the coordinated reinforcement of the deformation section of a shallow-buried tunnel with biased pressure and small clearance, comprising the following steps: S1. Within the deformation section of the tunnel, the surrounding rock of the deformation section is first reinforced by radial grouting to form a radial grouting body inside the tunnel, and grouting support piles are installed at the arch foot positions of the side walls on both sides of the tunnel. After the reinforcement is completed, the soil and rock are backfilled in layers inside the deformation section of the tunnel and compacted to form a backfill platform inside the tunnel. S2, Construct a surface-coordinated reinforcement structure; wherein, the surface-coordinated reinforcement structure includes a grouting reinforcement zone formed by surface grouting in the interstitial rock column area between the left and right tunnels, a lateral retaining structure constructed on the tunnel's biased low-mountain side, and a surface grouting reinforcement zone formed by grouting in the strata between the lateral retaining structure and the tunnel's outer contour; wherein, the first grouting pipe in the interstitial rock column grouting reinforcement zone overlaps with the radial grouting body inside the tunnel and the grouting support pile, and the second grouting pipe in the surface grouting reinforcement zone overlaps with the radial grouting body inside the tunnel and the grouting support pile, to form a three-dimensional integrated reinforcement structure; S3. After the three-dimensional overall reinforcement structure is formed, the backfill platform inside the tunnel is excavated in layers using the step method. As the excavation progresses, the original initial support is removed section by section and a new steel arch frame is erected. Shotcrete is then used to form a new initial support. When erecting the new steel arch frame, the steel arch frame of each step is connected as a whole by longitudinal channel steel, and a locking anchor pipe with an internal steel reinforcement cage is installed at the arch foot of each step. S4. Construct a secondary lining and reinforce the circumferential main reinforcement of the arch section of the secondary lining.

[0007] Preferably, step S1 includes the following steps: S11, within the tunnel deformation section, radial grouting is performed on the surrounding rock of the tunnel deformation section using boreholes with a diameter of 10-30mm to form the radial grouting body inside the tunnel. At the same time, drainage pipes are installed at intervals in the circumferential and longitudinal directions of the tunnel to drain the fissure water in the surrounding rock to the existing drainage system of the tunnel. The depth of the radial grouting reinforcement ensures that the radial grouting body inside the tunnel overlaps with the first and second grouting pipes constructed subsequently by at least 1 meter. S12, grouting support piles are installed at the arch foot positions of the two sidewalls of the tunnel; wherein, a first-specification grouting support pile is installed at the arch foot on the side of the tunnel biased towards the high mountain, and a second-specification grouting support pile is installed at the arch foot on the side of the tunnel biased towards the low mountain; the bearing capacity design value of the second-specification grouting support pile is greater than the bearing capacity design value of the first-specification grouting support pile; wherein, the length of the grouting support pile is ensured to form an overlap of not less than 1 meter with the subsequently installed first and second grouting pipes; S13, inside the tunnel deformation section, tunnel excavation waste is used for layered backfilling and compaction to form an in-tunnel backfill platform, and slope protection roads extending longitudinally along the tunnel are constructed at both ends of the in-tunnel backfill platform.

[0008] Preferably, step S2 includes the following steps: S21, the first grouting pipe is laid in the rock column area between the left and right tunnels and surface grouting is carried out to form a grouting reinforcement zone for the rock column; wherein, the first grouting pipe is connected to the radial grouting body in the tunnel and the grouting support pile, and the overlap length is not less than 1 meter. S22, Obtain the soil cover thickness measurement data outside the tunnel, and construct a pile-slab wall or a counterweight retaining wall as a lateral retaining structure on the biased side of the tunnel based on the soil cover thickness measurement data. S23, before constructing the lateral retaining structure, grouting reinforcement is carried out in the stratum between the lateral retaining structure and the outer contour of the tunnel to form the surface grouting reinforcement zone; wherein, the second grouting pipe is connected to the radial grouting body inside the tunnel and the grouting support pile, and the overlap length is not less than 1 meter. S24, after the lateral retaining structure is constructed, cement-stabilized soil is backfilled and compacted using the lateral retaining structure to form a counter-pressure backfill body; wherein, the counter-pressure backfill body transfers the load to the grouting reinforcement zone of the interlocking rock column through the lateral retaining structure and the surface grouting reinforcement zone, together forming the three-dimensional integral reinforcement structure.

[0009] Preferably, step S3 includes the following steps: S31, apply advanced support to the excavation area; S32, the backfill platform inside the tunnel is excavated in layers and steps in the order of upper step, middle step and lower step, and the initial support is replaced step by step; wherein, the excavation of each step follows the process of first excavating the corresponding backfill platform inside the tunnel, then removing the original initial support, then erecting a new steel arch frame, and finally spraying concrete, and the core soil is reserved when the upper step is excavated. S33, when erecting a new steel arch frame at each step, longitudinal channel steel is used to connect all adjacent new steel arch frames in this step into a continuous whole along the longitudinal direction of the tunnel. S34, at the arch foot position of each step, a locking anchor pipe with a built-in steel cage is constructed, and the end of the locking anchor pipe is fixedly connected to the new steel arch frame of the step.

[0010] Preferably, the reinforcement treatment of the arch circumferential main reinforcement of the secondary lining in step S4 includes the steps of: increasing the diameter of the existing arch circumferential main reinforcement and adding a new circumferential main reinforcement between two adjacent existing arch circumferential main reinforcements.

[0011] Preferably, step S21 includes the following steps: Multiple rows of first grouting pipes are laid out and grouting is carried out in the rock column area between the left and right tunnels to form the grouting reinforcement zone of the rock column. The overlap length between the first grouting pipe and the radial grouting body in the tunnel and the grouting support pile is not less than 1 meter. After grouting is completed, a layer of reinforced concrete cover plate is poured on the surface of the middle rock column area; wherein, the top of the first grouting pipe is anchored in the reinforced concrete cover plate, and the coverage of the reinforced concrete cover plate extends beyond the outermost first grouting pipe.

[0012] Preferably, step S22 includes the following steps: When the measured soil cover thickness is less than 10 meters, a pile-slab wall is constructed as the lateral retaining structure; when the measured soil cover thickness is between 10 and 16 meters, a counterweight retaining wall is constructed as the lateral retaining structure.

[0013] Preferably, step S23 includes the following steps: Multiple rows of second grouting pipes are laid in the stratum between the lateral retaining structure and the outer contour of the tunnel. The horizontal distance between the row of second grouting pipes closest to the outer contour of the tunnel and the outer contour of the tunnel is not less than 2 meters. Grouting is performed on the second grouting pipes to form the surface grouting reinforcement zone. The overlap length between the second grouting pipe and the radial grouting body inside the tunnel and the grouting support pile is not less than 1 meter.

[0014] Preferably, step 24 includes the step of: backfilling and compacting cement-stabilized soil with a cement content of 8% in layers using the lateral retaining structure to form the counter-pressure backfill body.

[0015] Preferably, the height of the upper step, middle step, and lower step is 3 to 3.5 meters.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention, through a process design that combines in-tunnel backfilling and surface reinforcement, creates an absolutely safe working environment for tunnel initial support replacement without requiring the erection of traditional high-risk temporary arch supports. By replacing temporary arch supports with layered compacted backfill within the tunnel, this invention eliminates the secondary disturbance risks associated with erecting and dismantling heavy structures within deformable structures, and transforms high-risk in-tunnel operations into controllable, standardized construction within a surface protection system. This fundamentally solves the problems of high risk, low efficiency, and high cost associated with traditional methods.

[0017] This invention utilizes the overlapping arrangement of the first and second grouting pipes in the surface collaborative reinforcement structure with the radial grouting body and grouting support piles inside the tunnel. The first grouting pipe, lateral retaining structure, second grouting pipe, backfill material, radial grouting body, and grouting support piles work together to reinforce the tunnel, fundamentally alleviating the unfavorable shallow-buried bias pressure condition. Simultaneously, a supportive three-dimensional integral reinforcement structure is formed around the tunnel, resisting external bias pressure and shallow-buried loads, facilitating subsequent excavation of the backfill section inside the tunnel. This three-dimensional integral reinforcement structure ensures continuous load transfer, allowing the surface back pressure load to be transferred through the lateral retaining structure and grouting area to the grouting support piles inside the tunnel. This proactively balances the bias load from the source, transforming passive resistance into active balancing, significantly improving the overall stiffness of the tunnel surrounding rock and effectively controlling uneven settlement and deformation.

[0018] This invention alleviates the adverse conditions of shallow-buried bias pressure in tunnels by using a method of backfilling and building platforms inside the tunnel in conjunction with surface reinforcement. At the same time, it forms a supportive three-dimensional integral reinforcement structure around the tunnel that can resist the influence of external bias pressure and shallow-buried loads. This ensures the construction and operation safety of the treatment of the weak surrounding rock deformation section of the shallow-buried bias pressure tunnel with small clearance. It has significant practical significance and engineering value for ensuring the safety and efficiency of tunnel construction under complex geological conditions. Attached Figure Description

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

[0020] Figure 1 This is a flowchart illustrating the collaborative reinforcement method in one embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the tunnel-inside-outside coordinated reinforcement and protection system in one embodiment of the present invention; Figure 3 This is a schematic diagram of the radial grouting and drainage pipe arrangement in one embodiment of the present invention; Figure 4 This is a schematic diagram of tunnel arch foot reinforcement in one embodiment of the present invention; Figure 5 This is a schematic longitudinal section of the backfill platform in a tunnel according to one embodiment of the present invention; Figure 6 This is a schematic cross-sectional view of the backfill platform in the tunnel according to one embodiment of the present invention; Figure 7 This is a schematic diagram of the reinforcement of the interbedded rock area in a tunnel according to an embodiment of the present invention; Figure 8This is a schematic cross-sectional view of a pile-slab wall + counter-pressure backfill in one embodiment of the present invention; Figure 9 This is a schematic longitudinal section of a surface pile-slab wall with counter-pressure backfill in one embodiment of the present invention. Figure 10 This is a schematic cross-sectional view of a counterweight retaining wall with counter-pressure backfill in one embodiment of the present invention. Figure 11 This is a schematic diagram of the installation of the locking anchor tube in one embodiment of the present invention; Figure 12 This is a schematic diagram of the installation of the longitudinal channel steel and side plate at the bottom of the steel arch frame in one embodiment of the present invention; Figure 13 This is a schematic cross-sectional view of the secondary lining crack-resistant reinforcement in one embodiment of the present invention. Figure 14 for Figure 13 A cross-sectional view along the AA direction.

[0021] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings.

[0022] Explanation of icon numbers: 10. Grouting support piles; 20. Drainage pipes; 21. Radial grouting pipes; 30. Backfill platform inside the tunnel; 31. Slope protection road; 40. Lateral retaining structure; 41. Pile-slab wall; 42. Counterweight retaining wall; 50. First grouting pipe; 51. Reinforced concrete cover plate; 60. Second grouting pipe; 61. Counter-pressure backfill; 70. Steel arch frame; 71. Longitudinal channel steel; 72. Circumferential main reinforcement of the arch; 721. Existing circumferential main reinforcement of the arch; 722. New circumferential main reinforcement; 73. Invert arch; 74. Side plate; 80. Tunnel; 81. Upper step; 82. Middle step; 83. Lower step; 84. Secondary lining; 85. Anchor pipe. Detailed Implementation

[0023] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] In this invention, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0026] Please see the appendix Figures 1 to 14 The present invention provides a method for the coordinated reinforcement of a shallow-buried tunnel deformation section with small clearance under bias pressure, comprising the following steps: S1. Within the deformation section of tunnel 80, the surrounding rock of the deformation section of tunnel 80 is first reinforced by radial grouting to form a radial grouting body inside the tunnel, and grouting support piles 10 are installed at the arch foot positions of the side walls of tunnel 80. After the reinforcement is completed, soil and rock are backfilled in layers inside the deformation section of tunnel 80 and compacted to form a backfill platform 30 inside the tunnel. S2, Construct a surface-coordinated reinforcement structure (not shown in the figure); wherein, the surface-coordinated reinforcement structure includes a grouting reinforcement zone formed by surface grouting in the interstitial rock column area between the left and right tunnels of Tunnel 80, a lateral retaining structure 40 constructed on the low mountain side of the tunnel biased, and a surface grouting reinforcement area formed by grouting in the strata between the lateral retaining structure 40 and the outer contour of Tunnel 80; wherein, the first grouting pipe 50 in the interstitial rock column grouting reinforcement zone overlaps with the radial grouting body inside the tunnel and the grouting support pile 10, and the second grouting pipe 60 in the surface grouting reinforcement area overlaps with the radial grouting body inside the tunnel and the grouting support pile 10 to form a three-dimensional integrated reinforcement structure; S3, after the three-dimensional overall reinforcement structure is formed, the backfill platform 30 inside the tunnel is excavated in layers using the step method. As the excavation progresses, the original initial support is removed section by section and a new steel arch frame 70 is erected. Shotcrete is sprayed to form a new initial support. When erecting the new steel arch frame 70, the steel arch frame 70 of each step is connected into a whole by longitudinal channel steel 71, and a locking anchor pipe 85 with built-in steel reinforcement cage is installed at the arch foot of each step. S4, construct the secondary lining 84, and reinforce the arch circumferential main reinforcement 72 of the secondary lining 84.

[0027] It should be noted that the overlap in this application refers to the grouting diffusion range of the first grouting pipe 50 or the second grouting pipe 60, which has a spatial geometric overlap of not less than 1 meter with the effective reinforcement range of the radial grouting body and grouting support pile 10 already constructed in the tunnel, forming an overall stress system through this spatial geometric overlap.

[0028] This application's solution, through a process design combining in-tunnel backfilling and surface reinforcement, creates an absolutely safe working environment for the initial support replacement of the tunnel (80%) without the need for traditional high-risk temporary arch supports. This invention replaces temporary arch supports with layered compacted backfill within the tunnel, eliminating the secondary disturbance risk of erecting and dismantling heavy structures within deformable structures. It also transforms high-risk in-tunnel operations into controllable, standardized construction within a surface protection system, fundamentally solving the problems of high risk, low efficiency, and high cost associated with traditional methods.

[0029] This invention utilizes the overlapping arrangement of the first grouting pipe 50 and the second grouting pipe 60 in the surface collaborative reinforcement structure with the radial grouting body and grouting support piles 10 inside the tunnel. The first grouting pipe 50, the lateral retaining structure 40, the second grouting pipe 60, the backfill material 61, the radial grouting body inside the tunnel, and the grouting support piles 10 provide collaborative reinforcement, fundamentally alleviating the unfavorable shallow-buried bias pressure condition of tunnel 80. Simultaneously, a supportive three-dimensional integral reinforcement structure is formed around tunnel 80, capable of resisting external bias pressure and shallow-buried loads, facilitating subsequent excavation of the backfill section inside the tunnel. This three-dimensional integral reinforcement structure ensures continuous load transfer, allowing the surface back pressure load to be transferred through the lateral retaining structure 40 and the grouting area to the grouting support piles 10 inside the tunnel. This proactively balances the bias pressure load from the source, transforming passive resistance into active balancing, significantly improving the overall stiffness of the surrounding rock of tunnel 80 and effectively controlling uneven settlement and deformation.

[0030] This invention alleviates the unfavorable shallow-buried bias pressure of Tunnel 80 from the root by using a method of backfilling and building platforms inside the tunnel and coordinating reinforcement with the ground surface. At the same time, it forms a supportive three-dimensional integral reinforcement structure around Tunnel 80 that can resist the influence of external bias pressure and shallow-buried loads. This ensures the construction and operation safety of the treatment of the weak surrounding rock deformation section of Tunnel 80 with shallow-buried bias pressure and small clearance. It has significant practical significance and engineering value for ensuring the safe and efficient construction of Tunnel 80 under complex geological conditions.

[0031] In a preferred embodiment, step S1 includes the following steps: S11, within the deformation section of tunnel 80, radial grouting reinforcement is carried out on the surrounding rock of the deformation section of tunnel 80 using boreholes with a diameter of 10-30mm to form the radial grouting body inside the tunnel. At the same time, drainage pipes 20 are installed at intervals in the circumferential and longitudinal directions of tunnel 80 to drain the fissure water in the surrounding rock to the existing drainage system of tunnel 80 (not shown in the figure). The depth of the radial grouting reinforcement ensures that the radial grouting body inside the tunnel overlaps with the first grouting pipe 50 and the second grouting pipe 60 constructed subsequently by at least 1 meter.

[0032] Compared with traditional grouting processes (which typically use boreholes with a diameter of 50mm or more), the small-diameter boreholes used in this step (i.e., micro-drilling) have the following advantages: Firstly, the reduced borehole diameter significantly reduces secondary disturbance to the already critically stable weak surrounding rock, avoiding the risk of new fissure expansion or local collapse induced by drilling. Secondly, the small-diameter borehole facilitates control of grouting pressure, allowing the grout to penetrate and diffuse evenly in the surrounding rock fissures, forming a dense grouting reinforcement ring. To ensure a reliable connection between the radial grouting body inside the tunnel and the subsequent surface grouting pipes, the depth of the radial grouting reinforcement is designed to ensure that the radial grouting body inside the tunnel overlaps with the first grouting pipe 50 and the second grouting pipe 60, respectively, by no less than 1 meter.

[0033] Meanwhile, drainage pipes 20 are installed at intervals along the circumference and longitudinal direction of Tunnel 80 to divert fissure water in the surrounding rock to the existing drainage system of Tunnel 80. Specifically, 50mm PVC drainage pipes 20 are arranged between grouting holes at circumferential intervals of 3 meters and longitudinal intervals of 4 meters. The pipes are 5 meters long, with perforations and covered with geotextile filter layers. This resolves the contradiction between groundwater in the weak surrounding rock and grouting reinforcement: on the one hand, the drainage pipes 20 divert fissure water in the surrounding rock in a timely manner, preventing water accumulation from softening the grout and surrounding rock, and ensuring the long-term stability of the grouting reinforcement effect; on the other hand, it reduces the pore water pressure in the surrounding rock during construction, effectively controlling the additional settlement caused by the consolidation of the strata due to water loss.

[0034] S12, grouting support piles 10 are installed at the arch foot positions of both sidewalls of tunnel 80; wherein, a first-specification grouting support pile 10 is installed at the arch foot on the side of the tunnel biased towards the high mountain, and a second-specification grouting support pile 10 is installed at the arch foot on the side of the tunnel biased towards the low mountain; the bearing capacity design value of the second-specification grouting support pile 10 is greater than the bearing capacity design value of the first-specification grouting support pile 10; wherein, the length of the grouting support pile 10 is ensured to form an overlap of not less than 1 meter with the subsequently installed first grouting pipe 50 and second grouting pipe 60 respectively. Grouting support piles 10 are installed at the arch abutments of both sidewalls of Tunnel 80. Considering the stress characteristics of the eccentric terrain, this step employs an asymmetrical design: grouting support piles 10 of the first specification are installed at the arch abutment on the eccentric mountain side of Tunnel 80, and grouting support piles 10 of the second specification are installed at the arch abutment on the low mountain side of Tunnel 80. The low mountain side of Tunnel 80 is the eccentric side of Tunnel 80, and the design bearing capacity of the second specification grouting support pile 10 is greater than that of the first specification grouting support pile 10.

[0035] Improving the design bearing capacity can be achieved by using larger diameter pipes, thicker walls, greater rock penetration depth, and stronger internal reinforcing cages. As a preferred example, the tunnel's eccentrically positioned arch foot on the high-mountain side uses two φ76×5mm grouting pipes drilled through φ135mm boreholes, while the arch foot on the low-mountain side uses two φ89×6mm grouting pipes drilled through φ150mm boreholes. The boreholes should avoid the initial support I-beams and transverse drainage pipes. The longitudinal spacing of the grouting pipes is 3m, with a length of 6-9m and a rock penetration depth of no less than 1.5m. The specific length is determined based on the geological conditions exposed during actual drilling. The two grouting pipes on each side are driven in a crisscross pattern, with the inner grouting pipe at a 15° angle to the vertical and the outer grouting pipe at a 45° angle. Reinforcing cages are installed within 10mm of each grouting support pile to enhance its strength and rigidity. Grouting support pile 10 is reinforced by injecting cement mortar into the surrounding rock. Before grouting, a grout stop plate with a thickness of not less than 50cm is constructed using cement mortar. After grouting, a 2cm thick pad is used to fix the grouting pipe to the lining or initial support I-beam. The width of the pad should exceed the borehole by not less than 30cm. At the same time, the bottom of grouting support pile 10 is enlarged and filled to form an end anchor body.

[0036] S13, inside the tunnel of the deformed section of the tunnel 80, the excavated waste from the tunnel 80 is used for layered backfilling and compaction to form a backfill platform 30 inside the tunnel, and slope protection roads 31 extending longitudinally along the tunnel 80 are constructed at both ends of the backfill platform 30 inside the tunnel.

[0037] Backfill material was sourced from excavated waste from Tunnel 80, achieving on-site resource utilization of construction waste and significantly reducing material transportation costs. Backfilling began at invert 73 and continued up to the upper step 81 area. Figure 6 As shown, a stable internal support platform is formed. The backfill height inside the tunnel reaches the upper step 81, and the backfill height is increased as much as possible while ensuring sufficient working space. Backfilling construction strictly adopts a layered backfilling and layer-by-layer compaction process, with the loose thickness of each layer controlled within 50cm. The purpose of layered compaction is twofold: first, to ensure that the backfill itself has sufficient density and bearing capacity to serve as a safe platform for subsequent arch replacement operations; and second, to ensure close contact between the backfill and the surrounding rock and initial support through compaction, providing a certain degree of lateral restraint.

[0038] To facilitate backfilling and subsequent arch replacement construction, slope protection channels 31 are constructed before and after the deformation section, with a length controlled between 15 and 25 meters. Slope protection channels 31 are constructed and compacted in layers using the same material as the backfill body. Their functions are: to ensure the stability of both ends of the backfill platform and prevent end instability and collapse; to provide a safe operating passage for machinery access and material transportation; and to serve as a buffer zone during subsequent excavation and arch replacement, facilitating construction organization and scheduling.

[0039] In a preferred embodiment, step S2 includes the following steps: S21, the first grouting pipe 50 is laid in the rock column area between the left and right tunnels of tunnel 80 and the surface grouting is carried out to form a grouting reinforcement zone for the rock column; wherein, the first grouting pipe 50 is connected to the radial grouting body in the tunnel and the grouting support pile 10, and the overlap length is not less than 1 meter. Traditional reinforcement of rock pillars in narrow-clearance tunnels typically involves extending the system anchor bolts. However, this method has a limited reinforcement range and effect, especially for shallow-buried tunnels with biased pressure and narrow clearance. It may not be able to adapt to large deformations and may lead to premature failure.

[0040] The purpose of this step is to deeply reinforce the weak rock pillar area between the left and right tunnels of Tunnel 80, improve its overall rigidity, reduce the mutual influence between the construction of the left and right tunnels of Tunnel 80, and ensure the stability of the rock pillars sandwiched between the left and right tunnels of Tunnel 80 with small clearance; secondly, through the reasonable layout of the first grouting pipe 50, it forms a spatial overlap with the radial grouting body and grouting support pile 10 already formed in the tunnel, laying the foundation for the subsequent formation of a three-dimensional overall reinforcement structure; thirdly, it can also act as a micro pile, especially for the shallow buried biased pressure tunnel 80, which can effectively resist part of the biased pressure load, improve the biased pressure situation of tunnel 80, and is conducive to the structural stability of tunnel 80.

[0041] As a preferred example, the first grouting pipe 50 in the middle rock column area is a φ108mm steel pipe, arranged in a quincunx pattern, with a longitudinal and transverse spacing of 2 meters. The grouting depth is controlled to be 15 to 18 meters below the ground surface. The grouting depth is determined according to the position of the radial grouting body and grouting support pile 10 in the tunnel to ensure that it forms an effective overlap of not less than 1 meter with the radial grouting body and grouting support pile 10 in the tunnel.

[0042] S22, obtain the soil cover thickness measurement data outside the tunnel 80, and construct a pile-slab wall 41 or a counterweight retaining wall 42 on the bias side of the tunnel 80 as a lateral retaining structure 40 based on the soil cover thickness measurement data. As a preferred example, step S22 includes the following steps: When the measured soil cover thickness is less than 10 meters, a pile-slab wall 41 is constructed as the lateral retaining structure 40; when the measured soil cover thickness is between 10 meters and 16 meters, a counterweight retaining wall 42 is constructed as the lateral retaining structure 40.

[0043] As a preferred example, for the extremely shallow buried section of the external tunnel 80 with a soil cover thickness of less than 10m, a pile-slab wall 41 combined with cement-stabilized soil backfill is used for treatment. To minimize the impact of the pile-slab wall 41 construction on the existing tunnel 80 while ensuring the effectiveness of the backfill, the pile-slab wall 41 is positioned 8–12m away from the outer contour of the tunnel 80. Before constructing the pile-slab wall 41, the stratum between the outer contour of the tunnel 80 and the pile-slab wall 41 is first reinforced with surface grouting. This serves two purposes: firstly, it reinforces the surrounding rock, providing a hardened working platform for the construction of the pile-slab wall 41; secondly, since the construction of the pile-slab wall 41 involves excavating holes before pouring concrete, the reinforcement of the surrounding rock effectively reduces the possibility of hole collapse during excavation, facilitating construction; and thirdly, the grouting pipes can also act as micropiles, to some extent preventing soil slippage. However, the nearest grouting pipe should be at least 2m away from the outer contour of the tunnel 80 to avoid grout diffusion during grouting and damage to the existing tunnel 80 lining structure. The pile-slab wall 41 consists of reinforcing piles and retaining plates. Designed for shallowly buried, weak surrounding rock sections under eccentric pressure, it primarily serves to prevent soil slippage. The reinforcing piles are 2.5×2m in size, spaced 5m apart longitudinally, with consistent pile top elevations for ease of backfilling and aesthetics. The pile bottoms must be embedded at least 3m into strongly weathered rock. Retaining plates are installed inside the reinforcing piles to act as retainers during subsequent cement-stabilized soil backfilling. After the pile-slab wall 41 is completed, backfilling is carried out using 8% cement-stabilized soil, which effectively alleviates the eccentric pressure on tunnel 80 and increases the overburden thickness. Additionally, a 30cm thick crushed stone filter layer is laid behind the pile-slab wall 41. Each retaining plate is equipped with two drainage pipes 20. The ground outside the pile-slab wall 41 is hardened with C20 concrete, with a hardening width of 1m, to facilitate drainage.

[0044] For the shallowly buried, biased-pressure section of tunnel 80 with a soil cover thickness of 10-16m outside the tunnel, a counterweight retaining wall 42 combined with cement-stabilized soil backfill is used for treatment. Since the counterweight retaining wall 42 has a counterweight platform, the backfill compacts and stabilizes the platform. To minimize the impact of the construction of the counterweight retaining wall 42 on the existing tunnel 80 while ensuring the effectiveness of the backfill, the retaining wall is positioned 8-12m away from the outer contour of tunnel 80. Before constructing the pile-slab wall 41, the stratum between the outer contour of tunnel 80 and the counterweight retaining wall 42 undergoes surface grouting reinforcement. This serves two purposes: firstly, it reinforces the surrounding rock, providing a hardened working platform for the retaining wall construction; secondly, the grouting pipes can act as micropiles, partially preventing soil slippage. However, the nearest grouting pipe should be at least 2m away from the outer contour of tunnel 80 to avoid grout diffusion during grouting, which could damage the existing tunnel 80 lining structure. The counterweight retaining wall 42 adopts different heights according to the terrain, while the pile top elevation remains consistent to facilitate backfilling and for aesthetic purposes. To meet the foundation bearing capacity requirements, the bottom of the retaining wall is reinforced with grouting and a stepped enlarged foundation is installed. To further limit slope slippage, the slope above the counterweight backfill 61 is further reinforced with anchor frame beams to reduce slope slippage force and improve slope stability.

[0045] S23, before constructing the lateral retaining structure 40, grouting reinforcement is carried out in the stratum between the lateral retaining structure 40 and the outer contour of the tunnel 80 to form the surface grouting reinforcement zone; wherein, the second grouting pipe 60 is connected to the radial grouting body inside the tunnel and the grouting support pile 10, and the overlap length is not less than 1 meter. As a preferred example, the horizontal distance between the second row of grouting pipes 60 closest to the outer contour of tunnel 80 and the outer contour of tunnel 80 is not less than 2 meters. Since the diffusion radius of grout during grouting is generally 0.8 to 1.2 meters, if the grouting pipe is too close to tunnel 80, the grout may intrude into the drainage system behind the lining of tunnel 80 or exert adverse additional pressure on the existing lining; maintaining a distance of not less than 2 meters ensures that the surface grouting reinforcement zone can be effectively connected with the surrounding rock of tunnel 80, while avoiding direct disturbance to the existing structure during grouting construction.

[0046] Meanwhile, the installation depth of the second grouting pipe 60 must ensure that it overlaps with the radial grouting body and the grouting support pile 10 inside the tunnel by at least 1 meter. In this embodiment, the second grouting pipe 60 is made of φ76×5mm steel pipe, with a longitudinal spacing of 1 meter and a transverse spacing of 1 meter. The depth of the second grouting pipe 60 ensures that it effectively overlaps with the radial grouting body and the grouting support pile 10 inside the tunnel.

[0047] S24, after the lateral retaining structure 40 is constructed, cement-stabilized soil is backfilled and compacted using the lateral retaining structure 40 to form a counter-pressure backfill 61; wherein, the counter-pressure backfill 61 transfers the load to the grouting reinforcement zone of the middle rock column through the lateral retaining structure 40 and the surface grouting reinforcement zone, together forming the three-dimensional overall reinforcement structure.

[0048] As a preferred example, step 24 includes the step of backfilling and compacting cement-stabilized soil with a cement content of 8% in layers using the lateral retaining structure 40 to form the counter-pressure backfill body 61.

[0049] This application embodiment uses "pile-slab wall 41 + cement-stabilized soil counter-pressure backfill" or "weighted retaining wall 42 + cement-stabilized soil counter-pressure backfill" to treat the extremely shallow buried biased pressure section on the ground surface. Through backfilling the tunnel top, the unilateral biased pressure caused by topographic elevation difference or uneven distribution of rock and soil is effectively reduced, the pressure difference between the surrounding rock on both sides of tunnel 80 is balanced, and the load is transferred to the tunnel 80 structure more evenly and symmetrically. The arch foot support piles inside the tunnel resist the remaining uneven biased load and the vertical load on the tunnel top, reducing the deformation of tunnel 80. In addition, the pile-slab wall 41, the counterweight retaining wall 42 and the outer contour of the tunnel 80 are reinforced by the second grouting pipe 60, which acts as a micro pile and forms a second "anti-slip zone". More importantly, the overlap length between the surface grouting pipe (i.e. the second grouting pipe 60) between the pile and the tunnel, the grouting support pile 10 at the arch foot inside the tunnel and the radial grouting pipe 21 (part of the radial grouting body inside the tunnel) at the arch waist inside the tunnel is not less than 1m, so that the tunnel and the outside are formed as an integral reinforcement structure, and provide a stable support for the grouting support pile 10 at the arch foot inside the tunnel, ensuring the arch foot support effect. This method effectively improves the stiffness of the surrounding rock of the tunnel 80 and reduces the uneven settlement and deformation of the tunnel 80. In this way, the first grouting pipe 50, the pile-slab wall 41 (or the counterweight retaining wall 42), the second grouting pipe 60, the surface counter-pressure backfill soil, the radial grouting body inside the tunnel, and the grouting support pile 10 are reinforced together, which alleviates the unfavorable situation of shallow buried bias pressure of tunnel 80 from the root. At the same time, a support-type three-dimensional integral reinforcement structure that can resist the influence of external bias pressure and shallow buried load is formed around tunnel 80, which is conducive to the subsequent excavation of the backfill section inside the tunnel.

[0050] In a preferred embodiment, step S3 includes the following steps: S31, apply advanced support to the excavation area; S32, the backfill platform 30 inside the tunnel is excavated in layers and steps in the order of upper step 81, middle step 82, and lower step 83, and the initial support is replaced step by step; wherein, the excavation of each step follows the process of first excavating the corresponding backfill platform 30 inside the tunnel, then removing the original initial support, then erecting a new steel arch frame 70, and finally spraying concrete, and core soil is reserved when excavating the upper step 81. S33, when a new steel arch frame 70 is erected at each step, longitudinal channel steel 71 is used to connect all adjacent new steel arch frames 70 in this step into a continuous whole along the longitudinal direction of the tunnel 80. S34, at the arch foot position of each step, a locking anchor pipe 85 with a built-in steel cage is constructed, and the end of the locking anchor pipe 85 is fixedly connected to the new steel arch frame 70 of the step.

[0051] As a preferred example, after the reinforcement of the interlocking rock pillar area and the backfilling of the surface outside the tunnel are completed, the backfilling platform section inside the tunnel (i.e., the backfilling platform 30 inside the tunnel) is excavated using the three-stage reserved core soil method. The height of each stage is 3-3.5m. During the excavation of each stage, the original initial support needs to be cut and a new steel arch frame 70 needs to be erected. In order to enhance the deformation resistance of the locking foot, two φ76×5mm locking foot small guide pipes are installed at the arch foot of each stage. The locking foot small guide pipes are equipped with steel cages to improve their rigidity and strength. In order to further improve the overall stability of the steel arch frame 70, 30a longitudinal channel steel 71 is installed at the stage boundary for connection. The longitudinal channel steel 71 is installed in sections, and the length of each section of longitudinal channel steel 71 is determined according to the spacing of the steel arch frame 70. Then, the adjacent longitudinal channel steel 71 is connected by welding with side plates 74 to form an integral structure.

[0052] The specific construction procedures are as follows: ① Construct advanced support; ② Excavate the upper bench 81 and reserve core soil. During excavation, the original initial support of this part needs to be cut; ③ After excavating the upper bench 81, spray concrete to the design thickness and then erect steel arch frame 70. The arch frame uses longitudinal channel steel 71 to connect adjacent steel arch frames 70 longitudinally and set up reinforced locking foot small guide pipes; ④ Excavate the reserved core soil; ⑤ Excavate the middle bench 82. During excavation, the original initial support of this part needs to be cut; ⑥ After excavating the middle bench 82, spray concrete to seal the rock surface and then erect a new steel arch frame 70. The steel arch frame 70 uses longitudinal channel steel 71 to connect adjacent steel arch frames 70 longitudinally and set up reinforced locking foot small guide pipes; ⑦ Excavate the lower bench 83. During excavation, the original initial support of this part needs to be cut; ⑧ After excavating the lower bench 83, spray concrete and then erect steel arch frame 70. The arch frame uses longitudinal channel steel 71 to connect adjacent steel arch frames 70 longitudinally and set up reinforced locking foot small guide pipes.

[0053] It is worth noting that the traditional initial support and arch replacement method involves constructing a temporary arch support before performing the initial support and arch replacement. This requires advancing the arch segment by segment and removing the temporary arch support at each stage. The traditional initial support and arch replacement method has the following limitations: ① High construction risk: Temporary arch supports often use steel arch frames (70mm). In extremely shallow, biased terrain, the surrounding rock deformation pressure is high, making the temporary arch support prone to deformation and failure, leading to large-scale collapses. Furthermore, the construction and removal of the arch support frequently disturb the surrounding rock, increasing construction risk; ② Low construction efficiency: Arch replacement requires segment-by-segment advancement, and to reduce construction risk, the length of each segment is shortened, making the process cumbersome and hindering rapid construction; ③ High cost and resource consumption: This method requires the installation of temporary arch supports, which are only used temporarily and must be removed later, adding extra costs for materials, labor, and equipment. Therefore, compared to the traditional initial support and arch replacement method, the backfilling and excavation method for arch replacement has the main advantages of lower construction risk, simpler construction process, and faster construction.

[0054] Further, the reinforcement treatment of the arch circumferential main reinforcement 72 of the secondary lining 84 in step S4 includes the following steps: increasing the diameter of the existing arch circumferential main reinforcement 721, and adding a new circumferential main reinforcement 722 between two adjacent existing arch circumferential main reinforcements 721. In this embodiment, the arch circumferential main reinforcement 72 includes the existing arch circumferential main reinforcement 721 and the new circumferential main reinforcement 722. The diameter of the existing arch circumferential main reinforcement 721 is increased (e.g., φ22 steel bars are adjusted to φ25 steel bars). At the same time, a new circumferential main reinforcement 722 is added in the center of two adjacent existing arch circumferential main reinforcements 721 on the inner side of the secondary lining 84 to achieve the purpose of crack resistance and reinforcement. Please refer to [link to relevant documentation]. Figure 14 .

[0055] Further, step S21 includes the following steps: In the area of ​​the interbed rock pillar between the tunnel 80 and the surrounding rock pillar, multiple rows of first grouting pipes 50 are laid out and grouting is carried out to form the grouting reinforcement zone of the interbed rock pillar. The overlap length between the first grouting pipe 50 and the radial grouting body in the tunnel and the grouting support pile 10 is not less than 1 meter. After grouting is completed, a layer of reinforced concrete cover plate 51 is poured on the surface of the middle rock column area; wherein, the top of the first grouting pipe 50 is anchored in the reinforced concrete cover plate 51, and the coverage of the reinforced concrete cover plate 51 extends beyond the outermost first grouting pipe 50.

[0056] After grouting is completed, a reinforced concrete cover plate 51 is poured on the surface of the interbedded rock column area. This cover plate has multiple functions: firstly, it acts as a grout stop, preventing grout from overflowing from the surface during grouting and ensuring effective establishment of grouting pressure; secondly, it serves as a permanent structure, anchoring the tops of each row of grouting pipes into a rigid top plate similar to a pile foundation cap; thirdly, it acts as a surface hardening layer, minimizing the adverse effects of surface water runoff on the stability of the surrounding rock; and fourthly, it serves as a surface leveling and hardening layer, providing a working platform for surface grouting reinforcement construction. Specifically, the top of the first grouting pipe 50 is embedded at least 10cm into the reinforced concrete cover plate 51 and is connected to the main reinforcement of the cover plate by reinforcing bars, achieving reliable anchoring between the first grouting pipe 50 and the reinforced concrete cover plate 51. The thickness of the reinforced concrete cover plate 51 is 20cm, its strength grade is C30, and the extent of the reinforced concrete cover plate 51 should extend at least 1m beyond the first grouting pipe 50.

[0057] Further, step S23 includes the following steps: Multiple rows of second grouting pipes 60 are laid in the stratum between the lateral retaining structure 40 and the outer contour of the tunnel 80. The horizontal distance between the row of second grouting pipes 60 closest to the outer contour of the tunnel 80 and the outer contour of the tunnel 80 is not less than 2 meters. Grouting is performed on the second grouting pipes 60 to form the surface grouting reinforcement zone. The overlap length between the second grouting pipes 60 and the radial grouting body inside the tunnel and the grouting support piles 10 is not less than 1 meter.

[0058] As a preferred example, the height of the upper step 81, the middle step 82, and the lower step 83 is 3 to 3.5 meters.

[0059] The above are merely preferred embodiments of the present invention and do not limit the scope of protection of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention’s specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A collaborative reinforcement method for the deformation section of a shallow-buried tunnel with biased pressure and small clearance, characterized in that, Includes the following steps: S1. Within the deformation section of the tunnel, the surrounding rock of the deformation section is first reinforced by radial grouting to form a radial grouting body inside the tunnel, and grouting support piles are installed at the arch foot positions of the side walls on both sides of the tunnel. After the reinforcement is completed, the soil and rock are backfilled in layers inside the deformation section of the tunnel and compacted to form a backfill platform inside the tunnel. S2, Construct a surface-coordinated reinforcement structure; wherein, the surface-coordinated reinforcement structure includes a grouting reinforcement zone formed by surface grouting in the interstitial rock column area between the left and right tunnels, a lateral retaining structure constructed on the tunnel's biased low-mountain side, and a surface grouting reinforcement zone formed by grouting in the strata between the lateral retaining structure and the tunnel's outer contour; wherein, the first grouting pipe in the interstitial rock column grouting reinforcement zone overlaps with the radial grouting body inside the tunnel and the grouting support pile, and the second grouting pipe in the surface grouting reinforcement zone overlaps with the radial grouting body inside the tunnel and the grouting support pile, to form a three-dimensional integrated reinforcement structure; S3. After the three-dimensional overall reinforcement structure is formed, the backfill platform inside the tunnel is excavated in layers using the step method. As the excavation progresses, the original initial support is removed section by section and a new steel arch frame is erected. Shotcrete is then used to form a new initial support. When erecting the new steel arch frame, the steel arch frame of each step is connected as a whole by longitudinal channel steel, and a locking anchor pipe with an internal steel reinforcement cage is installed at the arch foot of each step. S4, construct the secondary lining and reinforce the circumferential main reinforcement of the arch section of the secondary lining.

2. The method for coordinated reinforcement of the deformed section of a shallow-buried tunnel with bias pressure and small clearance according to claim 1, characterized in that, Step S1 includes the following steps: S11, within the tunnel deformation section, radial grouting is performed on the surrounding rock of the tunnel deformation section using boreholes with a diameter of 10-30mm to form the radial grouting body inside the tunnel. At the same time, drainage pipes are installed at intervals in the circumferential and longitudinal directions of the tunnel to drain the fissure water in the surrounding rock to the existing drainage system of the tunnel. The depth of the radial grouting reinforcement ensures that the radial grouting body inside the tunnel overlaps with the first and second grouting pipes constructed subsequently by at least 1 meter. S12, grouting support piles are installed at the arch foot positions of the two sidewalls of the tunnel; wherein, a first-specification grouting support pile is installed at the arch foot on the side of the tunnel biased towards the high mountain, and a second-specification grouting support pile is installed at the arch foot on the side of the tunnel biased towards the low mountain; the bearing capacity design value of the second-specification grouting support pile is greater than the bearing capacity design value of the first-specification grouting support pile; wherein, the length of the grouting support pile is ensured to form an overlap of not less than 1 meter with the subsequently installed first and second grouting pipes; S13, inside the tunnel deformation section, tunnel excavation waste is used for layered backfilling and compaction to form an in-tunnel backfill platform, and slope protection roads extending longitudinally along the tunnel are constructed at both ends of the in-tunnel backfill platform.

3. The method for coordinated reinforcement of the deformed section of a shallow-buried tunnel with bias pressure and small clearance according to claim 2, characterized in that, Step S2 includes the following steps: S21, the first grouting pipe is laid in the rock column area between the left and right tunnels and surface grouting is carried out to form a grouting reinforcement zone for the rock column; wherein, the first grouting pipe is connected to the radial grouting body in the tunnel and the grouting support pile, and the overlap length is not less than 1 meter. S22, Obtain the soil cover thickness measurement data outside the tunnel, and construct a pile-slab wall or a counterweight retaining wall as a lateral retaining structure on the biased side of the tunnel based on the soil cover thickness measurement data. S23, before constructing the lateral retaining structure, grouting reinforcement is carried out in the stratum between the lateral retaining structure and the outer contour of the tunnel to form the surface grouting reinforcement zone; wherein, the second grouting pipe is connected to the radial grouting body inside the tunnel and the grouting support pile, and the overlap length is not less than 1 meter. S24, after the lateral retaining structure is constructed, cement-stabilized soil is backfilled and compacted using the lateral retaining structure to form a counter-pressure backfill body; wherein, the counter-pressure backfill body transfers the load to the grouting reinforcement zone of the interlocking rock column through the lateral retaining structure and the surface grouting reinforcement zone, together forming the three-dimensional integral reinforcement structure.

4. The method for coordinated reinforcement of the deformation section of a shallow-buried tunnel with biased pressure and small clearance according to claim 1, characterized in that, Step S3 includes the following steps: S31, apply advanced support to the excavation area; S32, the backfill platform inside the tunnel is excavated in layers and steps in the order of upper step, middle step and lower step, and the initial support is replaced step by step; wherein, the excavation of each step follows the process of first excavating the corresponding backfill platform inside the tunnel, then removing the original initial support, then erecting a new steel arch frame, and finally spraying concrete, and the core soil is reserved when the upper step is excavated. S33, When erecting a new steel arch frame at each step, longitudinal channel steel is used to connect all adjacent new steel arch frames in this step into a continuous whole along the longitudinal direction of the tunnel. S34, at the arch foot position of each step, a locking anchor pipe with a built-in steel cage is constructed, and the end of the locking anchor pipe is fixedly connected to the new steel arch frame of the step.

5. The method for coordinated reinforcement of deformed sections of shallow-buried tunnels with small clearance under bias pressure according to claim 4, characterized in that, The step S4 of strengthening the arch circumferential main reinforcement of the secondary lining includes the following steps: increasing the diameter of the existing arch circumferential main reinforcement and adding a new circumferential main reinforcement between two adjacent existing arch circumferential main reinforcements.

6. The method for coordinated reinforcement of the deformed section of a shallow-buried tunnel with bias pressure and small clearance according to claim 3, characterized in that, Step S21 includes the following steps: Multiple rows of first grouting pipes are laid out and grouting is carried out in the rock column area between the left and right tunnels to form the grouting reinforcement zone of the rock column. The overlap length between the first grouting pipe and the radial grouting body in the tunnel and the grouting support pile is not less than 1 meter. After grouting is completed, a layer of reinforced concrete cover plate is poured on the surface of the middle rock column area; wherein, the top of the first grouting pipe is anchored in the reinforced concrete cover plate, and the coverage of the reinforced concrete cover plate extends beyond the outermost first grouting pipe.

7. The method for coordinated reinforcement of the deformed section of a shallow-buried tunnel with biased pressure and small clearance according to claim 3, characterized in that, Step S22 includes the following steps: When the measured soil cover thickness is less than 10 meters, a pile-slab wall is constructed as the lateral retaining structure; when the measured soil cover thickness is between 10 and 16 meters, a counterweight retaining wall is constructed as the lateral retaining structure.

8. The method for coordinated reinforcement of the deformed section of a shallow-buried tunnel with bias pressure and small clearance according to claim 3, characterized in that, Step S23 includes the following steps: Multiple rows of second grouting pipes are laid in the stratum between the lateral retaining structure and the outer contour of the tunnel. The horizontal distance between the row of second grouting pipes closest to the outer contour of the tunnel and the outer contour of the tunnel is not less than 2 meters. Grouting is performed on the second grouting pipes to form the surface grouting reinforcement zone. The overlap length between the second grouting pipe and the radial grouting body inside the tunnel and the grouting support pile is not less than 1 meter.

9. The method for coordinated reinforcement of the deformed section of a shallow-buried tunnel with biased pressure and small clearance according to claim 3, characterized in that, Step 24 includes the following steps: backfilling and compacting cement-stabilized soil with a cement content of 8% in layers using the lateral retaining structure to form the counter-pressure backfill body.

10. The method for collaborative reinforcement of the deformed section of a shallow-buried tunnel with biased pressure and small clearance according to claim 4, characterized in that, The height of the upper, middle, and lower steps is 3 to 3.5 meters.

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