Secondary lining construction method for high ground stress soft rock tunnel

Abstract

The invention discloses a secondary lining construction method for a high-crustal-stress soft rock tunnel, and relates to the technical field of secondary lining construction of the high-crustal-stress soft rock tunnel, and the secondary lining construction method for the high-crustal-stress soft rock tunnel comprises the steps that a primary support is constructed, and a convergence measuring pile is installed for monitoring; when the clearance convergence rate is 30-50 mm / d for three consecutive days, arch secondary lining construction is started, early strength concrete doped with a magnesium expanding agent is poured, and a closed-cell foam plastic board is pre-buried to form a stress release seam; and when the strength of the arch reaches 80% and the convergence rate is continuously stabilized at 0.5-2.0 mm / d for 7 days, carrying out secondary lining construction on a side wall and an inverted arch, and combining at an arch foot to form a closed lining ring. According to the method, staged construction is carried out in time when rock deformation is within a controllable range, the problem of overlarge load caused by too early construction is avoided, the supporting risk caused by too late construction is prevented, and therefore the overall stability and durability of a tunnel structure are improved.

Description

Technical Field

[0001] This invention relates to the field of secondary lining construction technology for soft rock tunnels under high ground stress, and particularly to a secondary lining construction method for soft rock tunnels under high ground stress. Background Technology

[0002] In high-stress soft rock tunnel engineering, due to the low strength and high ground stress of the surrounding rock, significant large deformations and continuous rheological phenomena easily occur after excavation. The deformation process is not only large in magnitude but also prolonged, making traditional tunnel secondary lining construction methods ineffective. Under normal geological conditions, secondary lining construction typically involves long-term monitoring after the initial support is completed, waiting for the surrounding rock deformation to stabilize—that is, when the clearance convergence rate drops to a low level—before using a full-section, one-time casting method to complete the concrete structure of the arch, sidewalls, and invert. However, in high-stress soft rock environments, the period required for surrounding rock deformation stabilization is often exceptionally long, potentially lasting months or even longer. This not only severely delays the project schedule but also significantly increases the maintenance costs and safety risks of the initial support. If secondary lining construction is implemented too early, the continuous deformation of the surrounding rock will impose excessive loads on the insufficiently hardened concrete, easily leading to cracking of the secondary lining; conversely, construction too late will subject the initial support to prolonged high ground stress, potentially causing support structure failure or accelerated deformation.

[0003] In existing technologies, the determination of construction timing mainly relies on a single net clearance convergence rate index; construction is initiated when the rate drops to a certain low threshold. However, this criterion is too coarse and cannot accurately reflect the nonlinear and staged characteristics of soft rock deformation under high ground stress, making it difficult to achieve a dynamic balance between continuous deformation of the surrounding rock and timely closure of the secondary lining. Furthermore, in high ground stress environments, the shrinkage stress of the concrete itself and the compressive load of the surrounding rock in a single-stage, full-section cast-in-place secondary lining structure result in the superposition of these stresses, leading to frequent structural cracks in critical areas such as the arch crown and arch waist. These cracks not only weaken the integrity and waterproofing performance of the lining but also accelerate structural deterioration, significantly reducing the long-term service life of the secondary lining. More importantly, traditional construction methods lack targeted stress release and deformation adaptation mechanisms. Rigid lining structures cannot coordinate with the large deformation characteristics of soft rock, causing an imbalance in the interaction between the lining and the surrounding rock, further inducing local stress concentration and structural damage, affecting the overall safety and durability of the tunnel. Summary of the Invention The main objective of this invention is to propose a secondary lining construction method for soft rock tunnels under high ground stress. This method aims to carry out phased construction in a timely manner when the deformation of the surrounding rock is within a controllable range. This avoids the problem of excessive load caused by premature construction and prevents the support risks caused by late construction, thereby improving the overall stability and durability of the tunnel structure.

[0004] To achieve the above objectives, the present invention proposes a secondary lining construction method for high-stress soft rock tunnels, the method comprising: After the tunnel is excavated, the initial support, including shotcrete, full-ring steel arch frame and system anchor bolts, is immediately constructed. Mechanical convergence test piles were installed on the initial support surface to begin continuous monitoring of tunnel clearance convergence and obtain monitoring data. Based on the monitoring data, the timing of secondary lining construction is determined as follows: when the net clearance convergence rate is in the range of 30 mm / d to 50 mm / d for three consecutive days, the first stage of arch secondary lining construction is initiated. An arc-shaped template is erected within a 120° range of the tunnel arch, and C35 early-strength concrete mixed with magnesium expansion agent is poured into the arc-shaped template. Along the longitudinal direction of the tunnel, a 20mm thick closed-cell foam plastic board is pre-embedded in the arc-shaped template at the arch position every 6 meters to form a longitudinal temporary stress relief joint. After the concrete strength of the secondary lining of the arch reaches 80% of the design value after 28 days in the first stage, monitoring continues. When the net clearance convergence rate is stable within the range of 0.5 mm / d to 2.0 mm / d for 7 consecutive days, the construction of the secondary lining of the sidewall and invert arch in the second stage is started. Remove the arch formwork and erect a full-section hydraulic trolley formwork. Starting from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork, pour concrete synchronously, symmetrically and continuously until the side walls and invert arch formwork are filled. Then, the second-stage side walls and invert arch lining are combined with the first-stage arch lining at the arch foot to form a closed lining ring.

[0005] In one embodiment, the steps of erecting an arc-shaped template within a 120° range of the tunnel arch and pouring C35 early-strength concrete mixed with a magnesium expansion agent into the arc-shaped template include: The magnesium-based expansive agent is dry-mixed with cement, fly ash, aggregates and admixtures at a mixing plant at a ratio of 6% to 8% of the total weight of cementitious materials for a dry mixing time of not less than 60 seconds. Then, mixing water is added for wet mixing for a wet mixing time of not less than 120 seconds to produce shrinkage-compensating concrete. The shrinkage-compensating concrete is pumped to the top inlet of the arc-shaped formwork using a concrete delivery pump, and poured in a slanted, layered, and horizontal manner, with the thickness of each layer controlled between 40 cm and 50 cm. After each layer is poured, immediately vibrate it through the lateral vibration window reserved in the arc-shaped template using an immersion vibrator with a diameter of 50mm. The vibration point spacing should not be greater than 40cm, and the vibrator should be inserted into the lower layer of concrete for no less than 5cm. Vibrate until the concrete surface is covered with slurry and no obvious air bubbles escape, and then proceed with the next layer pouring.

[0006] In one embodiment, after the step of pre-embedding a 20mm thick closed-cell foam plastic board at 6-meter intervals in the arched template at the arch crown along the tunnel longitudinal direction to form a longitudinal temporary stress relief joint, the secondary lining construction method for high-stress soft rock tunnels further includes: A row of ribbed short steel bars is pre-embedded in the concrete on both sides of the closed-cell foam plastic board; wherein the length of the ribbed short steel bar is 1.0 meter and the diameter is 25 mm, one end of the ribbed short steel bar extends into the concrete and the other end terminates in the side of the closed-cell foam plastic board, and the end of the ribbed short steel bar is coated with anti-rust paint. After the entire secondary lining is closed into a ring and the deformation is stable, use an electric hot wire cutting tool to remove the exposed closed-cell foam plastic board along the longitudinal direction of the tunnel to form a 20mm wide open seam. Use a manual caulking gun to inject polysulfide building sealant into the exposed joint in sections, with the injection depth not less than 80% of the joint depth, and then smooth the surface.

[0007] In one embodiment, the steps of removing the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork until the side walls and invert arch formwork are filled, and then combining the second-stage side walls and invert arch lining with the first-stage arch lining at the arch foot to form a closed lining ring, include: During the construction of the secondary lining of the arch in the first stage, a protruding trapezoidal reinforced concrete tenon is prefabricated at the end section of the arch foot of the secondary lining of the arch in the first stage. The outer surface of the tenon is roughened and a metal sleeve with an inner diameter of 25mm is pre-embedded in the tenon. Before the construction of the secondary lining of the side wall in the second stage, a slightly larger groove-shaped steel mold is installed on the inner side of the side wall formwork, corresponding to the position of the tenon, to form a reserved mortise space. When pouring the side wall concrete, the concrete fills the groove-shaped steel mold, wraps the tenon, and forms a mortise. After the concrete strength of the side wall reaches 70% of the design value, non-shrink cement mortar is injected into the contact interface between the tenon and the mortise concrete through the metal sleeve using a high-pressure grouting machine.

[0008] In one embodiment, after the step of pre-embedding a 20mm thick closed-cell foam plastic board at 6-meter intervals in the arched template at the arch crown along the tunnel longitudinal direction to form a longitudinal temporary stress relief joint, the secondary lining construction method for high-stress soft rock tunnels further includes: When tying the secondary lining steel bars of the arch, three bundles of corrugated metal pipes are pre-embedded at the arch crown and the two sides of the arch waist along the tunnel circumference to form prestressed ducts. After the concrete strength of the arch reaches 90% of the design value, a through-hole jack is used to tension the steel strands inserted into the corrugated metal pipe. The tension force of a single bundle is controlled to be 40% to 50% of the ultimate tensile strength of the steel strands. After tensioning is completed, cement grout is injected into the metal bellows using a vacuum-assisted grouting method, and then the anchorage is sealed with concrete.

[0009] In one embodiment, the step of removing the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork until the side walls and invert arch formwork are filled, and the second-stage side walls and invert arch lining are joined with the first-stage arch lining at the arch foot to form a closed lining ring, further includes: The 12-meter-long sidewall and invert arch of the single-pour section are divided into four independent pouring sections, each 3 meters long, along the longitudinal direction of the tunnel. The pouring shall be carried out in the order of No. 1, No. 3, No. 2, and No. 4, with an interval of no less than 72 hours between the start of pouring of adjacent No. 1 and No. 4. After the concrete of each compartment is poured, immediately cover the exposed concrete surface of the compartment with plastic film for water retention and curing, and lay circulating cooling water pipes on the outside of the formwork for water cooling.

[0010] In one embodiment, before the steps of erecting an arc-shaped template within a 120° range of the tunnel arch and pouring C35 early-strength concrete mixed with a magnesium expansion agent into the arc-shaped template, the secondary lining construction method for high-stress soft rock tunnels further includes: Select a density of 300 kg / m³ 3 Up to 400 kg / m 3 The hydrophobic rubber foam board is cut into standard panels that are 1000mm long, 500mm wide, and 80mm thick. Use a notched scraper to evenly apply the two-component polyurethane adhesive to the surface of the initial support shotcrete and the back of the hydrophobic rubber foam board, with a coating thickness of 3mm to 5mm. The hydrophobic rubber foam board coated with the adhesive is tightly adhered to the initial support surface, and gently tapped with a rubber mallet to ensure full adhesion.

[0011] In one embodiment, prior to the step of tightly bonding the hydrophobic rubber foam board coated with the adhesive to the initial support surface and gently tapping it with a rubber mallet to ensure full adhesion, the secondary lining construction method for high-stress soft rock tunnels further includes: A 0.2mm thick plastic film is laid on the surface of the hydrophobic rubber foam board as a release liner; On the plastic film, at 1.0 meter intervals, a prefabricated thin iron sheet with a central hole is fixed using plastic pads and binding wire. The thin iron sheet serves as a positioning base for the subsequent grouting pipe.

[0012] In one embodiment, during the construction of the secondary lining of the first stage arch, a protruding trapezoidal reinforced concrete tenon is prefabricated at the end section of the arch foot of the secondary lining of the first stage arch. The outer surface of the tenon is roughened, and a metal sleeve with an inner diameter of 25mm is pre-embedded in the tenon. A metal sleeve is pre-embedded at the top and on each of the two sides of the trapezoidal reinforced concrete tenon, with the axial direction of the metal sleeve pointing towards the contact surface between the tenon and the future mortise. After the concrete strength of the side wall reaches 70% of the design value, the step of injecting non-shrink cement mortar into the contact interface between the tenon and the mortise concrete using a high-pressure grouting machine through the metal sleeve includes: Grout is injected from the top metal sleeve. After the grout flows out of the side metal sleeves, grout is added from both side metal sleeves until all the outlets of the metal sleeves are full of grout.

[0013] In one embodiment, the step of removing the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork until the side walls and invert arch formwork are filled, and the second-stage side walls and invert arch lining are joined with the first-stage arch lining at the arch foot to form a closed lining ring, further includes: Measure the current horizontal distance between the convergence measuring stake fixing plate on the left side wall and the convergence measuring stake fixing plate on the right side wall; The current horizontal distance is compared with the initial installation reference distance of the left sidewall convergence measuring stake fixing plate and the right sidewall convergence measuring stake fixing plate to obtain an intuitive length difference value L; If the length difference L is greater than 50mm, the entire full-section hydraulic trolley template system will be horizontally pushed to the side with the longer current horizontal distance by the horizontal hydraulic jack at the bottom of the full-section hydraulic trolley, and the pre-displacement amount will be set to 20mm to 30mm. Under the pre-displacement state, the pouring and curing of the sidewall and invert arch concrete are completed.

[0014] The technical solution of this invention establishes a phased construction judgment mechanism based on a dual threshold range of net clearance convergence rate. Combined with early-strength concrete incorporating magnesium expansion agent into the arch secondary lining and longitudinal temporary stress relief joints formed by closed-cell foam plastic boards every 6 meters, a stress control system is constructed. This allows the secondary lining structure to intervene early during the active deformation period of the surrounding rock and actively adapt to the continuous large deformation characteristics of high-stress soft rock. It effectively absorbs the superposition effect of surrounding rock compression stress and concrete shrinkage stress, avoiding the problems of overall cracking and difficulty in grasping the timing of construction caused by traditional full-section one-time casting. Under the premise of ensuring structural safety, the construction cycle is significantly shortened, and the overall stability, long-term durability and construction safety of the support structure are improved. This provides an efficient and reliable technical solution for the secondary lining construction of high-stress soft rock tunnels. Timely phased construction when the surrounding rock deformation is within a controllable range avoids the problem of excessive load caused by premature construction and prevents the support risks caused by late construction, thereby improving the overall stability and durability of the tunnel structure. Attached Figure Description

[0015] 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.

[0016] Figure 1 This is a schematic flowchart of an embodiment of the secondary lining construction method for soft rock tunnels under high ground stress provided by the present invention.

[0017] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0018] 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.

[0019] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0020] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are 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. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When 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.

[0021] Existing methods for constructing secondary linings in high-stress soft rock tunnels suffer from several drawbacks when dealing with complex geological conditions. These include a reliance on a single standard for determining the timing of construction and an inability to balance continuous deformation of the surrounding rock with timely lining closure. This can easily lead to cracking of the secondary lining structure or extended construction periods. Furthermore, one-time full-section casting under high-stress conditions is prone to structural cracking due to continuous compression from the surrounding rock, and the superposition of concrete shrinkage stress and surrounding rock pressure reduces the long-term durability of the secondary lining. Simultaneously, traditional rigid lining structures lack targeted stress release and deformation adaptation measures, making them ill-suited to the large deformation characteristics of high-stress soft rock, thus affecting support effectiveness and structural safety.

[0022] To address this technical problem, this invention proposes a secondary lining construction method for soft rock tunnels under high ground stress.

[0023] Please see Figure 1 In one embodiment of the present invention, the secondary lining construction method for high-stress soft rock tunnels includes: S10, immediately after tunnel excavation, initial support including shotcrete, full-ring steel arch frame and system anchor bolts is constructed; S20, Install mechanical convergence measuring piles on the initial support surface to start continuous monitoring of tunnel clearance convergence and obtain monitoring data; S30, based on the monitoring data, determine the timing of secondary lining construction: when the net clearance convergence rate is in the range of 30 mm / d to 50 mm / d for three consecutive days, start the first stage of arch secondary lining construction; S40, an arc-shaped template is erected within a 120° range of the tunnel arch, and C35 early-strength concrete mixed with magnesium expansion agent is poured into the arc-shaped template; S50, along the longitudinal direction of the tunnel, a 20mm thick closed-cell foam plastic board is pre-embedded in the arc-shaped template at the arch position every 6 meters to form a longitudinal temporary stress relief joint. S60, after the concrete strength of the secondary lining of the arch in the first stage reaches 80% of the 28-day strength of the design value, continue monitoring. When the net clearance convergence rate is stable in the range of 0.5 mm / d to 2.0 mm / d for 7 consecutive days, start the construction of the secondary lining of the sidewall and invert arch in the second stage. S70, remove the arch formwork, erect a full-section hydraulic trolley formwork, and start pouring concrete synchronously, symmetrically and continuously from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork until the side walls and invert arch formwork are filled, and the second stage side walls and invert arch lining are combined with the first stage arch lining at the arch foot to form a closed lining ring.

[0024] To facilitate understanding of the technical solution in this embodiment, some key terms involved are explained below: Initial support refers to the temporary or semi-permanent support structure immediately constructed after tunnel excavation to resist surrounding rock pressure and maintain tunnel stability. It typically consists of shotcrete, steel arches, and anchor bolts, and its function is to limit surrounding rock deformation, creating conditions for subsequent secondary lining construction. Mechanical convergence piles are measuring devices used to monitor the deformation of tunnel surrounding rock or support structures. They obtain clearance convergence data by installing fixed points on the tunnel clearance surface and periodically measuring distance changes. Clearance convergence rate refers to the amount of inward displacement of the tunnel's internal contour per unit time after excavation; it is an important parameter for assessing the degree of surrounding rock deformation activity and judging the stability of the support structure. Magnesium-based expansive agents are admixtures added to concrete that generate expansion products through hydration reactions, thereby compensating for the concrete's own shrinkage or generating micro-expansion stress. Their function is to reduce concrete cracking and improve the density and durability of the structure. Closed-cell foam plastic board is a lightweight foam material board with an independent closed-cell structure. It is characterized by good compressibility and high resilience, and can be used as a temporary stress-relieving material in tunnel secondary lining to absorb some of the surrounding rock pressure or concrete shrinkage stress. Full-section hydraulic trolley formwork is a large-scale construction equipment used for pouring concrete for tunnel secondary lining. This formwork system uses hydraulic control to achieve the erection, dismantling, and movement of the formwork, and can cover the entire or most of the tunnel cross-section at once, ensuring the overall forming quality of the lining structure.

[0025] The construction method in this embodiment specifically includes the following steps: First, after the tunnel is excavated to the designed cross-section, initial support is immediately constructed. This initial support can be achieved by manually or mechanically spraying concrete onto the surrounding rock surface to form a shotcrete layer. Subsequently, according to design requirements, prefabricated steel arch frames are installed by welding or bolting, and systematic anchor bolts are implanted using drilling, grouting, or other methods to enhance the overall stability and load-bearing capacity of the surrounding rock.

[0026] Furthermore, after the initial support construction is completed, mechanical convergence measuring stakes are installed on the initial support surface to begin continuous monitoring of tunnel clearance convergence and obtain monitoring data. Specifically, multiple mechanical convergence measuring stakes can be set at different locations in the tunnel clearance. By periodically measuring the distance between the measuring stakes using a rangefinder or steel ruler, the raw data of tunnel clearance convergence can be obtained.

[0027] Based on the obtained monitoring data, the timing for secondary lining construction is determined. When the calculated clearance convergence rate is within a specific range of 30 mm / d to 50 mm / d for three consecutive days, it can be determined as a suitable time to start the first stage of arch secondary lining construction. This determination process can be completed manually or automatically through a preset program.

[0028] Subsequently, an arc-shaped formwork is erected within a 120° range of the tunnel arch, and C35 early-strength concrete mixed with a magnesium-based expansion agent is poured into this formwork. Specifically, segmented or monolithic arc-shaped formwork can be used to ensure sufficient space for concrete pouring between the formwork and the initial support. Concrete preparation can be carried out at an on-site mixing plant, where cement, aggregates, water, and appropriate amounts of magnesium-based expansion agent and early-strength agent are mixed and stirred evenly in proportion. The mixed concrete is then transported to the formwork for pouring via pumps or chutes.

[0029] As a preferred embodiment, a 20mm thick closed-cell foam plastic board is pre-embedded in the arched formwork at the arch crown every 6 meters along the tunnel's longitudinal direction to form a temporary longitudinal stress relief joint. Before erecting the arched formwork and preparing to pour concrete, closed-cell foam plastic boards can be pre-placed along the tunnel's longitudinal direction at the arch crown, according to design requirements. These plastic boards can be held in position during pouring by bonding, fixing, or simply placing them, thereby forming a predetermined longitudinal gap after the concrete hardens to absorb some of the stress.

[0030] After the concrete strength of the secondary lining of the arch in the first stage reaches 80% of the design strength after 28 days, the tunnel clearance convergence is monitored. By continuously collecting and analyzing the monitoring data, when the clearance convergence rate remains within a stable range of 0.5 mm / d to 2.0 mm / d for 7 consecutive days, it indicates that the surrounding rock deformation has tended to stabilize, and the construction of the secondary lining of the sidewalls and invert arch in the second stage can be started.

[0031] Finally, the arch formwork is removed, and a full-section hydraulic trolley formwork is erected. Starting from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork, concrete is poured synchronously, symmetrically, and continuously until the side walls and invert arch formwork are filled. Simultaneously, the second-stage side walls and invert arch lining are combined with the first-stage arch lining at the arch foot, forming a closed lining ring. Specifically, after the first-stage arch lining reaches the required standard, its construction formwork is removed. Then, the full-section hydraulic trolley formwork is advanced to the section to be constructed and accurately positioned and supported. Concrete pouring can begin from the reserved windows at the bottom of the side walls on both sides of the trolley formwork, using pumps or chutes to ensure that the concrete fills the side walls and invert arch area synchronously and symmetrically. The pouring process should be continuous until the entire side wall and invert arch formwork are completely filled, and the newly poured concrete is tightly bonded to the completed arch lining at the arch foot, ultimately forming a complete closed lining ring.

[0032] Therefore, the construction method in this embodiment, by combining phased secondary lining construction with dynamic monitoring, can accurately grasp the active and stable periods of deformation in the surrounding rock of soft rock tunnels under high ground stress, effectively avoiding secondary lining cracking and construction delays that may occur with traditional one-time pouring. The addition of magnesium-based expansion agent to the concrete and the setting of longitudinal temporary stress relief joints significantly improve the adaptability of the secondary lining structure to large deformations of the surrounding rock, effectively mitigating the damage to the lining caused by the superposition of surrounding rock compression and concrete shrinkage stress, thereby improving the long-term durability and overall safety of the secondary lining.

[0033] In an embodiment of the present invention, the steps of erecting an arc-shaped template within a 120° range of the tunnel arch and pouring C35 early-strength concrete mixed with a magnesium expansion agent into the arc-shaped template include: S41, the magnesium expansion agent is dry-mixed with cement, fly ash, aggregate and admixture at a mixing plant at a ratio of 6% to 8% of the total weight of cementitious materials, for a dry mixing time of not less than 60 seconds, and then mixing water is added for wet mixing for a wet mixing time of not less than 120 seconds to produce shrinkage-compensating concrete. S42, the shrinkage-compensating concrete is pumped to the top inlet of the arc-shaped formwork by a concrete delivery pump, and poured in a slanted layered and horizontally advanced manner, with the thickness of each layer controlled between 40 cm and 50 cm. S43. After each layer is poured, immediately use a 50mm diameter immersion vibrator through the lateral vibration window reserved in the arc-shaped template to vibrate the concrete. The spacing between vibration points should not exceed 40cm. Insert the vibrator into the lower layer of concrete for at least 5cm and vibrate until the concrete surface is covered with slurry and no obvious air bubbles escape. Then, proceed with the next layer pouring.

[0034] Specifically, the preparation of shrinkage-compensating concrete is crucial to ensuring its performance. The proportion of magnesium expansive agent is precisely controlled between 6% and 8% of the total weight of the cementitious materials. This aims to induce moderate expansion of the concrete during hardening, effectively compensating for its own shrinkage, thereby significantly reducing crack formation and improving the compactness and crack resistance of the lining. Dry mixing at the batching plant for at least 60 seconds ensures that the solid components, including cement, fly ash, aggregates, admixtures, and magnesium expansive agent, are fully and uniformly mixed, avoiding localized clumping or uneven composition. Subsequently, mixing water is added for wet mixing for at least 120 seconds, allowing all components to fully react with the water, forming a homogeneous and workable concrete paste, providing a solid foundation for subsequent pumping and pouring. This meticulous preparation method maximizes the effect of the magnesium expansive agent, ensuring the effective realization of the concrete's shrinkage-compensating properties.

[0035] During concrete pouring, the shrinkage-compensating concrete is pumped to the top inlet of the arched formwork using a concrete pump, ensuring continuous and stable delivery of concrete to the arched formwork at higher elevations. This avoids the segregation and inefficiency problems that can occur with traditional hoisting methods. A sloping, layered, horizontally progressive pouring method is adopted, meaning the concrete is not simply piled vertically within the formwork, but rather gradually advanced upwards and to both sides along a slope, with each layer's thickness strictly controlled between 40 cm and 50 cm. This method helps reduce the free fall of the concrete, significantly lowering the risk of segregation, while ensuring uniform distribution and density of the concrete within the formwork. This effectively avoids uneven stress on the formwork and stress concentration within the concrete caused by pouring too high at once.

[0036] Furthermore, after each layer is poured, vibration is immediately performed using a 50mm diameter immersion vibrator through the lateral vibration window provided in the curved template. This is a crucial step in ensuring the density of the concrete. The lateral vibration window greatly facilitates the operation of the vibrator, while the 50mm diameter immersion vibrator provides sufficient vibration force to effectively remove air from the concrete. The spacing between vibration points is no more than 40 cm, ensuring complete coverage of the vibration area without any dead zones. Simultaneously, the vibrator is inserted at least 5 cm into the lower layer of concrete to ensure a good bond between the old and new concrete layers, effectively eliminating cold joints between layers. Vibration continues until the concrete surface is covered with a layer of cement paste and no obvious air bubbles escape. This indicates that the concrete has reached its optimal density, thus ensuring the strength and durability of the lining.

[0037] Through the above technical solutions, this application effectively solves the problems of insufficient compaction, voids, and cold joints that may occur during the pouring of secondary lining concrete for the arch of soft rock tunnels under high ground stress. First, accurately controlling the proportion of magnesium expansion agent and adopting a dry-wet staged mixing process ensures the uniformity and workability of the shrinkage-compensating concrete, enabling it to effectively compensate for shrinkage and reduce cracking during hardening. Second, continuous pumping using a concrete delivery pump, combined with a slanted layered and horizontally advanced pouring method, effectively reduces the risk of concrete segregation and ensures uniform distribution of concrete within the formwork. Finally, lateral insertion vibration is performed immediately after each layer is poured, with strict control over the spacing and insertion depth of vibration points, ensuring sufficient compaction of the concrete and eliminating internal air bubbles and interlayer cold joints. These measures work together to significantly improve the overall quality and strength of the secondary lining concrete for the arch, enabling it to better resist surrounding rock deformation caused by high ground stress and enhancing the long-term stability and durability of the lining.

[0038] In an embodiment of the present invention, after the step of pre-embedding a 20mm thick closed-cell foam plastic board at 6-meter intervals in the arc-shaped template at the arch crown position along the longitudinal direction of the tunnel to form a longitudinal temporary stress relief joint, the secondary lining construction method for high-stress soft rock tunnels further includes: S501, a row of ribbed short steel bars is pre-embedded in the concrete on both sides of the closed-cell foam plastic board; wherein, the length of the ribbed short steel bar is 1.0 meter and the diameter is 25 mm, one end of the ribbed short steel bar extends into the concrete and the other end terminates in the side of the closed-cell foam plastic board, and the end of the ribbed short steel bar is coated with anti-rust paint. S502. After the entire secondary lining is closed into a ring and the deformation is stable, use an electric heating wire cutting tool to remove the exposed closed-cell foam plastic board along the longitudinal direction of the tunnel to form a 20mm wide open seam. S503, use a manual glue gun to inject polysulfide building sealant into the exposed joint in sections, with the injection depth not less than 80% of the joint depth, and then scrape the surface smooth.

[0039] Specifically, a row of ribbed short steel bars is pre-embedded in the concrete on both sides of the closed-cell foam plastic board. The main function of these ribbed short steel bars is to establish an effective structural connection between the concrete on both sides of the stress relief joint. After the initial deformation of the tunnel is completed, when the closed-cell foam plastic board is removed and subsequent processing is carried out, these steel bars ensure the integrity and continuity of the lining structure, prevent local stress concentration or cracking, and effectively transfer loads. During pre-embedding, positioning brackets or binding methods can be used to ensure the accurate positioning of the steel bars during concrete pouring. The ribbed design increases the bond strength between the steel bars and the concrete, improving pull-out resistance. The specifications of 1.0 meter length and 25 mm diameter are determined based on engineering experience and structural stress analysis, aiming to provide sufficient anchorage length and shear resistance. One end of the steel bar extends into the concrete, and the other end terminates on the side of the closed-cell foam plastic board, ensuring that the steel bar does not obstruct stress relief when the foam board is present, and that it can effectively connect the concrete on both sides after the foam board is removed. Applying anti-rust paint to the ends prevents corrosion of the steel bars in humid environments, thus ensuring their long-term durability.

[0040] After the entire secondary lining is sealed into a ring and its deformation stabilizes, the exposed closed-cell foam plastic board is removed along the longitudinal direction of the tunnel using a hot wire cutter, forming a 20mm wide open seam. This step aims to transform the temporary stress-relief structure into a permanent structure suitable for subsequent treatment. Removing the foam board creates a precisely sized, smooth open seam, facilitating subsequent sealing and grouting. The critical timing for this operation is "after the entire secondary lining is sealed into a ring and its deformation stabilizes," at which point the deformation of the surrounding rock has stabilized, the secondary lining structure has become a unified whole, and the temporary function of the stress-relief joint has been fulfilled. The hot wire cutter provides an accurate and smooth cut surface, avoiding damage to the concrete on both sides or creating burrs, ensuring uniform width and depth of the open seam. The 20mm width of the open seam matches the thickness of the original embedded foam board, facilitating the subsequent filling of the sealing material.

[0041] Subsequently, polysulfide building sealant is injected into the exposed joint in sections using a manual caulking gun, with the injection depth not less than 80% of the joint depth, and the surface is then smoothed. This step aims to permanently seal the formed exposed joint, preventing surface water or groundwater from seeping into the lining structure, while maintaining a certain degree of deformation capacity to accommodate minor future deformations that may occur in the tunnel. Polysulfide building sealant is a polymer material with excellent elasticity, adhesion, weather resistance, and water resistance, making it ideal for sealing joints in tunnel structures. The manual caulking gun is flexible and allows for easy control of the injection volume and speed, ensuring that the sealant fills the entire joint evenly and densely. The "sectioned injection" method effectively avoids problems such as hollow areas, incomplete filling, or material loss that may occur with long-distance injection in one go, ensuring that each section of the joint is fully filled. Injecting to a depth of not less than 80% of the joint depth ensures the reliability of the sealing effect while allowing for some deformation space for the sealant. Smoothing the surface not only improves the appearance but also prevents the accumulation of dust and debris, extending the service life of the sealant.

[0042] Through the aforementioned technical solution, the longitudinal temporary stress relief joint pre-embedded in the tunnel arch, after fulfilling its initial stress relief function, can be effectively transformed into a permanent structural joint with structural continuity and excellent sealing performance. Specifically, the ribbed short steel bars pre-embedded on both sides of the closed-cell foam board, after the foam board is removed, can firmly connect the concrete lining on both sides, effectively transferring shear and tensile forces, thereby avoiding structural weaknesses caused by the presence of the stress relief joint and ensuring the integrity and load-bearing capacity of the secondary lining structure. Simultaneously, after deformation stabilization, the foam board is accurately removed using a hot wire cutting tool, forming a regular open joint. Polysulfide building sealant is then injected in sections using a manual caulking gun. This not only completely solves the potential leakage hazards of the initial stress relief joint and effectively prevents groundwater erosion, but also ensures that the joint maintains a certain deformation capacity while possessing excellent durability and long-term stability. This treatment method perfectly combines temporary stress relief measures with permanent structural sealing and connection, significantly improving the long-term safety and service life of the secondary lining of high-stress soft rock tunnels.

[0043] In an embodiment of the present invention, the steps of removing the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork until the side walls and the invert arch formwork are filled, and then combining the second-stage side walls and the invert arch lining with the first-stage arch lining at the arch foot to form a closed lining ring, include: S71, during the construction of the secondary lining of the first stage arch, a protruding trapezoidal reinforced concrete tenon is prefabricated at the end section of the arch foot of the secondary lining of the first stage arch. The outer surface of the tenon is roughened, and a metal sleeve with an inner diameter of 25mm is pre-embedded in the tenon. S72, Before the construction of the secondary lining of the side wall in the second stage, a slightly larger groove-shaped steel mold is installed on the inner side of the side wall template, corresponding to the position of the tenon, to form a reserved mortise space; S73, When pouring the side wall concrete, the concrete fills the groove-shaped steel mold, wraps the tenon, and forms a mortise; S74. After the concrete strength of the side wall reaches 70% of the design value, non-shrink cement mortar is injected into the contact interface between the tenon and the mortise concrete through the metal sleeve using a high-pressure grouting machine.

[0044] Specifically, during the construction of the secondary lining of the arch in the first stage, a protruding trapezoidal reinforced concrete tenon is prefabricated at the end section of the arch foot of the secondary lining. The outer surface of the tenon is roughened, and a metal sleeve with an inner diameter of 25mm is pre-embedded inside the tenon. This technical feature aims to pre-set a connecting component with a specific geometry and internal structure at the end of the arch foot during the construction of the secondary lining of the arch in the first stage. The trapezoidal reinforced concrete tenon, through its protruding shape, provides a mechanical anchoring point for the subsequent sidewall concrete, forming an effective shear force transmission path and enhancing the shear resistance of the bonding surface. The reinforced concrete material ensures the strength and rigidity of the tenon itself. The roughening of the outer surface increases the roughness between the tenon and the subsequently poured concrete, thereby improving the interfacial adhesion and preventing interface slippage. The pre-embedded metal sleeve with an inner diameter of 25mm provides a channel for subsequent grouting operations, ensuring that the grouting material can be accurately and evenly injected into the bonding interface to fill any possible micro-gaps, further improving the density and integrity of the bonding surface.

[0045] Before the second-stage construction of the secondary lining of the sidewall, a slightly larger groove-shaped steel mold is installed on the inner side of the sidewall formwork, corresponding to the position of the tenon, forming a reserved mortise space. This technical feature describes the formwork setting method adopted during the second-stage construction of the secondary lining of the sidewall to achieve effective connection with the precast tenon. By installing a groove-shaped steel mold slightly larger than the tenon on the inner side of the sidewall formwork, a mortise space matching the shape of the tenon can be formed inside the sidewall concrete during the pouring of the sidewall concrete. This reserved mortise space ensures that the tenon can be completely wrapped by the sidewall concrete, forming a tight mechanical interlock, avoiding the problem of loose joint caused by construction errors, and laying the foundation for subsequent concrete pouring and structural connection.

[0046] When pouring the sidewall concrete, the concrete fills the grooved steel mold, enclosing the tenon to form a mortise. This technical feature details the formation mechanism of the tenon and mortise during the sidewall concrete pouring process. When the sidewall concrete is poured and filled into the grooved steel mold, the concrete naturally encloses the pre-set trapezoidal reinforced concrete tenon. As the concrete sets and hardens, a mortise is formed that fits tightly with the tenon. This enclosing and filling process creates a complete, interlocking mechanical connection structure between the tenon and the mortise, greatly enhancing the integrity and shear resistance of the arch foot joint and effectively avoiding the adverse effects of cold joints on structural integrity.

[0047] After the sidewall concrete reaches 70% of its design strength, non-shrink cement mortar is injected into the interface between the tenon and the mortise using a high-pressure grouting machine through the metal sleeve. This technical feature describes the post-treatment steps for the tenon-mortise interface after the sidewall concrete has reached a certain strength. Grouting is performed after the sidewall concrete reaches 70% of its design strength to ensure that the sidewall concrete itself has sufficient load-bearing capacity to withstand the grouting pressure without damage. Non-shrink cement mortar is injected into the interface between the tenon and the mortise using a high-pressure grouting machine through the pre-embedded metal sleeve. The non-shrink cement mortar effectively fills any small gaps and loose areas that may exist at the interface and compensates for concrete shrinkage, thereby eliminating the cold joint effect and improving the density, water tightness, and overall load-bearing capacity of the interface. High-pressure grouting ensures that the grout can fully penetrate and diffuse, achieving the best filling effect.

[0048] Through the above technical solution, at the junction of the arch foot of the first-stage arch lining and the second-stage sidewall and invert arch lining, mechanical interlocking is achieved by prefabricated trapezoidal reinforced concrete tenons and mortise grooves formed by the sidewall concrete. This effectively solves the cold joint problem caused by phased construction and significantly improves the shear strength and integrity of the arch foot joint surface. Roughening treatment increases interfacial adhesion, while the pre-embedded metal sleeve and subsequent high-pressure non-shrink cement mortar grouting further fill the tiny gaps in the joint surface, eliminating stress concentration and ensuring the density and watertightness of the joint surface. This composite connection method of tenon and mortise joint combined with grouting makes the entire lining ring form a continuous and robust whole at the arch foot, which can more effectively resist complex loads under high ground stress, preventing the arch foot from becoming a weak point in the lining structure, thereby improving the long-term stability and safety of the tunnel lining.

[0049] In an embodiment of the present invention, after the step of pre-embedding a 20mm thick closed-cell foam plastic board at 6-meter intervals in the arc-shaped template at the arch crown position along the longitudinal direction of the tunnel to form a longitudinal temporary stress relief joint, the secondary lining construction method for high-stress soft rock tunnels further includes: S510, when binding the secondary lining steel bars of the arch, three bundles of metal corrugated pipes are pre-embedded at the arch crown and the two sides of the arch waist along the tunnel circumference to form prestressed ducts. S520, after the concrete strength of the arch reaches 90% of the design value, a through-hole jack is used to tension the steel strands inserted into the corrugated metal pipe, and the tension force of a single bundle is controlled to be 40% to 50% of the ultimate tensile strength of the steel strands; S530, after tensioning, cement grout is injected into the metal corrugated pipe using vacuum-assisted grouting, and then the anchorage is sealed with concrete.

[0050] Specifically, during the tying of the secondary lining reinforcement in the arch, three bundles of corrugated metal pipes are pre-embedded along the tunnel circumference at the arch crown and both sides of the arch waist, forming prestressed ducts. Corrugated metal pipes are flexible conduits used to create pre-drilled ducts in concrete structures, providing protection and a force transmission path for the subsequently inserted steel strands. During the tying of the secondary lining reinforcement in the arch, the corrugated metal pipes are securely fixed to the reinforcement cage using ties or special fasteners, according to the design location, ensuring they do not shift or get damaged during concrete pouring. The pre-embedding locations are typically chosen in critical stress areas such as the arch crown and both sides of the arch waist to optimize the prestressing effect.

[0051] After the arch concrete reaches 90% of its design strength, a center-hole jack is used to tension the steel strands inserted into the corrugated metal pipe. The tension force per strand is controlled to be 40% to 50% of the ultimate tensile strength of the steel strand. The center-hole jack is a commonly used tensioning device in prestressed construction, with a central duct allowing the steel strands to pass through. After the arch concrete reaches 90% of its design strength, high-strength steel strands are inserted into the pre-embedded corrugated metal pipe, and anchors are installed at both ends. Tensioning the steel strands using the center-hole jack applies prestress to the concrete structure. Accurate control of the tension force is crucial and is typically monitored using pressure gauges or displacement sensors, maintaining it within 40% to 50% of the ultimate tensile strength of the steel strands. This ensures the effectiveness of the prestressing while preventing excessive fatigue or breakage of the steel strands and considering long-term stress loss.

[0052] After tensioning, cement grout is injected into the corrugated metal pipe using vacuum-assisted grouting, and then the anchorage is sealed with concrete. The purpose of grouting is to integrate the tensioned steel strands with the concrete or mortar in the duct, ensuring that the prestress is effectively transferred to the lining structure and providing corrosion protection for the steel strands. Vacuum-assisted grouting creates negative pressure in the duct, which helps the grout fill the duct more fully, reducing air bubbles and voids, and improving the grouting quality and density. After the grout hardens, the tensioning equipment is removed, and the anchorage area is sealed with concrete or mortar of a strength matching that of the lining concrete, integrating it with the surrounding structure and protecting the anchorage from corrosion and mechanical damage.

[0053] The above technical solution involves pre-embedding corrugated metal pipes to form prestressed ducts during the binding of the secondary lining reinforcement in the arch section. After the concrete reaches a certain strength, the inserted steel strands are tensioned, applying prestress to the arch lining structure. This prestress effectively offsets or significantly reduces the tensile stress that may occur in the lining under high ground stress, thereby improving the crack resistance and overall load-bearing capacity of the arch lining. Simultaneously, prestressing optimizes the internal stress distribution of the lining, reduces stress concentration, delays lining deformation, and enhances its long-term stability. Vacuum-assisted grouting ensures effective bonding and corrosion protection between the prestressed tendons and concrete, further improving the durability of the lining. This solution effectively solves the problem of easy cracking and insufficient load-bearing capacity of the arch lining in soft rock tunnels under long-term surrounding rock pressure, ensuring the safe and reliable operation of the tunnel lining structure.

[0054] In an embodiment of the present invention, the steps of removing the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork until the side walls and the invert arch formwork are filled, and combining the second-stage side walls and the invert arch lining with the first-stage arch lining at the arch foot to form a closed lining ring, further include: S601 divides the 12-meter-long sidewall and invert arch of a single pouring section into four independent pouring sections, each 3 meters long, along the longitudinal direction of the tunnel. S602, pouring is carried out in the order of No. 1, No. 3, No. 2, and No. 4 in a staggered manner, with the time interval between the start of pouring of adjacent No. 1 and No. 4 not less than 72 hours. S603 After the concrete of each compartment is poured, immediately cover the exposed concrete surface of the compartment with plastic film for water retention and curing, and lay circulating cooling water pipes on the outside of the formwork for water cooling.

[0055] Specifically, the 12-meter-long section of the sidewall and invert was divided longitudinally along the tunnel into four independent pouring sections, each 3 meters long. This approach aims to subdivide the long single-pour section into smaller, independently controllable pouring units. During tunnel secondary lining construction, the concrete volume for the sidewalls and invert is large. Pouring excessively long sections at once can easily lead to excessive internal temperature rise in the concrete, generating significant shrinkage stress and causing cracks. By dividing the section into independent pouring sections, the volume of concrete poured in a single pour can be effectively controlled, reducing the accumulation of hydration heat and facilitating subsequent staggered pouring and curing. The 3-meter length of each section is based on a comprehensive consideration of concrete hydration heat control, construction efficiency, and structural integrity requirements in engineering practice.

[0056] Based on this, the concrete is poured in the order of No. 1, No. 3, No. 2, and No. 4, with an interval of at least 72 hours between pours of adjacent sections. Intermittent skip-section pouring is an effective concrete construction method. By skipping adjacent sections, the heat accumulation between newly poured concrete is avoided, further reducing the internal temperature rise of the concrete. For example, No. 1 is poured first, then No. 3 is poured skipping No. 2. After the peak hydration heat of No. 1 and No. 3 has passed, No. 2 and No. 4 are poured in return. The at least 72-hour interval between pours of adjacent sections ensures that the concrete poured earlier has fully released its hydration heat and reached a certain strength and stiffness, thereby reducing the constraint stress exerted on it by the newly poured concrete and effectively controlling crack formation. This time interval can be adjusted appropriately according to factors such as concrete mix proportions, ambient temperature, and structural dimensions to achieve optimal temperature control.

[0057] In addition, immediately after each concrete section is poured, the exposed concrete surface is covered with a plastic film for moisture retention and curing, and circulating cooling water pipes are laid on the outside of the formwork for cooling. Immediately after concrete pouring, moisture retention measures, such as covering with a plastic film, are taken to prevent excessive evaporation of moisture from the concrete surface, avoid early drying shrinkage cracks, and ensure sufficient cement hydration, thereby improving the strength and density of the concrete. Simultaneously, the circulating cooling water pipes on the outside of the formwork are a proactive temperature control measure. The circulating water carries away heat from the outside of the formwork, indirectly reducing the internal temperature of the concrete, effectively controlling the temperature difference between the inside and outside of the concrete, reducing thermal stress, and further inhibiting the occurrence of temperature cracks. This combined internal and external curing and temperature control method is particularly important for secondary linings of high-stress soft rock tunnels, which have extremely high requirements for structural durability and stability.

[0058] By dividing a single pouring section into multiple independent pouring sections and employing an intermittent, skip-pouring method, the accumulation of hydration heat in the concrete is effectively dispersed, avoiding excessive internal temperature rise and thermal stress concentration that could result from continuous pouring of long sections. A pouring interval of at least 72 hours is set between adjacent sections, ensuring that the first poured concrete has sufficient time to release hydration heat and reach a certain strength, thereby reducing the constraint exerted by the newly poured concrete and significantly reducing the risk of temperature cracks. Furthermore, immediately after pouring, the exposed concrete surface is covered with a plastic film for water retention curing, effectively preventing moisture evaporation, inhibiting shrinkage cracks, and ensuring full hydration of the concrete. Simultaneously, circulating cooling water pipes are laid on the outside of the formwork for water cooling, further actively controlling the internal temperature of the concrete, reducing the internal and external temperature difference, thereby minimizing thermal stress and improving the crack resistance and durability of the concrete structure. These measures work synergistically to effectively solve the temperature control problem caused by large-volume concrete pouring in the secondary lining construction of soft rock tunnels under high ground stress, ensuring the long-term stability and safety of the lining structure.

[0059] In an embodiment of the present invention, before the steps of erecting an arc-shaped template within a 120° range of the tunnel arch and pouring C35 early-strength concrete mixed with a magnesium expansion agent into the arc-shaped template, the secondary lining construction method for high-stress soft rock tunnels further includes: S401, with a density of 300 kg / m³. 3 Up to 400 kg / m 3 The hydrophobic rubber foam board is cut into standard panels that are 1000mm long, 500mm wide, and 80mm thick. S402, using a notched scraper, apply the two-component polyurethane adhesive evenly to the surface of the initial support shotcrete and the back of the hydrophobic rubber foam board, with a coating thickness of 3mm to 5mm. S403, the hydrophobic rubber foam board coated with the adhesive is tightly adhered to the initial support surface, and a rubber mallet is used to gently tap it to ensure full adhesion.

[0060] First, a hydrophobic rubber foam board with a density of 300 kg / m³ to 400 kg / m³ is selected and cut into standard panels 1000 mm long, 500 mm wide, and 80 mm thick. The hydrophobic rubber foam board is an elastic material with a closed-cell structure, that is non-absorbent or has extremely low water absorption, and is commonly used for thermal insulation, waterproofing, and shock absorption. In this solution, its main function is to provide waterproofing, thermal insulation, and buffering, effectively preventing groundwater from seeping into the secondary lining structure, avoiding long-term dampness of the lining concrete, and reducing the impact of temperature fluctuations on the lining. Its density range ensures that the material possesses sufficient strength, durability, and good thermal insulation and hydrophobic properties. Cutting it into standard panels facilitates on-site construction and splicing, and ensures uniformity and continuity of the laying.

[0061] Next, using a notched trowel, the two-component polyurethane adhesive is evenly applied to the shotcrete surface of the initial support and the back of the hydrophobic rubber foam board, with a thickness of 3mm to 5mm. The two-component polyurethane adhesive is a chemically reacted and cured adhesive composed of components A and B, possessing excellent bonding strength, elasticity, and water resistance. Its function is to firmly bond the hydrophobic rubber foam board to the shotcrete surface of the initial support, forming a continuous waterproof and heat-insulating layer. Using a notched trowel for even application ensures a uniform adhesive layer thickness, preventing localized areas of excessive thickness or thinness that could affect the bonding effect, while also facilitating air removal and improving bonding strength.

[0062] Finally, the hydrophobic rubber foam board coated with the adhesive is tightly adhered to the initial support surface, and gently tapped with a rubber mallet to ensure full adhesion. This operation aims to ensure full adhesion between the hydrophobic rubber foam board and the initial support surface, eliminating any potential gaps. Tight adhesion reduces gaps between the board and the substrate, while gentle tapping with a rubber mallet helps remove air bubbles from the adhesive layer, ensuring full contact between the adhesive and the board and substrate, thereby achieving optimal bonding while avoiding damage to the foam board and ensuring the integrity and effectiveness of the waterproof and thermal insulation layer.

[0063] Through the above technical solution, a hydrophobic rubber foam board is laid on the initial support surface before the secondary lining concrete is poured, and firmly bonded using a two-component polyurethane adhesive, effectively constructing a continuous waterproof and heat-insulating layer. This hydrophobic rubber foam board can prevent seepage water from directly contacting the secondary lining concrete, significantly reducing the risk of moisture absorption in the lining concrete and thus improving its durability. Simultaneously, the foam board's heat insulation performance effectively buffers the thermal stress generated by temperature fluctuations within the tunnel on the secondary lining structure, reducing the risk of lining cracking caused by temperature changes. Furthermore, its elasticity provides a certain buffer against deformation of the surrounding rock, further ensuring the long-term stability and safety of the secondary lining structure. This pre-installed waterproof and heat-insulating layer solves the common problems of water seepage and temperature stress in high-stress soft rock tunnels from the source, providing a solid guarantee for the performance of the subsequent secondary lining concrete.

[0064] In an embodiment of the present invention, prior to the step of tightly bonding the hydrophobic rubber foam board coated with the adhesive to the initial support surface and gently tapping it with a rubber mallet to ensure full adhesion, the secondary lining construction method for high-stress soft rock tunnels further includes: S431, a 0.2mm thick plastic film is fully laid on the surface of the hydrophobic rubber foam board as a release liner; S432, on the plastic film, at 1.0 meter intervals, a prefabricated thin iron sheet with a central hole is fixed using plastic pads and binding wires, the thin iron sheet serving as a positioning base for the subsequent grouting pipe.

[0065] Specifically, the plastic film, acting as a release liner, primarily functions to form a physical barrier between the hydrophobic rubber foam board and the subsequent concrete or grouting materials. This film effectively prevents the foam board from being directly eroded or adhered to by concrete grout, thus protecting the integrity and function of the foam board. Simultaneously, it also prevents moisture penetration to some extent and provides a relatively smooth interface for subsequent grouting operations, facilitating grout flow. In practice, a 0.2mm thick polyethylene (PE) film or polyvinyl chloride (PVC) film can be selected, as it possesses good flexibility, waterproofing, and corrosion resistance. After the hydrophobic rubber foam board is pasted, the plastic film is laid flat on the foam board surface, and the edges of adjacent films are overlapped and sealed using tape or hot-melt methods to ensure the formation of a continuous release layer.

[0066] The thin iron sheet serves as a positioning base for the subsequent grouting pipe, its core function being to provide an accurate and stable grouting point for any future grouting operations. By pre-fixing the thin iron sheet with a central hole, it ensures that the grouting pipe can be accurately inserted into the predetermined position during installation, avoiding arbitrary punctures to the foam board or inaccurate positioning. The plastic pads and binding wires are used to firmly fix the thin iron sheet to the plastic film, preventing it from shifting during subsequent construction. The thin iron sheet can be prefabricated from galvanized steel or stainless steel plates with a thickness of 1mm to 2mm. The diameter of its central hole should be slightly larger than the outer diameter of the grouting pipe, for example, 20mm to 30mm, to allow the grouting pipe to pass through smoothly. The plastic pads can be made of high-strength engineering plastic with a certain thickness, providing support between the thin iron sheet and the plastic film and ensuring a certain gap between the thin iron sheet and the foam board. The binding wires can be galvanized iron wire or plastic cable ties, used to firmly bind the thin iron sheet to the plastic film through the pre-drilled holes in the plastic pads. In practice, you can first mark 1.0-meter intervals on the plastic film, then place the thin iron sheet on the marked points and fix it with pads and binding wire.

[0067] By covering the surface of the hydrophobic rubber foam board with a layer of plastic film as an isolation membrane, the foam board is effectively protected from damage during subsequent construction and favorable conditions are provided for the uniform diffusion of grout. Simultaneously, thin iron plates with central holes are fixed to the plastic film at 1.0-meter intervals as positioning bases for subsequent grouting pipes, ensuring accurate and stable positioning of the grouting pipes and preventing arbitrary punctures or inaccurate positioning of the foam board during grouting. This ensures the accuracy and effectiveness of the grouting operation. This pre-designed grouting positioning mechanism facilitates later maintenance and defect treatment of the tunnel secondary lining, improves grouting quality, and helps form a denser and more durable lining structure, effectively addressing potential deformation and leakage problems in high-stress soft rock tunnels.

[0068] In an embodiment of the present invention, during the construction of the secondary lining of the first stage arch, a protruding trapezoidal reinforced concrete tenon is prefabricated at the end section of the arch foot of the secondary lining of the first stage arch. The outer surface of the tenon is roughened, and a metal sleeve with an inner diameter of 25mm is pre-embedded in the tenon. S711, a metal sleeve is pre-embedded at the top and on each of the two sides of the trapezoidal reinforced concrete tenon, and the axial direction of the metal sleeve points to the contact surface between the tenon and the future mortise. After the concrete strength of the side wall reaches 70% of the design value, the step of injecting non-shrink cement mortar into the contact interface between the tenon and the mortise concrete using a high-pressure grouting machine through the metal sleeve includes: S741, grout is injected from the top metal sleeve. After the grout flows out of the side metal sleeve, grout is added from both side metal sleeves until the outlets of all metal sleeves are full of grout.

[0069] Specifically, a metal sleeve is pre-embedded at the top and on each of the two sides of the trapezoidal reinforced concrete tenon. These metal sleeves have an inner diameter of 25mm and are typically made of galvanized steel or PVC pipe. Their axial direction is carefully designed to point towards the contact surface between the tenon and the future mortise. This multi-point pre-embedded and oriented metal sleeve layout aims to provide multiple, evenly distributed grouting channels that directly reach the critical stress interface for subsequent grouting operations, ensuring that the grout effectively covers the entire connection area and avoiding dead zones or uneven filling caused by single-point grouting.

[0070] After the concrete strength of the side wall reaches 70% of the design value, non-shrink cement mortar is injected into the contact interface between the tenon and the mortise using a high-pressure grouting machine through the metal sleeves. The grouting process employs a step-by-step, orderly strategy: First, grout is injected from the top metal sleeve. Due to gravity, the grout flows downwards, initially filling the interface voids. When grout begins to flow from the side metal sleeves, it indicates that the lower space is essentially filled. At this point, top grouting is stopped, and supplementary grouting is then performed from the two side metal sleeves. This supplementary grouting provides secondary pressure and filling to the interface, effectively expelling any air that may remain and ensuring the density of the grout. Grouting continues until all outlets of the metal sleeves are filled with saturated grout, i.e., the grout flows out evenly and without air bubbles, indicating that the entire contact interface between the tenon and the mortise has been completely and densely filled with non-shrink cement mortar.

[0071] By employing the aforementioned technical solution, and by pre-embedding multiple directional metal sleeves at the top and sides of the tenon, and using a step-by-step grouting strategy—first the top and then the sides—it is possible to ensure that the non-shrink cement mortar is fully, uniformly, and densely filled at the interface between the tenon and the mortise. This refined grouting control effectively avoids the problems of local voids and incomplete filling that may result from traditional single-point or disordered grouting, significantly improving the connection strength and integrity of the arch secondary lining with the sidewalls and the invert secondary lining at the arch foot. The resulting closed lining ring can more effectively transfer loads and resist deformation caused by high ground stress, thereby enhancing the long-term stability and safety of the tunnel lining structure. This is particularly suitable for applications in high-stress soft rock tunnels where the overall stress performance requirements of the lining structure are extremely high.

[0072] In an embodiment of the present invention, the steps of removing the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork until the side walls and the invert arch formwork are filled, and combining the second-stage side walls and the invert arch lining with the first-stage arch lining at the arch foot to form a closed lining ring, further include: S710, Measure the current horizontal distance between the left sidewall convergence measuring stake fixing plate and the right sidewall convergence measuring stake fixing plate; S720, compare the current horizontal distance with the initial installation reference distance of the left sidewall convergence measuring stake fixing plate and the right sidewall convergence measuring stake fixing plate to obtain an intuitive length difference value L; S730, if the length difference L is greater than 50mm, the entire full-section hydraulic trolley template system is horizontally pushed to the side with the longer current horizontal distance by the horizontal hydraulic jack at the bottom of the full-section hydraulic trolley, and the pre-displacement amount is set to 20mm to 30mm. S740, under the pre-displacement state, the pouring and curing of the sidewall and invert arch concrete are completed.

[0073] Specifically, before the second-stage construction of the sidewalls and invert arch lining, it is necessary to first measure the current horizontal distance between the convergence measuring stakes on the left and right sides of the sidewall. These convergence measuring stakes are pre-installed as measurement benchmarks on the initial support or already poured lining structure to monitor the deformation of the tunnel clearance. By measuring the distance between these two stakes, the lateral deformation of the tunnel can be monitored in real time. This can be achieved through manual measurement using tools such as a high-precision laser rangefinder, a steel ruler, and a force gauge, or through continuous measurement using an automated monitoring system (such as an image recognition or laser scanning system) to ensure the accuracy and timeliness of the data.

[0074] Subsequently, the current horizontal distance is compared with the initial installation reference distances of the left and right sidewall convergence measuring stake fixing plates to obtain a direct length difference value L. The initial installation reference distance refers to the original design or initial measurement distance before the formwork system is installed after tunnel excavation or initial support is completed, representing the ideal state of the tunnel clearance. By comparing the current measurement value with this reference value, the convergence or expansion of the tunnel clearance in the lateral direction can be calculated, i.e., the length difference L. This difference L directly reflects the influence of surrounding rock deformation on the tunnel clearance, providing a quantitative basis for subsequent formwork adjustments.

[0075] If the length difference L is greater than 50mm, the entire full-section hydraulic trolley formwork system is horizontally pushed towards the side with the longer current horizontal distance using the transverse hydraulic jacks at the bottom of the trolley. The pre-displacement is set to 20mm to 30mm. When the length difference L exceeds a preset threshold (e.g., 50mm), it indicates that the tunnel clearance deformation has reached a level requiring intervention. Full-section hydraulic trolleys are typically equipped with multiple hydraulic jacks, which can work independently or collaboratively to achieve accurate movement of the formwork system. The transverse hydraulic jacks can horizontally push the entire formwork system towards the side with less deformation or no deformation to compensate for the deformation on the other side. The pre-displacement (20mm to 30mm) is set to pre-counteract some of the expected deformation before pouring concrete, ensuring that the final lining geometry is closer to the design requirements. This pre-displacement relies on accurate control of the hydraulic system and feedback from displacement sensors.

[0076] Finally, under the pre-displacement state, the concrete for the sidewalls and invert arch is poured and cured. This step ensures that, after accurate adjustment and pre-displacement of the formwork system, the concrete can be poured according to the corrected clearance shape. Under the pre-displacement state, the formwork system has taken into account the influence of surrounding rock deformation, allowing the poured concrete lining to better adapt to the actual surrounding rock conditions and restore or approach the design clearance as much as possible. The concrete pouring and curing process should be strictly carried out in accordance with conventional construction specifications, including layered pouring, vibration compaction, and timely curing, to ensure the strength and durability of the concrete.

[0077] The above technical solution effectively addresses the problem of tunnel clearance geometry deviating from the design due to surrounding rock deformation during secondary lining construction in high-stress soft rock tunnels. Before the second-stage sidewall and invert arch concrete pouring, the lateral deformation of the tunnel sidewalls is monitored in real time, and the full-section hydraulic trolley formwork system is actively and accurately pre-displaced according to the deformation amount, ensuring the geometric accuracy and stress uniformity of the final closed lining ring. This avoids lining structural defects caused by formwork misalignment, improves the overall stability and durability of the lining, reduces the need for later repairs and rework, and ensures the quality and safety of the tunnel project.

[0078] The following example will provide a more detailed explanation of the above technical solution: In a high-stress soft rock tunnel project, the construction team faced the technical challenges of large deformation and continuous rheology of the surrounding rock. To effectively address these issues, the team adopted a phased and meticulously controlled secondary lining construction method.

[0079] First, initial support is constructed immediately after tunnel excavation. This initial support consists of shotcrete, a full-ring steel arch frame, and a system of anchor bolts, designed to quickly stabilize the surrounding rock and create conditions for subsequent construction.

[0080] After the initial support is completed, construction workers install mechanical convergence test piles on the initial support surface and begin continuous monitoring of tunnel clearance convergence to obtain real-time monitoring data. This data is crucial for determining the timing of secondary lining construction.

[0081] Based on continuously acquired monitoring data, the construction team determined the timing for secondary lining construction. When monitoring data showed that the tunnel clearance convergence rate remained between 30 mm / d and 50 mm / d for three consecutive days, it indicated that the surrounding rock deformation had entered a relatively active but controllable stage. At this point, the first stage of arch secondary lining construction was initiated. Unlike the traditional approach of waiting for the surrounding rock deformation to stabilize before full-section pouring, this phased strategy allows for priority support of the most critically stressed arch section while the surrounding rock deformation is still relatively active, avoiding delays and increased initial support burden caused by prolonged waiting.

[0082] In the first phase of the arch secondary lining construction, the construction team erected arc-shaped formwork within a 120° range of the tunnel arch. Subsequently, C35 early-strength concrete incorporating a magnesium-based expansion agent was poured into the arc-shaped formwork. The preparation process for this concrete involved: dry-mixing the magnesium-based expansion agent at a ratio of 6% to 8% of the total weight of the cementitious materials with cement, fly ash, aggregates, and admixtures at a mixing plant for at least 60 seconds; then adding mixing water for wet mixing for at least 120 seconds to produce shrinkage-compensating concrete. This shrinkage-compensating concrete effectively counteracts the shrinkage stress of the concrete itself, reducing structural cracks caused by the combined effects of concrete shrinkage and surrounding rock compression, thus improving the long-term durability of the secondary lining. The concrete was pumped to the top inlet of the arc-shaped formwork using a pump, and poured in oblique layers with a horizontal pouring method, with each layer controlled to a thickness of 40 to 50 cm. After each layer is poured, immediately vibrate it through the lateral vibration window reserved in the arc-shaped template using an immersion vibrator with a diameter of 50mm. The vibration point spacing should not be greater than 40cm, and the vibrator should be inserted into the lower layer of concrete for at least 5cm. Vibrate until the concrete surface is covered with slurry and no obvious air bubbles escape. Then, pour the next layer to ensure the density and strength of the concrete.

[0083] Meanwhile, to accommodate the large deformation characteristics of soft rock under high ground stress, a 20mm thick closed-cell foam plastic board is pre-embedded in the arched template at the arch crown every 6 meters along the tunnel's longitudinal direction, forming a longitudinal temporary stress relief joint. This design allows for a certain degree of stress relief in the arch lining during the initial deformation process, preventing stress concentration that could lead to cracking. A row of ribbed short steel bars, 1.0 meter long and 25mm in diameter, is pre-embedded in the concrete on both sides of the closed-cell foam plastic board. One end extends into the concrete, and the other end terminates on the side of the closed-cell foam plastic board, with the ends coated with anti-rust paint to ensure the reliability of subsequent connections.

[0084] During the reinforcement binding of the secondary lining of the arch, three bundles of corrugated metal pipes are pre-embedded at the arch crown and both sides of the arch waist along the tunnel circumference, forming prestressed ducts. After the arch concrete reaches 90% of its design strength, through-hole jacks are used to tension the steel strands inserted into the corrugated metal pipes, with the tension force of each bundle controlled at 40% to 50% of the ultimate tensile strength of the steel strand. After tensioning, cement grout is injected into the corrugated metal pipes using vacuum-assisted grouting, and then the anchorages are sealed with concrete. This prestressed technology provides active support for the arch lining, enhancing its resistance to surrounding rock deformation. Compared to schemes relying solely on passive support, it significantly improves the support effect and structural safety.

[0085] During the construction of the secondary lining of the arch in the first stage, a protruding trapezoidal reinforced concrete tenon is prefabricated at the end section of the arch foot of the secondary lining. The outer surface of the tenon is roughened, and a metal sleeve with an inner diameter of 25mm is pre-embedded inside the tenon. Specifically, a metal sleeve is pre-embedded at the top and two sides of the trapezoidal reinforced concrete tenon, with the axis of the metal sleeve pointing towards the contact surface between the tenon and the future mortise. This tenon design provides a structural basis for the subsequent connection between the sidewall and the arch.

[0086] After the concrete strength of the secondary lining of the arch reached 80% of the design 28-day strength in the first stage, the construction team continued monitoring. When the net clearance convergence rate remained stable within the range of 0.5 mm / d to 2.0 mm / d for seven consecutive days, it indicated that the surrounding rock deformation had stabilized, and the second stage of sidewall and invert secondary lining construction was initiated. This phased and refined control of construction timing effectively solved the contradiction between the single construction timing and the difficulty in balancing surrounding rock deformation and timely lining closure in traditional methods.

[0087] Before the second phase of construction, the arch formwork was removed and a full-section hydraulic trolley formwork was erected. On the inner side of the side wall formwork, a slightly larger groove-shaped steel mold was installed at the position corresponding to the tenon, forming a reserved mortise space.

[0088] Before pouring the concrete for the sidewalls and invert, the construction team measured the current horizontal distance between the convergence measuring stakes on the left and right sides of the sidewall. This current horizontal distance was compared with the initial installation reference distances of the convergence measuring stakes on both sides to obtain a visual length difference L. If the length difference L was greater than 50mm, the entire full-section hydraulic trolley formwork system was horizontally pushed towards the side with the longer current horizontal distance using the transverse hydraulic jacks at the bottom of the trolley, with a pre-displacement amount set to 20mm to 30mm. Under this pre-displacement condition, the pouring and curing of the sidewalls and invert were completed. This pre-displacement measure actively adapts to the uneven deformation of the surrounding rock, ensuring the geometric accuracy and stress uniformity of the lining structure.

[0089] Subsequently, starting from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork, concrete is poured synchronously, symmetrically, and continuously until the side walls and invert arch formwork are filled. During the pouring of the side wall concrete, the concrete fills the grooved steel mold, wrapping the tenons to form mortises, allowing the second-stage side wall and invert arch lining to connect with the first-stage arch lining at the arch foot, forming a closed lining ring. This connection method ensures the integrity and stability of the lining structure.

[0090] To control the heat of hydration and shrinkage of the concrete, the 12-meter-long sidewalls and invert were divided into four independent pouring sections, each 3 meters long, along the tunnel's longitudinal direction. Pouring was carried out in an alternating, skip-section manner, following the sequence of section 1, section 3, section 2, and section 4, with a minimum 72-hour interval between pours of adjacent sections. After each section's concrete pour was completed, a plastic film was immediately placed over the exposed concrete surface for moisture retention and curing, and circulating cooling water pipes were laid on the outside of the formwork for cooling. These measures effectively reduced the concrete's temperature rise and shrinkage stress, minimizing crack formation.

[0091] After the concrete strength of the side wall reaches 70% of the design value, non-shrink cement mortar is injected into the contact interface between the tenon and the mortise using a high-pressure grouting machine through metal sleeves. Specifically, grout is injected from the top metal sleeve, and after grout flows out of the side metal sleeves, additional grout is injected from both side metal sleeves until all metal sleeve outlets are full of grout. This grouting method ensures a tight connection between the tenon and the mortise, forming a unified load-bearing structure that effectively transfers loads and avoids stress concentration problems that may occur with traditional rigid connections.

[0092] Finally, after the entire secondary lining is sealed into a ring and its deformation stabilizes, an electric hot wire cutting tool is used to remove the exposed closed-cell foam plastic board along the longitudinal direction of the tunnel, forming a 20mm wide open joint. Then, a manual caulking gun is used to inject polysulfide building sealant into the open joint in sections, with an injection depth of no less than 80% of the joint depth, and the surface is smoothed. This treatment method transforms the temporary stress relief joint into a permanent, deformable sealing joint, which can adapt to the long-term deformation of the surrounding rock while ensuring the waterproof performance and durability of the lining.

[0093] Through the synergistic effect of the above-mentioned series of technical features, this construction method achieves accurate control of the timing of secondary lining construction, effective compensation of concrete shrinkage stress, adaptive release of surrounding rock deformation, and improvement of the integrity and durability of the lining structure in the high-stress soft rock tunnel environment, effectively solving the challenges brought by large deformation and continuous rheology of surrounding rock to secondary lining construction.

[0094] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A method for secondary lining construction of tunnels in soft rock with high ground stress, characterized in that, The secondary lining construction method for high-stress soft rock tunnels includes: After the tunnel is excavated, the initial support, including shotcrete, full-ring steel arch frame and system anchor bolts, is immediately constructed. Mechanical convergence test piles were installed on the initial support surface to begin continuous monitoring of tunnel clearance convergence and obtain monitoring data. Based on the monitoring data, the timing of secondary lining construction is determined as follows: when the net clearance convergence rate is in the range of 30 mm / d to 50 mm / d for three consecutive days, the first stage of arch secondary lining construction is started. An arc-shaped template is erected within a 120° range of the tunnel arch, and C35 early-strength concrete mixed with magnesium expansion agent is poured into the arc-shaped template. Along the longitudinal direction of the tunnel, a 20mm thick closed-cell foam plastic board is pre-embedded in the arc-shaped template at the arch position every 6 meters to form a longitudinal temporary stress relief joint. After the concrete strength of the secondary lining of the arch reaches 80% of the design value after 28 days in the first stage, monitoring continues. When the net clearance convergence rate is stable within the range of 0.5 mm / d to 2.0 mm / d for 7 consecutive days, the construction of the secondary lining of the sidewall and invert arch in the second stage is started. Remove the arch formwork and erect a full-section hydraulic trolley formwork. Starting from the pouring windows at the bottom of the side walls on both sides of the full-section hydraulic trolley formwork, pour concrete synchronously, symmetrically and continuously until the side walls and invert arch formwork are filled. Then, the second-stage side walls and invert arch lining are combined with the first-stage arch lining at the arch foot to form a closed lining ring.

2. The secondary lining construction method for high-stress soft rock tunnels as described in claim 1, characterized in that, The steps of erecting an arc-shaped formwork within a 120° range of the tunnel arch and pouring C35 early-strength concrete mixed with a magnesium expansion agent into the arc-shaped formwork include: The magnesium-based expansive agent is dry-mixed with cement, fly ash, aggregates and admixtures at a mixing plant at a ratio of 6% to 8% of the total weight of cementitious materials for a dry mixing time of not less than 60 seconds. Then, mixing water is added for wet mixing for a wet mixing time of not less than 120 seconds to produce shrinkage-compensating concrete. The shrinkage-compensating concrete is pumped to the top inlet of the arc-shaped formwork using a concrete delivery pump, and poured in a slanted, layered, and horizontal manner, with the thickness of each layer controlled between 40 cm and 50 cm. After each layer is poured, immediately vibrate it through the lateral vibration window reserved in the arc-shaped template using an immersion vibrator with a diameter of 50mm. The vibration point spacing should not be greater than 40cm, and the vibrator should be inserted into the lower layer of concrete for no less than 5cm. Vibrate until the concrete surface is covered with slurry and no obvious air bubbles escape, and then proceed with the next layer pouring.

3. The secondary lining construction method for high-stress soft rock tunnels as described in claim 1, characterized in that, Following the step of pre-embedding a 20mm thick closed-cell foam plastic board every 6 meters along the longitudinal direction of the tunnel within the arched template at the arch crown to form a longitudinal temporary stress relief joint, the secondary lining construction method for high-stress soft rock tunnels further includes: A row of ribbed short steel bars is pre-embedded in the concrete on both sides of the closed-cell foam plastic board; wherein the length of the ribbed short steel bar is 1.0 meter and the diameter is 25 mm, one end of the ribbed short steel bar extends into the concrete and the other end terminates in the side of the closed-cell foam plastic board, and the end of the ribbed short steel bar is coated with anti-rust paint. After the entire secondary lining is closed into a ring and the deformation is stable, use an electric hot wire cutting tool to remove the exposed closed-cell foam plastic board along the longitudinal direction of the tunnel to form a 20mm wide open seam. Use a manual caulking gun to inject polysulfide building sealant into the exposed joint in sections, with the injection depth not less than 80% of the joint depth, and then smooth the surface.

4. The secondary lining construction method for high-stress soft rock tunnels as described in claim 1, characterized in that, The steps of dismantling the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the bottom of the sidewalls on both sides of the full-section hydraulic trolley formwork until the sidewalls and invert arch formwork are filled, and then combining the second-stage sidewalls and invert arch lining with the first-stage arch lining at the arch foot to form a closed lining ring, include: During the construction of the secondary lining of the arch in the first stage, a protruding trapezoidal reinforced concrete tenon is prefabricated at the end section of the arch foot of the secondary lining of the arch in the first stage. The outer surface of the tenon is roughened and a metal sleeve with an inner diameter of 25mm is pre-embedded in the tenon. Before the construction of the secondary lining of the side wall in the second stage, a slightly larger groove-shaped steel mold is installed on the inner side of the side wall formwork, corresponding to the position of the tenon, to form a reserved mortise space. When pouring the side wall concrete, the concrete fills the groove-shaped steel mold, wraps the tenon, and forms a mortise. After the concrete strength of the side wall reaches 70% of the design value, non-shrink cement mortar is injected into the contact interface between the tenon and the mortise concrete through the metal sleeve using a high-pressure grouting machine.

5. The secondary lining construction method for high-stress soft rock tunnels as described in claim 1, characterized in that, Following the step of pre-embedding a 20mm thick closed-cell foam plastic board every 6 meters along the longitudinal direction of the tunnel within the arched template at the arch crown to form a longitudinal temporary stress relief joint, the secondary lining construction method for high-stress soft rock tunnels further includes: When tying the secondary lining steel bars of the arch, three bundles of corrugated metal pipes are pre-embedded at the arch crown and the two sides of the arch waist along the tunnel circumference to form prestressed ducts. After the concrete strength of the arch reaches 90% of the design value, a through-hole jack is used to tension the steel strands inserted into the corrugated metal pipe. The tension force of a single bundle is controlled to be 40% to 50% of the ultimate tensile strength of the steel strands. After tensioning is completed, cement grout is injected into the metal corrugated pipe using vacuum-assisted grouting, and then the anchorage is sealed with concrete.

6. The secondary lining construction method for high-stress soft rock tunnels as described in claim 1, characterized in that, The steps of dismantling the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the bottom of the sidewalls on both sides of the full-section hydraulic trolley formwork until the sidewalls and invert arch formwork are filled, and then combining the second-stage sidewalls and invert arch lining with the first-stage arch lining at the arch foot to form a closed lining ring, further include: The 12-meter-long sidewall and invert arch of the single-pour section are divided into four independent pouring sections, each 3 meters long, along the longitudinal direction of the tunnel. The pouring shall be carried out in the order of No. 1, No. 3, No. 2, and No. 4, with an interval of no less than 72 hours between the start of pouring of adjacent No. 1 and No.

4. After the concrete of each compartment is poured, immediately cover the exposed concrete surface of the compartment with plastic film for water retention and curing, and lay circulating cooling water pipes on the outside of the formwork for water cooling.

7. The secondary lining construction method for high-stress soft rock tunnels as described in claim 1, characterized in that, Before the steps of erecting an arc-shaped formwork within a 120° range of the tunnel arch and pouring C35 early-strength concrete mixed with a magnesium expansion agent into the arc-shaped formwork, the secondary lining construction method for high-stress soft rock tunnels further includes: Select a density of 300 kg / m³ 3 Up to 400 kg / m 3 The hydrophobic rubber foam board is cut into standard panels that are 1000mm long, 500mm wide, and 80mm thick. Use a notched scraper to evenly apply the two-component polyurethane adhesive to the surface of the initial support shotcrete and the back of the hydrophobic rubber foam board, with a coating thickness of 3mm to 5mm. The hydrophobic rubber foam board coated with the adhesive is tightly adhered to the initial support surface, and gently tapped with a rubber mallet to ensure full adhesion.

8. The secondary lining construction method for high-stress soft rock tunnels as described in claim 7, characterized in that, Before the step of tightly bonding the hydrophobic rubber foam board coated with the adhesive to the initial support surface and gently tapping it with a rubber mallet to ensure full adhesion, the secondary lining construction method for high-stress soft rock tunnels further includes: A 0.2mm thick plastic film is laid on the surface of the hydrophobic rubber foam board as a release liner; On the plastic film, at 1.0 meter intervals, a prefabricated thin iron sheet with a central hole is fixed using plastic pads and binding wire. The thin iron sheet serves as a positioning base for the subsequent grouting pipe.

9. The secondary lining construction method for high-stress soft rock tunnels as described in claim 4, characterized in that, During the construction of the secondary lining of the arch in the first stage, a protruding trapezoidal reinforced concrete tenon is prefabricated at the end section of the arch foot of the secondary lining of the arch in the first stage. The outer surface of the tenon is roughened, and a metal sleeve with an inner diameter of 25mm is pre-embedded in the tenon. The steps include: A metal sleeve is pre-embedded at the top and on each of the two sides of the trapezoidal reinforced concrete tenon, with the axial direction of the metal sleeve pointing towards the contact surface between the tenon and the future mortise. After the concrete strength of the side wall reaches 70% of the design value, the step of injecting non-shrink cement mortar into the contact interface between the tenon and the mortise concrete using a high-pressure grouting machine through the metal sleeve includes: Grout is injected from the top metal sleeve. After the grout flows out of the side metal sleeves, grout is added from both side metal sleeves until all the outlets of the metal sleeves are full of grout.

10. The secondary lining construction method for high-stress soft rock tunnels as described in claim 1, characterized in that, The steps of dismantling the arch formwork, erecting a full-section hydraulic trolley formwork, and simultaneously, symmetrically, and continuously pouring concrete from the bottom of the sidewalls on both sides of the full-section hydraulic trolley formwork until the sidewalls and invert arch formwork are filled, and then combining the second-stage sidewalls and invert arch lining with the first-stage arch lining at the arch foot to form a closed lining ring, further include: Measure the current horizontal distance between the convergence measuring stake fixing plate on the left side wall and the convergence measuring stake fixing plate on the right side wall; The current horizontal distance is compared with the initial installation reference distance of the left sidewall convergence measuring stake fixing plate and the right sidewall convergence measuring stake fixing plate to obtain an intuitive length difference value L; If the length difference L is greater than 50mm, the entire full-section hydraulic trolley template system will be horizontally pushed to the side with the longer current horizontal distance by the horizontal hydraulic jack at the bottom of the full-section hydraulic trolley, and the pre-displacement amount will be set to 20mm to 30mm. Under the pre-displacement state, the pouring and curing of the sidewall and invert arch concrete are completed.

Images