Construction method for firstly assisting shield tunneling by small pilot tunnel mining method in extremely hard rock section

Abstract

The construction method comprises the steps that a vertical shaft is constructed on the ground in front of the terminal point of the ultra-hard rock section in the tunnel construction direction, and the bottom of the vertical shaft extends to be flush with the main line design axis of a tunnel; a small pilot tunnel is excavated along the tunnel main line design axis based on the vertical shaft, and the small pilot tunnel extends to the end point of the extremely hard rock section along the tunnel main line design axis; and the shield tunneling machine carries out tunneling construction along the main line design axis of the tunnel. According to the method, the vertical shaft is constructed on the ground, and the small pilot tunnel is excavated to penetrate through the extremely-hard rock section in advance, so that the technical problems that the tunneling resistance of a shield tunneling machine in the extremely-hard rock layer is large, and a cutter is seriously abraded are solved. According to the method, the shield tunneling load can be obviously reduced, the construction efficiency is improved, the cutter loss is effectively controlled, the surrounding rock stress is released in advance through the pilot tunnel, and the shield construction safety and the tunnel forming quality are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of urban rail transit engineering construction, specifically to a construction method for using a small pilot tunnel in extremely hard rock sections with preliminary auxiliary shield tunneling. Background Technology

[0002] In urban rail transit construction, especially in areas with complex geological conditions such as the western mountainous regions, tunnel lines often need to traverse long sections of extremely hard rock masses such as granite and quartzite. These rock masses have extremely high compressive strength, often exceeding the design rock-breaking limit of conventional shield tunneling cutters, posing a series of severe challenges to shield tunneling construction.

[0003] First, extremely hard rock causes severe wear on the tunnel boring machine (TBM) cutters, necessitating frequent replacements. This significantly increases the material and maintenance costs of the cutters, requires frequent hatching operations, creates a dangerous working environment, and severely hinders construction progress. Second, the high rock hardness causes a sharp decrease in the TBM's tunneling speed, resulting in extremely low tunneling efficiency and directly impacting the overall project schedule. Furthermore, the presence of fractured zones, densely jointed zones, and the risk of rockbursts caused by high ground stress in hard rock strata can easily lead to major engineering risks such as TBM jamming and loss of attitude control, resulting in poor safety.

[0004] Currently, for extremely hard rock formations, using the shield tunneling method for the entire face presents the aforementioned significant difficulties; while using mining methods such as drill-and-blast for the entire face loses the advantages of the shield tunneling method—its speed, continuity, and safety in soft soil or medium-hard rock formations—and the transition between the two methods is complex. Therefore, there is an urgent need for an innovative construction method that combines the advantages of both the shield tunneling method and mining methods, specifically designed for extremely hard rock sections. Summary of the Invention

[0005] The purpose of this invention is to provide a construction method for pre-construction of a small pilot tunnel in extremely hard rock sections using the mining method. This invention enters the main tunnel line through auxiliary shafts and horizontal cross passages. A small pilot tunnel is constructed in advance using the mining method. Before the tunnel boring machine (TBM) enters the extremely hard rock section, the small pilot tunnel is completed, providing a free face for the TBM. This also significantly reduces the pressure on the central cutterhead of the TBM. The small pilot tunnel also assists in muck removal during later TBM excavation. This largely solves the problems of severe cutter wear, frequent replacement, and low excavation efficiency in existing TBM construction in extremely hard rock sections, providing a new construction method that effectively improves excavation efficiency, reduces cutter wear, and ensures construction safety. Furthermore, in high-stress sections, the small pilot tunnel can also serve as a pre-stress release tunnel, avoiding the risk of the TBM getting stuck.

[0006] To achieve this objective, the present invention provides a construction method for pre-assisted shield tunneling in a small pilot tunnel in extremely hard rock sections, comprising the following steps: A vertical shaft is constructed on the ground ahead of the end of the extremely hard rock section along the tunnel construction direction, with the bottom of the shaft extending to be flush with the design axis of the tunnel main line. Based on the vertical shaft, a small pilot tunnel is excavated along the design axis of the main tunnel, so that the small pilot tunnel extends along the design axis of the main tunnel to the end of the extremely hard rock section; The tunnel boring machine (TBM) excavates along the designed axis of the tunnel's main line.

[0007] Furthermore, the method of constructing a vertical shaft on the ground ahead of the end point of the extremely hard rock section along the tunnel construction direction includes: constructing a vertical shaft on the ground ahead of the end point of the tunnel boring machine excavation along the tunnel construction direction, so that the vertical shaft does not coincide with the design axis of the tunnel main line in the vertical direction.

[0008] Furthermore, the method of excavating a small pilot tunnel based on the vertical shaft along the design axis of the tunnel main line includes: constructing a horizontal transverse passage at the bottom of the vertical shaft, so that one end of the horizontal transverse passage is connected to the bottom of the vertical shaft, and the other end extends horizontally to intersect with the design axis of the tunnel main line.

[0009] Furthermore, a small pilot tunnel is constructed based on the aforementioned horizontal transverse passage, so that the centerline of the small pilot tunnel coincides with the axis of the tunnel's main line design.

[0010] Furthermore, the pilot tunnel is a circular cross-section structure located in the central area of ​​the tunnel's main line section. The radius of the pilot tunnel is smaller than the radius of the tunnel boring machine's cutterhead but larger than the radius of the central cutter area of ​​the tunnel boring machine's cutterhead.

[0011] Furthermore, the retaining structure of the shaft is constructed in the soil section at the shaft construction location, and vertical excavation is carried out to the rock section at the shaft construction location; Support is provided in the rock strata section and vertical excavation is carried out until the bottom is flush with the design axis of the tunnel main line. A gantry crane in conjunction with a hopper is used for vertical slag removal.

[0012] Furthermore, before excavating the horizontal transverse passage, advanced pipe roofs are used to pre-support the opening where the horizontal transverse passage connects to the vertical shaft; After the pre-support is completed, the horizontal cross passage is constructed using a combination of the step method and blasting. Slopes were constructed within the horizontal cross passage to serve as transportation channels.

[0013] Furthermore, before the small pilot tunnel is excavated, a steel gantry is installed on the side of the horizontal cross passage close to the design axis of the tunnel main line.

[0014] Furthermore, when excavating the small pilot tunnel at the intersection of the horizontal cross passage and the main tunnel design axis, initial support is provided for the small pilot tunnel at the intersection of the horizontal cross passage and the main tunnel design axis.

[0015] Furthermore, after the tunnel boring machine has excavated to the horizontal transverse passage, the process includes backfilling and sealing the vertical shaft and the horizontal transverse passage; and before backfilling, a concrete sealing wall is constructed at the intersection of the horizontal transverse passage and the tunnel mainline design axis.

[0016] Furthermore, the soil section is supported by soil lining during excavation, and the rock section is supported by initial support of the rock strata in a vertical shaft.

[0017] Furthermore, the initial support for the small guide tunnel at the intersection of the horizontal cross passage and the small guide tunnel includes temporary scaffolding support.

[0018] Furthermore, after completing the excavation of the small pilot tunnel at the intersection of the horizontal cross passage and the main tunnel design axis, the small pilot tunnel at the intersection is reinforced with support. Furthermore, before implementing reinforced support, the initial support of the small guide tunnel at the intersection is removed.

[0019] Furthermore, the reinforced support includes a permanent support consisting of a steel arch frame combined with anchor mesh and spraying.

[0020] Furthermore, before the tunnel boring machine advances to the small pilot tunnel at the intersection of the horizontal cross passage and the main tunnel design axis, the steel gantry 12 installed in the horizontal cross passage and the reinforced support of the small pilot tunnel at the intersection of the horizontal cross passage and the main tunnel design axis are removed in advance.

[0021] Furthermore, based on the geological conditions of the surrounding rock, it is chosen whether to leave the small pilot tunnel unsupported or to provide only plain spraying support.

[0022] The beneficial effects of this invention are as follows: 1. Excavating a small pilot tunnel first to assist the tunnel boring machine (TBM) significantly reduces tunneling resistance and wear in extremely hard rock sections. The pilot tunnel, created by setting up a vertical shaft, provides access from the ground to the tunnel axis, making its excavation possible and avoiding the difficulties of excavating directly in front of the TBM. The pilot tunnel also releases rock stress in extremely hard rock sections, reducing the load on the TBM cutterhead, extending cutter life, and improving tunneling efficiency. The overall construction process is more controllable, reducing the risk of TBM jamming or malfunction, making it suitable for long-distance extremely hard rock tunnel projects.

[0023] 2. By placing the shaft to the side of the tunnel's main design axis, direct vertical overlap between the shaft and the tunnel's main design axis is avoided, improving construction flexibility and safety. The shaft does not interfere with the tunnel's main structure, allowing the tunnel boring machine to pass seamlessly during excavation without detours or adjustments. This reduces the potential impact of shaft construction on the stability of the tunnel's main structure and lowers construction risks. It also facilitates material transport and ventilation from the side, optimizing the construction layout.

[0024] 3. The horizontal cross passage connects the vertical shaft and the main tunnel design axis. As a transfer path, the horizontal cross passage enables the excavation equipment, personnel and materials of the pilot tunnel to quickly enter the construction site, improving construction efficiency. The layout of the cross passage is flexible and the angle and length can be adjusted according to geological conditions to adapt to different engineering needs. It provides a stable working platform for the excavation of the pilot tunnel and reduces the difficulty of excavating directly from the bottom of the vertical shaft.

[0025] 4. Ensuring that the centerline of the pilot tunnel coincides with the design axis of the main tunnel ensures precise centering of the tunnel boring machine. Alignment between the pilot tunnel and the design axis of the main tunnel eliminates the need for significant directional adjustments when the tunnel boring machine enters extremely hard rock sections, reducing correction time and energy consumption, improving the quality of tunnel formation, and avoiding rework or structural problems caused by axis deviation.

[0026] 5. The circular cross-section and radius design of the pilot tunnel optimizes its fit with the tunnel boring machine (TBM) cutterhead, improving tunneling efficiency. The circular cross-section structure has good stability, is easy to support, and reduces the risk of collapse. The radius is smaller than the TBM cutterhead radius but larger than the radius of the central cutter area, ensuring that the cutterhead can fully cover the small pilot tunnel while protecting the central cutter from excessive wear. This design allows the TBM to smoothly cut into the small pilot tunnel, reducing impact and vibration and extending equipment life.

[0027] 6. The shaft construction adopted layered excavation and support, and used a gantry crane for muck removal, ensuring the safety and efficiency of the shaft construction. The shaft retaining structure prevented collapse and water seepage in the soil section, improving construction safety. In the rock section, vertical excavation was carried out after support to avoid rock loosening and ensure the stability of the shaft structure. The gantry crane, in conjunction with the hopper, carried out vertical muck removal, which was fast, reduced the construction period, and lowered labor costs.

[0028] 7. By using advanced pipe roof pre-support and bench blasting, the safety and efficiency of horizontal tunnel excavation were improved. Advanced pipe roof enhanced the rock mass stability at the tunnel entrance, preventing collapse accidents during excavation. The bench method combined with blasting is suitable for hard rock conditions, controls the blasting impact range, and improves excavation accuracy. The sloping transport channel facilitates the entry and exit of vehicles and equipment, optimizes logistics, and accelerates the construction progress.

[0029] 8. The steel gantry reinforces the structural support at the intersection of the cross passage and the main tunnel line. The steel gantry provides rigid support, preventing deformation or damage to the rock mass at the intersection, ensuring the safety of the pilot tunnel excavation, providing a stable starting point for subsequent pilot tunnel construction, reducing the pressure on initial support, improving the overall structural durability, and making it suitable for long-term projects.

[0030] 9. Initial support at the intersection stabilized the rock mass in a timely manner, preventing loosening and collapse. Initial support (such as shotcrete or anchor bolts) quickly sealed the rock surface, reducing exposure time and safety risks. The excavation of the pilot tunnel created a safe working environment, improved construction continuity, avoided damage caused by stress concentration at the intersection, and ensured the integrity of the tunnel mainline.

[0031] 10. After the tunnel boring machine passes, the vertical shaft and cross passage are backfilled, and concrete sealing walls are constructed to ensure the tunnel's airtightness and long-term stability. The backfilling and sealing restores the ground condition, reducing the impact on the environment and ground activities. The earthen sealing walls prevent groundwater, debris, or gas from entering the tunnel, ensuring that the tunnel interior is dry and clean, improving the overall structural safety of the tunnel, and avoiding later maintenance problems. Attached Figure Description

[0032] Figure 1 This is a flowchart illustrating the construction method of a pre-assisted shield tunneling method for small pilot tunnels in extremely hard rock sections, according to the present invention. Figure 2 This is a schematic diagram of the auxiliary tunnel shaft, horizontal passage, and small pilot tunnel cross-section as described in an embodiment of the present invention; Figure 3 This is a schematic diagram of the cross-section of the auxiliary tunnel shaft and horizontal passage as described in an embodiment of the present invention; Figure 4 As described in the embodiments of the present invention Figure 2 Enlarged view of point A; Figure 5 This is a schematic diagram of the construction section of the vertical shaft to horizontal transverse passage leading to the main tunnel according to an embodiment of the present invention; Figure 6 This is a schematic diagram of the initial rock support according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the cross-sectional support (plain shotcrete) for the small pilot tunnel as described in an embodiment of the present invention. Figure 8 This is a schematic diagram of the small pilot tunnel-assisted shield tunneling and muck removal operation according to an embodiment of the present invention; Figure 9 This is a schematic diagram illustrating the maintenance and replacement of cutterhead tools for a tunnel boring machine using a small pilot tunnel as described in an embodiment of the present invention.

[0033] The tunnel is divided into the following sections: 1—vertical shaft; 2—horizontal cross passage; 3—soil section; 4—rock section; 5—advanced pipe shed; 6—vertical shaft retaining structure; 7—soil section inner lining support; 8—rock section initial support; 9—transportation passage; 10—bottom plate steel frame; 11—tunnel main line design axis; 12—steel gantry frame; 13—temporary shed support; 14—small pilot tunnel; 15—plain shotcrete support. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Example 1: like Figures 1-9 The method for constructing a small pilot tunnel in extremely hard rock sections using a pre-assisted shield tunneling technique includes the following steps: Shaft 1 is constructed on the ground ahead of the end of the extremely hard rock section along the tunnel construction direction. The bottom of shaft 1 extends to be flush with the design axis 11 of the tunnel main line. Based on shaft 1, a small pilot tunnel 14 is excavated along the design axis of the main tunnel, so that the small pilot tunnel 14 extends along the design axis 11 of the main tunnel to the end of the extremely hard rock section. The tunnel boring machine is excavating along the designed axis 11 of the tunnel's main line.

[0035] like Figure 2 and Figure 3 As shown, the site is selected in the vicinity of the extremely hard rock section. The plane position of the shaft 1 is on the ground in front of the end point of the extremely hard rock section along the tunnel construction direction. The bottom of the shaft 1 extends to be flush with the design axis 11 of the tunnel main line. The shaft retaining structure 6 is constructed first, and then the vertical excavation and support of the shaft 1 are carried out. The excavation progress of each cycle is strictly controlled. The slag is lifted vertically to the temporary slag disposal site outside the tunnel by gantry crane and hopper.

[0036] The shaft 1 is located on the ground in front of the end point of the extremely hard rock section. The bottom of the shaft 1 extends to a portion that is flush with the design axis 11 of the tunnel main line. A small pilot tunnel 14 is excavated along the design axis 1 of the tunnel main line. The small pilot tunnel 14 and the starting point of the extremely hard rock section form a small pilot tunnel 14 from the starting point to the end point of the extremely hard rock section. The small pilot tunnel 14 is connected to the end point of the extremely hard rock section. During the excavation of the small pilot tunnel 14 and the later shield machine tunneling process, the characteristic that one end of the small pilot tunnel 14 is connected to the shaft 1 can be used to assist in muck removal. When it is necessary to replace or repair the shield machine cutterhead, it can be replaced and repaired in a timely manner through the shaft 1 and the small pilot tunnel 14.

[0037] Through the aforementioned small guide tunnel 14, the tunnel boring machine can provide an open surface for the central cutter area of ​​the cutterhead during tunneling, thereby improving tunneling efficiency and reducing cutter wear.

[0038] In one embodiment, the method of constructing a shaft 1 on the ground ahead of the end point of the extremely hard rock section along the tunnel construction direction includes: constructing a shaft 1 on the ground ahead of the end point of the tunnel boring machine excavation along the tunnel construction direction, so that the shaft 1 does not coincide with the tunnel mainline design axis 11 in the vertical direction.

[0039] The vertical shaft 1 is not directly above the tunnel main line design axis 11, but is offset to one side of the tunnel main line design axis 11. The horizontal net distance between the vertical shaft 1 and the tunnel main line design axis 11 is determined according to a preset distance, thereby determining the horizontal position of the vertical shaft 1.

[0040] Preferably, the planar position of the excavation shaft 1 is 14-20m away from the design axis 11 of the tunnel main line. This satisfies the limit requirements of the standard specifications; on the other hand, the shaft can avoid the area of ​​strong surrounding rock stress caused by the construction of the tunnel main line design axis 11 and the range of blasting vibration transmission, effectively protecting the stability of the shaft wall structure and preventing safety risks such as cracking and tilting. At the same time, the shaft and the tunnel main line can be separated into independent construction operation areas, reducing cross-interference between personnel and machinery and improving construction safety and efficiency.

[0041] In one embodiment, the method of excavating a small pilot tunnel 14 based on the shaft 1 along the tunnel main line design axis 11 includes: constructing a horizontal cross passage 2 at the bottom of the shaft 1, so that one end of the horizontal cross passage 2 is connected to the bottom of the shaft 1, and the other end extends horizontally to intersect with the tunnel main line design axis 11.

[0042] In tunnel construction on extremely hard rock sections, the pilot tunnel 14 provides an open surface for the central cutting tool area of ​​the tunnel boring machine (TBM) cutterhead, eliminating the need for the central cutting tool to directly break the rock. This significantly improves tunneling efficiency, reduces tool wear and replacement frequency, and extends equipment life. The connection between the horizontal transverse passage 2 and the vertical shaft 1 forms an auxiliary muck removal channel, using small mechanical equipment to transport muck out, relieving pressure on the TBM's own muck removal system and accelerating the overall construction progress. Simultaneously, this channel provides a safe and convenient path for personnel access and tool maintenance, avoiding the high risks and low efficiency of traditional compressed air chamber operations and enhancing construction safety.

[0043] In one embodiment, a small pilot tunnel 14 is constructed based on the horizontal transverse passage 2, so that the centerline of the small pilot tunnel 14 coincides with the axis of the tunnel main line design axis 11.

[0044] In one embodiment, the small guide tunnel 14 is a guide tunnel structure with a circular cross-section. The radius of the small guide tunnel 14 is smaller than the radius of the shield machine cutterhead and larger than the radius of the central cutter area of ​​the shield machine cutterhead.

[0045] The selection of the cross-sectional shape and size of the small pilot tunnel 14 is mainly to provide an open face for shield tunneling after excavation. The center cutter spacing of the shield machine's atmospheric pressure cutterhead is large, resulting in poor rock breaking ability. After the small pilot tunnel is completed, the center cutter of the shield machine's cutterhead will not participate in rock breaking, which can improve the efficiency of shield tunneling. At the same time, it avoids the excavation section from colliding with the rock surface and causing damage to the shield tunneling cutterhead in the later stage. In addition, the area affected by the disturbance of the surrounding rock after excavation is small, and the self-bearing capacity of the surrounding rock meets the deformation requirements.

[0046] In one embodiment, a shaft retaining structure 6 is constructed in the soil section 3 at the construction location of shaft 1 and vertically excavated to the rock section 4 at the construction location of shaft 1. The soil section 3 is supported by the soil section inner lining 7; Support was provided in rock stratum section 4 and vertical excavation was carried out until the bottom was flush with the design axis 11 of the tunnel main line. The rock stratum 4 is subjected to initial rock stratum support 8; A gantry crane in conjunction with a hopper is used for vertical slag removal.

[0047] The specific process is as follows: first, construct the shaft retaining structure 6, then excavate the soil section 3, and at the same time, provide soil section inner lining support 7 for the soil section 3, then excavate the rock section 4, and at the same time, provide rock section initial support 8 for the rock section 4 in a timely manner.

[0048] During the construction of shaft 1, appropriate support techniques were adopted based on the characteristics of the soil layers to minimize construction risks. For soil section 3, a robust retaining structure was constructed to effectively prevent collapse and water seepage, ensuring operational safety. For rock section 4, a method of simultaneous support and vertical excavation was adopted to fully utilize the self-stabilizing properties of the rock mass and accelerate the excavation speed. The entire process was supplemented by a gantry crane and hopper for vertical muck removal. The gantry crane system took into account both muck removal and material transportation, reducing costs and shortening the construction period.

[0049] In one embodiment, before excavating the horizontal transverse passage 2, an advanced pipe roof 5 is used to pre-support the opening where the horizontal transverse passage 2 connects to the vertical shaft 1. After the pre-support is completed, the horizontal transverse passage 2 is constructed using a combination of step method and blasting. A slope is constructed within the horizontal cross passage 2 to serve as a transportation passage 9.

[0050] When the horizontal cross passage 2 reaches the centerline of the tunnel main line design axis 11, it intersects with the centerline of the tunnel main line design axis 11.

[0051] like Figure 4 As shown, the horizontal transverse passage 2 is excavated using the step method in the direction close to the design axis 11 of the tunnel main line. Before construction, the tunnel muck is used to fill the inclined transport channel 9 in the horizontal transverse passage 2.

[0052] The process of tunneling using the bench method combined with controlled blasting technology is as follows: First, the excavation outlines of the upper and lower benches and the positions of the blast holes are accurately located at the tunnel face through surveying and setting out. Based on the control requirements of blasting vibration velocity, a special blasting design is carried out. Then, blast holes are drilled according to the design, explosives are loaded, and millisecond delay detonators are used to achieve segmented detonation, with the upper and lower benches detonating simultaneously. After blasting, the blast debris is promptly cleared using small excavators, small loaders, and dump trucks. If necessary, plain shotcrete support is implemented on the exposed surrounding rock. During construction, the length of the upper and lower benches is controlled at 3-5m.

[0053] Before excavating the horizontal transverse passage 2, a pre-support pipe roof 5 was used to pre-support the tunnel entrance. A row of closely spaced steel pipes was pre-installed on the arch outside the excavation outline of the horizontal transverse passage 2, forming a robust umbrella-shaped protective shell. This effectively bears the load of the soil and rock above, significantly enhancing the integrity and stability of the surrounding rock at the tunnel entrance. Its core function is to control ground deformation in advance, preventing collapses and roof falls caused by sudden exposure of the tunnel entrance section, greatly improving construction safety. Simultaneously, it provides safe operating conditions for subsequent weak blasting excavation, ensuring the stability of the excavation face. This is a prerequisite safety technology measure to ensure the smooth and efficient excavation of the transverse passage to the center line of the tunnel mainline 11. The horizontal transverse passage 2 was excavated using a bench method combined with controlled blasting technology, achieving a balance between safety and efficiency. This method divides the cross-section of the horizontal transverse passage 2 into upper and lower benches for partial excavation, significantly reducing the span of each working face, thereby greatly reducing the risk of collapse during excavation and ensuring operational safety. Meanwhile, controlled blasting technology, namely weak blasting or controlled blasting methods, can effectively reduce the amount of explosives used and the intensity of vibration in a single blast, minimizing the disturbance to the shaft wall and surrounding rock, and protecting the existing structure. The combination of these two techniques enables efficient and steady tunneling in extremely hard rock formations under safe and controllable conditions.

[0054] In one embodiment, before the small pilot tunnel 14 is excavated, a steel gantry 12 is installed on the side of the horizontal cross passage 2 near the tunnel main line design axis 11.

[0055] Before entering the excavation area of ​​the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the tunnel main line design axis 11, a steel gantry frame 12 composed of a steel arch structure is set up at the intersection of the excavation outline of the horizontal cross passage 2 and the small pilot tunnel 14. The steel gantry frame 12 serves as the initial support for the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the tunnel main line design axis 11. The other side of the steel arch frame is used for foot support, and a base plate steel frame 10 is added to the bottom of the steel gantry frame 12. When excavating the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the tunnel main line design axis 11, temporary scaffolding support is promptly constructed. After the excavation work of the small pilot tunnel at the intersection section is completed, the steel arch frame and anchor mesh spray reinforcement support of the small pilot tunnel inside the tunnel are constructed below the original temporary scaffolding. Then, the excavation continues rapidly along the extension direction of the tunnel main line design axis 11 to the end of the extremely hard rock section to obtain the complete small pilot tunnel 14.

[0056] In one embodiment, when excavating the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the tunnel main line design axis 11, initial support is provided for the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the tunnel main line design axis 11.

[0057] The small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the main tunnel design axis 11 is the weakest link in the entire construction network, with the most complex stress distribution. Due to its large excavation span, irregular shape, and repeated blasting disturbances, the surrounding rock stress is highly concentrated, making it extremely prone to loosening, spalling, or even collapse. Immediately constructing temporary scaffolding for initial support can quickly provide strong external support to the exposed rock mass, actively control surrounding rock deformation, and effectively maintain the stability of the excavation face. This is not only a direct guarantee against local instability and ensures the safety of construction at the intersection, but also lays a solid foundation for the subsequent smooth implementation of the steel arch reinforcement support for the small pilot tunnel in this safe environment, as well as the final safe removal of the temporary structure to make way for the tunnel boring machine. It is a core measure for the safe passage of the entire project through this critical node. Preferably, the initial support for the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the small pilot tunnel 14 includes temporary scaffolding support 13.

[0058] Preferably, after the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the main tunnel design axis 11 is completed, the small pilot tunnel 14 at the intersection is reinforced with support. Preferably, the initial support of the small guide hole 14 at the intersection is removed before reinforcement is carried out.

[0059] Preferably, the reinforced support includes a reinforced support consisting of a steel arch frame combined with anchor mesh and sprayed concrete.

[0060] In one embodiment, after the tunnel boring machine has excavated to the horizontal transverse passage 2, the process includes backfilling and sealing the vertical shaft 1 and the horizontal transverse passage 2; and before backfilling, a concrete sealing wall is constructed at the intersection of the horizontal transverse passage 2 and the tunnel main line design axis 11.

[0061] After the tunnel boring machine passes through the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the main tunnel design axis 11, the shaft 1 and the horizontal cross passage 2 are backfilled and sealed. A concrete sealing wall is then constructed at the intersection of the horizontal cross passage 2 and the main tunnel design axis 11 to ensure the permanent safety and stability of the main tunnel design axis 11. This measure firstly completely isolates the temporary construction passage from the permanent operating tunnel main tunnel design axis 11 through a solid sealing wall, preventing the risk of water leakage in the main tunnel design axis 11 in the future, and ensuring the integrity and load-bearing capacity of the main tunnel lining structure. The overall backfilling of the shaft and passage effectively eliminates the potential for future collapse of these temporary structures and the resulting surface subsidence, restoring the original stress balance of the strata and the original use function of the surface land, thus achieving the dual objectives of safety and environmental protection.

[0062] Before the tunnel boring machine (TBM) reaches the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the main tunnel design axis 11, the temporary scaffolding and initial support of the small pilot tunnel 14 at the intersection are removed in advance. Simultaneously, the initial support of the horizontal cross passage 2 near the small pilot tunnel 14 at the intersection is also removed in advance. This creates an unobstructed working space for the TBM to pass smoothly through the intersection, avoiding obstruction of the TBM cutterhead excavation by support structures such as steel arches, steel mesh, and anchor bolts, ensuring a smooth excavation path and stable mechanical posture.

[0063] The permanent support structure, constructed from steel arch frames combined with anchor mesh and shotcrete, integrates with the surrounding rock to form a robust pressure-bearing ring. This ring can withstand complex ground stresses from both the horizontal cross passage 2 and the small pilot tunnel 14 at the intersection in a long-term and stable manner, thoroughly stabilizing the key area. This process ensured the safety of the small pilot tunnel 14 at the intersection during construction and cleared obstacles for the subsequent safe and smooth passage of the tunnel boring machine through this critical node.

[0064] Preferably, before the tunnel boring machine excavates to the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the design axis 11 of the tunnel main line, the steel gantry 12 installed in the horizontal cross passage 2 and the reinforced support of the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the design axis 11 of the tunnel main line are removed in advance.

[0065] Preferably, depending on the geological conditions of the surrounding rock, the small pilot tunnel 14 is either left unsupported or only supported by plain spraying.

[0066] In extremely hard rock formations, choosing to leave the pilot tunnel 14 unsupported or with only plain shotcrete support achieves an optimal balance between safety and economy. Due to the high strength and strong self-stabilizing ability of extremely hard rock, and the small excavation cross-section, it can maintain stability without additional support. This significantly reduces the cost of support materials and construction time, and substantially improves the efficiency of the pilot tunnel excavation. The thin layer of plain shotcrete primarily seals the rock surface, preventing small rock fragments from weathering and falling, ensuring operational safety, and providing a relatively flat free face for subsequent tunneling by the tunnel boring machine. This differentiated support strategy based on surrounding rock conditions avoids unnecessary over-support, maximizing resource allocation, reducing project costs, and shortening the construction period while ensuring absolute safety.

[0067] The mining method is as follows: during construction, manual drilling and blasting are used to excavate the entire cross-section of the small pilot tunnel 14. Small excavators and small dump trucks are used to transport the tunnel muck to the vertical shaft for vertical muck removal. The hard rock section of the small cross-section makes full use of the self-bearing capacity of the surrounding rock and does not require support. If necessary, wet shotcrete is used for support. This operation is repeated until the excavation of the hard rock section is completed.

[0068] Preferably, the steel gantry 12 is composed of two steel arches.

[0069] After completing the pilot tunnel 14, one end of the pilot tunnel 14 is located at the starting point of the extremely hard rock section, and the other end is connected to the vertical shaft 1. The tunnel boring machine (TBM) excavates from the starting point of the extremely hard rock section along the pilot tunnel 14 to the end point of the extremely hard rock section. During the excavation, the pilot tunnel 14 and the vertical shaft 1 can be used for muck removal at the connected end. When it is necessary to replace or repair the cutterhead of the TBM during the excavation, the vertical shaft 1 can be used to enter the pilot tunnel 14, and then the TBM can be reached through the pilot tunnel 14 to a position near the TBM for replacement or repair. After the surrounding rock deformation stabilizes, the temporary scaffolding support is removed, and the tunnel is excavated along the pilot tunnel 14 at the intersection towards the end point of the extremely hard rock section, thus obtaining the pilot tunnel 14.

[0070] Rock deformation stability refers to a rock settlement displacement rate of less than 0.2 mm / d or a cumulative settlement displacement value of less than 1 / 3 of the design limit displacement value.

[0071] The small pilot tunnel 14 at the intersection was excavated first and initial support was installed. The intersection area, which was the most geologically complex and under the most unfavorable stress in the entire pilot tunnel construction, was treated as a key node in advance. Through strong initial support, the deformation of the surrounding rock was actively controlled, which effectively avoided the risk of collapse caused by stress concentration and laid a stable foundation for the subsequent long-distance small pilot tunnel excavation.

[0072] The small pilot tunnel 14 at the intersection adopts phased and multi-layered support measures to cope with the complex mechanical environment. The temporary scaffolding support is erected immediately after excavation. Its function is to quickly provide top support force, actively control the deformation of the surrounding rock, and effectively prevent local rockfalls or collapses caused by stress release, stress concentration and blasting vibration in the most critical initial stage of excavation, thus providing immediate protection for subsequent safe operations.

[0073] The specific implementation process of this invention is as follows: Step 1: Near the extremely hard rock section identified through exploration, select a location with relatively good site conditions, approximately 14m to 20m outside the tunnel's main design axis 11, as the construction site for shaft 1. First, construct the shaft retaining structure 6, then excavate the soil section 3, simultaneously installing soil lining support 7. Next, excavate the rock section 4, simultaneously installing initial rock lining support 8. The excavation depth for each cycle must be strictly controlled according to geological conditions to ensure the stability of the shaft wall of shaft 1. During the excavation of shaft 1, a gantry crane located at the shaft opening can be used in conjunction with a hopper to vertically lift and remove slag.

[0074] Step 2: After the vertical shaft 1 is excavated to the same depth as the bottom of the small pilot tunnel 14, it is horizontally excavated in the direction close to the small pilot tunnel 14 to construct the horizontal transverse passage 2. Before the horizontal transverse passage 2 is excavated into the tunnel, it is pre-supported by the advanced pipe roof 5. The excavation adopts the step method and controlled blasting to ensure construction safety. After the horizontal transverse passage 2 is excavated and supported, its interior is filled with tunnel slag to form a sloping transport channel 9, which facilitates the entry and exit of subsequent mechanical equipment.

[0075] Step 3: The horizontal cross passage 2 is excavated to the point where it intersects with the design axis 11 of the main tunnel. The horizontal cross passage 2 enters the design axis 11 of the main tunnel through a flat slope excavation and is excavated along the design axis 11 of the main tunnel using the step method. Temporary scaffolding support 13 is constructed on the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the design axis 11 of the main tunnel, and a sloping transport passage serves as the transport passage 9. After the construction on the small pilot tunnel 14 at the intersection is completed, the steel arch frame of the small pilot tunnel combined with anchor mesh spraying is constructed within the range of the temporary scaffolding support 13. After the deformation stabilizes, the vertical supports of the temporary scaffolding support 13 are removed, and the small pilot tunnel 14 is excavated along the design axis 11 of the main tunnel towards the end point of the extremely hard rock section.

[0076] The pilot tunnel 14 is designed with a circular cross-section. The cross-sectional dimensions must cover the central cutter area of ​​the shield machine cutterhead to ensure that a free face is completely formed. After excavation, if the integrity and stability of the surrounding rock are good, it is possible to choose not to take support measures. If necessary, the tunnel wall can be supported by plain concrete spraying to achieve rapid tunneling. The slag is transported out through the horizontal cross passage 2 and the vertical shaft 1 by small transport equipment.

[0077] Step 4: Before the tunnel boring machine (TBM) reaches the extremely hard rock section, the small pilot tunnel 14 has been excavated as designed. After the TBM begins excavation, the central area of ​​its cutterhead is largely free from excavation pressure due to the excavation of the small pilot tunnel 14. The main wear is concentrated on the outer cutterhead, improving rock breaking efficiency and extending cutter life.

[0078] Step 5: When the tunnel boring machine (TBM) reaches the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the tunnel mainline design axis 11, the steel arch frame, anchor mesh, and sprayed support at the intersection section should be removed in advance. After the TBM has completely passed through the extremely hard rock section and crossed the small pilot tunnel 14 at the intersection of the horizontal cross passage 2 and the tunnel mainline design axis 11, a concrete sealing wall with a thickness greater than 2m should be poured immediately at the intersection section where the horizontal cross passage 2 intersects with the already formed tunnel mainline design axis 11 lining to ensure the tunnel's airtightness and structural safety. Finally, the excavated soil and rock debris should be used to backfill the horizontal cross passage 2 and shaft 1 to restore the original surface condition.

[0079] like Figure 8 As shown, during shield tunneling, small excavators / loaders and small dump trucks can be organized to enter the small guide tunnel 14 through the horizontal cross passage 2 to load and transport slag in front of the shield machine cutterhead, which greatly relieves the pressure on the shield machine's own slag removal system and speeds up the overall slag removal speed.

[0080] When tool maintenance or replacement is required, such as Figure 8 As shown, workers can carry tools or new cutting tools and safely approach the area in front of the cutterhead for inspection and operation through the vertical shaft 1, the horizontal transverse passage 2 and the safe small guide hole 14, avoiding the high risk and low efficiency of traditional compressed air entry operations.

[0081] When the tunnel boring machine (TBM) advances to the small pilot tunnel 14 near the intersection of the horizontal and horizontal passage 2 and the main tunnel design axis 11, it is necessary to stop the excavation in advance, organize personnel to enter the intersection section, and dismantle the previously constructed steel arch frame and anchor mesh and other support structures to clear obstacles for the TBM to pass smoothly.

[0082] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A construction method of a pilot heading auxiliary shield tunneling of an extremely hard rock section small pilot hole mine method, characterized in that, The application relates to a tunnel construction method. The application comprises the following steps: A vertical shaft (1) is constructed in front of the end of the extremely hard rock section along the tunnel construction direction, and the bottom of the vertical shaft (1) is extended to be flush with the tunnel design axis (11); A small pilot tunnel (14) is constructed based on the vertical shaft (1) along the tunnel design axis (11), and the small pilot tunnel (14) is extended to the end of the extremely hard rock section along the tunnel design axis (11); 2. The construction method of the pilot heading of the small pilot hole of the extremely hard rock section of the mine method assisted by the shield tunneling according to claim 1, characterized in that, The shield machine is constructed along the tunnel design axis (11).

3. The construction method of the pilot heading of the small pilot hole of the extremely hard rock section of the mine method assisted by the shield tunneling according to claim 2, characterized in that, The method for constructing the vertical shaft (1) in front of the end of the extremely hard rock section along the tunnel construction direction comprises the following steps: a vertical shaft (1) is constructed in front of the end of the extremely hard rock section along the tunnel construction direction, and the vertical shaft (1) is not vertically overlapped with the tunnel design axis (11).

4. The construction method of the pilot heading of the small pilot hole of the extremely hard rock section of the mine method assisted by the shield tunneling according to claim 3, characterized in that, The method for constructing the small pilot tunnel (14) based on the vertical shaft (1) along the tunnel design axis (11) comprises the following steps: a horizontal cross passage (2) is constructed at the bottom of the vertical shaft (1), one end of the horizontal cross passage (2) is communicated with the bottom of the vertical shaft (1), and the other end is extended to cross the tunnel design axis in the horizontal direction.

5. The construction method of the pilot heading of the small pilot hole of the extremely hard rock section of the mine method assisted by the shield tunneling according to claim 4, characterized in that, The small pilot tunnel (14) is constructed based on the horizontal cross passage (2), and the center line of the small pilot tunnel (14) is overlapped with the axis of the tunnel design axis (11).

6. The construction method of the pilot heading of the small pilot hole of the extremely hard rock section of the mine method assisted by the shield tunneling according to claim 1, characterized in that, The small pilot tunnel (14) is a circular cross-section structure, the radius of the small pilot tunnel (14) is smaller than the radius of the cutter head of the shield machine and larger than the radius of the central cutter region of the cutter head of the shield machine. A vertical shaft support structure (6) is constructed in the soil section (3) of the vertical shaft (1) construction position and is vertically excavated to the rock section (4) of the vertical shaft (1) construction position. The rock section (4) is supported and vertically excavated to be flush with the bottom of the tunnel design axis (11).

7. The construction method of the pilot heading of the small pilot hole of the extremely hard rock section of the mine method assisted by the shield tunneling according to claim 3, characterized in that, A portal crane is used to vertically discharge the slag. Before the horizontal cross passage (2) is excavated, an advanced pipe shed (5) is used to pre-support the hole opening where the horizontal cross passage (2) is connected with the vertical shaft (1). After the pre-supporting is completed, the horizontal cross passage (2) is constructed by using the bench method combined with blasting.

8. The construction method of the pilot heading auxiliary shield tunneling of the extremely hard rock section small pilot hole mine method according to claim 7, characterized in that, A slope is filled in the horizontal cross passage (2) to serve as a transportation passage (9).

9. The construction method of the pilot heading auxiliary shield tunneling of the extremely hard rock section small pilot hole mine method according to claim 8, characterized in that, Before the small pilot tunnel (14) is excavated, a profile steel portal (12) is arranged on the side of the horizontal cross passage (2) close to the tunnel design axis (11).

10. The construction method of the pilot heading auxiliary shield tunneling of the extremely hard rock section small pilot hole mine method according to claim 9, characterized in that, When the small pilot tunnel (14) at the intersection of the horizontal cross passage (2) and the tunnel design axis (11) is excavated, the small pilot tunnel (14) is initially supported. After the shield machine is excavated to the horizontal cross passage (2), the vertical shaft (1) and the horizontal cross passage (2) are backfilled and closed, and a concrete blocking wall is constructed at the intersection of the horizontal cross passage (2) and the tunnel design axis (11) before backfilling.

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