Supporting construction method for large-section tunnel under unstable slope condition

Abstract

This invention provides a construction method for supporting large-section tunnels under unstable slope conditions. The method includes dividing the tunnel into four zones based on the spatial relationship between the unstable landslide surface and the large-section tunnel; before tunnel excavation, driving anti-slide piles on both sides of the target tunnel entrance; reinforcing the unstable landslide body on the sliding surface with NPR anchor cables, avoiding the target tunnel; drilling grouting holes in Zone I for grouting; constructing pipe roof support for the tunnel; using a combination of denser NPR long anchor cables and NPR short anchor cables for support on the upper and lower steps of Zone I, with the arch of Zone I within the pipe roof support range; using denser NPR long anchor cables for support on the arch of Zone II; using NPR long anchor cables for support in Zone III; and using ordinary support methods or NPR short anchor cables for support in Zone IV. This construction method transforms the slope from an unstable state to a stable state and greatly improves the support effect of large-section tunnels under unstable slope conditions.

Description

Technical Field

[0001] This invention belongs to the field of tunnel support construction technology, specifically relating to a method for supporting large-section tunnels under unstable slope conditions. Background Technology

[0002] An unstable slope refers to a slope where the soil or rock mass, under the influence of various potential factors and gravity, has a tendency to slide along the weak surface, and its stability is easily disturbed. There are two types of unstable slopes: the first is a slope where sliding has already occurred, in which case the slope becomes relatively steep; the second is a slope where a landslide has already occurred, in which case the slope is relatively gentle, but will further slide under disturbance.

[0003] Large-section tunnels refer to tunnels with a clear cross-sectional area of ​​50 to 100 m2. Due to their large cross-sectional area, they place strict requirements on construction. When excavating large-section tunnels in rock and soil, stress redistribution can lead to significant stress concentration and substantial deformation.

[0004] In actual construction, large-section tunnels must cross unstable slopes and ensure the safety of tunnel construction and subsequent operation, guaranteeing safe entry into the tunnel and avoiding safety accidents such as tunnel collapse in unstable landslide sections.

[0005] Currently, common support methods for slope collapse disasters include ordinary anchor bolt reinforcement and wire mesh reinforcement. Slope collapse and landslides are large-deformation rock mass disasters, and most of the more threatening collapsed rock masses are also large in size. During the disaster process, they release enormous energy, making conventional anchor bolt and wire mesh support measures ineffective in supporting jointed rock masses. Conventional ordinary anchor bolts are small-deformation materials, and their absorption of rock deformation energy during the entire deformation process is extremely limited, ultimately leading to breakage and failure due to large deformation. On the other hand, when tunnels pass through landslides, the excavation process easily disturbs the landslide, causing the tunnel body to shift under the interaction with the landslide, resulting in tunnel structure damage. Unstable slopes and large-section tunnels influence each other, and arch frame twisting and deformation, as well as anchor bolt failure and detachment, frequently occur at construction sites.

[0006] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0007] The purpose of this invention is to provide a construction method for NPR anchor cable support of large-section tunnels under unstable slope conditions, so as to at least solve the problem that traditional support methods are prone to failure under the mutual influence of unstable slopes and large-section tunnels.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A construction method for supporting large-section tunnels under unstable slope conditions, the method comprising dividing the tunnel into four zones according to the spatial relationship between the unstable landslide surface and the large-section tunnel: the pre-buried section near the tunnel entrance is the portal section, designated as Zone I; the other areas of the sliding surface excluding the portal section are the strongly affected slope sections, designated as Zone II; the section of the slope top close to the sliding surface is the weakly affected slope section, designated as Zone III; and the part far from the sliding surface is the normal support section, designated as Zone IV.

[0010] Before tunnel excavation, anti-slide piles were installed on both sides of the target tunnel entrance.

[0011] NPR anchor cables are installed on the unstable landslide surface for reinforcement, and the NPR anchor cables are installed away from the target tunnel.

[0012] Grouting was carried out in Zone I by drilling grouting holes.

[0013] Pipe roof pre-support construction is being carried out in the tunnel;

[0014] In Zone I, the upper and lower steps are supported by a combination of densified NPR long anchor cables and NPR short anchor cables. The arch of Zone I is within the pipe roof support range.

[0015] In Zone II, the arch section is supported by reinforced NPR long anchor cables;

[0016] In Zone III, long NPR anchor cables are used for support; in Zone IV, ordinary support methods or short NPR anchor cables are used for support.

[0017] The above-described method for supporting large-section tunnels under unstable slope conditions preferably includes NPR anchor cables installed on the unstable landslide body with sliding surface, which include both ordinary anchor cables and giant anchor cables.

[0018] The ordinary type of anchor cable is evenly distributed on the entire unstable landslide body to connect the landslide body into a whole;

[0019] The giant anchor cables are spaced out on the unstable landslide body and anchored into the deep rock mass.

[0020] In the above-described construction method for large-section tunnel support under unstable slope conditions, preferably, the specifications of the common type anchor cable are: 5000~10300mm NPR anchor cable, with a row spacing of 2000×2000mm;

[0021] Giant anchor cables: 35,000-50,000 mm NPR anchor cables, with a row spacing of 16,000 × 8,000 mm.

[0022] The construction method for large-section tunnel support under unstable slope conditions as described above is preferably characterized by uniformly drilling grouting holes in Zone I, with the grouting holes avoiding the target tunnel, and the grouting holes covering the upper part of the tunnel and both sides of the tunnel axis.

[0023] Grouting is performed by inserting grouting anchors or grouting pipes into the grouting holes.

[0024] In the above-described construction method for supporting large-section tunnels under unstable slope conditions, preferably, the spacing between the grouting holes is 1.5m × 1.5m, arranged in a quincunx pattern; grouting pipes with a diameter of 50mm are inserted into the grouting holes for grouting reinforcement.

[0025] The above-described method for supporting large-section tunnels under unstable slope conditions preferably employs anchor mesh, steel arch frame, and shotcrete as initial support in the arch of Zone I, and densified NPR long and short combination anchor cables in the middle and lower steps, in conjunction with anchor mesh, steel arch frame, and shotcrete for initial support.

[0026] The spacing between the long and short NPR anchor cables is 1m × 1.2m; one row of 4m NPR short anchor cables and one row of 8m NPR long anchor cables are arranged in an alternating quincunx pattern.

[0027] The above-described method for supporting large-section tunnels under unstable slope conditions preferably involves installing denser NPR long anchor cables in the arch section of Zone II, along with anchor mesh, steel arch frame, and shotcrete for initial support.

[0028] In the remaining part of Zone II, a combination of long and short NPR anchor cables with densification, anchor mesh, steel arch frame and shotcrete are used for initial support.

[0029] The above-described method for supporting large-section tunnels under unstable slope conditions preferably includes the following anchor cable arrangement parameters in Zone II: the arch anchor cables are 8m NPR long anchor cables with a spacing of 1m×1.2m, arranged in a quincunx pattern; in other areas, the spacing between long and short anchor cables is 1m×1.2m, arranged in an alternating quincunx pattern.

[0030] The above-mentioned construction method for large-section tunnel support under unstable slope conditions preferably adopts NPR long anchor cables in the entire section of Zone III, in conjunction with anchor mesh, steel arch frame and shotcrete for initial support;

[0031] In Zone IV, NPR short anchor cables were used throughout the entire section, along with anchor mesh, steel arch frames, and shotcrete for initial support.

[0032] As described above, the preferred method for supporting large-section tunnels under unstable slope conditions is as follows: the anchor cable arrangement parameters for Zone III are: 8m NPR long anchor cables are used throughout the entire section, with a spacing of 2m × 1.2m, arranged in a quincunx pattern; the anchor cable arrangement parameters for Zone IV are: 4m NPR short anchor cables are used throughout the entire section, with a spacing of 2m × 1.2m, arranged in a quincunx pattern.

[0033] Beneficial effects:

[0034] 1. The steps are clear, the design is reasonable, and the construction is simple.

[0035] 2. It transforms the slope from an unstable state to a stable state, and the slope failure process is easily detected in the event of extreme situations, which can provide time for the evacuation and relocation of personnel.

[0036] 3. The tunnel adopts zoned support, which focuses on economic benefits, and the use of NPR anchor cable support can greatly reduce stratum deformation.

[0037] 4. The upper bench of the tunnel is excavated using short benches, while the middle and lower benches are excavated using ultra-short benches. This speeds up the construction process, allows the secondary lining to be sealed in a timely manner, and ensures that the tunnel structure is subjected to uniform stress. Attached Figure Description

[0038] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0039] Figure 1 This is a schematic diagram of the slope-tunnel strata zoning in an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of unstable slope reinforcement in an embodiment of the present invention;

[0041] Figure 3 This is a diagram showing the surface grouting reinforcement layout of the ultra-shallow buried tunnel in an embodiment of the present invention.

[0042] Figure 4 This is a schematic diagram of tunnel support in Zone I of this invention.

[0043] Figure 5 This is a schematic diagram of tunnel support in Zone II of this invention.

[0044] Figure 6 This is a schematic diagram of tunnel support in Zone III of this invention.

[0045] In the diagram: 1. Anti-slide pile; 2. Grouting pipe; 3. Grouting hole; 4. NPR long anchor cable; 5. NPR short anchor cable; 10. Tunnel. Detailed Implementation

[0046] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0047] In the description of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," and "bottom," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. The terms "connected" and "linked" used in this invention should be interpreted broadly. For example, they can refer to a fixed connection or a detachable connection; they can refer to a direct connection or an indirect connection through intermediate components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0048] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0049] According to specific embodiments of the present invention, such as Figure 1 As shown, the present invention provides a construction method for supporting large-section tunnels under unstable slope conditions. The construction method includes dividing the tunnel into four regions according to the spatial relationship between the unstable landslide surface and the large-section tunnel: the pre-buried section near the tunnel entrance is the portal section, which is region I; the other areas of the sliding surface excluding the portal section are the strong slope influence sections, which is region II; the section of the slope top close to the sliding surface is the weak slope influence section, which is region III; and the part far from the sliding surface is the normal support section, which is region IV.

[0050] Before tunnel excavation, anti-slide piles are installed on both sides of the target tunnel entrance. The construction of anti-slide piles mainly includes casing installation, drilling and cleaning, steel cage fabrication and installation, guide pipe installation, and concrete pouring.

[0051] The unstable landslide body on the sliding surface is reinforced by installing NPR anchor cables, which are installed away from the target tunnel. In this embodiment, the NPR anchor cable construction is carried out after the anti-slide piles are installed, including drilling, NPR anchor cable processing, anchor cable placement, anchor cable grouting, frame pouring, anchor cable tensioning, and anchor sealing.

[0052] The NPR anchor cables installed on the unstable landslide body include ordinary anchor cables and mega-anchor cables; the ordinary anchor cables are evenly distributed on the entire unstable landslide body to connect the landslide body into a whole; the mega-anchor cables are spaced out on the unstable landslide body and are anchored into the deep rock mass.

[0053] In this embodiment, for shallow potential sliding surfaces, ordinary anchor cables should be used, and the spacing between them can be 3 to 5 meters; when the potential sliding surface is deep, a combination of giant anchor cables and ordinary anchor cables should be used.

[0054] Regardless of the depth or shallowness of the sliding surface, standard anchor cables are installed on the sliding surface. These standard anchor cables connect multiple shallow, dangerous sliding surfaces together, increasing interlayer friction and forming a "composite beam" structure, which significantly reduces the internal stress of the soil and rock in the shallow sliding zone; that is, for shallow sliding surfaces, standard anchor cables are used to integrate them into a whole. Mega-anchor cables mainly play a "suspension role," connecting the "composite beam" structure to the stable surrounding rock. In other words, the most unfavorable dangerous sliding surface of a large slope is generally deep, requiring anchor cables to anchor the sliding body into stable deep rock mass. In this case, mega-anchor cables are used to ensure the stability of the sliding surface. The combination of the two types (long and short combinations) can better ensure the stability of large slopes and the subsequent disturbance of tunnel construction, significantly improving the stability of the surrounding rock.

[0055] The specifications for the standard anchor cables are: 5000–10300 mm NPR anchor cables with a spacing of 2000 × 2000 mm; and 35000–50000 mm NPR anchor cables with a spacing of 16000 × 8000 mm. In this embodiment, the preload of both the standard and giant anchor cables is not less than 350 kN. As can be seen from the anchor cable specifications, the giant anchor cables are much longer than the standard anchor cables, and their spacing is also much greater, enabling them to provide better anchoring and fix the position of the unstable landslide body on the entire sliding surface. In contrast, the standard anchor cables have a denser spacing, allowing them to anchor the unstable landslide body as a whole.

[0056] Grouting is performed by drilling grouting holes in Zone I. These holes are evenly spaced within Zone I, avoiding the target tunnel, and cover the upper part of the tunnel and both sides along its axial direction. Grouting anchors or pipes are then inserted into these holes for grouting. This setup offers several advantages over using pure cement jet grouting piles. First, grouting avoids the tunnel excavation face, reducing the amount of grout required, saving construction costs, and facilitating tunnel excavation. Second, the grouting pipes or anchors act as reinforcing ribs anchored in the grouting zone, significantly improving the overall integrity of the grouting area.

[0057] The grouting holes are arranged in a quincunx pattern with a spacing of 1.5m × 1.5m. Grouting is performed by inserting 50mm diameter grouting pipes into the grouting holes. In this embodiment, grouting pipes are used for grouting; in other embodiments, grouting anchor bolts can also be used.

[0058] The tunnel underwent pre-support construction with pipe roof. The tunnel adopted a three-stage excavation method, with short-stage excavation for the upper stage and ultra-short-stage excavation for the middle and lower stages. This accelerated the construction progress, allowed for timely closure of the secondary lining, and ensured uniform stress distribution on the tunnel structure.

[0059] In Zone I, the upper and lower steps are supported by a combination of densified NPR long anchor cables and NPR short anchor cables. The arch of Zone I is within the range of pipe roof support.

[0060] In Zone I, anchor mesh, steel arch frames, and shotcrete are used as initial support for the arch. In the middle and lower steps, a combination of long and short NPR anchor cables is used, along with anchor mesh, steel arch frames, and shotcrete for initial support. In this embodiment, the spacing between the long and short NPR anchor cables is 1m × 1.2m; one row of 4m short NPR anchor cables and one row of 8m long NPR anchor cables are arranged in an alternating quincunx pattern.

[0061] In this embodiment, the anchor mesh is made of NPR material, and the steel arch spacing is 0.5m. In Zone I, the NPR long and short anchor cables (middle and lower steps) are anchored from the inside of the tunnel to the depths on both sides, while the grouting pipes on both sides of the tunnel are anchored from the ground downwards. This forms a three-dimensional anchoring structure with the NPR long and short anchor cables and the grouting pipes on both sides of the tunnel. After the grouting pipes grout the surrounding rock in Zone I into a single structure, the part of the NPR long and short anchor cables extending into Zone I acts as a reinforcing rib, further strengthening the overall structural strength of Zone I. At the same time, the NPR long and short anchor cables are anchored into the deep stable surrounding rock, which not only ensures the stability of the tunnel, but also makes Zone I more stable, providing a more stable support foundation for the unstable landslide.

[0062] In Zone II, the arch section is supported by densified NPR long anchor cables. Specifically, densified NPR long anchor cables are installed in the arch section of Zone II, along with anchor mesh, steel arch frame and shotcrete for initial support. In the remaining parts of Zone II, densified NPR long and short combination anchor cables are used, along with anchor mesh, steel arch frame and shotcrete for initial support.

[0063] The anchor cable arrangement parameters in Zone II are as follows: the arch anchor cables are 8m NPR long anchor cables with a spacing of 1m×1.2m between rows, arranged in a quincunx pattern; in other areas, the spacing between long and short anchor cables is 1m×1.2m, arranged in an alternating quincunx pattern.

[0064] In this embodiment, the anchor mesh is made of NPR material, and the steel arch spacing is 0.5m. The tunnel in this area is located in a strong influence zone, and the closer to the upper part, the greater the influence of the slope. The arch here gradually changes from the arch in Zone I. The pipe roof and ground grouting reinforcement used in Zone I eliminated the installation of anchor cables in the tunnel arch. However, the arch in Zone II uses denser long anchor cables to ensure that the arch in Zone II can receive more sufficient support. The combination of long and short anchor cables in other areas of Zone II can further reduce investment and reduce construction costs. On this basis, the anchor cables driven from the inside of the tunnel outward and the anchor cables driven into the surrounding rock depth on the sliding surface are interwoven to form a composite support system, which greatly improves the support effect of large-section tunnels under unstable slope conditions.

[0065] In Zone III, long NPR anchor cables are used for support; in Zone IV, ordinary support methods or short NPR anchor cables are used for support.

[0066] In this embodiment, NPR long anchor cables are used throughout the entire section of Zone III, in conjunction with anchor mesh, steel arch frame and shotcrete for initial support; NPR short anchor cables are used throughout the entire section of Zone IV, in conjunction with anchor mesh, steel arch frame and shotcrete for initial support.

[0067] The anchor cable arrangement parameters for Zone III are as follows: 8m NPR long anchor cables are used throughout the section, with a spacing of 2m × 1.2m between rows, arranged in a quincunx pattern; the anchor cable arrangement parameters for Zone IV are as follows: 4m NPR short anchor cables are used throughout the section, with a spacing of 2m × 1.2m between rows, arranged in a quincunx pattern.

[0068] In this embodiment, Zone III is a weakly affected area of ​​the unstable sliding surface. The spacing between anchor cables in Zone III is larger than that in Zones I and II. All anchor cables in Zone III are set as long anchor cables because Zone III is relatively close to the unstable sliding surface. The long anchor cables set outward in the tunnel of Zone III and the anchor cables driven into the surrounding rock depth on the sliding surface are interwoven to form a composite support system. This not only ensures that the tunnel is effectively supported, but also ensures that the unstable sliding surface is further reinforced.

[0069] In this construction method, before tunnel construction, NPR anchor cables are installed on the unstable landslide body on the sliding surface to initially reinforce the sliding surface. Zone I, as the portal area, has a relatively shallow burial depth, which means that the arch of Zone I cannot be reinforced with anchor bolts. This construction method first performs grouting treatment on Zone I, forming a unified whole, thereby greatly improving the stability of Zone I. Since Zone I is located at the lowest point of the sliding surface, improving the integrity of Zone I also ensures that the sliding surface has a more stable bottom support. Simultaneously, pipe roof pre-support construction is carried out, providing better support for the arch of Zone I. This setup ensures better stability of the unstable landslide body.

[0070] Based on this, during tunnel construction, the upper and lower benches of Zone I were supported by denser NPR long anchor cables, while the arch of Zone II and the entire section of Zone III were supported by denser NPR long anchor cables. This allowed the anchor cables extending radially along the tunnel and the grouting pipes around the tunnel to form cross-support with the anchor cables installed on the sliding surface. As a result, the surrounding rock of the tunnel near the unstable landslide was anchored into a whole by the crisscrossing anchor cables, which not only greatly improved the stability of the unstable landslide but also ensured better support for the large-section tunnel.

[0071] In summary, the technical solution for the construction method of large-section tunnel support under unstable slope conditions provided by this invention involves first grouting zone I, which integrates the grout into a unified whole, thereby greatly improving the stability of zone I. Since zone I is located at the lowest point of the sliding surface, improving the integrity of zone I also ensures that the sliding surface has a more stable bottom support. Simultaneously, pipe roof pre-support construction is carried out, which provides better support for the arch of zone I. This arrangement ensures better stability of the unstable landslide body. On this basis, anchor cables are driven outward from inside the tunnel and interwoven with anchor cables driven deep into the surrounding rock on the sliding surface, forming a composite support system, which greatly improves the support effect of large-section tunnels under unstable slope conditions.

[0072] It is understood that the above description is merely exemplary and the embodiments of this application do not limit the scope of the application.

[0073] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention shall be within the scope of protection of the pending claims of the present invention.

Claims

1. A method for supporting large-section tunnels under unstable slope conditions, characterized in that, The construction method includes dividing the tunnel into four zones based on the spatial relationship between the unstable landslide surface and the large-section tunnel: the pre-buried section near the tunnel entrance is the portal section, which is Zone I; the other areas of the sliding surface excluding the portal section are the slope strongly affected sections, which is Zone II; the section of the slope top close to the sliding surface is the slope weakly affected section, which is Zone III; and the part far from the sliding surface is the normal support section, which is Zone IV. Before tunnel excavation, anti-slide piles were installed on both sides of the target tunnel entrance. NPR anchor cables are installed on the unstable landslide surface for reinforcement, and the NPR anchor cables are installed away from the target tunnel. Grouting was carried out in Zone I by drilling grouting holes. Pipe roof pre-support construction is being carried out in the tunnel; In Zone I, the upper and lower steps are supported by a combination of densified NPR long anchor cables and NPR short anchor cables. The arch of Zone I is within the pipe roof support range. In Zone II, the arch section is supported by reinforced NPR long anchor cables; In Zone III, long NPR anchor cables are used for support; in Zone IV, ordinary support methods or short NPR anchor cables are used for support. The NPR anchor cables installed on the unstable landslide body include ordinary anchor cables and giant anchor cables. The ordinary type of anchor cable is evenly distributed on the entire unstable landslide body to connect the landslide body into a whole; The giant anchor cables are spaced out on the unstable landslide body and are anchored into the deep rock mass. Grouting holes are evenly drilled in Zone I, avoiding the target tunnel. The grouting holes cover the upper part of the tunnel and both sides of the tunnel axis. Grouting is performed by inserting grouting anchors or grouting pipes into the grouting holes; the anchor cables extending radially along the tunnel and the grouting pipes around the tunnel form cross-supports with the anchor cables installed on the sliding surface; In Zone I, anchor mesh, steel arch frame and shotcrete are used as initial support for the arch. In the middle and lower steps, densified NPR long and short combination anchor cables are used in conjunction with anchor mesh, steel arch frame and shotcrete for initial support. In Zone II, dense NPR long anchor cables are installed in the arch, and initial support is provided in conjunction with anchor mesh, steel arch frame and shotcrete. In the remaining part of Zone II, a combination of long and short NPR anchor cables with densification, anchor mesh, steel arch frame and shotcrete are used for initial support; In Zone III, NPR long anchor cables were used throughout the entire section, along with anchor mesh, steel arch frames, and shotcrete for initial support. In Zone IV, NPR short anchor cables are used throughout the entire section, along with anchor mesh, steel arch frame and shotcrete for initial support. The specifications of the common type of anchor cable are: 5000~10300mm NPR anchor cable, with a row spacing of 2000×2000mm. Giant anchor cables: 35,000~50,000 mm NPR anchor cables, with a row spacing of 16,000×8,000 mm.

2. The construction method for large-section tunnel support under unstable slope conditions according to claim 1, characterized in that, The grouting holes are arranged in a quincunx pattern with a spacing of 1.5m × 1.5m. Grouting reinforcement is carried out by inserting grouting pipes with a diameter of 50mm into the grouting holes.

3. The construction method for large-section tunnel support under unstable slope conditions according to claim 1, characterized in that, The spacing between the long and short NPR anchor cables is 1m × 1.2m; one row of 4m NPR short anchor cables and one row of 8m NPR long anchor cables are arranged in an alternating quincunx pattern.

4. The construction method for large-section tunnel support under unstable slope conditions according to claim 1, characterized in that, The anchor cable arrangement parameters in Zone II are as follows: the arch anchor cables are 8m NPR long anchor cables with a spacing of 1m×1.2m between rows, arranged in a quincunx pattern; in other areas, the spacing between long and short anchor cables is 1m×1.2m, arranged in an alternating quincunx pattern.

5. The construction method for large-section tunnel support under unstable slope conditions according to claim 1, characterized in that, The anchor cable arrangement parameters for Zone III are as follows: 8m NPR long anchor cables are used throughout the section, with a spacing of 2m × 1.2m between rows, arranged in a quincunx pattern; the anchor cable arrangement parameters for Zone IV are as follows: 4m NPR short anchor cables are used throughout the section, with a spacing of 2m × 1.2m between rows, arranged in a quincunx pattern.

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