Method for repairing lining cracks in tunnel during operation of skylight period

Abstract

This invention relates to the field of tunnel lining repair technology, providing a rapid repair method for lining cracks in operational tunnels during maintenance windows. The maintenance window is the daily nighttime train downtime, with each window lasting approximately 4 hours. It employs four maintenance window adaptation processes: diagnosis, anchoring, waterproofing, and load-bearing capacity assessment. Through continuous maintenance window operations, the reinforced structure gradually reaches its load-bearing strength and meets the conditions for opening. The process includes: the first maintenance window for accurate diagnosis and rapid anchoring; the second maintenance window for base reconstruction and rapid-setting waterproofing; the third maintenance window for steel mesh installation and the first layer of spraying; the fourth maintenance window for layered spraying and opening determination; and the operational interval curing stage. This invention, under the strict constraint of extremely short maintenance windows, effectively achieves a systematic engineering approach that unifies radical repair of tunnel linings with long-term durability. This invention adopts an open-formulation design, supporting flexible replacement of various cement-based grouting materials and various fiber-reinforced concretes.

Description

Technical Field

[0001] This invention relates to the field of tunnel lining repair technology, and in particular to a rapid repair method for lining cracks in operational tunnels during tunnel maintenance windows. Background Technology

[0002] As highway and railway networks age, many tunnels are entering a period of high incidence of defects. Affected by multiple factors such as low early construction standards, insufficient construction quality control, changes in surrounding rock pressure, natural material deterioration, and environmental erosion, operating tunnels commonly exhibit defects such as lining cracks, water leakage, backfill voids, and concrete spalling. Some defects have progressed to severe states such as lining deformation, cracking, misalignment, and spalling, significantly reducing the structural bearing capacity and seriously endangering traffic safety and personal safety.

[0003] Traditional tunnel repair methods primarily employ the formwork arch reinforcement method, which involves casting a reinforced concrete arch over the existing lining. While this method can improve the stiffness, strength, and stability of the lining, it suffers from the following significant problems: (1) Severe operational disruption. The construction period for arch-mounted tunnels usually takes 30-60 days, requiring the complete closure of the tunnel or interruption of line operation, resulting in huge transportation losses and social impact. For high-speed railways and busy trunk lines, long-term track closures are economically unacceptable, leading to the failure to address defects in a timely manner and their continued development and expansion.

[0004] (2) Significant encroachment on clearance. The thickness of the arch is generally not less than 25cm. For tunnels with tight cross-sectional clearance, this will severely compress the effective clearance, which may not meet the building clearance requirements and may even affect the layout of operation facilities such as ventilation and lighting.

[0005] (3) Construction quality is difficult to control. The bonding quality between the arch and the existing lining is difficult to guarantee, and new voids are easily formed; the heat of hydration of large-volume concrete is prone to cause temperature cracks; improper treatment of construction joints is prone to forming water seepage channels.

[0006] (4) Poor economic efficiency. It requires a large amount of materials, high labor costs, and high machine operating costs, resulting in a significantly higher overall cost than other reinforcement methods.

[0007] To shorten the construction period, some projects have attempted to use shotcrete reinforcement technology, but the existing technology still has obvious shortcomings: First, ordinary shotcrete develops strength slowly in the early stages, requiring more than 24 hours to reach the requirements for opening to traffic, which cannot adapt to the 2-4 hour daily operation window; second, there is a lack of a systematic process that matches the length of the operation window, and improper connection between various procedures leads to wasted time; third, there is no scientific and rapid judgment standard, and the decision to open the line relies on experience, resulting in high safety risks; fourth, there is a lack of a collaborative maintenance mechanism during operation, and insufficient early maintenance leads to strength reduction and surface cracking.

[0008] Fiber-reinforced concrete possesses excellent crack resistance, impermeability, and toughness. A volumetric admixture of 0.05% to 0.1% can improve impermeability by over 40% and reduce permeability height by 30% to 70%. It also exhibits outstanding resistance to chemical corrosion and fatigue resistance, making it an ideal material for tunnel reinforcement. However, applying fiber-reinforced concrete to rapid repair during tunnel maintenance windows requires addressing a series of technical challenges, including rapid setting and early strength of the material, layered spraying and interlayer bonding, rapid detection and opening determination, and operational vibration and early curing. Existing technologies have not yet provided a systematic solution.

[0009] Therefore, there is an urgent need to develop a rapid repair technology for lining cracks that is well-suited to operational window periods. This technology should enable a highly efficient repair model of "daily window period operation and normal operation the next day" while ensuring structural safety and reliability, thereby fundamentally alleviating the conflict between operation and construction. Summary of the Invention

[0010] The purpose of this invention is to solve at least one technical problem in the background art and to provide a rapid repair method for lining cracks in operating tunnels during tunnel maintenance windows.

[0011] To achieve the above objectives, this invention provides a rapid repair method for lining cracks in operating tunnels during maintenance windows. The maintenance window is the daily nighttime train shutdown period, with a single window lasting 4 hours. It employs four maintenance window adaptation processes: diagnostics, anchoring, waterproofing, and load-bearing capacity assessment. Through four consecutive maintenance window operations, the reinforced structure gradually reaches its load-bearing strength and meets the conditions for reopening. The method includes: First window period: accurate diagnosis and rapid treatment of diseases. During operational breaks, a combination of non-destructive testing with ground-penetrating radar and manual tapping is used to quickly determine the extent of cavities behind the lining, the direction of cracks, and the depth of the loosened zone in the surrounding rock. Then, grouting anchor pipes with both anchoring and grouting functions are installed in the determined area. The grouting anchor pipes have quincunx-shaped overflow holes on their walls and grout-stopping anchor sections at their tails. The grouting anchor pipes are arranged in a quincunx pattern. Through the grouting anchor pipes, one-time, pressure-controlled grouting is performed into the cavities behind the lining and the surrounding rock. A fast-setting cement-based grouting material is used to ensure that the grout strength is ≥5MPa at the end of the first day window. The second day of the window period: base surface reconstruction and rapid-setting waterproofing: Remove the deteriorated concrete from the surface and seal the cracks with pressure-injected adhesive. Then, continuously spray a wet-curing, fast-setting waterproof layer onto the base surface. The sprayed waterproof layer uses a high-elasticity, reverse-adhesion, fast-setting waterproof coating with a thickness of 1.2-2.5 mm. It is surface-dry within 30 minutes after spraying and fully dry by the end of the second day's window period. Seal the root of the grouting anchor pipe with adhesive and thicken the wrapping to a local thickness of not less than 4 mm. During the third window period, the steel mesh is installed and the first layer of spraying is carried out: After the sprayed waterproof layer has cured, immediately install the steel mesh and directly weld or tie it to the exposed non-threaded section of the grouting anchor pipe; the steel mesh is a single-layer cold-drawn steel mesh; then spray the first layer of fiber concrete, 4-6cm thick, to form a leveling and filling layer; the compressive strength is ≥5MPa at the end of the third day window after spraying. Fourth window period, layered spray molding and opening determination: After the first layer of fiber-reinforced concrete has initially set, the second and third layers of fiber-reinforced concrete are sprayed sequentially. The second layer of fiber-reinforced concrete is 6-8 cm thick and serves as the main structural layer. The third layer of fiber-reinforced concrete is 2-4 cm thick, with a higher mortar volume ratio than the previous two layers. The spraying interval between the second and third layers of fiber-reinforced concrete is less than 2 hours. The water-cement weight ratio of each layer of fiber-reinforced concrete is 0.35-0.40, and it contains 3%-5% accelerator and 2%-4% early-strength agent to form early-strength and fast-hardening concrete. After spraying, the surface is leveled. After leveling, the surface is inspected and accepted according to the fourth day window period and the concrete strength assessment standard. The second layer of fiber-reinforced concrete has a compressive strength ≥10MPa at the end of the fourth day window period, which is considered to meet the conditions for commissioning. Maintenance phase: After the fourth day window of construction is completed, the sprayed surface layer is cured for at least 14 consecutive days.

[0012] According to one aspect of the present invention, during the first window period, the quick-setting cement-based grouting material is a sulfoaluminate cement-based ultra-early strength grouting material with an initial setting time of 30-60 minutes, a compressive strength of ≥5MPa at 1 hour, and a compressive strength of ≥30MPa at 24 hours.

[0013] According to one aspect of the present invention, during the first window period, the grouting anchor pipe adopts a segmented structure: the front end is a drilling section with a tapered guide head, the middle part is a grouting section with the plum blossom-shaped overflow hole, and the tail end is a grout-stopping anchoring section with external threads; the diameter of the plum blossom-shaped overflow hole is 4-8mm, and the hole spacing is 10-20cm.

[0014] According to one aspect of the present invention, during the second window period, the pressure grouting sealant uses a modified epoxy resin grout with a viscosity of 100-500 mPa·s, suitable for cracks with a width of less than 0.2 mm; or a modified polyurea grout with a viscosity of 500-2000 mPa·s, suitable for cracks with a width of 0.2-2 mm; the grouting pressure is 0.2-0.5 MPa, and the grout initially sets 30 minutes after grouting.

[0015] According to one aspect of the present invention, during the second window period, the elongation at break of the high elastic modulus anti-adhesion waterproof coating is ≥300%, the bond strength with the concrete substrate is ≥1.0MPa, and the curing time under damp substrate conditions is 30%-50% shorter than that under dry substrate conditions.

[0016] According to one aspect of the invention, during the third and fourth daylighting periods, the mix proportion of the fiber-reinforced concrete is: cement:sand:stone = 1:1.5:2.5.

[0017] According to one aspect of the present invention, during the fourth window period, when the second layer of fiber-reinforced concrete is sprayed, a stress monitoring plate is embedded between the steel mesh and the first layer of fiber-reinforced concrete to monitor the interlayer bonding state in real time; the sand ratio of the third layer of fiber-reinforced concrete is increased by 5%-8% compared with the first two layers, thereby reducing the surface rebound rate and increasing the density.

[0018] According to one aspect of the present invention, the operation sequence control of the fourth window period is as follows: after the start of the window period, the second layer of fiber concrete spraying is completed within a first preset time; after an interval of a second preset time, the third layer of fiber concrete spraying is completed within a third preset time; and a fourth preset time is reserved for surface leveling and rapid strength testing; the rapid strength testing adopts a rebound hammer or an ultrasonic rebound combined method, and the spacing between the measuring points is ≤2m. The first preset time is 0.5-1 hour, the second preset time is 1-1.5 hours, the third preset time is 0.5-1 hour, and the fourth preset time is 0.5 hours.

[0019] According to one aspect of the present invention, during the operational interval maintenance phase, an automated spray maintenance system is adopted, the system comprising atomizing nozzles arranged longitudinally along the tunnel, a timer controller and a water source, with a spray pressure of 0.2-0.4 MPa and a droplet diameter of 50-100 μm.

[0020] According to one aspect of the present invention, under the stringent condition of not interrupting daytime railway operations, efficient and orderly operation during four consecutive nighttime maintenance windows enables rapid and safe repair of tunnel linings, from defect diagnosis and structural reinforcement to load-bearing capacity restoration. This successfully resolves the long-standing contradiction between the extremely short maintenance window and the high quality requirements for repairs in operating tunnels. By precisely deconstructing and adapting the comprehensive overhaul project, which requires continuous line closures in traditional solutions, to four consecutive nighttime maintenance windows, a revolutionary synergy between nighttime segmented construction and safe daytime operation is achieved. This not only minimizes disruption to transportation organization but also provides a standardized solution for the preventive maintenance and rapid defect treatment of a large number of operating tunnels.

[0021] Employing a rapid diagnostic technique combining ground-penetrating radar and manual tapping, the spatial distribution of defects can be accurately pinpointed within a very short time after the start of the grouting window, enabling precise guidance. A single pressure grouting operation is performed using grouting anchors that combine anchoring and grouting functions, allowing the grout to initially set on the first day of the grouting window. This process not only fills the voids behind the lining but, more importantly, immediately anchors and consolidates the loosened surrounding rock, creating a stable load-bearing foundation for subsequent construction on the first night of operation—a crucial safety prerequisite for the entire rapid repair process.

[0022] Pressure injection of adhesive to seal the cracks fundamentally prevents moisture and harmful media from continuing to penetrate along the original cracks, eliminating the root cause of the damage. Spraying a moisture-curing waterproof coating allows it to fully dry on a damp substrate within the window period, forming a continuous sealing film with high elasticity (elongation at break ≥800%) and high adhesion (bonding strength ≥1.0MPa). This waterproof layer acts as a reliable physical barrier, permanently isolating water from the old lining, ensuring that the newly reinforced structure is in a dry service environment, and greatly improving the long-term durability after repair.

[0023] The steel mesh is directly fixed to the exposed end of the pre-embedded grouting anchor pipe, so that the newly added steel mesh, anchoring system and original lining and surrounding rock are connected to form an integral load-bearing skeleton; the first layer of early-strength and fast-hardening fiber concrete is sprayed. This layer not only plays a leveling role, but also forms a rigid base layer with a certain initial bearing capacity by the end of the third window period, providing a solid and stable working surface for the spraying of the final main structural layer.

[0024] The layered spraying process (a second 6-8cm main layer and a third 2-4cm protective layer) effectively reduces rebound, ensures concrete density and interlayer bonding quality, and efficiently constructs a composite lining reinforcement structure. The final safety test is conducted based on a triple criterion of time, strength, and vibration velocity before the end of the maintenance window and the opening of the line.

[0025] According to one aspect of the present invention, during the first day's grouting window, the quick-setting cement-based grouting material is a sulfoaluminate cement-based ultra-early strength grouting material with an initial setting time of 30-60 minutes, a compressive strength of ≥5 MPa at 1 hour, and a compressive strength of ≥30 MPa at 24 hours. The sulfoaluminate cement-based ultra-early strength grouting material plays a crucial role in rapid stabilization and strength foundation development throughout the entire rapid repair system. Through its precisely controllable setting time and early strength development, it ensures that the critical anchoring process on the first day can be completed with high quality within the stringent time window. Furthermore, its superior later-stage strength provides a solid and reliable foundation for the subsequent three consecutive nighttime operations and the century-long lifespan of the repaired structure. This material selection is a vital material guarantee for the present invention to achieve the core objective of adapting to the four-stage grouting window.

[0026] According to one aspect of the present invention, during the first drilling window, the grouting anchor pipe adopts a segmented structure: the front end is a drilling section with a conical guide head, the middle part is a grouting section with the aforementioned quincunx-shaped overflow holes, and the rear end is a grout-stopping anchoring section with external threads; the diameter of the quincunx-shaped overflow holes is 4-8mm, the hole spacing is 10-20cm, and the length of the grout-stopping section is ≥30cm. The design of the drilling section with a conical guide head at the front end allows the grouting anchor pipe itself to be directly drilled into the surrounding rock at a predetermined depth under the drive of the drilling rig, eliminating the cumbersome steps of drilling first, then retracting the drill, and then inserting the anchor rod or grouting pipe, combining multiple processes into a one-time drilling to the desired depth. During the critical drilling window, this can save at least 30% of the operation time, leaving more safety margin for subsequent grouting and setting; the middle grouting section and the quincunx-shaped overflow holes (diameter 4-8mm, hole spacing 10-20cm) are key, and the hole diameter size can... It effectively prevents fine aggregates in the grout from clogging the holes, ensuring smooth grout overflow while preventing excessive weakening of the pipe structure strength. The staggered arrangement of the quincunx pattern and the 10-20cm hole spacing in three-dimensional space ensures that the grout can uniformly and three-dimensionally radiate out from multiple points around and along the longitudinal direction of the anchor pipe, achieving all-round, dead-angle-free filling and penetration of the voids behind the lining and the surrounding loose rock mass. Compared with a single outlet or a straight arrangement, it can form a more uniform and continuous grout vein network and reinforcement ring, significantly improving the integrity and reliability of grouting reinforcement.

[0027] According to one aspect of the present invention, the rapid installation (one-time drilling) of the grouting anchor pipe saves valuable operating time for the ultra-early strength grouting material. Its reliable grout-stopping ability ensures that pressure grouting can be implemented, allowing the quick-setting grout to penetrate better under pressure. The pipe structure and material properties complement each other, jointly ensuring that targets such as initial setting within 2 hours can be achieved under real working conditions. The reinforcement ring formed by its plum blossom-shaped overflow holes stabilizes the surrounding rock and creates a safe space for surface operations during the second and third day windows. Its exposed threaded anchoring section eliminates the need for additional drilling or implantation of chemical anchors in the subsequent steel mesh installation process, achieving immediate installation and fixation. This significantly shortens the preparation time for the third and fourth day windows, ensuring that the entire four-stage process can be accurately completed in four consecutive nights.

[0028] According to one aspect of the present invention, during the second window period, pressure injection sealing uses a two-component modified epoxy resin grout with a viscosity of 100-500 mPa·s, suitable for cracks less than 0.2 mm wide; or a modified polyurea grout with a viscosity of 500-2000 mPa·s, suitable for cracks 0.2-2 mm wide; the injection pressure is 0.2-0.5 MPa, and initial setting occurs 30 minutes after injection. This second window period pressure injection sealing process, through a systematic design that matches materials to cracks, balances pressure and filling, and tightly integrates time and procedures, achieves comprehensive repair effects from microscopic to macroscopic, and from short-term to long-term, within a limited window period. It is not only a surface seal but also an internal repair of the damage, building a dry, solid, and durable foundation for the entire four-stage rapid repair system, and is a key link in ensuring that the repair results do not recur or fail.

[0029] According to one aspect of the present invention, during the second window period, the elongation at break of the high elastic modulus anti-adhesion waterproof coating is ≥300%, the bond strength with the concrete substrate is ≥1.0MPa, and the curing time under damp substrate conditions is 30%-50% shorter than that under dry substrate conditions. The high-elasticity, anti-adhesion waterproof coating forms a waterproof layer that firmly adheres to the surface of the old lining after being sealed with adhesive. It establishes a highly elastic, highly adhesive, and impermeable permanent isolation layer between the old structure (which may still have hidden defects or moisture) and the new reinforced structure. This ensures that external water pressure and corrosive media are completely blocked during operation, preventing them from eroding the newly sprayed reinforced concrete reinforcement layer and protecting the steel bars from corrosion, thus guaranteeing the century-long durability of the reinforced structure. Its high bonding strength (≥1.0MPa) and rapid setting and drying characteristics allow the first layer of fiber-reinforced concrete sprayed during the third window to form an extremely strong rigid-flexible bond with the waterproof layer. This avoids the phenomenon of two separate layers formed between the waterproof layer and the subsequent concrete due to poor adhesion in traditional repairs, ensuring effective load transfer and enabling the reinforced layer and the old lining to truly work together.

[0030] According to one aspect of the present invention, during the third and fourth day windows, the mix proportion of fiber-reinforced concrete (e.g., polypropylene fiber concrete) is: cement:sand:aggregate = 1:1.5:2.5, with a polypropylene fiber content of 0.6-0.9 kg / m³, an aluminate-based accelerator, and calcium formate as the early-strength agent. The lower water-cement ratio and rich cement paste ensure a tight chemical bond and mechanical interlocking between the concrete and the high-strength waterproofing layer constructed during the second day window. Simultaneously, the addition of polypropylene fibers reduces the elastic modulus of the new concrete, improving its deformation capacity and enabling better coordination with the deformation of the old lining and waterproofing layer with different stiffnesses. This reduces interlayer shear stress caused by deformation incoordination and avoids the risk of voids. The dense skeleton structure and the fiber's ability to suppress cracks significantly reduce the porosity and permeability of the concrete, making it difficult for external moisture and corrosive media (such as chlorides) to penetrate. This effectively protects the internal steel mesh and grouting anchors from corrosion, ensuring the durability of the reinforcement system within its design life.

[0031] According to one aspect of the present invention, during the fourth day window period, when the second layer of fiber-reinforced concrete is sprayed, a stress monitoring plate is embedded between the steel mesh and the first layer of fiber-reinforced concrete to monitor the interlayer bonding state in real time; the sand ratio of the third layer of fiber-reinforced concrete is increased by 5%-8% compared with the first two layers, reducing the surface rebound rate and increasing the density. The stress monitoring patch can monitor and record the development and changes of interlayer shear stress and normal stress in real time throughout the entire process of second and third layer concrete spraying, setting, and even simulated vibration testing. The monitoring data can directly reveal whether the load transfer between the old and new concrete layers is smooth and whether abnormal slippage or delamination occurs at the bond interface. In determining whether a system is ready for operation, it not only serves as a criterion for qualification but also provides scientific evidence for why it is qualified or where potential risks exist, elevating safety decisions from experience-based judgment to data-driven approaches. During the spraying of the third layer of concrete and subsequent processes, the monitoring data can be fed back in real time. If the data shows that the interlayer stress increases abnormally slowly or abruptly in the early stages of concrete setting, construction personnel can immediately determine whether poor bonding is caused by improper interface treatment, humidity mismatch, or material performance issues. This allows for remedial measures such as local reinforcement during the maintenance window, greatly improving the reliability of successful completion of complex processes on the first attempt. This stress monitoring patch can be designed as a permanently embedded element. After train operation resumes, it can continuously monitor the stress response evolution of the repaired area under long-term train dynamic loads and temperature cycles. This provides a unique basis for assessing the long-term service performance of reinforced structures and providing early warning of potential fatigue damage. The unique in-situ data source enables a seamless connection between rapid repair and long-term intelligent monitoring. Increasing the sand ratio of the third layer of concrete by 5%-8% compared to the first two layers is a precise material design based on its function as a mortar-enriched protective layer, with direct and significant effects. In shotcrete construction, coarse aggregate (stone) is the main component of rebound loss. Increasing the sand ratio means reducing the proportion of coarse aggregate and increasing the content of fine aggregate (sand) and cement paste. This makes the concrete mixture more cohesive and flexible, allowing it to adhere better to the sprayed surface rather than bounce back. This directly reduces material waste. This reduces costs, speeds up construction, and ensures that the designed thickness (2-4cm) can be achieved accurately and efficiently. It is a key process optimization to ensure that the work is completed within the tunnel window. The higher sand ratio allows the slurry to more fully wrap and fill all the gaps between the aggregates, forming a denser mortar enrichment layer with lower porosity on the surface. The dense surface layer can effectively block water vapor and corrosive media from penetrating the internal structure, better resist the scouring of wind pressure and water flow in the tunnel, as well as possible minor collisions. It is also easier to obtain a smoother base surface, improve the appearance, and provide a good base for possible interior decoration.

[0032] According to one aspect of the present invention, the operation sequence control during the fourth window period is as follows: after the start of the window period, the second layer of fiber-reinforced concrete is sprayed within a first preset time; after an interval of a second preset time, the third layer of fiber-reinforced concrete is sprayed within a third preset time; a fourth preset time is reserved for surface leveling and rapid strength testing; the rapid strength testing adopts a rebound hammer or a combined ultrasonic rebound method, with the spacing between measuring points ≤ 2m; the first preset time is 0.5-1 hour, the second preset time is 1-1.5 hours, the third preset time is 0.5-1 hour, and the fourth preset time is 0.5 hours; wherein, the time from the completion of the second layer of fiber-reinforced concrete spraying to the end of the fourth window period is ≥ 3 hours. The regulation that the second layer of concrete must have at least 3 hours of continuous, undisturbed strength gain before the main load-bearing layer is opened is institutionally locked in. This directly and rigidly supports the core safety criterion of ≥10MPa strength at the end of the load-bearing period, reliably linking the early strength performance (10MPa in 4 hours) in the materials laboratory with the final goal of on-site construction. Setting the rhythm of spraying the second layer at the first preset time (0.5-1 hour) to spraying the third layer at the second preset time (1-1.5 hours) to the third preset time (0.5-1 hour) has a dual optimization effect: providing sufficient initial setting time for the second layer: the 1-1.5 hour interval ensures that the second layer has reached sufficient initial strength to stably bear the load of the third layer without being damaged; matching the heat release law of cement hydration: this interval precisely covers the beginning stage of the accelerated hydration period of the second layer of concrete, allowing it to form an initial structure under relatively static conditions before covering the third layer, which helps to reduce temperature stress and improve overall integrity.

[0033] According to the present invention, a complete solution for the rapid repair of operational tunnels that is plannable, executable, and verifiable is provided. Under the strict constraints of extremely short tunnel windows, it can effectively achieve a systematic engineering approach that unifies radical repair of tunnel lining with long-term durability. The method of the present invention integrates a complete technological ecosystem of materials science, structural engineering, construction machinery, and intelligent monitoring, and achieves an optimal balance among multiple objectives such as operational safety, repair quality, and transportation efficiency. Attached Figure Description

[0034] Figure 1 The flowchart schematically illustrates a method for rapid repair of lining cracks in operational tunnels during tunnel maintenance windows, according to one embodiment of the present invention. Detailed Implementation

[0035] The invention will now be discussed with reference to exemplary embodiments. It should be understood that the described embodiments are merely intended to enable those skilled in the art to better understand and thus implement the invention, and are not intended to imply any limitation on the scope of the invention.

[0036] As used herein, the term "comprising" and its variations are to be interpreted as open-ended terms meaning "including but not limited to". The term "based on" is to be interpreted as "at least partially based on". The terms "one embodiment" and "an embodiment" are to be interpreted as "at least one embodiment".

[0037] Figure 1 This is a schematic flowchart illustrating a method for rapid repair of lining cracks in operational tunnels during tunnel maintenance windows, according to one embodiment of the present invention. Figure 1 As shown in this embodiment, a rapid repair method for lining cracks in operating tunnels is applicable during the tunnel maintenance window period. The maintenance window period is the daily nighttime train shutdown period, with a single duration of 4 hours. It employs four maintenance window period adaptation processes: diagnostics, anchoring, waterproofing, and load-bearing capacity. Through four consecutive maintenance window periods, the reinforced structure gradually reaches its load-bearing strength and meets the conditions for opening to traffic. This includes: First window period: accurate diagnosis and rapid treatment of diseases. During operational breaks, a combination of non-destructive testing with ground-penetrating radar and manual tapping is used to quickly determine the extent of cavities behind the lining, the direction of cracks, and the depth of the loosened zone in the surrounding rock. Then, grouting anchor pipes with both anchoring and grouting functions are installed in the determined area. These anchor pipes have quincunx-shaped overflow holes on their walls and a grout-stopping anchoring section at the tail end, arranged in a quincunx pattern. One-time, pressure-controlled grouting is then performed through these anchor pipes into the cavities behind the lining and the surrounding rock. The grouting pressure is controlled between 0.5 and 1.0 MPa, and a fast-setting cement-based grouting material is used to ensure that the grout strength is ≥5 MPa at the end of the first day's grouting window. The second day of the window period: base surface reconstruction and rapid-setting waterproofing: Remove the deteriorated concrete from the surface and seal the cracks with pressure-injected adhesive. Then, continuously spray a wet-curing, fast-setting waterproof layer onto the base surface. The sprayed waterproof layer uses a high-elasticity, reverse-adhesive waterproof coating (or other high-elasticity, fast-setting waterproof material) with a thickness of 1.2-2.5 mm. It is surface-dry within 30 minutes after spraying and fully dry by the end of the second day's window period. Seal the root of the grouting anchor pipe with adhesive and thicken the wrapping to a local thickness of not less than 4 mm. During the third window period, the steel mesh is installed and the first layer of spraying is carried out: After the sprayed waterproof layer has cured, immediately install the steel mesh and weld or tie it directly to the exposed non-threaded section of the grouting anchor pipe; the steel mesh is a single-layer cold-drawn steel mesh with a mesh spacing ≤150mm×150mm; then spray the first layer of polypropylene fiber (or other fiber) concrete, 4-6cm thick, to form a leveling and filling layer; the compressive strength is ≥5MPa at the end of the third day window after spraying. Fourth window period, layered spray molding and opening determination: After the first layer of fiber-reinforced concrete has initially set, the second and third layers of fiber-reinforced concrete are sprayed sequentially. The second layer of fiber-reinforced concrete is 6-8 cm thick and serves as the main structural layer. The third layer of fiber-reinforced concrete is 2-4 cm thick, with a higher mortar volume ratio than the previous two layers. The spraying interval between the second and third layers of fiber-reinforced concrete is less than 2 hours. The water-cement weight ratio of each layer of fiber-reinforced concrete is 0.35-0.40, and it contains 3%-5% (by weight) of accelerator and 2%-4% (by weight) of early-strength agent to form early-strength and fast-hardening concrete. After spraying, the surface is leveled. After leveling, the surface is inspected and accepted based on a triple criterion of the fourth day window period, concrete strength, and vibration velocity. The second layer of fiber-reinforced concrete has a compressive strength ≥10MPa at the end of the fourth day window period, which is considered to meet the conditions for commissioning. Maintenance phase: After the fourth day window of construction is completed, the sprayed surface layer is maintained by high-frequency spraying or watering during subsequent day windows for more than 14 consecutive days.

[0038] Based on the above solutions, the method of this invention, under the stringent condition of not interrupting daytime railway operations, achieves rapid and safe repair of tunnel lining from defect diagnosis and structural reinforcement to load-bearing restoration through efficient and orderly operation during four consecutive nighttime maintenance windows. It successfully resolves the long-standing contradiction between the extremely short maintenance window and the high quality requirements of repair for operating tunnels. By precisely deconstructing and adapting the comprehensive overhaul project, which requires continuous line closure in traditional solutions, to four consecutive nighttime maintenance windows, a revolutionary synergy of nighttime segmented construction and safe daytime operation is achieved. This not only minimizes interference with transportation organization but also provides a standardized solution for the preventive maintenance and rapid treatment of defects in a large number of operating tunnels.

[0039] In this embodiment, a rapid diagnostic technique combining ground-penetrating radar and manual tapping is employed. This allows for precise spatial identification of the defects within a very short time after the start of the grouting window, enabling accurate guidance. A single pressure grouting operation is performed using grouting anchors that combine anchoring and grouting functions, allowing the grout to initially set on the first day of the grouting window. This process not only fills the voids behind the lining but, more importantly, immediately anchors and consolidates the loose surrounding rock, creating a stable load-bearing foundation for subsequent construction on the first night of operation. This is a crucial safety prerequisite for the entire rapid repair process.

[0040] In this embodiment, pressure injection of adhesive sealant is used to seal the cracks, fundamentally preventing the continued intrusion of moisture and harmful media along the original cracks and eliminating the root cause of the disease. Spraying a moisture-curing waterproof coating can fully dry on a damp substrate within the window period, forming a continuous sealing film with high elasticity (elongation at break ≥800%) and high adhesion (bonding strength ≥1.0MPa). This waterproof layer acts as a reliable physical barrier, permanently isolating water from the old lining and ensuring that the newly reinforced structure is in a dry service environment, greatly improving the long-term durability after repair.

[0041] In this embodiment, the steel mesh is directly fixed to the exposed end of the pre-embedded grouting anchor pipe, so that the newly added steel mesh, anchoring system and original lining and surrounding rock are connected to form an integral load-bearing skeleton; the first layer of early-strength and fast-hardening fiber concrete is sprayed. This layer not only plays a leveling role, but also forms a rigid base layer with a certain initial bearing capacity by the end of the third window period, providing a solid and stable working surface for the spraying of the final main structural layer.

[0042] In this embodiment, a layered spraying process is adopted (a second layer of 6-8cm main layer and a third layer of 2-4cm protective layer) to effectively reduce rebound, ensure concrete density and interlayer bonding quality, and efficiently construct a composite lining reinforcement main body; the time, strength and vibration velocity triple judgment criteria are used as the final safety test before the end of the maintenance window and the opening of the line.

[0043] Furthermore, according to one embodiment of the present invention, during the first day's window period, the quick-setting cement-based grouting material is a sulfoaluminate cement-based ultra-early strength grout (or other quick-setting cement-based materials), with an initial setting time of 30-60 minutes, a 1-hour compressive strength ≥5MPa, and a 24-hour compressive strength ≥30MPa. In this embodiment, the sulfoaluminate cement-based ultra-early strength grout plays a role in rapid stabilization and strength foundation laying in the entire rapid repair system. Through its precisely controllable setting time and early strength development, it ensures that the key anchoring process on the first day can be completed with high quality within the stringent time window. Furthermore, its excellent later-stage strength provides a solid and reliable foundation for the subsequent three consecutive nighttime operations and the century-long lifespan of the repaired structure. This material selection is a crucial material guarantee for the present invention to achieve the core content of adapting to the four-stage window period.

[0044] Furthermore, according to one embodiment of the present invention, during the first drilling window, the grouting anchor pipe adopts a segmented structure: the front end is a drilling section with a conical guide head, the middle part is a grouting section with the aforementioned quincunx-shaped overflow holes, and the tail end is a grout-stopping anchoring section with external threads; the diameter of the quincunx-shaped overflow holes is 4-8mm, the hole spacing is 10-20cm, and the length of the grout-stopping anchoring section is ≥30cm. In this embodiment, the design of the front end as a drilling section with a conical guide head allows the grouting anchor pipe itself to be directly drilled into the surrounding rock at a predetermined depth under the drive of the drilling rig, eliminating the cumbersome steps of drilling first, then retracting the drill, and then inserting the anchor rod or grouting pipe, combining multiple processes into a one-time drilling to the desired depth. During the critical drilling window, this can save at least 30% of the operation time, leaving more safety margin for subsequent grouting and setting; the middle grouting section and the quincunx-shaped overflow holes (diameter 4-8mm, hole spacing 10-20cm) are key. The aperture size effectively prevents fine aggregates in the grout from clogging the holes, ensuring smooth grout overflow while preventing excessive weakening of the pipe structure strength. The staggered arrangement of the quincunx pattern and the 10-20cm hole spacing in three-dimensional space ensures that the grout can uniformly and three-dimensionally radiate out from multiple points around and along the longitudinal direction of the anchor pipe, achieving all-round, dead-angle-free filling and penetration of the voids behind the lining and the surrounding loose rock mass. Compared with a single outlet or a straight arrangement, it can form a more uniform and continuous grout vein network and reinforcement ring, significantly improving the integrity and reliability of grouting reinforcement.

[0045] In this embodiment, the rapid installation (one-time drilling) of the grouting anchor pipe saves valuable operation time for the ultra-early strength grouting material. Its reliable grout-stopping ability ensures that pressure grouting can be implemented, allowing the quick-setting grout to penetrate better under pressure. The pipe structure and material properties complement each other, jointly ensuring that targets such as initial setting within 2 hours can be achieved under real working conditions. The reinforcement ring formed by its plum blossom-shaped overflow holes stabilizes the surrounding rock and creates a safe space for surface operations during the second and third day windows. Its exposed threaded anchoring section eliminates the need for additional drilling or chemical anchoring in the subsequent steel mesh installation process, achieving immediate installation and fixation. This significantly shortens the preparation time for the third and fourth day windows, ensuring that the entire four-stage process can be accurately completed in four consecutive nights.

[0046] Furthermore, according to one embodiment of the present invention, during the second window period, the pressure injection sealing uses a modified epoxy resin grout with a viscosity of 100-500 mPa·s, suitable for cracks less than 0.2 mm wide; or a modified polyurea grout with a viscosity of 500-2000 mPa·s, suitable for cracks 0.2-2 mm wide; the injection pressure is 0.2-0.5 MPa, and initial setting occurs 30 minutes after injection. In this embodiment, the crack pressure injection sealing process during the second window period, through a systematic design that matches materials to cracks, balances pressure and filling, and tightly integrates time and procedures, achieves a comprehensive repair effect from micro to macro and from short to long term within a limited window period. It is not only a surface seal but also an internal repair of the defect, building a dry, solid, and durable foundation for the entire four-stage rapid repair system, and is a key link to ensure that the repair results do not recur or fail.

[0047] Furthermore, according to one embodiment of the present invention, during the second window period, the elongation at break of the high elastic modulus anti-adhesion waterproof coating is ≥300%, the bond strength with the concrete substrate is ≥1.0MPa, and the curing time under damp substrate conditions is 30%-50% shorter than that under dry substrate conditions. In this embodiment, the waterproof layer formed by the high-elasticity anti-adhesion waterproof coating firmly adheres to the surface of the old lining that has been sealed with adhesive. A permanent isolation layer with high elasticity, high adhesion, and impermeability is established between the old structure (which may still have hidden defects or moisture) and the new reinforcement structure. This ensures that external water pressure and corrosive media are completely blocked during operation, preventing them from corroding the newly sprayed reinforced concrete reinforcement layer and protecting the steel bars from corrosion, thereby ensuring the century-long durability of the reinforcement structure. Its high bonding strength (≥1.0MPa) and rapid setting and drying characteristics enable the first layer of fiber concrete sprayed during the third window to form an extremely strong rigid-flexible bond with the waterproof layer. This avoids the phenomenon of two separate skins formed between the waterproof layer and the post-poured concrete due to poor adhesion in traditional repairs, ensuring that the load can be effectively transferred and enabling the reinforcement layer and the old lining to truly work together.

[0048] Furthermore, according to one embodiment of the present invention, during the third and fourth day windows, the mix proportion of fiber-reinforced concrete (e.g., polypropylene fiber-reinforced concrete) is: cement:sand:stone = 1:1.5:2.5, the polypropylene fiber content is 0.6-0.9 kg / m³, the accelerator is an aluminate accelerator, and the early strength agent is calcium formate. In this embodiment, the low water-cement ratio and rich cement paste ensure a tight chemical bond and mechanical interlock between the concrete and the high-strength waterproof layer applied during the second-day window. Simultaneously, the addition of polypropylene fibers reduces the elastic modulus of the new concrete, improving its deformation capacity and allowing it to better coordinate with the deformation of the existing lining and waterproof layer, which have different stiffnesses. This reduces interlayer shear stress caused by deformation incompatibility and avoids the risk of voids. The dense skeleton structure and the fiber's ability to suppress cracks significantly reduce the porosity and permeability of the concrete, making it difficult for external moisture and corrosive media (such as chlorides) to penetrate. This effectively protects the internal steel mesh and grouting anchors from corrosion, ensuring the durability of the reinforcement system within its design life.

[0049] Furthermore, according to one embodiment of the present invention, during the fourth window period, when the second layer of fiber concrete is sprayed, a stress monitoring plate is embedded between the steel mesh and the first layer of fiber concrete to monitor the interlayer bonding state in real time; the sand ratio of the third layer of fiber concrete is increased by 5%-8% compared with the first two layers, reducing the surface rebound rate and increasing the density. In this embodiment, the stress monitoring plate can monitor and record the development and changes of interlayer shear stress and normal stress in real time throughout the entire process of second and third layer concrete spraying, setting, and even simulated vibration testing. The monitoring data can directly reveal whether the load transfer between the old and new concrete layers is smooth and whether abnormal slippage or delamination occurs at the bond interface. When determining whether a system is ready for operation, it is not only a criterion for qualification but also provides scientific evidence for why it is qualified or where potential risks exist, elevating safety decision-making from experience-based judgment to data-driven approaches. During the spraying of the third layer of concrete and subsequent processes, the monitoring data can be fed back in real time. If the data shows that the interlayer stress increases abnormally slowly or abruptly in the early stage of concrete setting, the construction personnel can immediately determine whether there is poor bonding due to improper interface treatment, humidity mismatch, or material performance problems. This allows for the opportunity to take remedial measures such as local reinforcement during the maintenance window, greatly improving the reliability of successful completion of complex processes on the first attempt. The stress monitoring plate can be designed as a permanently embedded element. After the train resumes operation, it can continuously monitor the stress response evolution of the repaired area under long-term train dynamic load and temperature cycling. This provides a basis for assessing the long-term service performance of the reinforced structure and providing early warning of potential fatigue damage. It provides a unique in-situ data source, enabling seamless integration of rapid repair and long-term intelligent monitoring; increasing the sand ratio of the third layer of concrete by 5%-8% compared to the first two layers is a precise material design based on its mortar-enriched protective layer function, with direct and significant effects. In shotcrete construction, coarse aggregate (stone) is the main component of rebound loss. Increasing the sand ratio means reducing the proportion of coarse aggregate and increasing the content of fine aggregate (sand) and cement paste. This makes the concrete mixture more cohesive and flexible, allowing it to adhere better to the sprayed surface rather than bounce back. This not only directly reduces material... This reduces material waste, speeds up construction, and ensures that the designed thickness (2-4cm) can be achieved accurately and efficiently. It is a key process optimization to ensure that the work is completed within the tunnel window. The higher sand ratio allows the slurry to more fully wrap and fill all the gaps between the aggregates, forming a denser mortar enrichment layer with lower porosity on the surface. The dense surface layer can effectively block water vapor and corrosive media from penetrating the internal structure, better resist the scouring of wind pressure and water flow in the tunnel, as well as possible minor collisions. It is also easier to obtain a flatter and smoother base surface, improve the appearance, and provide a good base for possible interior decoration.

[0050] Furthermore, according to one embodiment of the present invention, the operation sequence control of the fourth window period is as follows: after the start of the window period, the second layer of fiber concrete spraying is completed within a first preset time, and the third layer of fiber concrete spraying is completed within a third preset time after a second preset time interval, with a fourth preset time reserved for surface leveling and rapid strength testing; the rapid strength testing adopts a rebound hammer or ultrasonic rebound combined method, with the spacing between measuring points ≤2m; The first preset time is 0.5-1 hour, the second preset time is 1-1.5 hours, the third preset time is 0.5-1 hour, and the fourth preset time is 0.5 hours. Among them, the time from the completion of the second layer of fiber concrete spraying to the end of the fourth day window period is ≥3 hours. In this embodiment, the requirement that ≥3 hours remain between the completion of the second layer spraying and the end of the window period effectively locks in the system, ensuring that the second layer of concrete, as the main load-bearing layer, must have at least 3 hours of continuous, undisturbed strength growth time before opening. This directly and rigidly supports the core safety criterion of a strength ≥10MPa at the end of the window period, reliably linking the early strength performance (10MPa in 4 hours) in the materials laboratory with the final goal of on-site construction. Setting a rhythm of spraying the second layer at the first preset time (0.5-1 hour) and then spraying the third layer at the second preset time (1-1.5 hours) and the third preset time (0.5-1 hour) has a dual optimization effect: providing sufficient initial setting time for the second layer: the 1-1.5 hour interval ensures that the second layer has reached sufficient initial strength to stably bear the load of the third layer without being damaged; matching the heat release law of cement hydration: this interval precisely covers the beginning stage of the accelerated hydration period of the second layer of concrete, allowing it to form an initial structure under relatively static conditions before covering the third layer, which helps to reduce temperature stress and improve overall integrity.

[0051] Furthermore, according to one embodiment of the present invention, in addition to time and strength judgment criteria, a vibration velocity judgment criterion may also be optionally included. The simulated train vibration test uses a portable vibration table, the vibration frequency is consistent with the measured frequency when an operating train passes by, the vibration duration is ≥10 minutes, and the test location is located in the middle and edge of the newly sprayed concrete layer. In this embodiment, through high-fidelity load simulation, continuous pressure application, monitoring of key locations, and quantified qualification criteria, the decision to open the line to traffic is transformed from prediction based on static extrapolation to verification based on dynamic empirical evidence, which can effectively ensure construction quality and safety.

[0052] Furthermore, according to one embodiment of the present invention, during the curing stage, an automated spray curing system is employed. The system includes atomizing nozzles arranged longitudinally along the tunnel, a timer controller, and a water source. The spray pressure is 0.2-0.4 MPa, and the droplet diameter is 50-100 μm. This configuration ensures that the cement hydration reaction receives the necessary moisture, allowing the concrete's strength, density, and impermeability to develop fully, ultimately achieving the designed durability requirements.

[0053] In summary, this invention provides a complete solution for the rapid repair of operational tunnels that is plannable, executable, and verifiable. Under the strict constraints of extremely short tunnel windows, it can effectively achieve a systematic engineering approach that unifies radical repair of tunnel lining with long-term durability. The method of this invention integrates a complete technological ecosystem of materials science, structural engineering, construction machinery, and intelligent monitoring, achieving an optimal balance among multiple objectives: operational safety, repair quality, and transportation efficiency.

[0054] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in this application.

[0055] It should be understood that the sequence number of each step in the invention and its embodiments does not absolutely imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

Claims

1. A method for rapid repair of lining cracks in operating tunnels during maintenance windows, wherein the maintenance window is the daily nighttime train shutdown period, with a single duration of 4 hours, characterized in that... The process employs a four-stage adaptation process: diagnostics, anchoring, waterproofing, and load-bearing capacity assessment. Through four consecutive stages of operation, the reinforced structure gradually reaches its load-bearing strength and meets the conditions for opening to traffic. This includes: First window period: accurate diagnosis and rapid treatment of diseases. A combination of non-destructive testing with ground-penetrating radar and manual tapping was used to quickly determine the extent of cavities behind the lining, the direction of cracks, and the depth of the loosened zone in the surrounding rock. Then, grouting anchor pipes, which combine anchoring and grouting functions, were installed in the determined area. These anchor pipes had quincunx-shaped overflow holes on their walls and a grout-stopping anchoring section at the tail end, arranged in a quincunx pattern. One-time, pressure-controlled grouting was then performed through these anchor pipes into the cavities behind the lining and the surrounding rock, using a fast-setting cement-based grouting material to ensure the grout strength was ≥5 MPa at the end of the first day's grouting window. The second day of the window period: base surface reconstruction and rapid-setting waterproofing: Remove the deteriorated concrete from the surface and seal the cracks with pressure-injected adhesive. Then, continuously spray a wet-curing, fast-setting waterproof layer onto the base surface. The sprayed waterproof layer uses a high-elasticity, reverse-adhesion, fast-setting waterproof coating with a thickness of 1.2-2.5 mm. It is surface-dry within 30 minutes after spraying and fully dry by the end of the second day's window period. Seal the root of the grouting anchor pipe with adhesive and thicken the wrapping to a local thickness of not less than 4 mm. During the third window period, the steel mesh is installed and the first layer of spraying is carried out: After the sprayed waterproof layer has cured, immediately install the steel mesh and directly weld or tie it to the exposed non-threaded section of the grouting anchor pipe; the steel mesh is a single-layer cold-drawn steel mesh; then spray the first layer of fiber concrete, 4-6cm thick, to form a leveling and filling layer; the compressive strength is ≥5MPa at the end of the third day window after spraying. Fourth window period, layered spray molding and opening determination: After the first layer of fiber-reinforced concrete has initially set, the second and third layers of fiber-reinforced concrete are sprayed sequentially. The second layer of fiber-reinforced concrete is 6-8 cm thick and serves as the main structural layer. The third layer of fiber-reinforced concrete is 2-4 cm thick, and its mortar volume ratio is higher than that of the first two layers. The spraying interval between the second and third layers of fiber-reinforced concrete is less than 2 hours. The water-cement weight ratio in each layer of fiber-reinforced concrete is 0.35-0.40, and 3%-5% of an accelerator and 2%-4% of an early-strength agent are added to form early-strength and fast-hardening concrete. After spraying, the surface is leveled. After leveling, the surface is inspected and accepted according to the fourth day window period and the concrete strength assessment standard. The second layer of fiber-reinforced concrete has a compressive strength ≥10MPa at the end of the fourth day window period, which is considered to meet the conditions for commissioning. Maintenance phase: After the fourth day window of construction is completed, the sprayed surface layer is cured for at least 14 consecutive days.

2. The rapid repair method for lining cracks in operational tunnels during tunnel maintenance windows, as described in claim 1, is characterized in that... During the first window period, the quick-setting cement-based grouting material is a sulfoaluminate cement-based ultra-early strength grouting material with an initial setting time of 30-60 minutes, a compressive strength of ≥5MPa at 1 hour, and a compressive strength of ≥30MPa at 24 hours.

3. The method for rapid repair of lining cracks in operational tunnels during tunnel maintenance windows, as described in claim 1, is characterized in that... During the first window period, the grouting anchor pipe adopts a segmented structure: the front end is a drilling section with a conical guide head, the middle part is a grouting section with the plum blossom-shaped overflow hole, and the tail end is a grout-stopping anchoring section with external threads; the diameter of the plum blossom-shaped overflow hole is 4-8mm, and the hole spacing is 10-20cm.

4. The rapid repair method for lining cracks in operational tunnels during tunnel maintenance windows, as described in claim 1, is characterized in that... During the second window period, the pressure grouting sealant uses modified epoxy resin grout with a viscosity of 100-500 mPa·s, suitable for cracks less than 0.2 mm wide; or modified polyurea grout with a viscosity of 500-2000 mPa·s, suitable for cracks 0.2-2 mm wide; the grouting pressure is 0.2-0.5 MPa, and initial setting occurs 30 minutes after grouting.

5. The method for rapid repair of lining cracks in operational tunnels during tunnel maintenance windows, as described in claim 1, is characterized in that... During the second window period, the high elastic modulus reverse adhesive waterproof coating has an elongation at break of ≥300%, an adhesion strength to the concrete substrate of ≥1.0MPa, and a curing time of 30%-50% shorter under damp substrate conditions compared to dry substrate conditions.

6. The method for rapid repair of lining cracks in operational tunnels during tunnel maintenance windows, as described in claim 1, is characterized in that... During the third and fourth daylighting periods, the mix proportion of the fiber-reinforced concrete is: cement:sand:stone = 1:1.5:2.

5.

7. The method for rapid repair of lining cracks in operational tunnels during tunnel maintenance windows, as described in claim 1, is characterized in that... During the fourth window period, when the second layer of fiber concrete is sprayed, stress monitoring plates are embedded between the steel mesh and the first layer of fiber concrete to monitor the interlayer bonding status in real time; the sand ratio of the third layer of fiber concrete is increased by 5%-8% compared with the first two layers, reducing the surface rebound rate and increasing the density.

8. The method for rapid repair of lining cracks in operational tunnels during tunnel maintenance windows, as described in claim 1, is characterized in that... The operation sequence control for the fourth window period is as follows: after the start of the window period, the second layer of fiber concrete spraying is completed within the first preset time, and the third layer of fiber concrete spraying is completed within the third preset time after the second preset time interval. A fourth preset time is reserved for surface leveling and rapid strength testing. The rapid strength testing adopts a rebound hammer or a combined ultrasonic rebound method, with the spacing between measuring points ≤2m. The first preset time is 0.5-1 hour, the second preset time is 1-1.5 hours, the third preset time is 0.5-1 hour, and the fourth preset time is 0.5 hours.

9. The method for rapid repair of lining cracks in operational tunnels during tunnel maintenance windows, as described in claim 1, is characterized in that... During the operational interval maintenance phase, an automated spray maintenance system is adopted. The system includes atomizing nozzles arranged longitudinally along the tunnel, a timer controller, and a water source. The spray pressure is 0.2-0.4 MPa, and the droplet diameter is 50-100 μm.

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