Tunnel blasting excavation method for large deformation section of soft rock

Abstract

The invention discloses a tunnel blasting excavation method for a large-deformation section of soft rock, and relates to the technical field of tunnel blasting construction of the large-deformation section of the soft rock, and the tunnel blasting excavation method for the large-deformation section of the soft rock comprises the steps that a glass fiber anchor rod is drilled on a soft rock tunnel face; defining a reserved area on the soft rock tunnel face; according to the geological condition of the soft rock tunnel face, the arch portion of the excavated section and the middle-upper portion area of the side wall are marked as high-attention areas, and the other areas are marked as common areas; digital detonators are used for networking, and shot holes in different parts are detonated in sequence; after blasting ventilation, when the steel arch is installed, a foot-lock anchor pipe hole is drilled in the arch foot position, an anchor pipe is installed, grouting is conducted, and then a torque wrench is used for applying torque to the exposed end of the anchor pipe for tensioning. According to the method, large deformation of the soft rock in the tunnel blasting construction process of the large deformation section of the soft rock is effectively restrained, and tunnel construction safety and project progress are guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel blasting construction of soft rock large deformation section, and particularly relates to a tunnel blasting excavation method for soft rock large deformation section. BACKGROUND

[0002] In tunnel construction, soft rock large deformation section as a typical adverse geological condition, its excavation technology faces severe challenges. Soft rock generally presents the characteristics of low strength, poor self-stability and easy softening when encountering water. When disturbed by blasting excavation, the surrounding rock is prone to significant deformation, and in severe cases, it can cause support structure failure and even tunnel collapse accidents. Therefore, developing a safe and efficient blasting excavation method is crucial to ensure construction safety and project progress.

[0003] Current engineering practice mainly uses the drill and blast method to deal with such problems. Conventional measures include shortening the excavation footage, enhancing support strength, and accelerating the closure speed of the surrounding rock exposure surface. In terms of blasting parameter design, measures such as reducing the single blasting charge, increasing the peripheral hole density, and optimizing the initiation sequence are commonly adopted to reduce the impact effect of blasting vibration on the surrounding rock. The support system relies mainly on the combination of sprayed concrete, steel arches, and anchor rods, and the support effect is evaluated through surrounding rock deformation monitoring. Some projects use the method of reserving core soil or partial excavation to form temporary support with unexcavated soil to delay the deformation rate of the excavated section.

[0004] However, the existing technology has systematic defects when dealing with soft rock large deformation. The blasting parameter design often uses a unified standard, failing to make fine adjustments according to the geological differences in different areas of the working face, such as not fully considering the changes in rock properties at the arch and sidewall, resulting in excessive disturbance in local areas and low excavation efficiency in other areas. The core soil reservation method can provide temporary support, but it requires additional mechanical crushing and slag removal procedures, which is tedious and lacks effective pre-reinforcement measures in the core soil area, posing a significant safety hazard. The anchoring structure in the traditional support system is a passive load-bearing mechanism that cannot establish active prestress, making it difficult to effectively suppress the continuous creep deformation of soft rock under long-term load. The control accuracy of the surrounding rock exposure time during construction is insufficient, and the timing of sprayed concrete and the matching of support strength are poor, often missing the best support window period. These defects collectively result in longer construction period, higher safety risk, and increased support cost for soft rock large deformation section. SUMMARY

[0005] The main purpose of the present application is to provide a tunnel blasting excavation method for soft rock large deformation section, which aims to effectively suppress the deformation of soft rock in tunnel blasting construction of soft rock large deformation section, reduce the risk of collapse, and improve the safety and efficiency of construction.

[0006] To achieve the above object, the tunnel blasting excavation method for soft rock large deformation section is proposed, which is implemented in each excavation cycle, and comprises the following steps: Drilling the front glass fiber anchor rod with a depth of 4.5 meters in a quincunx arrangement on the soft rock face; A trapezoidal area in the lower part of the soft rock face is designated as a reserved area, and the single-hole charge amount of the blast hole in the reserved area is reduced to 30%-40% of the normal design value; According to the geological conditions of the soft rock face, the arch and the upper area of the side wall are marked as high attention areas, and the remaining areas are marked as ordinary areas; For the high attention area, the blast hole spacing is 0.4-0.5 meters, the single-hole charge amount is 0.4-0.6 kg, and the length of the clay plug is not less than 45% of the blast hole depth; The digital detonator is connected in network, and the blast holes in different parts are initiated in the following order: first, the cutting eyes and auxiliary eyes located in the middle of the soft rock face are initiated, then the auxiliary eyes and peripheral eyes of the arch are initiated, then the auxiliary eyes and peripheral eyes of the side wall are initiated, and finally the floor eyes are initiated; wherein the blast hole initiation time of the arch is more than 50 milliseconds earlier than the blast hole initiation time of the same row of side wall; After blasting and ventilation, the concrete mixed with early strength shrinkage compensation agent is sprayed to close the rock surface within 15 minutes, and the steel arch is installed, the locking anchor pipe hole is drilled downward at an angle of 30-45 degrees at the arch foot position, and the anchor pipe is installed and grouted, then the exposed end of the anchor pipe is tensioned by applying a torque of 60N·m-80N·m using a torque wrench.

[0007] The technical scheme of the present application enhances the overall stability of the surrounding rock by pre-arranging glass fiber anchors on the soft rock face. The design of the reserved area and the differentiated blasting parameters effectively reduce the disturbance to the core soil, creating favorable conditions for subsequent support. The fine blasting parameter setting of the high attention area achieves targeted control of different geological areas. The accurate initiation sequence of the digital detonator optimizes the blasting effect and reduces the damage to the surrounding rock. Fast spraying of early strength concrete and active tensioning of the locking anchor pipe shortens the exposure time of the surrounding rock and provides timely and active support, thereby effectively suppressing the large deformation of soft rock and ensuring the safety of tunnel construction and the progress of the project. BRIEF DESCRIPTION OF DRAWINGS

[0008] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings described below only show some of the embodiments of the present application, and the drawings shown can be used by the ordinary skilled in the art to obtain other drawings without creative effort.

[0009] Figure 1 The flowchart of an embodiment of the tunnel blasting excavation method for soft rock large deformation section provided by the present application.

[0010] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and drawings. DETAILED DESCRIPTION

[0011] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by the ordinary skilled in the art without creative effort are within the scope of protection of the present application.

[0012] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement condition, etc. between the components in a certain posture, and if the certain posture changes, the directional indications will also change accordingly.

[0013] In addition, if the embodiments of the present application involve descriptions of "first", "second", etc., the descriptions of "first", "second", etc. are only for description purposes, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include at least one of the features. In addition, "and / or" or "and / or" appearing throughout the text means that the three parallel schemes are included, for example, "A and / or B" includes A scheme, or B scheme, or A and B simultaneously satisfy the scheme. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the fact that the ordinary skilled in the art can realize it, and when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, and is not within the scope of protection claimed by the present application.

[0014] Excavation of soft rock sections with large deformation faces numerous challenges in existing tunnel construction. Blasting parameter design fails to adequately consider geological differences at the tunnel face, leading to excessive disturbance in localized areas or low excavation efficiency. While pre-reserved core soil methods can provide temporary support, subsequent procedures are complex and lack effective pre-reinforcement measures. Traditional anchoring structures are mostly passive load-bearing, making it difficult to effectively suppress the continuous creep deformation of soft rock. Furthermore, the control of surrounding rock exposure time during construction is not accurate enough, and the matching between closure speed and support strength is insufficient, easily missing the optimal support opportunity, resulting in long construction periods, high safety risks, and high support costs.

[0015] To address this technical problem, this invention proposes a tunnel blasting excavation method for soft rock sections with large deformation.

[0016] Please see Figure 1 In one embodiment of the present invention, the tunnel blasting excavation method for soft rock sections with large deformation is performed in each excavation cycle, and the tunnel blasting excavation method for soft rock sections with large deformation includes: S10, drill fiberglass anchors with a depth of 4.5 meters in a quincunx pattern on the soft rock face; S20, a trapezoidal area in the lower part of the soft rock face is designated as a reserved area, and the single-hole charge of the blast holes in the reserved area is reduced to 30% to 40% of the normal design value; S30, based on the geological conditions of the soft rock face, the arch and upper part of the sidewall of the excavation section are marked as high concern areas, and the remaining areas are marked as ordinary areas; S40, for the high-concern area, blasting parameters are set with a borehole spacing of 0.4 to 0.5 meters, a single-hole charge of 0.4 to 0.6 kg, and a stemming length of not less than 45% of the borehole depth; S50 uses a digital detonator network and detonates the blast holes in different locations in the following order: first, detonates the slotted holes and auxiliary holes located in the middle of the soft rock face; second, detonates the auxiliary holes and peripheral holes in the arch; then, detonates the auxiliary holes and peripheral holes in the sidewalls; and finally, detonates the bottom plate holes. The blast holes in the arch are detonated at least 50 milliseconds earlier than the blast holes in the sidewalls in the same row. S60, after blasting and ventilation, within 15 minutes, start spraying concrete mixed with early strength compensating shrinkage agent to seal the rock surface. When installing the steel arch frame, drill anchor pipe holes with a downward inclination of 30 to 45 degrees at the arch foot position. After installing the anchor pipe and grouting, use a torque wrench to apply a torque of 60 N·m to 80 N·m to the exposed end of the anchor pipe for tensioning.

[0017] For ease of understanding, the following explains some key terms in this embodiment: Soft rock face: refers to the rock working face that has not yet been excavated during tunnel excavation. This working face is composed of weak rock, characterized by low strength and poor self-stabilization, and is prone to deformation under blasting disturbance.

[0018] Fiberglass anchors: A type of rod made of fiberglass reinforced composite material, used for anchoring and support in geotechnical engineering. They are characterized by high tensile strength, corrosion resistance, ease of cutting, and minimal impact on subsequent construction during blasting excavation.

[0019] Reserved Zone: A specific area designated in the lower part of the soft rock face. During blasting excavation, a lower charge is used in this zone to minimize disturbance to the core soil and provide favorable conditions for subsequent mechanical crushing and reinforcement support.

[0020] High-concern zone and ordinary zone: These are areas where the excavation section is divided based on the geological conditions of the soft rock face. The high-concern zone typically refers to areas with more complex geological conditions and a higher risk of surrounding rock deformation, such as the arch and upper part of the sidewalls, requiring more precise control of blasting parameters. The ordinary zone refers to areas with relatively stable geological conditions and a lower risk of deformation.

[0021] Digital detonator: An electronic detonator with accurate delay function. By networking digital detonators, the detonation time of different blast holes can be accurately controlled, thereby optimizing the blasting effect and reducing the disturbance of blasting vibration to the surrounding rock.

[0022] Cut holes, auxiliary holes, peripheral holes, and floor holes: These are different types of blast holes classified according to their location and function in blasting excavation. Cut holes are located in the middle of the tunnel face and are used to form a free face; auxiliary holes are used to enlarge the tunnel cavity and assist in excavation; peripheral holes are arranged along the excavation outline and are used to form a flat excavation face; and floor holes are used to excavate the bottom of the tunnel.

[0023] Early strength compensating shrinkage agent: an admixture added to concrete. This admixture can accelerate the early strength development of concrete and compensate for the shrinkage of concrete during the hardening process, thereby improving the early support effect and compactness of shotcrete.

[0024] Anchor pipe: An anchoring component installed at the arch foot of a steel arch frame. This anchor pipe connects the steel arch frame to the deep surrounding rock through drilling, grouting, and prestressing, providing active support, enhancing the stability of the arch foot, and effectively suppressing deformation of the surrounding rock.

[0025] This embodiment provides a tunnel blasting excavation method for soft rock sections with large deformation.

[0026] When drilling fiberglass anchors to a depth of 4.5 meters in a quincunx pattern on a soft rock face, conventional drilling rigs can be used for drilling, with the drilling depth controlled at 4.5 meters. The fiberglass anchors are then inserted into the boreholes and grouted for fixation. Ordinary cement grout can be used for grouting, which can be done manually or with simple grouting equipment. After the anchors are installed, simple nut tightening can be performed.

[0027] A trapezoidal area in the lower part of the soft rock face is designated as a reserve zone. Within this zone, the charge per borehole is reduced to 30%–40% of the normal design value. The reserve zone can be defined manually by measurement and marking, and its shape can be trapezoidal. The charge per borehole within this reserve zone is set lower than the normal design value, for example, reduced to 30%–40%. After charging, the boreholes can be plugged with conventional stemming material.

[0028] Based on the geological conditions of the soft rock face, the arch and upper-middle area of ​​the sidewall of the excavation section were designated as high-concern areas, while the remaining areas were designated as ordinary areas. The geological conditions of the face can be preliminarily assessed through on-site visual observation or a simple geological survey. Based on the assessment results, the arch and upper-middle area of ​​the sidewall of the excavation section were manually marked as high-concern areas, while other areas were considered ordinary areas.

[0029] For this high-concern area, blasting parameters were set as follows: borehole spacing of 0.4–0.5 meters, single-hole charge of 0.4–0.6 kg, and stemming length not less than 45% of the borehole depth. In the high-concern area, borehole spacing can be set between 0.4 and 0.5 meters. Single-hole charge is controlled between 0.4 and 0.6 kg. Stemming length is set to not less than 45% of the borehole depth. These parameters can be achieved through manual measurement and adjustment.

[0030] The blasting is controlled by a network of digital detonators, with the following sequence of detonation for different locations: first, the slotted and auxiliary holes in the center of the soft rock face; second, the auxiliary and peripheral holes in the arch; third, the auxiliary and peripheral holes in the sidewalls; and finally, the bottom hole. The detonation time for the arch holes is at least 50 milliseconds earlier than the detonation time for the sidewall holes in the same row. The detonation sequence is set as follows: first, the slotted and auxiliary holes in the center of the face; then, the auxiliary and peripheral holes in the arch; next, the auxiliary and peripheral holes in the sidewalls; and finally, the bottom hole. During the detonation process, the detonation time for the arch holes is set at least 50 milliseconds earlier than the detonation time for the sidewall holes in the same row.

[0031] After blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent is sprayed onto the rock surface within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot positions. After installing the anchor pipes and grouting, a torque wrench is used to apply a torque of 60 N·m to 80 N·m to the exposed end of the anchor pipe for tensioning. After blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent can be sprayed onto the rock surface manually or using simple spraying equipment within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees can be drilled at the arch foot positions. After the anchor pipes are installed, grouting is performed for fixation. After grouting, a torque wrench is used to apply a torque of 60 N·m to 80 N·m to the exposed end of the anchor pipe for tensioning.

[0032] This method enhances the overall stability of the surrounding rock by pre-installing fiberglass anchors at the soft rock face. The design of the reserved zone and differentiated blasting parameters effectively reduce disturbance to the core soil, creating favorable conditions for subsequent support. The refined blasting parameter settings for high-concern zones enable targeted control for different geological areas. The accurate detonation sequence of digital detonators optimizes the blasting effect and reduces damage to the surrounding rock. Rapidly sprayed early-strength concrete and actively tensioned anchor bolts shorten the exposure time of the surrounding rock, providing timely and proactive support, thereby effectively suppressing large deformations in soft rock and ensuring tunnel construction safety and project progress.

[0033] In an embodiment of the present invention, the step of drilling fiberglass anchors to a depth of 4.5 meters in a quincunx pattern at the soft rock face includes: S11. Using a light drilling rig equipped with a 42 mm diameter drill bit, drill holes in a 1.0 m * 1.0 m quincunx pattern at the soft rock face. The drilling direction is perpendicular to the soft rock face, the depth is controlled at 4.5 m, and the hole opening deviation is no more than 5 cm. S12, after drilling is completed, insert a fully threaded fiberglass anchor rod with a length of 4.2 meters and a rod diameter of 25 millimeters; S13, connect the grouting pump through the hollow channel of the anchor bolt, inject early-strength cement grout with a water-cement ratio of 0.4~0.45, and maintain the grouting pressure at 0.8~1.0 MPa until thick grout continuously returns from the borehole; S14, install a washer and nut at the orifice, and apply a preload of 30 N·m to 40 N·m to the nut using a torque wrench.

[0034] Specifically, a lightweight drilling rig equipped with a 42mm diameter drill bit is used to drill holes in a 1.0m x 1.0m quincunx pattern at the soft rock face. The drilling direction is perpendicular to the soft rock face, the depth is controlled at 4.5 meters, and the borehole deviation is no more than 5cm. The lightweight drilling rig, due to its small size and light weight, facilitates flexible operation and rapid deployment in the narrow space of the tunnel, making it particularly suitable for soft rock geological conditions and minimizing disturbance to the surrounding rock. The 42mm diameter drill bit is designed to provide a suitable borehole diameter for the subsequently inserted fiberglass anchor bolts, ensuring sufficient grouting space between the anchor bolts and the borehole wall, while avoiding uneconomical grouting or poor anchoring effect due to excessively large borehole diameters. The 1.0m x 1.0m quincunx pattern allows the anchor bolts to be evenly distributed on the plane, forming a mutually supporting grid structure, thereby more effectively dispersing and transmitting surrounding rock pressure and improving the overall stability of the support. The drilling direction is perpendicular to the soft rock face to ensure that the anchor bolts can maximize their pull-out and shear resistance, directly resisting the deformation force of the surrounding rock in the direction of the face and improving anchoring efficiency. The depth is controlled at 4.5 meters to allow the anchor bolts to penetrate a certain depth of unstable rock strata at the face and enter relatively stable deep rock mass, providing sufficient anchoring length and bearing capacity. Strict control of the borehole deviation to no more than 5 centimeters ensures that the actual position of the anchor bolts is consistent with the designed position, avoiding uneven stress on the anchor bolt group due to excessive deviation, which would affect the overall support effect, and ensuring smooth installation of subsequent washers and nuts.

[0035] After drilling is completed, a 4.2-meter-long, 25-millimeter-diameter, fully threaded fiberglass anchor bolt is inserted. Fiberglass anchor bolts offer advantages such as high strength, corrosion resistance, and ease of cutting, making them particularly suitable for soft rock and applications requiring further excavation. The fully threaded design ensures strong adhesion between the anchor bolt and the grouting material throughout its anchoring length, guaranteeing effective load transfer. Its 4.2-meter length matches the 4.5-meter drilling depth, providing sufficient space at the borehole opening for installing washers, nuts, and grouting pipes, while ensuring the effective anchoring length. The 25-millimeter diameter is determined based on the anchor bolt strength requirements and the borehole diameter, designed to provide sufficient load-bearing capacity.

[0036] A grouting pump is connected to the hollow channel of the anchor bolt, and early-strength cement grout with a water-cement ratio of 0.4~0.45 is injected. The grouting pressure is maintained at 0.8~1.0 MPa until thick grout continuously returns from the borehole. Fiberglass anchor bolts are typically designed with a hollow structure, facilitating the insertion of the grouting pipe and starting grouting from the bottom of the anchor bolt. This ensures that the grout fills the entire pore from bottom to top, expelling air and water, forming a dense, defect-free anchoring section. The low water-cement ratio (0.4~0.45) ensures that the grout has high strength and low shrinkage, enabling it to quickly reach the design strength and provide reliable anchoring force for the anchor bolt. The early-strength cement grout shortens the grout setting and hardening time, accelerates the support construction progress, and allows the anchor bolt to play its supporting role as soon as possible, effectively controlling the deformation of the surrounding rock. Appropriate grouting pressure allows the grout to fully penetrate into the fissures of the surrounding rock, filling the pores, improving the integrity and strength of the surrounding rock, while ensuring that the grout is tightly bonded to the anchor bolt body and borehole wall, forming an effective anchor. The grouting saturation is judged by the continuous return of thick grout from the borehole opening. This indicates that the grout has completely filled the borehole and that the grout quality meets the requirements, thus ensuring the integrity and effectiveness of the anchoring section.

[0037] A washer and nut are installed at the orifice, and a preload of 30 N·m to 40 N·m is applied to the nut using a torque wrench. The washer increases the contact area between the anchor bolt end and the surrounding rock, disperses stress, and prevents localized stress concentration that could lead to rock failure. The nut is used to fix the anchor bolt, and tightening the nut applies a preload to the anchor bolt. Applying a preload is a crucial step in anchor bolt support. Accurately controlling the preload within the range of 30 N·m to 40 N·m using a torque wrench ensures that the anchor bolt is under stress before surrounding rock deformation occurs, actively restraining rock deformation and improving the self-supporting capacity of the surrounding rock.

[0038] Through the above technical solutions, when installing fiberglass anchors at soft rock faces, the use of lightweight drilling rigs with drill bits of specific diameters enables accurate and efficient drilling operations, ensuring the accuracy of hole position, depth, and direction, thus laying the foundation for effective anchor installation. Inserting fully threaded fiberglass anchors and employing hollow channel grouting technology, combined with early-strength cement grout with a specific water-cement ratio and precisely controlled grouting pressure, ensures that the grout fully fills the pores, forming a dense, high-strength anchoring section, effectively improving the bond between the anchor and the surrounding rock. More importantly, after the anchor installation is completed, using washers and nuts, and applying a pre-tightening force of 30 N·m to 40 N·m to the nuts with a torque wrench, ensures that the anchor is under stress before surrounding rock deformation occurs, exerting active constraint on the surrounding rock. This effectively suppresses the initial development of large deformation in soft rock, significantly enhancing the overall stability and self-supporting capacity of the surrounding rock, creating more favorable conditions for subsequent blasting excavation and support construction, and effectively controlling the surrounding rock deformation in the soft rock section of the tunnel.

[0039] In an embodiment of the present invention, a trapezoidal region in the lower part of the soft rock face is designated as a reserved area, and the step of reducing the single-hole charge of the blast holes in the reserved area to 30% to 40% of the normal design value includes: S21. According to the tunnel design excavation outline, a trapezoidal area is marked on the soft rock face. The upper base width of the trapezoidal area is half of the current tunnel excavation width, the lower base width is the same as the excavation width, and the height is 2.5 meters to 3.5 meters, forming the reserved area. S22, within the reserved area, the hole spacing and row spacing of the blast holes are consistent with those of the external area, but the charge amount of each blast hole is controlled within 30% to 40% of the designed conventional charge amount; S23. After the charge is completed, use plastic gun clay made of clay and sand in a 1:1 volume ratio to plug the hole. The plugging length of each hole should be no less than 40 cm and it should be tamped down tightly.

[0040] Specifically, based on the tunnel design excavation outline, a trapezoidal area is marked on the soft rock face. The upper base width of the trapezoidal area is half the current excavation width of the tunnel, the lower base width is the same as the excavation width, and the height is 2.5 meters to 3.5 meters, forming the reserved area. This technical feature defines the geometry and dimensions of the reserved area in detail, ensuring that the reserved area can accurately cover the core rock mass that needs to be protected in the lower part of the tunnel. By defining the reserved area as a trapezoidal region with an upper base width half the current excavation width of the tunnel, a lower base width the same as the excavation width, and a height of 2.5 meters to 3.5 meters, excessive disturbance to the core soil at the bottom and sides of the tunnel during blasting can be effectively avoided. This accurate geometric definition helps to clarify the construction scope before blasting and guides the precise control of blast hole layout and charge quantity. In actual operation, the design outline can be accurately projected onto the face through measurement and layout, laser scanning, etc., and marked according to the preset trapezoidal dimensions.

[0041] Based on this, within the reserved area, the hole spacing and row spacing of the blast holes are consistent with those of the external area, but the charge amount of each blast hole is controlled within 30% to 40% of the designed conventional charge amount. This technical feature clarifies the arrangement of blast holes and the charge amount control strategy within the reserved area. Maintaining consistency between the hole spacing and row spacing and the external area ensures the uniformity and continuity of the blasting effect, avoiding uneven distribution of blasting energy due to changes in hole spacing and row spacing. Simultaneously, strictly controlling the charge amount of each blast hole within the reserved area to 30% to 40% of the designed conventional charge amount aims to significantly reduce the blasting intensity in this area. This low charge amount strategy effectively reduces the damage to the core rock mass caused by blasting vibration and shock waves, avoiding excessive cracks and loosening, thereby maximizing the protection of the integrity of the reserved area and creating favorable conditions for subsequent mechanical excavation.

[0042] In addition, after the explosive charge is loaded, plastic stemming clay, prepared by mixing clay and sand in a 1:1 volume ratio, is used for plugging. The plugging length for each blast hole is no less than 40 cm, and the clay is compacted tightly. This technical feature specifies the plugging material and construction requirements for the reserved area blast holes. The use of plastic stemming clay, prepared by mixing clay and sand in a 1:1 volume ratio, as the plugging material is due to its good plasticity and compactness, which effectively improves the plugging quality. Plastic stemming clay can better resist the impact of blasting gases during blasting, reducing the escape of blasting gases, thereby improving the utilization rate of blasting energy and reducing the impact of flyrock and shock waves on the surrounding environment. The plugging length for each blast hole is no less than 40 cm, and the clay is compacted tightly to ensure the effectiveness of the plugging. Sufficient plugging length and compaction ensure that the blasting energy mainly acts on rock mass fracture, reducing energy loss, further refining the control of the blasting effect, and avoiding unnecessary damage to the rock mass outside the reserved area.

[0043] By accurately defining the geometry and dimensions of the reserved area and strictly controlling the charge amount in the blast holes within that area, this application effectively reduces the blasting intensity within the reserved area, minimizing disturbance and damage to the core rock mass. Specifically, the accurate delineation of the trapezoidal area ensures the clarity of the protection range, avoiding indiscriminate blasting. Simultaneously, while maintaining the uniformity of the blast hole layout, the charge amount is significantly reduced, concentrating blasting energy on rock fragmentation rather than excessive impact, effectively controlling the expansion of blast fractures. Furthermore, the use of a specific ratio of plastic stemming material for tight sealing further improves the utilization efficiency of blasting energy and reduces the escape of blasting gases. This ensures the integrity of the rock mass in the reserved area while providing stable and undamaged boundary conditions for subsequent mechanical excavation of the core soil, significantly improving the construction quality and safety of tunnel excavation in soft rock sections with large deformation.

[0044] In an embodiment of the invention, prior to the step of drilling 4.5-meter-deep frontal fiberglass anchors in a staggered pattern at the soft rock face in the next excavation cycle, the tunnel blasting excavation method for soft rock sections with large deformations further includes: S101 uses a hydraulic breaker to mechanically break the core soil. The breaking sequence is from top to bottom and from both sides to the middle. S102, the crushed slag is immediately removed from the tunnel by a loader; S103. After the core soil is completely removed and the new soft rock face is fully exposed, immediately use a drilling rig to drill holes with a depth of 4.5 meters at intervals of 0.8 meters * 0.8 meters within the new soft rock face area corresponding to the reserved area of ​​the previous cycle. At the same time, complete the installation and grouting of the glass fiber anchor rods to form a reinforcing anchor rod. S104. After the grouting slurry of the reinforcing anchor has fully set, a new cycle of full-section blast hole drilling will begin.

[0045] Specifically, the core soil mass refers to the rock and soil mass within the reserved area that has not been completely loosened by blasting due to reduced explosive charge. Mechanical crushing using a hydraulic breaker aims to avoid secondary disturbance to the surrounding rock caused by re-blasting, while simultaneously achieving accurate and controlled removal of the core soil mass. The hydraulic breaker uses high-frequency impact force to break the rock and soil mass into small pieces, with the crushing sequence proceeding from top to bottom and from both sides towards the center. This helps maintain the overall stability of the tunnel face, avoids local instability, and creates favorable conditions for subsequent muck removal. This crushing method effectively controls the crushing range and intensity, reducing the impact on the surrounding supported or soon-to-be-supported rock mass.

[0046] The immediate removal of crushed debris from the tunnel is crucial for ensuring a clean and safe working face, and preventing debris accumulation that could hinder subsequent operations. In soft rock sections experiencing large deformations, timely removal of debris is essential for maintaining face stability and minimizing exposure time to the surrounding rock, effectively preventing further deformation without support. Loaders, as efficient removal equipment, can quickly transport the crushed earth and rock away from the work area, providing ample space and time for subsequent support and anchoring work.

[0047] After the core soil is removed, the new soft rock face will be fully exposed. At this point, immediate installation of reinforcing anchors is crucial. These anchors are designed to locally strengthen the surrounding rock in the original reserved area (where the core soil has been removed), compensating for potential microscopic damage during blasting and improving overall stability. The borehole spacing of 0.8m x 0.8m is denser than the conventional anchor spacing of 1.0m x 1.0m, and the depth of 4.5m is consistent with the conventional anchor depth, indicating a denser arrangement of reinforcing anchors and providing stronger support. Simultaneous installation and grouting of fiberglass anchors ensures their timely effectiveness, forming a unified whole between the anchors and the surrounding rock to jointly resist ground deformation. Fiberglass anchors, due to their excellent shear and tensile strength and lack of impact on subsequent tunneling, offer significant advantages as reinforcing anchors in this location.

[0048] The final setting of the grout in the reinforcing anchor bolts signifies a stable connection between the anchor bolts and the surrounding rock, with the anchoring force essentially established. Only after this point does a new cycle of full-face blasting begin. This is to ensure sufficient local stability at the tunnel face before the next round of blasting, especially in the original reserved area, which, reinforced by the reinforcing anchor bolts, can better resist blasting impacts and surrounding rock deformation. This sequence reflects the principle of "support before excavation," effectively controlling the stability of the surrounding rock in sections of soft rock with large deformation.

[0049] Through the above technical solution, in each excavation cycle, the core soil formed after blasting in the reserved area is mechanically crushed using a hydraulic breaker, proceeding from top to bottom and from both sides towards the center. This effectively avoids disturbance to the surrounding rock caused by secondary blasting and reduces the impact of blasting vibration on the surrounding rock and initial support structure. The crushed slag is immediately removed by a loader, ensuring timely clearing of the working face and creating a safe and efficient environment for subsequent operations. More importantly, after the core soil is removed, fiberglass reinforced anchors are immediately drilled and installed within the corresponding working face area of ​​the original reserved area. The next cycle of drilling is only carried out after the grout has fully set. This significantly strengthens the original reserved area before the next round of blasting. This strategy of first removing the core soil and then performing local reinforcement and anchoring effectively improves the overall stability of the soft rock working face, especially providing additional support for weak surrounding rock areas prone to large deformations. This significantly reduces the risk of surrounding rock deformation and ensures the continuity and safety of tunnel excavation.

[0050] In an embodiment of the present invention, the step of designating the upper part of the arch and sidewall of the excavation section as a high-concern area and the remaining area as a normal area, based on the geological conditions of the soft rock face, includes: S31, when the lithology revealed by the soft rock face is carbonaceous shale, mudstone, or a weak rock layer with a uniaxial compressive strength of less than 15 MPa calculated from the field point load test, the area is designated as the high concern area; S32, for the high-concern area of ​​the arch, the spacing between the blast holes of the peripheral holes is reduced to 0.35 meters to 0.45 meters, and when loading the explosive, a water-filled plastic soft bag with a length of 10 centimeters and a diameter smaller than the diameter of the blast hole is placed between every two standard explosive cartridges, and the soft bag is filled with water before loading the explosive. S33, for the high-concern area of ​​the sidewall, when loading explosives, a rubber damping pad with a thickness of 8 mm to 10 mm is embedded between the explosive cartridge and the borehole wall on the side facing the inside of the tunnel.

[0051] Specifically, during tunnel blasting excavation, a detailed geological survey and assessment of the soft rock face is required first. When the lithology revealed at the face is typical weak rock layers such as carbonaceous shale or mudstone, or when the uniaxial compressive strength calculated through on-site point load tests is less than 15 MPa, the area is clearly designated as a high-concern zone. This clear criterion ensures that the identification of high-concern zones no longer relies on vague empirical judgments but is based on objective geological and mechanical indicators, guaranteeing the accuracy and consistency of the identification.

[0052] To further optimize the blasting effect in the high-concern area of ​​the arch, the spacing between the blast holes was reduced to 0.35 to 0.45 meters. This reduced spacing allows for a denser arrangement of blast holes along the arch's outline, enabling a more even release of energy during blasting, avoiding localized stress concentration, and contributing to a smooth excavation profile while reducing over-excavation and under-excavation. Simultaneously, during the charging process, a 10-centimeter-long, water-filled plastic bag with a diameter smaller than the blast hole diameter is placed between every two standard explosive charges, and filled with water before charging. The water-filled plastic bag acts as a hydraulic coupling and energy damping agent during blasting. Water, as an incompressible medium, can more evenly distribute blasting energy to the surrounding rock, while its damping effect effectively absorbs and attenuates the peak pressure of the blast shock wave, significantly reducing the damage to the arch's surrounding rock and inhibiting the generation and propagation of blast fractures.

[0053] For high-concern areas of the sidewall, a rubber damping pad with a thickness of 8 mm to 10 mm is embedded between the explosive charge and the borehole wall on the side facing inwards towards the tunnel. Utilizing its excellent elasticity and energy absorption properties, the rubber damping pad effectively absorbs and dissipates some of the blast energy at the moment of detonation, preventing it from directly impacting the surrounding rock inside the tunnel. This significantly reduces the damage to the sidewall surrounding rock caused by blasting vibrations, reduces the range of blast-induced microcracks and loosening zones, thereby better protecting the stability of the sidewall and providing a more solid foundation for subsequent initial support.

[0054] Through the aforementioned technical solutions, this application clarifies the specific geological criteria for identifying high-concern zones, enabling more accurate identification of extremely soft surrounding rock areas during tunnel blasting excavation in soft rock sections with large deformation. For the high-concern zone in the arch, by reducing the spacing between boreholes and using water-filled plastic bags for charging, blasting energy is effectively dispersed, reducing stress concentration at single points. Simultaneously, the damping effect of the water bags significantly weakens the damage of the blast shock wave to the surrounding rock, thus achieving refined protection of the arch surrounding rock and reducing over-excavation and crack propagation. For the high-concern zone in the sidewalls, rubber damping pads are embedded between the explosive charge and the borehole wall. Utilizing the elastic energy absorption properties of rubber, excessive transmission of blasting energy to the inner surrounding rock of the tunnel is effectively blocked, further controlling the damage to the sidewalls from blasting vibration and ensuring the stability of the sidewalls. These measures work together to significantly improve the surrounding rock control effect during blasting excavation in extremely soft strata, effectively suppressing blast-induced large deformations and providing a more stable foundation for subsequent support.

[0055] In an embodiment of the present invention, a digital detonator network is used, and the blast holes at different locations are detonated in the following order: first, the slotted holes and auxiliary holes located in the middle of the soft rock face are detonated; second, the auxiliary holes and peripheral holes in the arch are detonated; then, the auxiliary holes and peripheral holes in the sidewalls are detonated; and finally, the bottom plate holes are detonated. S51, using a digital detonator with a five-segment millisecond delay sequence, the first segment is delayed by 0 to 15 milliseconds to detonate the wedge-shaped cut hole located in the center of the soft rock face; the second segment is delayed by 30 to 50 milliseconds to detonate the auxiliary holes used to expand the cavity and the first ring of auxiliary holes at the top of the arch; the third segment is delayed by 75 to 100 milliseconds to detonate all the peripheral holes on the arch design outline and the remaining auxiliary holes in the arch; the fourth segment is delayed by 125 to 150 milliseconds to detonate the auxiliary holes and peripheral holes at the side walls and corners, and the detonators for the blast holes located at the arch feet on both sides are set to detonate 8 to 12 milliseconds earlier than the blast holes on other side walls in the same segment; the fifth segment is delayed by 175 to 200 milliseconds to detonate all the bottom plate holes.

[0056] Among them, the digital detonator is an electronic detonator with a programmable delay time. Its delay time accuracy is high, down to the millisecond level, and it can be centrally controlled and programmed via a network. Employing a five-segment millisecond delay sequence means dividing the entire blasting process into five independent delay stages, each corresponding to a different group of blast holes, with a precisely set delay time. This refined delay control effectively optimizes the release path and timing of blasting energy, avoids the superposition effect of blasting shock waves, thereby reducing disturbance to the surrounding rock, minimizing blasting vibration, and facilitating the formation of a regular excavation profile.

[0057] A cut-out is the first blast hole detonated during blasting excavation. Its main function is to create a free face or expanded space in the center of the tunnel face, providing pressure relief conditions for subsequent blasting. A wedge-shaped cut-out, through the combination of multiple blast holes, forms a conical or wedge-shaped cut-out space. Setting the first delay to an extremely short period of 0 to 15 milliseconds aims to rapidly create an initial pressure relief space in the core area of ​​the tunnel face, guiding the blasting energy inward and preventing energy transfer to deeper parts of the surrounding rock, thereby effectively controlling the blasting's damage to the surrounding rock mass.

[0058] The purpose of auxiliary holes is to expand the free surface formed by the cut-out holes and further fracture the rock mass. In the second delayed stage, the auxiliary holes used to expand the cut cavity are detonated to further increase the blasting space and create a larger free surface for subsequent blasting holes. Simultaneously, the first ring of auxiliary holes at the top of the tunnel arch is detonated to release stress in advance in this critical stress-bearing area, reducing initial stress concentration in the surrounding rock and providing favorable conditions for subsequent blasting of holes around the arch, thus contributing to the stability of the surrounding rock.

[0059] Peripheral boreholes are blast holes arranged along the tunnel's designed outline, and their blasting effect directly affects the tunnel's forming quality and the stability of the surrounding rock. In the third extension phase, all peripheral boreholes along the arch's designed outline are blasted to accurately control the arch's excavation profile and reduce over- or under-excavation. Simultaneously, the remaining auxiliary boreholes in the arch further fracture the arch rock mass, ensuring sufficient loosening and stress relief of the surrounding rock, providing a good foundation for the subsequent installation of support structures.

[0060] Auxiliary and peripheral holes at the sidewalls and corners are responsible for forming the tunnel's sidewall profile. During the fourth extension, these holes are detonated to complete the excavation of the tunnel sidewalls. Specifically, the detonators at the arch feet are detonated 8 to 12 milliseconds earlier than other sidewall holes in the same section. This is to release stress in advance at the arch feet, a critical area of ​​stress concentration and structural transition, guiding the blasting energy and avoiding excessive impact on the arch feet from the overall blasting of the sidewalls. This effectively protects the surrounding rock structure in the arch foot area, reducing the risk of deformation and damage.

[0061] The floor holes are the blast holes in the bottom area of ​​the tunnel, where blasting completes the rock fragmentation for the entire excavation cycle. In the fifth extension phase, all floor holes are detonated to clear the bottom rock and form a complete tunnel cross-section. This extended extension ensures that the blasting energy in the upper arch and sidewall areas is fully released, avoiding mutual interference between blasting energies and thus guaranteeing the flatness of the floor and the quality of the excavation.

[0062] The aforementioned refined five-stage millisecond delay blasting scheme, utilizing the high-precision control capabilities of digital detonators, enables accurate regulation of blasting energy release. First, by detonating the wedge-shaped cut holes with an extremely short delay, a pressure relief space is rapidly created in the center of the tunnel face, effectively guiding blasting energy and reducing initial disturbance to the surrounding rock. Second, the staged detonation of the arch crown, arch perimeter holes, and auxiliary holes gradually releases stress in the arch surrounding rock, accurately controlling the arch profile, reducing over-excavation, and creating favorable conditions for subsequent support. Especially in the fourth stage delay, the advance detonation of the blast holes at the arch foot effectively alleviates stress concentration at the arch foot, preventing excessive impact from the overall blasting of the sidewalls on the arch foot, thus significantly reducing the risk of deformation and damage to the surrounding rock in the arch foot area and enhancing the overall stability of the tunnel structure. Finally, the bottom slab holes are detonated to complete the excavation of the entire cross-section. This segmented, time-based, and refined detonation sequence effectively avoids the superposition and mutual interference of blasting energy, minimizes the disturbance of soft rock surroundings by blasting, and reduces blasting vibration. As a result, in the tunnel excavation of soft rock sections with large deformation, it is possible to better control the deformation of the surrounding rock, improve the tunnel forming quality, ensure construction safety, and provide more stable surrounding rock conditions for subsequent initial support construction.

[0063] In an embodiment of the present invention, after blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent is sprayed within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot position. After installing the anchor pipes and grouting, the steps of applying a torque of 60 N·m to 80 N·m to the exposed end of the anchor pipe for tensioning include: S61. After blasting, the ventilation system is activated to ensure that the air quality near the soft rock face meets the operational requirements within 10 to 15 minutes. Then, a wet spraying robot is immediately used to spray C25 concrete mixed with an early strength compensating shrinkage agent onto the exposed surrounding rock surface. The dosage of the early strength compensating shrinkage agent is 8% to 10% of the total weight of cement and admixtures in the sprayed concrete, and the spraying thickness is 5 to 8 centimeters. S62, using a rock drilling rig, drill two anchor holes with a downward inclination of 30 to 45 degrees, a depth of 4.0 meters and a diameter of 50 millimeters at the left and right arch feet of each steel arch frame. S63 is a hot-rolled seamless steel pipe with a diameter of 42 mm, a wall thickness of 3.5 mm, and a tapered front end installed in a hole. S64, a grouting pump is connected through the hollow channel of the anchor pipe to inject pure cement grout with a water-cement ratio of 0.38~0.42. The grouting pressure is gradually increased to 1.0 MPa~1.5 MPa and stabilized for 3 minutes.

[0064] Specifically, after blasting operations, a large amount of smoke and harmful gases are generated at the working face, seriously affecting the health of construction workers and their visibility. Quickly activating the ventilation system and restoring air quality to operational standards within 10 to 15 minutes is a crucial prerequisite for ensuring the timely and safe execution of subsequent initial support work. This helps shorten the interval between blasting and support installation, creating conditions for rapid rock face closure and support installation.

[0065] Subsequently, a wet-spraying robotic arm was used to spray C25 concrete mixed with an early-strength shrinkage-compensating agent onto the exposed surrounding rock surface. A wet-spraying robotic arm is an automated or semi-automated shotcrete equipment that, through robotic arm operation, can achieve long-distance, large-area, and uniform concrete spraying. Compared to manual spraying, wet-spraying robotic arms offer higher operating efficiency, more stable spraying quality, and effectively prevent construction workers from being directly exposed to hazardous areas, thus improving construction safety. In soft rock sections with large deformation, the surrounding rock deforms rapidly after exposure, requiring the rapid formation of initial support. The C25 concrete mixed with an early-strength shrinkage-compensating agent significantly improves the early strength development rate of the concrete, enabling it to reach sufficient load-bearing capacity in a short time and effectively resist surrounding rock deformation. Simultaneously, the shrinkage-compensating agent reduces shrinkage cracks during the concrete hardening process, improving the density and durability of the shotcrete and enhancing its sealing and support function for the surrounding rock. C25 concrete indicates a 28-day compressive strength of not less than 25 MPa, ensuring sufficient structural strength. The dosage of the early-strength shrinkage-compensating agent is 8% to 10% of the total weight of cement and admixtures in the shotcrete. This dosage range is an optimized ratio verified through experiments, ensuring that the concrete meets the early-strength requirements while also compensating for shrinkage, avoiding performance degradation or increased costs due to excessive dosage. The spraying thickness is 5 to 8 cm, a commonly used thickness for initial shotcrete application, aiming to quickly form a closed layer with certain strength and toughness, effectively preventing weathering and loosening of the surrounding rock, and providing a stable working surface for subsequent steel arch installation.

[0066] Furthermore, using a rock drilling rig, two anchor holes with a downward inclination of 30 to 45 degrees, a depth of 4.0 meters, and a diameter of 50 millimeters were drilled at each of the left and right arch feet of each steel arch frame. The rock drilling rig is a highly efficient and accurate drilling device, ensuring that the drilling position, direction, and depth meet design requirements. Drilling anchor holes at the arch feet of the steel arch frame requires high precision; the use of the rock drilling rig ensures drilling quality and lays the foundation for effective anchor installation. The arch feet of the steel arch frame are key components that bear the load from the surrounding rock above and transmit it to the foundation. Setting two anchor holes at each arch foot creates a more stable anchoring structure, effectively resisting lateral displacement and upward lifting of the arch foot, and enhancing the overall stability of the steel arch frame. The inclination angle design of the anchor holes allows the anchor pipes to penetrate deep into the surrounding rock, forming a stress angle adapted to the direction of deformation of the surrounding rock. This inclination arrangement better utilizes the pull-out and shear resistance of the anchor pipes, effectively limiting the displacement of the arch foot and improving the anchoring effect. The depth and diameter of the anchor hole are important parameters affecting the anchoring force. A depth of 4.0 meters ensures that the anchor can penetrate shallow, loose surrounding rock and anchor into relatively stable deep rock. A diameter of 50 millimeters provides sufficient space for anchor installation and grouting, and ensures sufficient contact area between the anchor and the surrounding rock to transfer the anchoring force.

[0067] A 42 mm diameter, 3.5 mm wall thickness, and tapered front end hot-rolled seamless steel pipe is installed inside the borehole. The hot-rolled seamless steel pipe possesses high strength, toughness, and corrosion resistance, enabling it to withstand significant tensile and shear forces and resist erosion from groundwater and surrounding rock, ensuring the long-term stability of the anchor pipe. These dimensions ensure sufficient load-bearing capacity and rigidity of the steel pipe, while forming a suitable gap with the 50 mm borehole diameter, facilitating thorough filling of the grout. The tapered design at the front end of the anchor pipe helps it be smoothly inserted into the borehole, reducing installation resistance. Simultaneously, the tapered end acts as a guide during grouting, promoting uniform diffusion and filling of the grout within the borehole.

[0068] Finally, a grouting pump is connected to the hollow channel of the anchor pipe, and pure cement grout with a water-cement ratio of 0.38~0.42 is injected. The grouting pressure is gradually increased to 1.0 MPa~1.5 MPa and stabilized for 3 minutes. The hollow channel inside the anchor pipe is a dedicated channel for grouting. The grout is injected under high pressure by the grouting pump to ensure that the grout can fully fill the annular space between the anchor pipe and the borehole wall, as well as the surrounding rock fissures, forming a dense anchor body. Pure cement grout has good fluidity and early strength. The water-cement ratio is controlled within the range of 0.38~0.42 to ensure that the grout has a suitable consistency, which can be injected smoothly and ensure the strength and density after consolidation. Gradually increasing the grouting pressure helps the grout to fully penetrate into the surrounding rock fissures and compact the loose surrounding rock. Reaching a high pressure of 1.0 MPa to 1.5 MPa and stabilizing it for 3 minutes ensures that the grout fully diffuses, fills, and consolidates within the borehole and surrounding rock, forming a high-strength, high-density anchor body, which significantly improves the anchoring force of the anchor pipe and the overall stability of the surrounding rock.

[0069] Through the aforementioned technical solutions, in the tunnel blasting excavation of soft rock sections with large deformation, a rapid ventilation system is first used to ensure that the working environment meets safety requirements within a very short time, saving valuable time for subsequent support operations. Subsequently, a wet-spraying robot efficiently and uniformly sprays C25 concrete mixed with an early-strength shrinkage-compensating agent. This concrete rapidly forms a closed layer with high early strength and low shrinkage characteristics, effectively suppressing surrounding rock deformation and providing a stable foundation for the installation of the steel arch frame. Furthermore, a rock drilling rig accurately drills inclined deep holes at the arch foot of the steel arch frame, and high-strength conical hot-rolled seamless steel pipes are installed as anchor pipes. Combined with high-pressure, stable pure cement grouting, this ensures an extremely dense and high-strength anchor body is formed between the anchor pipes and the surrounding rock. This refined anchoring measure significantly enhances the pull-out and shear resistance of the steel arch frame's arch foot, effectively limiting the displacement and upward movement of the arch foot, thereby greatly improving the overall stability of the steel arch frame and the reliability of the initial support. This effectively addresses the challenges posed by large deformation in soft rock, ensuring tunnel construction safety and structural stability.

[0070] In an embodiment of the present invention, after blasting and ventilation, within 15 minutes, concrete mixed with an early-strength shrinkage-compensating agent is sprayed to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot position. After installing the anchor pipes and grouting, the step of applying a torque of 60 N·m to 80 N·m to the exposed end of the anchor pipe using a torque wrench for tensioning further includes: S65, after the grout has initially set, install the steel pad, spherical washer and nut in sequence on the exposed threaded end of the anchor pipe; S66, using a calibrated torque wrench, apply torque in two stages: in the first stage, apply torque smoothly to 40 N·m, stop and hold for 2 minutes; in the second stage, continue to apply torque smoothly to 80 N·m, and then lock the nut; during tensioning, use a hydraulic jack and pressure sensor to check and ensure that the initial preload of a single anchor pipe is not less than 50 kN.

[0071] Specifically, tensioning is performed after the grout in the anchor pipe has initially set, i.e., when the grout has gained some early strength but has not yet fully hardened. Tensioning during the initial setting stage ensures that the grout can effectively transfer the tension force of the anchor pipe to the surrounding rock, while avoiding potential damage to the grout-anchor pipe interface or stress concentration that might occur if tensioning is performed after the grout has fully hardened. Subsequently, a steel washer, a spherical washer, and a nut are installed sequentially at the exposed threaded end of the anchor pipe. The steel washer increases the contact area between the anchor pipe and the surrounding rock, dispersing stress and preventing localized crushing; the spherical washer compensates for any angular deviation between the anchor pipe and the surrounding rock surface, ensuring uniform tension force transmission and avoiding eccentric stress; the nut secures the anchor pipe and applies preload by tightening it.

[0072] During tensioning, a calibrated torque wrench is used to ensure accurate and reliable applied torque, thereby guaranteeing precise control of the anchor tension. The tensioning process is divided into two stages: In the first stage, the torque is smoothly applied to 40 N·m and held for 2 minutes. This stage aims to eliminate the initial gap between the anchor and the surrounding rock, allowing the anchor to be fully positioned and permitting initial stress adjustment and creep in the surrounding rock and grout. Subsequently, in the second stage, the torque is smoothly applied to 80 N·m, and after reaching the designed preload, the locking nut is used to maintain this preload. This refined method of applying torque in stages helps reduce stress concentration and improves the uniformity and durability of the anchoring effect. Simultaneously, during tensioning, a pressure sensor in conjunction with a hydraulic jack is used for verification, a direct means of measuring the anchor tension. Real-time monitoring and verification of the actual tension force through the pressure sensor verifies the correspondence between torque and tension force, ensuring that each anchor reaches a design initial preload of no less than 50 kN, providing a reliable quantitative guarantee for the active support function of the anchor.

[0073] Through the aforementioned technical solution, after the initial setting of the grout in the anchor pipe, the anchor pipe is tensioned in stages with precise torque control, supplemented by pressure sensors for verification, enabling the anchor pipe to establish a reliable initial prestress. This active prestressing method transforms the anchor pipe from passive support to active support, enabling it to resist the initial deformation of soft rock earlier and more effectively, suppressing the relaxation and displacement of the surrounding rock, thereby significantly improving the stiffness and bearing capacity of the tunnel's initial support. The staged tensioning and verification mechanism ensures the uniformity and reliability of the prestress, avoiding anchorage failure or poor support effect caused by excessive or insufficient tension in a single operation, providing a strong guarantee for the stability of the tunnel in soft rock sections with large deformation.

[0074] In an embodiment of the present invention, after blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent is sprayed within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot position. After installing the anchor pipes and grouting, a torque of 60 N·m to 80 N·m is applied to the exposed end of the anchor pipe using a torque wrench for tensioning. Following this step, the tunnel blasting excavation method for soft rock sections with large deformation further includes: S71, on the section where the initial support has been completed, concrete observation piles with precision reflectors are installed at five locations: the arch crown, the two sides of the arch waist, and the two sides of the sidewalls. S72, using a total station, conduct a round of clearance convergence measurement at 1 hour, 2 hours and 4 hours after the blasting ventilation is completed; S73. If the cumulative net clearance convergence value measured at the cross section in the 4th hour exceeds 15 mm, or if the convergence rate from the 2nd to the 4th hour does not show a decreasing trend, then the cross section is judged to be deformed abnormally. S74. For sections with abnormal deformation, in the next adjacent excavation cycle, the spacing of the steel arches designed within 5 meters before and after the section mileage is temporarily adjusted from 0.6 meters to 0.5 meters. At the same time, the design length of the system anchor bolts is increased by 0.5 meters. When blasting in this range, the single-hole charge amount in the high-concern area is reduced by 10%.

[0075] Specifically, in the section where the initial support has been completed, concrete observation piles equipped with precision reflectors are installed at five locations: the arch crown, the two sides of the arch waist, and the two sides of the sidewalls. These concrete observation piles serve as benchmarks for monitoring the deformation of the tunnel's surrounding rock or initial support structure. The precision reflectors allow high-precision measuring equipment (such as total stations) to perform non-contact measurements, thereby improving measurement efficiency and accuracy. The observation piles are typically made of reinforced concrete or precast concrete blocks, embedded in the surface of the initial support concrete. The reflectors can be prism sheets or reflective patches to ensure that the measuring equipment can accurately capture the target. The selection of five locations—the arch crown, the two sides of the arch waist, and the two sides of the sidewalls—is to comprehensively reflect the deformation of the tunnel section; these locations are typically deformation-sensitive areas.

[0076] Subsequently, using a total station, clearance convergence measurements were conducted at 1 hour, 2 hours, and 4 hours after the blasting ventilation was completed. A total station is a precision measuring instrument integrating angle measurement, distance measurement, and data processing, capable of accurately measuring the distance changes between observation points to obtain tunnel clearance convergence data. After blasting ventilation, the surrounding rock deformation typically experiences a rapid development period; therefore, measurements at 1 hour, 2 hours, and 4 hours can capture early and rapid deformation trends, providing data support for timely assessment of surrounding rock stability. During the measurements, the total station was set up on stable reference points within the tunnel, and measurements were taken using reflectors on each observation point. By comparing the measurement data at different time points, the relative displacement between each point was calculated, thus obtaining the clearance convergence value.

[0077] Furthermore, if the cumulative net clearance convergence value measured at the cross-section exceeds 15 mm in the 4th hour, or if the convergence rate from the 2nd to the 4th hour does not show a decreasing trend, the cross-section is judged to be deformed abnormally. This is the standard for judging deformation data. A cumulative net clearance convergence value exceeding the threshold (15 mm) directly indicates a large deformation; a convergence rate not showing a decreasing trend indicates that deformation is still actively developing, potentially indicating a risk of surrounding rock instability. Meeting either of these conditions triggers the "deformation abnormality" judgment, requiring further measures. The measurement data is processed and analyzed by software, automatically calculating the cumulative convergence value and convergence rate. The preset judgment logic is implemented in the software; once the conditions are met, the system will issue an alarm or prompt.

[0078] For sections with abnormal deformation, in the next adjacent excavation cycle, the spacing of the designed steel arches within a 5-meter radius before and after the section is temporarily adjusted from 0.6 meters to 0.5 meters. Simultaneously, the design length of the system anchor bolts is increased by 0.5 meters, and the single-hole charge in the high-concern area is further reduced by 10% during blasting. This is a dynamic adjustment and reinforcement measure for sections with abnormal deformation. Reducing the steel arch spacing (from 0.6 meters to 0.5 meters) means increasing the number of steel arches per unit length, thereby improving support stiffness and load-bearing capacity, and more effectively resisting surrounding rock deformation. Increasing the anchor bolt length (0.5 meters) allows the anchor bolts to penetrate deeper into the more stable surrounding rock, improving anchoring effect and overall support stability. Further reducing the blasting charge in the high-concern area (arch and upper sidewall area) by another 10% aims to further reduce blasting disturbance to the surrounding rock, reduce secondary damage to the deformed surrounding rock caused by blasting vibration, and thus control further deformation. Based on the results of the abnormal deformation assessment, the construction personnel will make on-site adjustments to the support design and blasting parameters within the affected mileage range (5 meters before and after) in the next excavation cycle. This requires the construction management system to have the ability to respond and adjust quickly, and to ensure that the on-site operators strictly implement the adjusted plan.

[0079] Through the aforementioned technical solution, this application enables timely and accurate detection of early deformation trends and anomalies in the tunnel surrounding rock by installing observation piles and conducting early, high-frequency clearance convergence measurements after the initial support is completed. Based on preset judgment criteria, a dynamic adjustment mechanism is immediately activated upon detection of deformation anomalies, including densifying the steel arch frame, increasing the length of anchor bolts, and further reducing the explosive charge in high-concern areas. This dynamic monitoring and feedback adjustment mechanism allows the tunnel blasting excavation method to optimize support and blasting parameters in real time based on the actual deformation response of the surrounding rock. This not only effectively controls the further development of large deformations in soft rock and avoids engineering risks caused by insufficient support, but also avoids resource waste caused by excessive support in unnecessary areas, thereby improving the targeting and effectiveness of support and ensuring the safety and economy of tunnel construction.

[0080] In an embodiment of the present invention, after blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent is sprayed within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot position. After installing the anchor pipes and grouting, a torque of 60 N·m to 80 N·m is applied to the exposed end of the anchor pipe using a torque wrench for tensioning. Following this step, the tunnel blasting excavation method for soft rock sections with large deformation further includes: S610, after the earthwork of the invert arch section of the soft rock with large deformation is excavated to the design elevation, a layer of C25 early strength concrete with a thickness of 8 cm to 10 cm is immediately sprayed with a wet spraying machine for preliminary sealing. S620: After the initial shotcrete strength reaches 5 MPa, tie the invert arch connecting bars and fasten the steel arch frame of the invert arch section to the side wall arch frame with connecting plates and high-strength bolts. S630, within 24 hours after the connection is completed, the first layer of invert arch structure concrete is poured, with a thickness of 60% of the total design thickness. This layer of concrete is mixed with a high-efficiency early strength agent, and its 12-hour compressive strength is not less than 8 MPa. S640. After the strength of the first layer of concrete reaches 10 MPa in the test block under the same conditions, the second layer of concrete is poured immediately. Before pouring, a steel mesh with a diameter of 8 mm and a grid spacing of 20 cm * 20 cm is laid on the arch surface of the invert, and finally the thickened reinforced concrete closed structure of the entire invert is completed.

[0081] After the excavation of the invert section of the soft rock with large deformation reaches the design elevation, a layer of C25 early-strength concrete, 8-10 cm thick, is immediately sprayed using a wet shotcrete machine for initial sealing. This step aims to quickly and effectively seal the newly excavated invert surface. In soft rock with large deformation, the exposed surrounding rock is highly susceptible to deformation and weathering. Immediate spraying of early-strength concrete rapidly forms a protective layer, inhibiting initial loosening and deformation of the surrounding rock and preventing moisture erosion. The wet shotcrete process ensures good adhesion between the concrete and the rock surface, reduces rebound, and improves construction efficiency and concrete quality. The use of C25 early-strength concrete ensures sufficient strength is achieved in a short time, providing a stable working face for subsequent support operations.

[0082] After the initial shotcrete strength reaches 5 MPa, the invert arch connecting bars are tied, and the steel arch frame of the invert arch section is securely connected to the sidewall arch frame using connecting plates and high-strength bolts. The initial shotcrete strength of 5 MPa is fundamental for subsequent work, ensuring structural stability during the tying of the invert arch connecting bars and the connection of the steel arch frame. Tying the invert arch connecting bars effectively connects the invert arch structure to the sidewall structure, forming a unified, load-bearing ring structure. Securely connecting the steel arch frame of the invert arch section to the sidewall arch frame using connecting plates and high-strength bolts transfers the load-bearing capacity of the invert arch to the entire tunnel support system, forming a closed load-bearing ring, thereby significantly improving the overall stiffness and deformation resistance of the tunnel.

[0083] Within 24 hours of the connection completion, the first layer of invert arch concrete was poured, with a thickness of 60% of the designed total thickness. This layer of concrete incorporated a high-efficiency early-strength agent, and its 12-hour compressive strength was not less than 8 MPa. Pouring the first layer of invert arch concrete within 24 hours of the connection completion reflects the urgency of the construction, aiming to quickly establish the load-bearing structure of the invert arch to resist surrounding rock deformation. The first layer of concrete, accounting for 60% of the designed total thickness, provides the main load-bearing capacity for the invert arch. The addition of a high-efficiency early-strength agent and the requirement of a 12-hour compressive strength of not less than 8 MPa ensured that the invert arch structure reached high strength in a very short time, enabling it to quickly bear the pressure of the surrounding rock and effectively control deformation.

[0084] After the first layer of concrete reached a strength of 10 MPa as tested by test blocks under the same conditions, the second layer of concrete was poured immediately. Before pouring, a steel mesh with a diameter of 8 mm and a grid spacing of 20 cm x 20 cm was laid on the curved surface of the invert arch, ultimately completing the thickened reinforced concrete enclosure structure of the entire invert arch. The first layer of concrete reaching a strength of 10 MPa was a necessary condition for pouring the second layer, ensuring that the lower layer of concrete could withstand the load of the upper layer. Pouring the second layer of concrete immediately was to complete the enclosure structure of the invert arch as quickly as possible. Laying a steel mesh with a diameter of 8 mm and a grid spacing of 20 cm x 20 cm on the curved surface of the invert arch significantly improved the tensile strength and crack resistance of the invert arch concrete, enhancing its integrity and ductility. Through the pouring of two layers of concrete and the reinforcement of the steel mesh, a thickened reinforced concrete enclosure structure was ultimately formed, providing a solid and durable bottom support for the tunnel.

[0085] Through the aforementioned rapid, layered, and reinforced sealing measures for the invert arch, this application effectively solves the problem of insufficient long-term stability of the invert arch in soft rock sections with large deformation. Immediate spraying of early-strength concrete can quickly seal the rock surface and suppress initial deformation; the tight connection of the invert arch connecting bars and the steel arch frame forms a complete closed loop between the invert arch and the sidewall support, significantly improving the overall load-bearing capacity and deformation resistance of the tunnel. Layered pouring of concrete mixed with a high-efficiency early-strength agent, combined with steel mesh, not only ensures that the invert arch structure reaches its design strength in a short time, effectively resisting deformation caused by ground stress, but also forms a robust, thickened reinforced concrete closed structure, providing long-term, reliable bottom support for the tunnel, thereby significantly improving the overall stability and safety of the tunnel and effectively controlling the long-term deformation of soft rock sections with large deformation.

[0086] The following example will provide a more detailed explanation of the above technical solution: In a tunnel excavation project involving large deformation in soft rock, the construction team faced challenges such as low surrounding rock strength, poor self-stabilizing ability, easy softening upon contact with water, and significant deformation easily generated after blasting disturbance. Traditional blasting methods often result in long construction periods and high safety risks due to factors such as imprecise parameter design, cumbersome core soil treatment, passive load-bearing of anchoring structures, and untimely initial support. To address these issues, the construction team adopted a new tunnel blasting excavation method.

[0087] At the start of each excavation cycle, the soft rock face is pre-reinforced. Using a lightweight drilling rig equipped with a 42mm diameter drill bit, workers drill holes in a 1.0m x 1.0m quincunx pattern on the face, perpendicular to the face, to a depth of 4.5 meters, with a borehole deviation of no more than 5cm. After drilling, 4.2m long, 25mm diameter fully threaded fiberglass anchors are inserted. A grouting pump is connected through the hollow channel of the anchor, injecting early-strength cement grout with a water-cement ratio of 0.4-0.45. The grouting pressure is maintained at 0.8-1.0 MPa until thick grout continuously flows back from the borehole. Subsequently, a washer and nut are installed at the borehole opening, and a torque wrench is used to apply a pre-tightening force of 30N·m-40N·m to the nut. Unlike traditional passive anchors, this type of prestressed fiberglass anchor applies active restraint to the surrounding rock before blasting, effectively improving the overall stability of the tunnel face, creating favorable conditions for subsequent blasting operations, and mitigating the initial deformation of the surrounding rock before blasting disturbance.

[0088] Next, based on the tunnel excavation outline, a trapezoidal area was marked as a reserved zone in the lower part of the soft rock face. The upper base width of this trapezoidal area is half the current excavation width of the tunnel, the lower base width is the same as the excavation width, and the height is 2.5 meters to 3.5 meters. Within the reserved zone, the hole spacing and row spacing of the blast holes are consistent with the external area, but the charge amount of each blast hole is reduced to 30% to 40% of the normal design value. After charging, plastic blasting mud made of clay and sand in a 1:1 volume ratio is used for plugging, with a plugging length of no less than 40 centimeters for each blast hole, and it is compacted tightly. This reserved zone design, by reducing the blasting intensity of the core soil, allows it to maintain a certain bearing capacity after blasting, forming temporary support for the upper surrounding rock and effectively controlling the rapid deformation of the surrounding rock in the early stage of blasting. Compared with the traditional method of reserving core soil, this method, through precise control of the charge amount in the reserved zone, avoids excessive fragmentation of the core soil, facilitates subsequent mechanical crushing and removal, and reduces safety hazards.

[0089] Meanwhile, the construction team divided the excavation section into zones based on the geological conditions revealed at the soft rock face. For example, when the rock type revealed at the face was carbonaceous shale, mudstone, or a weak rock layer with a uniaxial compressive strength of less than 15 MPa calculated from on-site point load tests, this area was designated as a high-concern zone, typically located in the upper and middle parts of the arch and sidewalls. The remaining areas were marked as ordinary zones. For the high-concern zones, blasting parameters were set with a borehole spacing of 0.4–0.5 meters, a single-hole charge of 0.4–0.6 kg, and a mud plugging length of not less than 45% of the borehole depth. Specifically, for the high-concern zone in the arch, the borehole spacing of the peripheral holes was reduced to 0.35–0.45 meters, and during charging, a 10 cm long, water-filled plastic bag with a diameter smaller than the borehole diameter was placed between every two standard charge cartridges, and the bag was filled with water before charging. For the high-concern zone of the sidewall, a rubber damping pad with a thickness of 8 mm to 10 mm is embedded between the explosive charge and the borehole wall on the side facing inwards towards the tunnel. This refined zoning and differentiated blasting parameter design overcomes the problem of standardized blasting parameters in traditional methods. It allows for accurate control of blasting energy based on the actual geological conditions of the surrounding rock, reducing excessive disturbance to weak surrounding rock and effectively suppressing deformation caused by blasting. Furthermore, the application of water-filled soft bags and rubber damping pads further reduces the damage to the surrounding rock caused by the blast shock wave, achieving flexible blasting.

[0090] The blasting initiation utilizes a digitally networked detonator control system, strictly adhering to a five-stage millisecond delay sequence. First, using the first delay of 0-15 milliseconds, the wedge-shaped cut in the center of the soft rock face is detonated to create a free face. Second, using the second delay of 30-50 milliseconds, auxiliary cuts used to expand the cavity and the first ring of auxiliary cuts at the arch top are detonated. Then, using the third delay of 75-100 milliseconds, all peripheral cuts along the arch's design outline and the remaining auxiliary cuts in the arch are detonated. Next, using the fourth delay of 125-150 milliseconds, auxiliary and peripheral cuts at the side walls and corners are detonated, with the detonators at the arch feet set to detonate 8-12 milliseconds earlier than other side wall cuts in the same section, ensuring that the arch feet are depressurized first. Finally, using the fifth delay of 175-200 milliseconds, all bottom plate cuts are detonated. This segmented, regional, and differentiated detonation sequence, especially the design of detonating the arch blast holes more than 50 milliseconds earlier than the blast holes on the side walls in the same row, and the design of detonating the arch foot blast holes in advance, optimizes the energy release path, guides the blasting energy to concentrate on the free surface, effectively reduces the disturbance of blasting vibration to the surrounding rock, and avoids excessive loosening and deformation of the surrounding rock.

[0091] Following the blasting ventilation, the construction team immediately activated the ventilation system, ensuring the air quality near the soft rock face met operational requirements within 10-15 minutes. Then, within 15 minutes, a wet-spraying robot was used to spray C25 concrete mixed with an early-strength shrinkage-compensating agent onto the exposed rock surface. The spray thickness was 5-8 cm, with the agent accounting for 8%-10% of the total weight of cement and admixtures in the shotcrete. This rapid sealing of the rock surface effectively prevented the soft rock from weathering and softening due to prolonged exposure to air, thus avoiding missed opportunities for optimal support. The addition of the early-strength shrinkage-compensating agent allowed the shotcrete to quickly reach its design strength and effectively compensate for shrinkage, improving the stability of the initial support.

[0092] Immediately after the initial setting of the shotcrete, the steel arch frame is installed. Simultaneously, using a rock drilling rig, two anchor pipe holes, each 4.0 meters deep and 50 mm in diameter, inclined downwards at 30-45 degrees at the left and right arch feet of each steel arch frame are drilled. Hot-rolled seamless steel pipes, 42 mm in diameter, 3.5 mm thick, and tapered at the front end, are installed inside the holes. A grouting pump is connected through the hollow channel of the anchor pipe, and pure cement grout with a water-cement ratio of 0.38-0.42 is injected. The grouting pressure is gradually increased to 1.0 MPa-1.5 MPa and stabilized for 3 minutes. After the grout has initially set, steel washers, ball washers, and nuts are sequentially installed on the exposed threaded end of the anchor pipe. Using a calibrated torque wrench, torque is applied in two stages: in the first stage, the torque is steadily applied to 40 N·m, stopped, and held for 2 minutes; in the second stage, the torque is steadily applied to 80 N·m, and then the nut is locked. During tensioning, a hydraulic jack and pressure sensor are used for verification to ensure that the initial preload of a single anchor pipe is not less than 50 kN. This active tensioning anchor pipe design differs from traditional passive anchoring. It applies active prestress to the arch foot during the initial support stage, effectively suppressing the continuous creep deformation of soft rock, enhancing the bearing capacity and overall stability of the arch foot, and significantly improving the deformation resistance of the support structure.

[0093] At the section where initial support has been completed, concrete observation piles equipped with precision reflectors are installed at five locations: the arch crown, the two side arch waists, and the two side walls. Using a total station, a round of net clearance convergence measurements is performed at 1 hour, 2 hours, and 4 hours after blasting and ventilation. If the cumulative net clearance convergence value measured at the 4th hour exceeds 15 mm, or if the convergence rate does not show a decreasing trend from the 2nd to the 4th hour, the section is considered to have abnormal deformation. For sections with abnormal deformation, in the next adjacent excavation cycle, the spacing of the designed steel arch frames within 5 meters before and after the section is temporarily adjusted from 0.6 meters to 0.5 meters. At the same time, the design length of the system anchor bolts is increased by 0.5 meters, and when blasting within this range, the single-hole charge in the high-concern area is further reduced by 10%. This real-time monitoring and dynamic adjustment mechanism can promptly detect abnormal deformation of the surrounding rock and immediately take targeted reinforcement measures, avoiding the problems of delayed or insufficient support in traditional methods, and ensuring construction safety and project quality.

[0094] After the excavation of the invert arch section of the soft rock with large deformation reaches the design elevation, a layer of C25 early-strength concrete with a thickness of 8-10 cm is immediately sprayed using a wet shotcrete machine for initial sealing. Once the initial shotcrete strength reaches 5 MPa, the invert arch connecting bars are tied, and the steel arch frame of the invert arch section is securely connected to the side wall arch frame using connecting plates and high-strength bolts. Within 24 hours of the connection completion, the first layer of invert arch structural concrete is poured, with a thickness of 60% of the total design thickness. This layer of concrete incorporates a high-efficiency early-strength agent, and its 12-hour compressive strength is not less than 8 MPa. After the strength of the first layer of concrete reaches 10 MPa as tested by test blocks under the same conditions, the second layer of concrete is immediately poured. Before pouring, a steel mesh with a diameter of 8 mm and a grid spacing of 20 cm x 20 cm is laid on the curved surface of the invert arch, ultimately completing the thickened reinforced concrete sealing structure of the entire invert arch. This rapid, layered, and thickened invert arch closure construction method can quickly form a closed ring, effectively resisting the deformation of soft rock bottom heave. Compared with traditional invert arch construction, it significantly shortens the exposure time of the surrounding rock, improves the overall stiffness and bearing capacity of the invert arch structure, and further ensures the long-term stability of the tunnel.

[0095] Before the next excavation cycle's step of drilling 4.5-meter-deep fiberglass anchors in a quincunx pattern on the soft rock face, the construction team used a hydraulic breaker to mechanically break up the core soil reserved in the previous cycle, proceeding from top to bottom and from both sides towards the center. The broken material was immediately removed from the tunnel by a loader. After the core soil was completely removed and the new soft rock face was fully exposed, drilling rigs were immediately used to drill 4.5-meter-deep holes at 0.8-meter x 0.8-meter intervals within the new soft rock face area corresponding to the reserved area from the previous cycle. Simultaneously, fiberglass anchors were installed and grouted to form reinforcing anchors. After the grout for the reinforcing anchors had fully set, full-section blasting operations for the new cycle began. This core soil treatment method, replacing secondary blasting with mechanical breaking, avoided secondary disturbance to the already supported surrounding rock, improving construction safety. Meanwhile, anchor bolts were immediately reinforced after the core soil was removed, and the area was actively reinforced, which solved the problem of the lack of effective advanced reinforcement measures in the traditional reserved core soil area and further enhanced the overall stability of the surrounding rock.

[0096] Through the synergistic combination of the above-mentioned technical features, this tunnel blasting excavation method effectively solves the problems of large blasting disturbance, difficulty in controlling surrounding rock deformation, and delayed support in the construction of soft rock sections with large deformation, and significantly improves construction efficiency and safety.

[0097] 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 tunnel blasting excavation in soft rock sections with large deformation, characterized in that, The tunnel blasting excavation method for soft rock sections with large deformation is implemented in each excavation cycle, and the tunnel blasting excavation method for soft rock sections with large deformation includes: On the soft rock face, fiberglass anchors with a depth of 4.5 meters are drilled in a quincunx pattern. A trapezoidal area in the lower part of the soft rock face is designated as a reserved area, and the single-hole charge of the blast holes in the reserved area is reduced to 30% to 40% of the normal design value; Based on the geological conditions of the soft rock face, the arch and upper part of the sidewall of the excavation section are marked as high concern areas, and the remaining areas are marked as ordinary areas. For the high-concern area, blasting parameters are set as follows: borehole spacing is 0.4 to 0.5 meters, single-hole charge is 0.4 to 0.6 kg, and the length of the stemming material is not less than 45% of the borehole depth. The blast holes in different locations are detonated in the following order using digital detonators networked together: first, the slotted holes and auxiliary holes in the middle of the soft rock face are detonated; second, the auxiliary holes and peripheral holes in the arch are detonated; then, the auxiliary holes and peripheral holes in the sidewalls are detonated; and finally, the bottom plate holes are detonated. The detonation time of the blast holes in the arch is more than 50 milliseconds earlier than the detonation time of the blast holes in the sidewalls in the same row. After blasting and ventilation, concrete mixed with early strength compensating shrinkage agent is sprayed within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes with a downward inclination of 30 to 45 degrees are drilled at the arch foot position. After the anchor pipes are installed and grouting is performed, a torque wrench is used to apply a torque of 60 N·m to 80 N·m to the exposed end of the anchor pipe for tensioning.

2. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 1, characterized in that, The steps for drilling fiberglass anchors to a depth of 4.5 meters in a quincunx pattern at the soft rock face include: Using a light drilling rig equipped with a 42 mm diameter drill bit, drill holes in a 1.0 m * 1.0 m quincunx pattern at the soft rock face. The drilling direction is perpendicular to the soft rock face, the depth is controlled at 4.5 m, and the hole opening deviation is no more than 5 cm. After drilling is completed, a fully threaded fiberglass anchor rod with a length of 4.2 meters and a rod diameter of 25 millimeters is inserted. The grouting pump is connected through the hollow channel of the anchor bolt, and early-strength cement grout with a water-cement ratio of 0.4~0.45 is injected. The grouting pressure is maintained at 0.8~1.0 MPa until thick grout continues to return from the borehole. Install a washer and nut at the orifice, and apply a preload of 30 N·m to 40 N·m to the nut using a torque wrench.

3. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 2, characterized in that, The step of designating a trapezoidal region in the lower part of the soft rock face as a reserved area, and reducing the single-hole charge of the blast holes in the reserved area to 30% to 40% of the normal design value, includes: According to the tunnel design excavation outline, a trapezoidal area is marked on the soft rock face. The upper base width of the trapezoidal area is half of the current excavation width of the tunnel, the lower base width is the same as the excavation width, and the height is 2.5 meters to 3.5 meters, forming the reserved area. Within the reserved area, the hole spacing and row spacing of the blast holes are consistent with those of the external area, but the charge amount of each blast hole is controlled within 30% to 40% of the designed conventional charge amount. After the explosive charge is loaded, use plastic gun clay made of clay and sand in a 1:1 volume ratio to plug the hole. The plugging length of each hole should be no less than 40 cm, and it should be tamped down tightly.

4. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 3, characterized in that, Before the step of drilling 4.5-meter-deep frontal fiberglass anchors in a staggered pattern at the soft rock face in the next excavation cycle, the tunnel blasting excavation method for soft rock sections with large deformations further includes: A hydraulic breaker was used to mechanically break up the core soil, with the breaking sequence proceeding from top to bottom and from both sides toward the center. The crushed slag was immediately removed from the tunnel by a loader; After the core soil is completely removed and the new soft rock face is fully exposed, immediately use a drilling rig to drill holes with a depth of 4.5 meters at intervals of 0.8 meters * 0.8 meters within the new soft rock face area corresponding to the reserved area of ​​the previous cycle, and simultaneously complete the installation and grouting of the glass fiber anchor rods to form a reinforcing anchor rod. After the grouting slurry for the reinforcing anchor has fully set, a new cycle of full-section blast hole drilling will begin.

5. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 1, characterized in that, Based on the geological conditions of the soft rock face, the steps of designating the arch and upper part of the sidewall of the excavation section as high-concern areas and the remaining areas as ordinary areas include: When the lithology revealed by the soft rock face is carbonaceous shale, mudstone, or a weak rock layer with a uniaxial compressive strength of less than 15 MPa calculated from the field point load test, the area is designated as the high concern area. For the high-concern area of ​​the arch, the spacing between the blast holes of the surrounding holes is reduced to 0.35 meters to 0.45 meters. When loading the explosive, a water-filled plastic bag with a length of 10 centimeters and a diameter smaller than the diameter of the blast hole is placed between every two standard explosive cartridges. The soft bag is filled with water before loading the explosive. For the high-concern area of ​​the sidewall, when loading explosives, a rubber damping pad with a thickness of 8 mm to 10 mm is embedded between the explosive cartridge and the borehole wall on the side facing the inside of the tunnel.

6. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 1, characterized in that, The steps of using digital detonators networked together and detonating the blast holes in different locations in the following order are as follows: first, detonating the slotted hole and auxiliary hole located in the middle of the soft rock face; second, detonating the auxiliary hole and peripheral hole in the arch; then, detonating the auxiliary hole and peripheral hole in the sidewall; and finally, detonating the bottom hole. Using a digital detonator with a five-segment millisecond delay sequence, the first segment is delayed by 0 to 15 milliseconds to detonate the wedge-shaped cut hole located in the center of the soft rock face; the second segment is delayed by 30 to 50 milliseconds to detonate the auxiliary holes used to expand the cavity and the first ring of auxiliary holes at the top of the arch; the third segment is delayed by 75 to 100 milliseconds to detonate all the peripheral holes along the arch's design outline and the remaining auxiliary holes in the arch; the fourth segment is delayed by 125 to 150 milliseconds to detonate the auxiliary holes and peripheral holes at the side walls and corners, with the detonators at the arch feet on both sides set to detonate 8 to 12 milliseconds earlier than other side wall holes in the same segment; and the fifth segment is delayed by 175 to 200 milliseconds to detonate all the bottom plate holes.

7. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 1, characterized in that, After blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent is sprayed within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot position. After installing the anchor pipes and grouting, the following steps are taken to apply a torque of 60 N·m to 80 N·m to the exposed end of the anchor pipe for tensioning: After blasting, the ventilation system is activated to ensure that the air quality near the soft rock face meets the operational requirements within 10 to 15 minutes. Then, a wet spraying robot is immediately used to spray C25 concrete mixed with an early strength compensating shrinkage agent onto the exposed surrounding rock surface. The dosage of the early strength compensating shrinkage agent is 8% to 10% of the total weight of cement and admixtures in the sprayed concrete, and the spraying thickness is 5 to 8 centimeters. Using a rock drilling rig, two anchor holes with a downward inclination of 30 to 45 degrees, a depth of 4.0 meters, and a diameter of 50 millimeters are drilled at the left and right arch feet of each steel arch frame. A hot-rolled seamless steel pipe with a diameter of 42 mm, a wall thickness of 3.5 mm, and a tapered front end is installed inside the hole; The grouting pump is connected through the hollow channel of the anchor pipe, and pure cement grout with a water-cement ratio of 0.38~0.42 is injected. The grouting pressure is gradually increased to 1.0 MPa~1.5 MPa and stabilized for 3 minutes.

8. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 7, characterized in that, After blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent is sprayed within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot. After installing the anchors and grouting, the following steps are taken: Tensioning is performed by applying a torque of 60 N·m to 80 N·m to the exposed end of the anchors using a torque wrench. After the grout has initially set, install the steel pad, spherical washer and nut in sequence on the exposed threaded end of the anchor pipe; Using a calibrated torque wrench, apply torque in two stages: in the first stage, apply torque smoothly to 40 N·m, stop and hold for 2 minutes; in the second stage, continue to apply torque smoothly to 80 N·m, and then lock the nut; during tensioning, use a hydraulic jack and pressure sensor to check and ensure that the initial preload of a single anchor pipe is not less than 50 kN.

9. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 1, characterized in that, After blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent is sprayed within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot. After installing the anchor pipes and grouting, a torque of 60 N·m to 80 N·m is applied to the exposed end of the anchor pipe using a torque wrench for tensioning. Following this step, the tunnel blasting excavation method for soft rock sections with large deformations further includes: On the section where the initial support has been completed, concrete observation piles with precision reflectors are installed at five locations: the arch crown, the two sides of the arch waist, and the two sides of the sidewalls. Using a total station, a round of clearance convergence measurements were conducted at 1 hour, 2 hours, and 4 hours after the blasting ventilation was completed. If the cumulative net clearance convergence value measured at the cross section in the 4th hour exceeds 15 mm, or if the convergence rate from the 2nd to the 4th hour does not show a decreasing trend, then the cross section is judged to be deformed abnormally. For sections with abnormal deformation, in the next adjacent excavation cycle, the spacing of the steel arches designed within 5 meters before and after the section mileage will be temporarily adjusted from 0.6 meters to 0.5 meters. At the same time, the design length of the system anchor bolts will be increased by 0.5 meters, and when blasting in this range, the single-hole charge amount in the high-concern area will be reduced by 10%.

10. The tunnel blasting excavation method for soft rock sections with large deformation as described in claim 1, characterized in that, After blasting and ventilation, concrete mixed with an early-strength shrinkage-compensating agent is sprayed within 15 minutes to seal the rock surface. When installing the steel arch frame, anchor holes inclined downwards at 30 to 45 degrees are drilled at the arch foot. After installing the anchor pipes and grouting, a torque of 60 N·m to 80 N·m is applied to the exposed end of the anchor pipe using a torque wrench for tensioning. Following this step, the tunnel blasting excavation method for soft rock sections with large deformations further includes: After the earthwork at the invert arch section of the soft rock with large deformation is excavated to the design elevation, a layer of C25 early strength concrete with a thickness of 8 cm to 10 cm is immediately sprayed using a wet spraying machine for preliminary sealing. After the initial shotcrete strength reaches 5 MPa, the invert arch connecting bars are tied, and the steel arch frame of the invert arch section is fastened to the side wall arch frame through connecting plates and high-strength bolts. Within 24 hours of the connection being completed, the first layer of inverted arch structure concrete was poured, with a thickness of 60% of the total design thickness. This layer of concrete was mixed with a high-efficiency early-strength agent, and its 12-hour compressive strength was not less than 8 MPa. Once the strength of the first layer of concrete reaches 10 MPa as tested by test blocks under the same conditions, the second layer of concrete is poured immediately. Before pouring, a steel mesh with a diameter of 8 mm and a grid spacing of 20 cm * 20 cm is laid on the arch surface of the invert, thus completing the thickened reinforced concrete closed structure of the entire invert.

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