A method for expanding a single tunnel

Abstract

The present invention discloses a method for expanding a single tunnel, comprising: providing initial support for a right guide tunnel of an expanded tunnel 3 along the outer side of an existing small-section tunnel 2, including initial support for a first arch wall section, initial support for a second arch wall section and initial support for a first invert arch section; dismantling a part of the structure of the small-section tunnel 2 inside the expanded tunnel 3; connecting the expanded tunnel 3 according to a design contour line of the expanded tunnel 3, using the lining structure of the existing tunnel as part of the reconstruction and expansion project and taking reasonable structural conversion and reinforcement measures, thereby reducing the amount of new support structure engineering, saving engineering costs, integrating the existing tunnel lining structure into the new tunnel system, and improving the stability and safety of the overall structure.

Description

Technical Field

[0001] The invention relates to the field of tunnel engineering, in particular to a method for expanding a single tunnel. Background Art

[0002] With the acceleration of urbanization and the continuous growth of traffic volume, many tunnels built in the early stage can no longer meet the current and future traffic demand due to their small cross-section and low grade. These tunnels are often limited by factors such as traffic conditions and project costs during the construction period, resulting in the failure to fully foresee future traffic growth during planning. Therefore, expanding the original road project (including tunnels on the route) has become an inevitable choice to ease traffic pressure and improve road traffic capacity.

[0003] At present, the practical projects of existing tunnel expansion are mostly in the following two situations: (1) Synchronous expansion of the original up and down tunnels: This method is suitable for the situation where both tunnels have traffic bottlenecks and the expansion space is relatively sufficient; (2) Expansion of a single tunnel: This method is suitable for the original tunnel is only a single-hole tunnel, which is expanded according to the traffic volume, and there is no problem of affecting the other tunnel. In recent years, there have also been practical cases in the engineering community where the expansion section is asymmetric and the left and right holes are small clearance tunnels. In this case, if only the small-section tunnel is expanded, the following problems will be faced: 1) The clearance between the two tunnels is small, the construction space for the expansion is limited, and the existing support measures for the expansion tunnel are easy to damage the support system of the existing large-section tunnel; 2) In the existing technology, the construction method of the expansion blasting operation will have a certain impact on the structure of the existing large-section tunnel; 3) The existing expansion method has many adverse effects on the surrounding environment and existing traffic.

[0004] Therefore, it is urgent to provide an improved single-hole tunnel expansion method to ensure the structural safety and normal operation of the existing tunnel during the expansion process. Summary of the invention

[0005] The present invention aims to provide a single-hole tunnel expansion method capable of solving the above-mentioned technical problems.

[0006] According to one aspect of the present invention, a method for expanding a single tunnel is provided, comprising: providing initial support for a right guide tunnel of an expanded tunnel 3 along the outer side of an existing small-section tunnel 2, including initial support for a first arch wall section, initial support for a second arch wall section, and initial support for a first invert arch section; dismantling a portion of the structure of the small-section tunnel 2 inside the expanded tunnel 3; and connecting the expanded tunnel 3 according to a designed contour line of the expanded tunnel 3.

[0007] Preferably, before constructing the right guide tunnel of the expansion tunnel 3, safety protection is implemented on the existing large-section tunnel 1 and the small-section tunnel 2, including: arranging a plurality of transverse steel arch frames at intervals along the inner wall of the large-section tunnel 1, and the spacing between two adjacent transverse steel arch frames along the longitudinal direction of the tunnel is 1m; burying a plurality of monitoring devices at the arch top and arch waist of the large-section tunnel 1 and the small-section tunnel 2 to monitor the deformation of the tunnel structure.

[0008] Preferably, excavating along the outer side of the small-section tunnel 2 to construct a right guide tunnel for the expanded tunnel 3 includes: determining the right guide tunnel located outside the small-section tunnel 2 according to the design contour line of the expanded tunnel 3; dividing the right guide tunnel into an upper right guide tunnel and a lower right guide tunnel according to the excavation sequence; excavating the upper right guide tunnel; and excavating the lower right guide tunnel.

[0009] Preferably, excavating the upper right guide tunnel includes: applying advance support along the arch contour line of the upper right guide tunnel; applying initial support for the first arch wall section as the excavation proceeds, including a first arch wall section system anchor rod, a first arch wall section steel arch frame, a first arch wall section shotcrete and a first arch wall section locking anchor rod, wherein: one end of the first arch wall section steel arch frame is supported on the arch of the small-section tunnel 2; the first arch wall section locking anchor rod is respectively located at both ends of the arch contour line of the upper right guide tunnel.

[0010] Preferably, excavating the lower right guide tunnel includes: excavating the lower right guide tunnel after excavating the upper right guide tunnel to a certain step distance; performing initial support for the second arch wall section and initial support for the first inverted arch section as the excavation is carried out, wherein the initial support for the second arch wall section includes a second arch wall section system anchor rod, a second arch wall section steel arch frame and second arch wall section sprayed concrete, and the initial support for the first inverted arch section includes a first inverted arch section steel arch frame, a first inverted arch section sprayed concrete and a first inverted arch section locking anchor rod located at both ends of the first inverted arch section.

[0011] Preferably, dismantling part of the structure of the small-section tunnel 2 inside the expansion tunnel 3 includes: dismantling part of the bottom plate of the small-section tunnel 2; providing initial support for the second inverted arch section of the expansion tunnel 3 along the bottom of the bottom plate of the small-section tunnel 2, wherein the second inverted arch section and the first inverted arch section are separated by a rock mass for supporting the small-section tunnel 2; providing temporary support for the small-section tunnel 2 and the right pilot tunnel; and dismantling part of the arch wall of the small-section tunnel 2.

[0012] Preferably, the temporary support includes: a plurality of first vertical steel arch frames, located in the right guide tunnel and tangent to the outer wall of the small-section tunnel 2, and connected at both ends to the initial support of the first arch wall section and the initial support of the first inverted arch section respectively; a plurality of second vertical steel arch frames, located in the small-section tunnel 2, with the upper ends connected to the intersection of the small-section tunnel 2 and the right guide tunnel, and the lower ends connected to the initial support of the second inverted arch section; the spacing between two adjacent first vertical steel arch frames and two adjacent second vertical steel arch frames along the longitudinal direction of the tunnel is 1m.

[0013] Preferably, dismantling part of the arch wall of the small-section tunnel 2 includes: dismantling the lining structure of the small-section tunnel 2 located between the first vertical steel arch frame and the second vertical steel arch frame; breaking the rock mass used to support the small-section tunnel 2; and constructing an inverted arch connecting section to connect the first inverted arch section and the second inverted arch section.

[0014] Preferably, according to the design outline of the expansion tunnel 3, connecting the expansion tunnel 3 includes: determining the cavity area according to the design outline of the expansion tunnel 3 and the undemolished structure of the small-section tunnel 2; filling the cavity area with concrete numbered C15-C20; and sequentially constructing the waterproof layer and secondary lining structure of the expansion tunnel 3.

[0015] Preferably, according to the design outline of the expansion tunnel 3, connecting the expansion tunnel 3 also includes: after filling the cavity area, removing the temporary support located in the small-section tunnel 2 and the right guide tunnel, including multiple first vertical steel arch frames and multiple second vertical steel arch frames. After completing the secondary lining structure of the proposed tunnel 3, remove the multiple transverse steel arch frames located in the large-section tunnel 1.

[0016] The present invention discloses a method for expanding a single tunnel, comprising: providing initial support for a right guide tunnel of an expanded tunnel 3 along the outer side of an existing small-section tunnel 2, including initial support for a first arch wall section, initial support for a second arch wall section and initial support for a first invert arch section; dismantling a part of the structure of the small-section tunnel 2 inside the expanded tunnel 3; connecting the expanded tunnel 3 according to a design contour line of the expanded tunnel 3, using the lining structure of the existing tunnel as part of the reconstruction and expansion project and taking reasonable structural conversion and reinforcement measures, thereby reducing the amount of new support structure engineering, saving engineering costs, integrating the existing tunnel lining structure into the new tunnel system, and improving the stability and safety of the overall structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] FIG1 is a schematic diagram of the expansion steps of a single tunnel expansion method according to an embodiment of the present invention;

[0019] Among them: 1. Large-section tunnel; 2. Small-section tunnel; 3. Expanded tunnel. DETAILED DESCRIPTION

[0020] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0021] Reference will now be made in detail to various embodiments of the present invention, examples of which are shown in the accompanying drawings and described below. For ease of interpretation and precise definition in the appended claims, the terms "upper", "lower", "inner" and "outer" are used to describe features of the exemplary embodiments shown in the drawings with reference to their positions.

[0022] Fig. 1 shows a schematic diagram of the expansion steps of a single-hole tunnel expansion method according to an embodiment of the present invention. The embodiment of the present invention provides a single-hole tunnel expansion method, as shown in Fig. 1, comprising: providing initial support for the right guide tunnel of the expansion tunnel 3 along the outer side of the existing small-section tunnel 2, including the initial support of the first arch wall section, the initial support of the second arch wall section and the initial support of the first invert arch section; dismantling part of the structure of the small-section tunnel 2 inside the expansion tunnel 3; and connecting the expansion tunnel 3 according to the design contour line of the expansion tunnel 3.

[0023] In the related art, in the expansion project of asymmetric small-clearance tunnels, the original tunnel is usually demolished first and then the new expansion tunnel is excavated, which leads to high construction risks and has a greater impact on the structure of the tunnel on the other side. The present invention adopts a method of "digging first and then demolishing + excavation in stages". First, the lining structure of the existing tunnel is used as part of the renovation and expansion project. Through reasonable structural conversion, the area that originally required large-span excavation is converted into multiple small-span excavation sections. Secondly, the renovation and expansion area is divided into multiple small-span excavation sections, and excavation is carried out one by one, which can effectively control the deformation and stress distribution during the excavation process and reduce the impact on the existing tunnel. Finally, while excavating the new tunnel space, the lining structure of the existing tunnel is kept intact. After the support of the newly excavated section is completed and reaches stability, the existing tunnel lining part in the expansion tunnel is gradually dismantled.

[0024] According to an embodiment of the present invention, before constructing the right guide tunnel of the expansion tunnel 3, safety protection is implemented on the existing large-section tunnel 1 and the small-section tunnel 2, including: a plurality of transverse steel arch frames are arranged at intervals along the inner wall of the large-section tunnel 1, and the spacing between two adjacent transverse steel arch frames along the longitudinal direction of the tunnel is 1m; a plurality of monitoring devices are buried at the arch top and arch waist of the large-section tunnel 1 and the small-section tunnel 2 to monitor the deformation of the tunnel structure.

[0025] The embodiment of the present invention, on the one hand, reinforces the structure of the existing tunnel by setting up temporary support for the existing tunnel, and on the other hand, sets up a monitoring device in the existing tunnel to monitor the stress condition of the existing tunnel in real time and determine the timing of subsequent demolition of the existing structure.

[0026] According to an embodiment of the present invention, excavating along the outer side of the small-section tunnel 2 to construct a right guide tunnel for the expanded tunnel 3 includes: determining the right guide tunnel located outside the small-section tunnel 2 according to the design contour line of the expanded tunnel 3; dividing the right guide tunnel into an upper right guide tunnel and a lower right guide tunnel according to an excavation sequence; excavating the upper right guide tunnel; and excavating the lower right guide tunnel.

[0027] According to an embodiment of the present invention, excavating the upper right guide tunnel includes: applying advance support along the arch contour line of the upper right guide tunnel; applying initial support of the first arch wall section as the excavation proceeds, including a first arch wall section system anchor rod, a first arch wall section steel arch frame, a first arch wall section shotcrete and a first arch wall section locking anchor rod, wherein: one end of the first arch wall section steel arch frame is supported on the arch of the small-section tunnel 2; the first arch wall section locking anchor rod is respectively located at both ends of the arch contour line of the upper right guide tunnel.

[0028] According to an embodiment of the present invention, excavating the lower right guide tunnel includes: excavating the lower right guide tunnel after excavating the upper right guide tunnel to a certain step distance; performing initial support for the second arch wall section and initial support for the first inverted arch section as the excavation is carried out, wherein the initial support for the second arch wall section includes a second arch wall section system anchor rod, a second arch wall section steel arch frame and second arch wall section sprayed concrete, and the initial support for the first inverted arch section includes a first inverted arch section steel arch frame, a first inverted arch section sprayed concrete and a first inverted arch section locking anchor rod located at both ends of the first inverted arch section.

[0029] The embodiment of the present invention reduces the difficulty and risk of excavation by converting large spans into small spans, reduces the impact of blasting operations on existing tunnels, and reduces construction risks. At the same time, the construction sequence of excavation in stages helps to speed up the construction progress, shorten the construction period, and reduce indirect costs.

[0030] According to an embodiment of the present invention, dismantling part of the structure of the small-section tunnel 2 inside the expansion tunnel 3 includes: dismantling part of the bottom plate of the small-section tunnel 2; providing initial support for the second inverted arch section of the expansion tunnel 3 along the bottom of the bottom plate of the small-section tunnel 2, wherein the second inverted arch section and the first inverted arch section are separated by a rock mass for supporting the small-section tunnel 2; providing temporary support for the small-section tunnel 2 and the right guide tunnel; and dismantling part of the arch wall of the small-section tunnel 2.

[0031] According to an embodiment of the present invention, the temporary support includes: a plurality of first vertical steel arch frames, which are located in the right guide tunnel and tangent to the outer wall of the small-section tunnel 2, and whose two ends are respectively connected to the initial support of the first arch wall section and the initial support of the first inverted arch section; a plurality of second vertical steel arch frames, which are located in the small-section tunnel 2, whose upper ends are connected to the intersection of the small-section tunnel 2 and the right guide tunnel, and whose lower ends are connected to the initial support of the second inverted arch section; the spacing between two adjacent first vertical steel arch frames and two adjacent second vertical steel arch frames along the longitudinal direction of the tunnel is 1m.

[0032] According to an embodiment of the present invention, dismantling part of the arch wall of the small-section tunnel 2 includes: dismantling the lining structure of the small-section tunnel 2 located between the first vertical steel arch frame and the second vertical steel arch frame; breaking the rock mass used to support the small-section tunnel 2; and constructing an inverted arch connecting section to connect the first inverted arch section and the second inverted arch section.

[0033] According to an embodiment of the present invention, based on the design outline of the expansion tunnel 3, connecting the expansion tunnel 3 includes: determining a cavity area based on the design outline of the expansion tunnel 3 and the undemolished structure of the small-section tunnel 2; filling the cavity area with concrete numbered C15-C20; and sequentially constructing a waterproof layer and a secondary lining structure of the expansion tunnel 3.

[0034] According to an embodiment of the present invention, according to the design outline of the expansion tunnel 3, connecting the expansion tunnel 3 further includes: after filling the cavity area, removing the temporary support located in the small-section tunnel 2 and the right guide tunnel, including multiple first vertical steel arch frames and multiple second vertical steel arch frames. After completing the secondary lining structure of the proposed tunnel 3, remove the multiple transverse steel arch frames located in the large-section tunnel 1.

[0035] The embodiment of the present invention utilizes the existing lining structure to reduce the amount of new support structure engineering and reduce the engineering cost. At the same time, through structural conversion and reinforcement measures, the existing structure is integrated into the new tunnel support system to achieve an organic combination of the old and new structures, thereby improving the engineering economy.

[0036] The following is a detailed description of the construction steps of the single tunnel expansion method in conjunction with Figure 1:

[0037] Ⅰ: Ⅰ-1, set up temporary steel arch frames with a spacing of 1m in the existing large-section tunnel 1 that is not to be rebuilt, and first reinforce the existing tunnel. Ⅰ-2, bury arch settlement and horizontal clearance convergence monitoring points in the large-section tunnel 1 and the existing small-section tunnel 2. The monitoring points are arranged at the tunnel arch and arch waist to monitor the deformation of the tunnel in real time, providing important data support for the conversion of the reconstruction and expansion process of the existing small-section tunnel 2.

[0038] Ⅱ: Ⅱ-1, construct the right upper pilot tunnel advance support along the outer side of the arch contour line of the planned expansion tunnel 3. Ⅱ-2, then excavate the rock mass. Ⅱ-3, timely implement the initial support (including system anchors, shotcrete, steel arch frame and locking anchors), among which the steel arch frame at the intersection with the small-section tunnel 2 is connected to the lining structure of the small-section tunnel 2 with a steel plate bottom support, and locking anchors are set to ensure its stability.

[0039] III: III-1, after the upper right pilot tunnel is excavated forward for a certain step, the rock mass of the lower right pilot tunnel is excavated. III-2, initial support is carried out in time.

[0040] IV: IV-1, remove the structural bottom plate inside the small-section tunnel 2. IV-2, excavate the bottom invert within the scope of the expansion tunnel 3, and promptly implement the initial support and locking anchor rods at the invert of the expansion tunnel 3. IV-3, temporarily retain the rock mass under the outer wall of the small-section tunnel 2.

[0041] V: Temporary vertical steel arch frames are set up along the outer wall of the lining of small-section tunnel 2 and below the intersection of the steel arch frame of expanded tunnel 3 and small-section tunnel 2, with a spacing of 1m to provide sufficient support to prevent tunnel deformation and collapse.

[0042] VI: According to the monitoring and measurement results, VI-1, choose a reasonable time to break the lining structure of the small-section tunnel 2 and the rock mass below the side wall that invades the expansion tunnel 3. VI-2, complete the initial support of the remaining parts of the invert arch, so that the initial support is closed into a ring.

[0043] VII: VII-1, pouring the invert and backfill layer of the expanded tunnel 3. VII-2, at the same time, the cavity between the left wall of the small-section tunnel 2 and the expanded tunnel 3 is filled with low-grade concrete.

[0044] VIII: Based on the monitoring and measurement results, the temporary vertical steel arch frame was removed and then a waterproof layer was laid in the expansion tunnel 3.

[0045] Ⅸ: Cast the secondary lining of the expanded tunnel 3 in sections and across the entire section. Choose a reasonable time to dismantle the temporary steel arch frame in the large-section tunnel 1 based on the monitoring and measurement data, and thus complete the expansion project of the small-section tunnel 2.

[0046] The technical effects of the present invention are as follows:

[0047] (1) Significantly improve traffic capacity: By renovating and expanding the existing asymmetric small-clearance tunnel into a single tunnel, the tunnel's traffic section is significantly increased, effectively alleviating traffic pressure and improving road traffic capacity.

[0048] (2) Efficient use of existing structures: By using the existing tunnel lining structure as part of the renovation and expansion project, the maximum utilization of resources is achieved, the amount of new support structure engineering is reduced, and the project cost is saved.

[0049] (3) Reduce construction risks and shorten construction period: The area that originally required large-span excavation was converted into multiple small-span excavation sections, and phased excavation was adopted to effectively control the deformation and stress distribution during the excavation process, reduce the impact of blasting operations on existing tunnels, and reduce construction difficulty and risks. Phased excavation and the construction sequence of excavation first and demolition later accelerated the construction progress, shortened the construction period, and reduced indirect costs.

[0050] (4) Improving structural safety performance: Through reasonable structural conversion and reinforcement measures, the existing tunnel lining structure is integrated into the new tunnel system, achieving an organic combination of the old and new structures and improving the stability and safety of the overall structure.

[0051] (5) Reduce environmental impact: The construction process has little impact on the surrounding environment and existing traffic, which is in line with the current concept and requirements of sustainable development and is conducive to protecting the ecological environment and reducing social impact.

[0052] The above embodiments are only examples for clearly explaining the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications may be made based on the following description, and these various changes, modifications, substitutions and deformations derived from the principles and spirit of the present invention still fall within the scope of protection of the present invention.

Claims

1. A method for expanding a single tunnel, characterized in that: include: Performing initial support for the right guide tunnel of the expanded tunnel (3) along the outer side of the existing small-section tunnel (2), including initial support for the first arch wall section, initial support for the second arch wall section and initial support for the first invert arch section; Dismantling a portion of the structure of the small-section tunnel (2) inside the expanded tunnel (3) comprises: Removing part of the bottom plate of the small-section tunnel (2); Initial support of a second inverted arch section of the expanded tunnel (3) is provided along the bottom of the bottom plate of the small-section tunnel (2), wherein a rock mass for supporting the small-section tunnel (2) is provided between the second inverted arch section and the first inverted arch section; Temporary support is applied to the small-section tunnel (2) and the right guide tunnel, wherein the temporary support comprises: a plurality of first vertical steel arch frames, located in the right guide tunnel and tangent to the outer wall of the small-section tunnel (2), and having two ends connected to the first arch wall section initial support and the first invert arch section initial support respectively; a plurality of second vertical steel arch frames, located in the small-section tunnel (2), having an upper end connected to the intersection of the small-section tunnel (2) and the right guide tunnel, and a lower end connected to the second invert arch section initial support; the spacing between two adjacent first vertical steel arch frames and two adjacent second vertical steel arch frames along the longitudinal direction of the tunnel is 1 m; Removing part of the arch wall of the small-section tunnel (2), comprising: removing the lining structure of the small-section tunnel (2) between the first vertical steel arch frame and the second vertical steel arch frame; breaking the rock mass used to support the small-section tunnel (2); constructing an inverted arch connection section to connect the first inverted arch section and the second inverted arch section; The expanded tunnel (3) is connected according to the design outline of the expanded tunnel (3).

2. The single tunnel expansion method according to claim 1, characterized in that: Before constructing the right guide tunnel of the expansion tunnel (3), safety protection is provided to the existing large-section tunnel (1) and the small-section tunnel (2), including: A plurality of transverse steel arch frames are arranged at intervals along the inner wall of the large-section tunnel (1), and the distance between two adjacent transverse steel arch frames along the longitudinal direction of the tunnel is 1 m; A plurality of monitoring devices are buried at the arch top and arch waist of the large-section tunnel (1) and the small-section tunnel (2) to monitor the deformation of the tunnel structure.

3. The single tunnel expansion method according to claim 1, characterized in that: Excavating along the outer side of the small-section tunnel (2) to construct the right guide tunnel of the expanded tunnel (3) includes: According to the design outline of the expanded tunnel (3), determining the right guide tunnel located outside the small-section tunnel (2); According to the excavation sequence, the right pilot tunnel is divided into a right upper pilot tunnel and a right lower pilot tunnel; Excavating the upper right pilot tunnel; Excavate the lower right pilot tunnel.

4. The single tunnel expansion method according to claim 3, characterized in that: Excavating the upper right guide tunnel includes: Perform advance support along the arch contour line of the upper right pilot tunnel; The initial support of the first arch wall section is implemented as the excavation progresses, including the first arch wall section system anchor rod, the first arch wall section steel arch frame, the first arch wall section shotcrete and the first arch wall section locking anchor rod, wherein: One end of the first arch wall section steel arch frame is supported on the arch portion of the small-section tunnel (2); The first arch wall section locking anchor rods are respectively located at two ends of the arch contour line of the upper right guide hole.

5. The single tunnel expansion method according to claim 3, characterized in that: Excavating the lower right pilot tunnel includes: After the upper right pilot tunnel is excavated to a certain step distance, the lower right pilot tunnel is excavated; The initial support of the second arch wall section and the initial support of the first inverted arch section are implemented simultaneously with the excavation, wherein the initial support of the second arch wall section includes the second arch wall section system anchor rods, the second arch wall section steel arch frame and the second arch wall section shotcrete, and the initial support of the first inverted arch section includes the first inverted arch section steel arch frame, the first inverted arch section shotcrete and the first inverted arch section locking anchor rods located at both ends of the first inverted arch section.

6. The single tunnel expansion method according to claim 2, characterized in that: According to the design outline of the expansion tunnel (3), connecting the expansion tunnel (3) comprises: Determining the cavity area according to the design outline of the expanded tunnel (3) and the undemolished structure of the small-section tunnel (2); Filling the cavity area with concrete labeled C15-C20; The waterproof layer and the secondary lining structure of the expanded tunnel (3) are sequentially constructed.

7. The single-hole tunnel expansion method according to claim 6, characterized in that: According to the design outline of the expansion tunnel (3), connecting the expansion tunnel (3) also includes: After filling the cavity area, removing temporary supports located in the small-section tunnel (2) and the right guide tunnel, including a plurality of first vertical steel arch frames and a plurality of second vertical steel arch frames; After the secondary lining structure of the expanded tunnel (3) is completed, a plurality of transverse steel arch frames located in the large-section tunnel (1) are removed.

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