Tunneling construction method

Abstract

This application relates to a method for tunnel excavation using the cut-and-cover technique, comprising: dividing the area above the top elevation of the tunnel floor slab into three sections: Upper Bench 1, Middle Bench 2, Upper Bench 3, Middle Bench 4, and Upper Bench 5 and Middle Bench 6 in the middle; sequentially excavating these upper and middle benches using the bench method, and constructing the corresponding arch frames and central diaphragm walls; dividing the area below the top elevation of the tunnel floor slab into three sections: Lower Bench 7, Lower Bench 8, and Lower Bench 9; excavating Lower Bench 7 and 8, constructing the corresponding arch frames and central diaphragm walls, and installing inclined temporary anchor bolts on the central diaphragm walls of Lower Bench 7 and 8, welding them to the two central diaphragm walls as support structures; excavating Lower Bench 9, and constructing the corresponding invert arch, connecting the arch frame on the invert arch with the already installed arch frame above the invert arch to form a closed loop. This method eliminates the need for installing temporary invert arches and for extending the arch frame of the central diaphragm wall after excavating the lower benches, reducing construction difficulty and cost.

Description

Technical Field

[0001] This application relates to the field of tunnel construction, specifically to a method for tunnel excavation using the cut-and-cover technique. Background Technology

[0002] Tunnel excavation using the cut-and-cover method is a construction method that involves excavation underground, characterized by minimal impact on the surface. Cut-and-cover tunnel construction primarily employs composite lining, where the initial support bears the entire basic load, while the secondary lining serves as a safety reserve. It utilizes various auxiliary methods, such as pre-support, to improve and reinforce the surrounding rock, mobilizing some of the rock's self-supporting capacity. Simultaneously, different excavation methods are employed to promptly form a closed support ring, working in conjunction with the surrounding rock to create a combined support system. Furthermore, it emphasizes information-based design and construction.

[0003] Among related technologies, the New Austrian Tunneling Method (NATM) has summarized the double-side wall pilot tunnel method for the construction of large-section soft surrounding rock tunnels. However, although this method can effectively control settlement and ensure construction safety, it is not conducive to mechanized construction due to the existence of temporary invert arches, limited space, and the time and effort required to extend the middle diaphragm wall. Summary of the Invention

[0004] This application provides a method for tunnel excavation by using the bench method to excavate the soil above the top elevation of the tunnel floor, eliminating the need for the installation of temporary invert arches; by excavating the No. 7 and No. 8 lower benches below the top elevation of the tunnel floor, and installing inclined temporary anchors on the two intermediate partition walls, which are then welded to the intermediate partition walls as support structures, the method eliminates the need for extending the arch frame of the intermediate partition walls after the lower benches are excavated, thus reducing construction difficulty and cost.

[0005] This application provides a method for tunnel excavation using the cut-and-cover technique, comprising: The area above the top elevation of the tunnel floor is divided into the No. 1 upper bench, the No. 2 middle bench, the No. 3 upper bench, the No. 4 middle bench, and the No. 5 upper bench and the No. 6 middle bench in the middle. The bench method is used to excavate these upper and middle bench sections in sequence, and the arch frame and the middle partition wall are constructed in the corresponding areas. The area below the top elevation of the tunnel floor is divided into three lower benches: No. 7, No. 8, and No. 9. Lower benches No. 7 and No. 8 are excavated, and the arch frames and central diaphragm walls in the corresponding areas are constructed. Inclined temporary anchor bolts are installed on the central diaphragm walls of lower benches No. 7 and No. 8 and welded to the two central diaphragm walls as support structures. Excavate the No. 9 lower step and carry out the corresponding invert arch construction, connecting the arch frame on the invert arch with the already installed arch frame above the invert arch to form a closed ring.

[0006] In one embodiment, the section dividing the area above the tunnel floor slab into four levels—upper step 1, middle step 2, upper step 3, middle step 4, and upper step 5 and middle step 6 in the middle—and sequentially excavating these upper and middle steps using a step-by-step method, followed by the construction of the corresponding arch frames and central diaphragm walls, includes: Install a small guide pipe on one side of the upper pilot tunnel and perform grouting to reinforce the strata; The step method was used for excavation. First, the soil of the first upper step was excavated, and then the soil of the second middle step was excavated. Construction of the arch frame and central diaphragm wall was carried out, and initial support was implemented. Locking steel pipes were welded together with the steel frame to limit the settlement and lateral displacement of the arch frame.

[0007] In one embodiment, the section dividing the area above the tunnel floor slab into four levels—upper step 1, middle step 2, upper step 3, middle step 4, and upper step 5 and middle step 6 in the middle—and sequentially excavating these upper and middle steps using a step-by-step method, followed by the construction of the corresponding arch frames and central diaphragm walls, includes: Construct the advanced small guide pipe on the other side of the upper pilot tunnel and perform grouting to reinforce the strata; The step method was used for excavation. First, the soil of the No. 3 upper step was excavated, and then the soil of the No. 4 middle step was excavated. Construction of the arch frame and central diaphragm wall was carried out, and initial support was implemented. Locking steel pipes were welded together with the steel frame to limit the settlement and lateral displacement of the arch frame.

[0008] In one embodiment, the section dividing the area above the tunnel floor slab into four levels—upper step 1, middle step 2, upper step 3, middle step 4, and upper step 5 and middle step 6 in the middle—and sequentially excavating these upper and middle steps using a step-by-step method, followed by the construction of the corresponding arch frames and central diaphragm walls, includes: The step method was used for excavation. First, the soil of the No. 5 upper step was excavated, and then the soil of the No. 6 middle step was excavated. The arch frame was constructed and the initial support was carried out.

[0009] In one embodiment, the process of dividing the area below the top elevation of the tunnel floor into three lower benches—number seven, number eight, and number nine—and excavating lower benches seven and eight, constructing the corresponding arch frames and central diaphragms, and installing oblique temporary anchor bolts on the central diaphragms of lower benches seven and eight, welding them to the two central diaphragms as support structures, includes: Excavate the soil of the lower steps of No. 7 and No. 8, and carry out the construction of the arch frame and the central partition wall in the corresponding area; Construct corbels and install inclined temporary anchor bolts. Pass the inclined temporary anchor bolts through the corbels and weld them to the two intermediate partitions to form a stable support system.

[0010] In one embodiment, the excavation of the No. 9 lower bench and the corresponding invert arch construction, connecting the arch frame on the invert arch with the already installed arch frame above the invert arch to form a closed ring, includes: Excavate the soil of the No. 9 lower bench, construct vertical temporary anchor bolts, and connect them to the middle partition wall of the No. 7 and No. 8 lower benches to limit the settlement of the arch frame; Construct the arch frame in the corresponding area and apply initial support so that the arch frame and initial support together form a stable support structure. Connect the arch frame on the inverted arch to the existing arch frame above the inverted arch to form a closed loop.

[0011] In one embodiment, after excavating the No. 9 lower bench and constructing the corresponding invert arch, connecting the arch frame on the invert arch with the already installed arch frame above the invert arch to form a closed ring, the process includes: Cut off the exposed temporary anchor rods to ensure a flat surface. Level the cut surface at set intervals to ensure overall flatness. A waterproof layer is laid on the leveled surface, and a secondary lining arch is constructed on the waterproof layer to ensure a tight connection between the arch and the arch frame. Secondary lining construction was carried out on the sidewalls, and a large-section overall closed ring operation was performed.

[0012] In one embodiment, before dividing the area above the tunnel floor slab into upper step 1, middle step 2, upper step 3, middle step 4, and upper step 5 and middle step 6 in the middle, and sequentially excavating these upper and middle steps using the step method to construct the corresponding arch frame and central diaphragm, the process includes: Pre-grouting with small guide pipes was carried out in the tunnel arch to reinforce the strata.

[0013] In one implementation, the excavation width of the No. 1 upper step, the No. 2 middle step, the No. 3 upper step, and the No. 4 middle step does not exceed one-third of the tunnel width, and the excavation width of the No. 5 upper step and the No. 6 middle step does not exceed one-third of the tunnel width.

[0014] In one implementation, the excavation step distance of the No. 1 upper step, No. 2 middle step, No. 3 upper step, No. 4 middle step, No. 5 upper step and No. 6 middle step is L, 3m≤L≤5m, and the distance between the invert arch of the No. 7, No. 8 and No. 9 lower steps and the secondary lining concrete does not exceed 15m.

[0015] The beneficial effects of the technical solutions provided in this application include: By employing the step-by-step method to excavate the soil of the No. 1 upper step, No. 2 middle step, No. 3 upper step, No. 4 middle step, No. 5 upper step, and No. 6 middle step, the installation of temporary invert arches was eliminated. By excavating the No. 7 and No. 8 lower steps below the top elevation of the tunnel floor slab, invert arch construction was carried out in these two lower steps, and inclined temporary anchor rods were installed on the two middle partition walls and welded to the middle partition walls as support structures. This eliminated the need to extend the arch frame of the middle partition walls after the lower steps were excavated, reducing construction difficulty and cost. This excavation method can ensure that the settlement is within the allowable range and improve construction efficiency. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of the structure of the tunnel face during cut-and-cover excavation. Figure 2 This is a schematic diagram showing the connection between vertical and diagonal temporary anchors, corbels, and arch frames.

[0018] In the diagram: 1. First step; 2. Second step; 3. Third step; 4. Fourth step; 5. Fifth step; 6. Sixth step; 7. Third step; 8. Eighth step; 9. Ninth step; 10. Arch frame; 11. Middle partition wall; 12. Advanced small guide pipe; 13. Locking foot steel pipe; 14. Temporary anchor bolt; 15. Corbel. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0020] This application provides a method for tunnel excavation using the cut-and-cover technique, which solves the problems of limited space and unfavorable conditions for mechanized construction due to the presence of temporary invert arches in the New Austrian Tunneling Method (NATM); and the time-consuming and labor-intensive process of extending the diaphragm wall, which reduces construction efficiency.

[0021] like Figure 1 As shown in the figure, this application provides a method for tunnel excavation using the cut-and-cover technique, which includes: S100: The area above the top elevation of the tunnel floor is divided into the No. 1 upper bench 1, the No. 2 middle bench 2, the No. 3 upper bench 3, the No. 4 middle bench 4, and the No. 5 upper bench 5 and the No. 6 middle bench 6 in the middle section. The bench method is used to excavate these upper and middle bench sections in sequence, and the corresponding arch frame 10 and middle partition wall 11 are constructed. S200: Divide the area below the top elevation of the tunnel floor into three lower benches: No. 7, No. 8, and No. 9. Excavate the No. 7 and No. 8 lower benches, construct the corresponding arch frame 10 and central diaphragm wall 11, and install inclined temporary anchor bolts 14 on the central diaphragm wall 11 of the No. 7 and No. 8 lower benches, and weld them to the two central diaphragm walls 11 as support structures. S300: Excavate the No. 9 lower step 9 and carry out the corresponding invert arch construction, connecting the arch frame 10 on the invert arch with the installed arch frame 10 above the invert arch to form a closed ring.

[0022] Among them, see Figure 1 The tunnel floor is divided into six areas above the top elevation. The first layer, from left to right, consists of the No. 1 upper step, the No. 5 upper step, and the No. 3 upper step. The second layer, from left to right, consists of the No. 2 middle step, the No. 6 middle step, and the No. 4 middle step. The No. 2 middle step is located below the No. 1 upper step, the No. 6 middle step is located below the No. 5 upper step, and the No. 4 middle step is located below the No. 3 upper step. The tunnel floor is divided into three areas below the top elevation. From left to right, these consist of the No. 7 lower step, the No. 8 lower step, and the No. 9 lower step. The No. 7 lower step is located below the No. 2 middle step, the No. 8 lower step is located below the No. 4 middle step, and the No. 9 lower step is located below the No. 6 middle step.

[0023] In this embodiment, the portion above the top elevation of the tunnel floor is divided into two steps: Upper Step 1, Middle Step 2, Upper Step 3, Middle Step 4, Upper Step 5, and Middle Step 6, located in the middle. Using a step-by-step method, these upper and middle steps are excavated sequentially. During excavation, corresponding arch frames 10 and central diaphragm walls 11 are constructed to ensure tunnel stability. Step-by-step excavation effectively controls tunnel deformation and stress release, improving construction safety. The construction of arch frames 10 and central diaphragm walls 11 enhances the overall stability of the tunnel, preventing collapse during excavation. Step-by-step excavation reduces the span of a single excavation, minimizing disturbance to the surrounding rock and contributing to tunnel stability. Timely construction of arch frames 10 and central diaphragm walls 11 effectively supports the surrounding rock, preventing excessive deformation or collapse.

[0024] The section below the top elevation of the tunnel floor is divided into three lower benches: No. 7 (lower bench), No. 8 (lower bench), and No. 9 (lower bench). Lower benches No. 7 and No. 8 (lower bench) are excavated, and the corresponding arch frames 10 and central diaphragm walls 11 are constructed. Inclined temporary anchor bolts 14 are installed on the central diaphragm walls 11 of lower benches No. 7 and No. 8 (lower benches), and welded to the two central diaphragm walls 11 to form a stable support structure. By excavating lower benches No. 7 and No. 8 (lower benches), the tunnel construction process is further advanced. The installation of temporary anchor bolts 14 and their welding to the central diaphragm walls 11 can enhance the stability of the lower benches and prepare for the subsequent excavation of lower bench No. 9 (lower bench).

[0025] The excavation and construction of the support structure of the No. 7 and No. 8 lower benches provide a stable working environment for the excavation of the No. 9 lower bench. The installation of temporary anchor bolts 14 and the welding of the central diaphragm wall 11 can effectively prevent the lower bench from collapsing or undergoing excessive deformation during the excavation process. The No. 9 lower bench is excavated, and the corresponding invert arch is constructed on the No. 9 lower bench. The arch frame 10 on the invert arch is connected to the already installed arch frame 10 above the invert arch to form a closed loop, thus forming a complete tunnel support structure. By excavating the No. 9 lower bench and completing the invert arch construction, the tunnel structure can be further improved. The closed loop arch frame 10 structure can enhance the overall stability of the tunnel and improve its load-bearing capacity. The excavation of the No. 9 lower bench and the construction of the invert arch can make the tunnel form a complete closed loop structure, improving its overall stability. The construction of the invert arch can also effectively prevent groundwater from seeping into the tunnel, protecting the internal structure and safety of the tunnel.

[0026] In summary, by adopting the step method to excavate the soil of the No. 1 upper step 1, the No. 2 middle step 2, the No. 3 upper step 3, the No. 4 middle step 4, the No. 5 upper step 5, and the No. 6 middle step 6, the installation of temporary invert arches was eliminated. By excavating the No. 7 and No. 8 lower steps 8 below the top elevation of the tunnel floor slab, invert arch construction was carried out in these two lower steps, and inclined temporary anchor rods 14 were installed on the two middle partition walls 11 and welded to the middle partition walls 11 as support structures. This eliminated the need to extend the arch frame 10 of the middle partition walls 11 after the lower steps were excavated, reducing construction difficulty and cost. This excavation method can ensure that the settlement is within the allowable range and improve construction efficiency.

[0027] In one implementation, step S100 includes the following steps: S101: Construct the advanced small guide pipe 12 on one side of the upper guide tunnel and perform grouting to reinforce the formation; S102: The step method is used for excavation. First, the soil of the upper step 1 is excavated, and then the soil of the middle step 2 is excavated. S103: Construct the arch frame 10 and the central diaphragm wall 11, and perform initial support. Use locking steel pipes 13 to weld together with the steel frame to limit the sinking and lateral displacement of the arch frame 10.

[0028] In this embodiment, at the upper pilot pit location on one side of the tunnel, advanced small guide pipes 12 are installed according to the designed spacing and angle. Grout is injected into the stratum through the small guide pipes to reinforce the stratum and improve its bearing capacity and stability. Grouting through the advanced small guide pipes 12 can reinforce the stratum, improve its self-stabilizing ability, and provide a stable working environment for subsequent excavation. Grouting can also fill fissures and cavities in the stratum, prevent groundwater from seeping into the tunnel, and reduce construction risks. It reinforces the stratum, improves tunnel stability, and ensures construction safety. It prevents groundwater seepage, protects the internal structure of the tunnel, and reduces later maintenance costs. Following the requirements of the bench method, the soil of the first upper bench 1 is excavated first, with strict control over-excavation and under-excavation during the excavation process. After the excavation of the first upper bench 1 is completed, the soil of the second middle bench 2 is excavated promptly, with similarly strict control over excavation quality. The bench method excavation can reduce the span of a single excavation, reduce disturbance to the surrounding rock, and is beneficial to tunnel stability. The stepped excavation also facilitates the subsequent construction of the arch frame 10 and the central diaphragm wall 11, reducing construction difficulty and risk while improving efficiency. It also contributes to tunnel stability, preventing collapse and deformation. After excavation, the construction of the arch frame 10 and central diaphragm wall 11 should proceed promptly, with positioning and installation according to design requirements. Initial support should be implemented, including shotcrete and waterproofing. Locking steel pipes 13 are welded to the steel frame to form a stable support structure, limiting the settlement and lateral displacement of the arch frame 10. The construction of the arch frame 10 and central diaphragm wall 11 enhances the overall stability of the tunnel, preventing collapse and deformation. Initial support protects the tunnel's internal structure, preventing groundwater infiltration and surrounding rock weathering. Welding the locking steel pipes 13 to the steel frame restricts the movement of the arch frame 10, ensuring tunnel stability. This enhances the overall stability of the tunnel, increasing its load-bearing capacity, protecting the tunnel's internal structure, extending its service life, reducing later maintenance costs, and improving economic efficiency.

[0029] In one implementation, step S100 includes the following steps: S104: Construct the advanced small guide pipe 12 on the other side of the upper guide tunnel and perform grouting to reinforce the formation; S105: The step method is used for excavation. First, the soil of the upper step 3 is excavated, and then the soil of the middle step 4 is excavated. S106: Construct the arch frame 10 and the central diaphragm wall 11, and perform initial support. Use locking steel pipes 13 to weld together with the steel frame to limit the sinking and lateral displacement of the arch frame 10.

[0030] In this embodiment, by constructing the advanced small guide pipe 12 on the other side of the upper pilot tunnel and grouting to reinforce the stratum, the stability of the stratum during tunnel excavation can be ensured, preventing safety accidents such as collapses due to soft stratum or the presence of fissures. Grouting reinforcement can also improve the bearing capacity of the stratum, providing a stable working environment for subsequent excavation and support construction. With the stratum reinforced, the overall stability of the tunnel is improved, ensuring construction safety. It reduces construction risks caused by stratum problems and improves construction efficiency. Using the step method for excavation can effectively control tunnel deformation and stress release, improving construction safety. Excavating the soil of the third upper step 3 first, and then excavating the soil of the fourth middle step 4, can reduce the span of a single excavation, reduce disturbance to the surrounding rock, and is beneficial to tunnel stability. Tunnel deformation and stress release are effectively controlled, and construction safety is improved. Step excavation reduces construction difficulty and risk, and improves construction efficiency. The overall stability of the tunnel is enhanced. Construction of the arch frame 10 and the central diaphragm wall 11 can enhance the overall stability of the tunnel and prevent collapse and deformation. Initial support construction protects the tunnel's internal structure, preventing groundwater infiltration and surrounding rock weathering. The use of locking steel pipes 13 welded to the steel frame restricts the movement of the arch frame 10, ensuring tunnel stability. This further enhances the tunnel's overall stability and improves its load-bearing capacity. The tunnel's internal structure is effectively protected, extending its service life. It also reduces later maintenance costs and improves economic efficiency. Furthermore, it facilitates subsequent use and maintenance of the tunnel.

[0031] In one implementation, step S100 includes the following steps: S107: The step method is used for excavation. First, the soil of the upper step 5 is excavated, and then the soil of the middle step 6 is excavated. The arch frame 10 is constructed and the initial support is carried out.

[0032] In this embodiment, the step method gradually reduces the excavation span by first excavating the soil of the upper step 5 and then excavating the soil of the middle step 6, thereby reducing the disturbance to the surrounding rock, reducing the risk of collapse, and improving the safety of the construction process.

[0033] In one implementation, step S200 includes the following steps: S201: Excavate the soil of the lower steps 8 of No. 7 and No. 8, and carry out the corresponding construction of the arch frame 10 and the central diaphragm wall 11; S202: Construct the corbel 15 and install inclined temporary anchor bolts 14. Pass the inclined temporary anchor bolts 14 through the corbel 15 and weld them to the two intermediate partition walls 11 to form a stable support system. Figure 2 This is a schematic diagram showing the connection between the central partition wall 11 at point 7 of the seventh step and the inclined temporary anchor rod 14 and corbel 15.

[0034] In this embodiment, the soil of the lower benches 8 (numbers 7 and 8) is excavated, and the arch frame 10 and central diaphragm wall 11 are constructed. Through step-by-step excavation and timely support, the deformation of the surrounding rock is controlled, maintaining tunnel stability. The result is the formation of left and right chambers supported by the central diaphragm wall 11, providing a safe working environment for subsequent construction. The corbels 15 are constructed, and inclined temporary anchor bolts 14 are installed and welded to the central diaphragm wall 11 to form a stable support system. This eliminates the need to extend the arch frame 10 of the central diaphragm wall 11 after the lower bench excavation, reducing construction difficulty and cost. This step aims to further enhance the stability of the tunnel and prevent collapse and deformation. The effect is to improve the overall load-bearing capacity of the tunnel and ensure safety during construction.

[0035] In one implementation, step S300 includes the following steps: S301: Excavate the soil of the lower step 9, construct the vertical temporary anchor 14, and connect it to the middle partition wall 11 of the lower steps 7 and 8 to limit the sinking of the arch frame 10. S302: Carry out the corresponding arch frame 10 construction and implement initial support so that the arch frame 10 and the initial support together form a stable support structure. S303: Connect the arch frame 10 on the invert arch to the installed arch frame 10 above the invert arch to form a closed loop.

[0036] In this embodiment, excavating the soil of the lower bench 9 is to further advance the tunnel construction process. Constructing vertical temporary anchor bolts 14 and connecting them to the central diaphragm walls 11 of the lower benches 7 and 8 provides a temporary stable support structure to prevent the arch frame 10 from sinking or deforming due to soil pressure during the lower bench excavation. By connecting the temporary anchor bolts 14 and the central diaphragm walls 11, a stable temporary support system is formed, effectively limiting the sinking and deformation of the arch frame 10. This ensures the stability and safety during tunnel excavation. The corresponding construction of the arch frame 10 is to provide a permanent support structure after tunnel excavation. The initial support is constructed to form a more stable support structure together with the arch frame 10 to withstand soil pressure and other external loads above the tunnel. The combination of the arch frame 10 and the initial support forms a strong support system, effectively improving the overall stability and load-bearing capacity of the tunnel. This ensures the safety of the tunnel during construction and use. Connecting the arch frame 10 on the invert to the installed arch frame 10 above the invert is to form a closed ring support structure. The purpose of this closed ring is to further improve the overall stability and load-bearing capacity of the tunnel, preventing deformation or damage due to external loads. By connecting the arch frame 10 on the invert and the installed arch frame 10, a complete ring support system is formed, effectively improving the overall stability and load-bearing capacity of the tunnel. This enhances the tunnel's resistance to external loads, ensuring its long-term stability and safety.

[0037] In one implementation, after S300, the following steps are included: S401: Cut off the exposed temporary anchor rod 14 to ensure the surface is flat. Level the surface after cutting, and do so at set intervals to ensure overall flatness. S402: Lay a waterproof layer on the leveled surface, and construct a secondary lining arch on the waterproof layer to ensure that it is tightly connected to the arch frame 10. S403: Perform secondary lining construction on the sidewalls and carry out large-section overall closure ring operation.

[0038] In this embodiment, removing the exposed temporary anchor bolts 14 is to eliminate uneven surfaces inside the tunnel, providing a smooth foundation for subsequent waterproofing and secondary lining construction. Leveling the removed surface ensures the smoothness of the tunnel's interior surface, improving its aesthetics and usability. The smoother tunnel surface after removing the temporary anchor bolts 14 and undergoing leveling provides a good working foundation for subsequent construction. This enhances the overall aesthetics of the tunnel interior and also contributes to improving its usability and durability.

[0039] Laying a waterproof layer on the leveled surface prevents groundwater or other liquids from seeping into the tunnel, protecting the tunnel structure and internal facilities. Constructing a secondary lining invert on top of the waterproof layer provides an additional support structure, enhancing the tunnel's overall stability and load-bearing capacity. Ensuring a tight connection between the secondary lining invert and the invert arch frame 10 forms a continuous support system, improving the tunnel's overall performance. The waterproof layer effectively prevents the seepage of groundwater or other liquids, protecting the tunnel structure and internal facilities. The construction of the secondary lining invert provides an additional support structure, enhancing the tunnel's overall stability and load-bearing capacity. The tightly connected secondary lining invert and invert arch frame 10 form a continuous support system, improving the tunnel's overall performance and service life. Secondary lining construction on the sidewalls provides an additional protective layer, preventing erosion and damage from the external environment. Large-section overall closure and ring-forming work forms a complete tunnel structure, improving the tunnel's overall stability and usability. The secondary lining construction provides an additional protective layer for the tunnel sidewalls, enhancing their durability and erosion resistance. The large-section, fully enclosed ring construction creates a complete tunnel structure, improving the tunnel's overall stability and performance. It also contributes to enhancing the tunnel's aesthetics and lifespan.

[0040] In one implementation, prior to S100, the following steps are included: S000: Grouting is performed on the tunnel arch using advanced small guide pipe 12 to reinforce the strata.

[0041] In this embodiment, the pre-grouting with small guide pipe 12 significantly strengthens the strata of the tunnel arch. During tunnel excavation, pre-grouting with small guide pipe 12 is an important pre-support method, especially suitable for weak and fractured zones with short self-stabilization times. After grouting, the grout fills and splits, replacing moisture and air between soil particles and in rock fissures. After solidification, it binds the original loose soil particles or fissures into a whole, forming a new structure. This structure is not only strong but also has excellent waterproofing performance, significantly improving the loose and fractured state of the surrounding rock and effectively enhancing its stability. This is beneficial for the stability of the surrounding rock after excavation and during the initial support period, preventing instability and collapse. Furthermore, this process also has a water-blocking effect, making it suitable for weak and fractured surrounding rock with abundant groundwater.

[0042] In one embodiment, the excavation width of the No. 1 upper step 1, the No. 2 middle step 2, the No. 3 upper step 3, and the No. 4 middle step 4 does not exceed one-third of the tunnel width, and the excavation width of the No. 5 upper step 5 and the No. 6 middle step 6 does not exceed one-third of the tunnel width.

[0043] In this embodiment, by excavating in stages, the width of each stage accounts for no more than or no less than one-third of the total tunnel width, which helps to maintain the stability of the excavation face and reduce disturbance to the surrounding rock.

[0044] In one embodiment, the excavation step distance of the No. 1 upper step 1, the No. 2 middle step 2, the No. 3 upper step 3, the No. 4 middle step 4, the No. 5 upper step 5 and the No. 6 middle step 6 is L, 3m≤L≤5m, and the distance between the inverted arch of the No. 7, No. 8 and No. 9 lower steps 9 and the secondary lining concrete does not exceed 15m.

[0045] In this embodiment, the excavation step distance is specified to ensure the stability and safety of the excavation operation and reduce the risk of surrounding rock disturbance and collapse. A reasonable design of the step height and number, along with clear excavation advance requirements, helps improve construction efficiency and accelerate project progress. Controlling the distance between the lower step invert and the secondary lining concrete (not exceeding 15m) helps to promptly close the tunnel into a ring, enhancing the overall stability of the tunnel structure.

[0046] In the description of this application, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this application can be understood according to the specific circumstances.

[0047] It should be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0048] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for tunnel excavation using the cut-and-cover technique, characterized in that, It includes: The area above the top elevation of the tunnel floor is divided into the No. 1 upper bench, the No. 2 middle bench, the No. 3 upper bench, the No. 4 middle bench, and the No. 5 upper bench and the No. 6 middle bench in the middle. The bench method is used to excavate these upper and middle bench sections in sequence, and the arch frame and the middle partition wall are constructed in the corresponding areas. The area below the top elevation of the tunnel floor is divided into three lower benches: No. 7, No. 8, and No.

9. Lower benches No. 7 and No. 8 are excavated, and the arch frames and central diaphragm walls in the corresponding areas are constructed. Inclined temporary anchor bolts are installed on the central diaphragm walls of lower benches No. 7 and No. 8 and welded to the two central diaphragm walls as support structures. Excavate the No. 9 lower step and carry out the corresponding invert arch construction, connecting the arch frame on the invert arch with the already installed arch frame above the invert arch to form a closed ring.

2. The tunnel excavation method as described in claim 1, characterized in that, The tunnel floor slab is divided into four sections above the top elevation: Upper Step 1, Middle Step 2, Upper Step 3, Middle Step 4, and Upper Step 5 and Middle Step 6 in the middle. These upper and middle steps are excavated sequentially using the step method, and the corresponding arch frames and central diaphragm walls are constructed, including: Install a small guide pipe on one side of the upper pilot tunnel and perform grouting to reinforce the strata; The step method was used for excavation. First, the soil of the first upper step was excavated, and then the soil of the second middle step was excavated. Construction of the arch frame and central diaphragm wall was carried out, and initial support was implemented. Locking steel pipes were welded together with the steel frame to limit the settlement and lateral displacement of the arch frame.

3. The tunnel excavation method as described in claim 1, characterized in that, The tunnel floor slab is divided into four sections above the top elevation: Upper Step 1, Middle Step 2, Upper Step 3, Middle Step 4, and Upper Step 5 and Middle Step 6 in the middle. These upper and middle steps are excavated sequentially using the step method, and the corresponding arch frames and central diaphragm walls are constructed, including: Construct a pre-conduit pipe for the upper pilot tunnel on the other side and perform grouting to reinforce the formation; The step method was used for excavation. First, the soil of the No. 3 upper step was excavated, and then the soil of the No. 4 middle step was excavated. Construction of the arch frame and central diaphragm wall was carried out, and initial support was implemented. Locking steel pipes were welded together with the steel frame to limit the settlement and lateral displacement of the arch frame.

4. The tunnel excavation method as described in claim 1, characterized in that, The tunnel floor slab is divided into four sections above the top elevation: Upper Step 1, Middle Step 2, Upper Step 3, Middle Step 4, and Upper Step 5 and Middle Step 6 in the middle. These upper and middle steps are excavated sequentially using the step method, and the corresponding arch frames and central diaphragm walls are constructed, including: The step method was used for excavation. First, the soil of the No. 5 upper step was excavated, and then the soil of the No. 6 middle step was excavated. The arch frame was constructed and the initial support was carried out.

5. The tunnel excavation method as described in claim 1, characterized in that, The process involves dividing the area below the top elevation of the tunnel floor into three lower benches: No. 7, No. 8, and No.

9. Excavation of lower benches No. 7 and No. 8 is conducted, and the corresponding arch frames and central diaphragm walls are constructed. Inclined temporary anchor bolts are installed on the central diaphragm walls of lower benches No. 7 and No. 8, and welded to these two central diaphragm walls as support structures. This includes: Excavate the soil of the lower steps of No. 7 and No. 8, and carry out the construction of the arch frame and the central partition wall in the corresponding area; Construct corbels and install inclined temporary anchor bolts. Pass the inclined temporary anchor bolts through the corbels and weld them to the two intermediate partitions to form a stable support system.

6. The tunnel excavation method as described in claim 1, characterized in that, The excavation of the No. 9 lower bench and the corresponding invert arch construction, connecting the arch frame on the invert arch with the existing arch frame above the invert arch to form a closed ring, includes: Excavate the soil of the No. 9 lower bench, construct vertical temporary anchor bolts, and connect them to the middle partition wall of the No. 7 and No. 8 lower benches to limit the settlement of the arch frame; Construct the arch frame in the corresponding area and apply initial support so that the arch frame and initial support together form a stable support structure. Connect the arch frame on the inverted arch to the existing arch frame above the inverted arch to form a closed loop.

7. The tunnel excavation method as described in claim 1, characterized in that, After excavating the No. 9 lower bench and constructing the corresponding invert arch, connecting the arch frame on the invert arch with the existing arch frame above the invert arch to form a closed ring, the process includes: Cut off the exposed temporary anchor rods to ensure a flat surface. Level the cut surface at set intervals to ensure overall flatness. A waterproof layer is laid on the leveled surface, and a secondary lining arch is constructed on the waterproof layer to ensure a tight connection between the arch and the arch frame. Secondary lining construction was carried out on the sidewalls, and a large-section overall closed ring operation was performed.

8. The tunnel excavation method as described in claim 1, characterized in that, Before dividing the area above the tunnel floor slab into three sections—upper bench, middle bench, upper bench, middle bench, and upper bench five and middle bench six—and sequentially excavating these upper and middle benches using the bench method, and constructing the corresponding arch frames and central diaphragm walls, the following steps are included: Pre-grouting with small guide pipes was carried out in the tunnel arch to reinforce the strata.

9. The tunnel excavation method as described in claim 1, characterized in that, The excavation width of the No. 1 upper step, the No. 2 middle step, the No. 3 upper step, and the No. 4 middle step shall not exceed one-third of the tunnel width, while the excavation width of the No. 5 upper step and the No. 6 middle step shall not be less than one-third of the tunnel width.

10. The tunnel excavation method as described in claim 1, characterized in that, The excavation step distance for the No. 1 upper step, No. 2 middle step, No. 3 upper step, No. 4 middle step, No. 5 upper step and No. 6 middle step is L, 3m≤L≤5m. The distance between the invert arch of the No. 7, No. 8 and No. 9 lower steps and the secondary lining concrete does not exceed 15m.

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