Tunnel support structures, tunnels, and tunnel construction methods

Abstract

We propose a tunnel support structure and tunnel construction method that can suppress axial displacement with a relatively simple configuration. [Solution] A tunnel T is formed by an excavation process to excavate the ground and a support process to close the ground surface exposed by the excavation of the ground with a tunnel support structure. The tunnel support structure comprises sprayed concrete sprayed onto the ground surface exposed by the excavation of the tunnel T, and a plurality of steel supports provided at predetermined intervals along the axial direction of the tunnel T. Adjacent steel supports are fixed to each other via linear members.

Description

Technical Field

[0004] , , , ,

[0005] , , ,

[0003] , , , ,

[0001] The present invention relates to a tunnel support structure for mountain tunnels, tunnels, and tunnel construction methods.

Background Art

[0002] In the construction of mountain tunnels such as NATM, after the ground surface exposed by excavation is closed with a support work combined with shotcrete, steel support work, and rock bolts, etc., a covering concrete with a predetermined thickness is placed on the inner space side of the support work. This is common. The steel support work is installed at predetermined intervals in the tunnel axis direction. When erecting the steel support work, a connecting member is horizontally installed between the adjacent existing steel support works for the purpose of preventing the steel support work from falling and positioning. As such a connecting member, for example, as shown in Patent Document 1, a steel bar formed with hooks at both ends is generally used. This connecting member is horizontally installed between the steel support works by inserting the hooks into the sheath pipes fixed in advance to the steel support works.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The covering concrete generally receives the displacement (loosening of the ground) of the ground that occurs immediately after the excavation of the ground by the support work and is placed after the ground is stabilized. The structure of the support work is determined in advance according to the assumed ground grade, and auxiliary construction methods are adopted as necessary for sections where a crushed zone, etc. is assumed.

[0005] When tunnels such as pilot tunnels are widened, the surrounding ground loosens and is pushed towards the widened section, resulting in tensile forces acting on the tunnel walls and potentially causing cracks. In addition, tunnels may contain locally weak ground. In sections with locally weak ground, axial displacement differences occur in the tunnel, which can cause shear forces to act on the shotcrete, potentially leading to cracks. On the other hand, it is difficult to identify locally weak ground even with prior investigations, so it may not be possible to prepare countermeasures such as auxiliary construction methods in advance for locally weak ground.

[0006] The present invention aims to propose a tunnel support structure, a tunnel, and a tunnel construction method that can suppress axial displacement with a relatively simple configuration. [Means for solving the problem]

[0007] The tunnel support structure of the present invention, which solves the aforementioned problems, comprises sprayed concrete applied to the ground surface exposed by tunnel excavation, and a plurality of steel supports provided at predetermined intervals along the axial direction of the tunnel. Adjacent steel supports are fixed to each other via linear members. The linear members are provided separately from connecting members horizontally installed between adjacent steel supports. The linear members may be steel materials (e.g., steel plates) welded to the internal flanges of the steel supports, or shaped steel welded to the steel supports.

[0008] Furthermore, the tunnel of the present invention comprises an advanced pilot tunnel supported by a pilot tunnel support structure and a main tunnel supported by a main tunnel support structure. The pilot tunnel support structure comprises sprayed concrete sprayed onto the exposed ground surface due to the excavation of the advanced pilot tunnel, a plurality of steel support structures for the pilot tunnel provided at intervals in the axial direction of the advanced pilot tunnel, and linear members for the pilot tunnel that connect adjacent steel support structures for the pilot tunnel. The main tunnel support structure comprises sprayed concrete sprayed onto the exposed ground surface due to the excavation of the main tunnel, a plurality of steel support structures for the main tunnel provided at intervals in the axial direction of the main tunnel, and linear members for the main tunnel that connect adjacent steel support structures for the main tunnel. The linear members for the pilot tunnel may be steel plates welded to the internal flanges of the steel support structures for the pilot tunnel. Furthermore, the linear members for the main tunnel may be shaped steel welded to the ground-side flange of the steel support structure for the pilot tunnel. In addition, connecting members may be horizontally installed between adjacent steel support structures for the main tunnel, separate from the linear members for the main tunnel.

[0009] Furthermore, the tunnel construction method of the present invention forms a tunnel by an excavation step of excavating the ground and a support step of closing the ground surface exposed by the excavation of the ground with support structures. The support structure comprises sprayed concrete sprayed onto the ground surface and a plurality of steel support structures provided at predetermined intervals. In the support step, a support structure installation work is performed in which a new steel support structure is erected on the face side of an existing steel support structure, and a linear member fixing work is performed in which linear members are welded to the existing steel support structure and the new steel support structure to fix the new steel support structure to the existing steel support structure.

[0010] With this support structure, tunnel, and tunnel construction method, axial displacement can be suppressed because the steel supports arranged at the front and rear are fixed to each other by linear members. Furthermore, even if there are locally weak ground, settlement of the legs of the steel supports can be suppressed, and the difference in axial displacement (increase in the distance between the front and rear steel supports) can be suppressed. As a result, shear strain occurring in the shotcrete can also be suppressed.

[0011] Furthermore, if the tunnel is a so-called pilot tunnel, a second excavation process is carried out to excavate the ground surrounding the tunnel, and a second support process is carried out to close the ground surface exposed by the excavation in the second excavation process with a second support structure, thereby constructing a widened tunnel (for example, the main tunnel). With this tunnel construction method, even if ground extrusion (loosening of the ground ahead) occurs at the face of the tunnel during ground excavation in the second excavation process, the axial displacement caused by the ground extrusion displacement can be suppressed because the steel support structures arranged before and after are fixed to each other by linear members.

[0012] If the second support structure comprises a second sprayed concrete applied to the ground surface and a plurality of second steel supports installed at predetermined intervals, the second support process includes a second support structure installation operation in which a new second steel support structure is erected on the face side of an existing second steel support structure, and a second linear member fixing operation in which a second linear member is welded to the existing second steel support structure and the new second steel support structure to fix the new second steel support structure to the existing second steel support structure. In addition, in the linear member fixing operation, the linear member made of steel plate may be welded to the surface of the internal flange of the existing steel support structure and the surface of the internal flange of the new steel support structure. Furthermore, in the second linear member fixing work, the second linear member made of shaped steel may be welded to the inner surface of the ground-side flange of the existing second steel support structure and to the inner surface of the ground-side flange of the newly installed steel support structure. [Effects of the Invention]

[0013] According to the tunnel support structure, tunnel, and tunnel construction method of the present invention, it is possible to suppress shear strain occurring in shotcrete by suppressing the difference in axial displacement with a relatively simple configuration. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view showing the tunnel support structure of this embodiment. [Figure 2] This flowchart shows the procedure for the tunnel construction method according to this embodiment. [Figure 3] (a) is a cross-sectional view showing the pilot tunnel excavation process, (b) is a cross-sectional view showing the pilot tunnel support process, (c) is a cross-sectional view showing the pilot tunnel invert construction process, and (d) is a cross-sectional view showing the pilot tunnel invert construction process following (c). [Figure 4] This is a front view of the tunnel support structure for the pilot tunnel. [Figure 5] (a) is a cross-sectional view showing the main tunnel excavation process, (b) is a cross-sectional view of the main tunnel excavation process following (a), and (c) is a cross-sectional view showing the main tunnel support process. [Figure 6] This diagram shows reinforcing steel members, with (a) being a side view and (b) being a top view. [Figure 7] This is a cross-sectional view showing the construction process of the main tunnel invert, where (a) is during invert excavation and (b) is during support structure construction. [Figure 8] (a) and (b) are side views illustrating other methods of fixing the linear member, respectively. [Modes for carrying out the invention]

[0015] This embodiment describes the case in which a tunnel T is constructed using a mountain tunneling method such as NATM. In the mountain tunneling method, a tunnel T of a predetermined length is formed by repeatedly excavating the ground G to advance the face K (the leading edge of the tunnel T) and closing the ground G exposed by the excavation of the tunnel T with support structures. Figure 1 shows a cross-sectional view of the tunnel T. As shown in Figure 1, this embodiment describes the case in which an advance pilot tunnel T1 is formed, and then the area around the advance pilot tunnel Td is widened to form the main tunnel Th (tunnel T).

[0016] Hereinafter, the tunnel construction method of this embodiment will be described. The procedure of the tunnel construction method is shown in FIG. 2. As shown in FIG. 2, the tunnel construction method includes an adit excavation step S1, an adit support step S2, an adit invert construction step S3, a main tunnel excavation step S4 (second excavation step), a main tunnel support step S5 (second support step), and a main tunnel invert construction step S6. FIG. 3 shows the adit excavation step S1 to the adit invert construction step S3.

[0017] In the adit excavation step S1, the ground G (Gd) in front of the face K is excavated. As shown in FIG. 1, in this embodiment, an advanced adit Td with a circular cross-section is formed at the central part of the cross-section of the main tunnel Th (tunnel T). Note that the cross-sectional shape of the advanced adit Td in this embodiment is circular, but the cross-sectional shape of the advanced adit Td is not limited and may be, for example, horseshoe-shaped. As shown in FIG. 3(a), in the adit excavation step S1 of this embodiment, the part other than the adit invert Id (the shaded part in FIG. 3(a)) is excavated by full-face excavation.

[0018] In the adit support step S2, the ground surface exposed by the excavation of the ground G is closed by the tunnel support structure 2 for the adit. FIG. 4 shows the tunnel support structure 2 for the adit. As shown in FIGS. 3(b) and 4, the tunnel support structure 2 for the adit includes sprayed concrete 21 sprayed on the ground surface exposed by the excavation of the ground G, a plurality of steel support members 22 for the adit provided at predetermined intervals along the axial direction of the tunnel T, and a plurality of reinforcing plates 23 (linear members) connecting adjacent steel support members 22 for the adit.

[0019] In the pilot tunnel support work S2, together with the spraying operation S21 of spraying the shotcrete 21 on the natural ground surface, as shown in Fig. 3(b), a support construction operation S22 is carried out to build a newly installed steel support 222 for the pilot tunnel on the face side of the existing steel support 221 for the pilot tunnel, which is the existing steel support 22 for the pilot tunnel. The steel support 22 for the pilot tunnel is formed by processing section steel such as H-shaped steel. The steel support 22 for the pilot tunnel is formed in an arch shape by combining a plurality of members. Note that the spraying operation S21 may be carried out before (primary spraying) and after (secondary spraying) the construction of the steel support 22 for the pilot tunnel to ensure a predetermined thickness by spraying, or may be sprayed with a predetermined thickness before or after the construction of the steel support 22 for the pilot tunnel.

[0020] In this embodiment, after repeating the pilot tunnel excavation process S1 and the pilot tunnel support process S2 six times and building six sets of steel supports 22 for the pilot tunnel, these steel supports 22 for the pilot tunnel are connected by a reinforcing plate 23 (linear member fixing operation). The reinforcing plate 23 of this embodiment is made of a steel plate having a length of 6 m (arrangement pitch of the steel support for the pilot tunnel × 6), and connects seven sets of steel supports 22 for the pilot tunnel, including the existing steel support 22 for the pilot tunnel provided on the most face side of the six newly installed sets of steel supports 22 for the pilot tunnel. As shown in Fig. 4, the reinforcing plate 23 is welded to the flange surface on the inner cavity side of the steel support 22 for the pilot tunnel at four locations in two upper and lower stages (a total of four locations) of the leg and shoulder on the left and right.

[0021] Note that the length and installation timing of the reinforcing plate 23 are not limited. For example, when the arrangement pitch of the steel support 22 for the pilot tunnel is 1 m and the reinforcing plate 23 is installed every time a steel support for the pilot tunnel is built, the length of the reinforcing plate 23 may be set to 1 m to connect the existing steel support 221 for the pilot tunnel and the newly installed steel support 222 for the pilot tunnel. Also, when the reinforcing plate 23 is fixed at the stage when five sets of steel supports 22 for the pilot tunnel are built with an arrangement pitch of 1.2 m, the reinforcing plate may be 6 m. Furthermore, the timing of installing the reinforcing plate 23 is not limited to before the start of the main tunnel excavation process S4; for example, it may be installed all at once along the entire length of the pilot tunnel Td after the construction of the pilot tunnel Td.

[0022] In the pilot tunnel invert construction process S3, as shown in Figure 3(c), first, the pilot tunnel invert Id is excavated behind the face of the advanced pilot tunnel T1 (for example, 3 m behind the face). In this embodiment, the invert excavation is carried out so that the cross-sectional shape of the advanced pilot tunnel T1 becomes circular. Next, sprayed concrete is sprayed onto the exposed ground surface due to the invert excavation, and steel support structures for the pilot tunnel invert are installed to form the pilot tunnel invert support structure 24. The steel support structure for the pilot tunnel invert consists of steel materials processed into an arc shape (for example, H-beams), and is connected to the steel support structure for the pilot tunnel 22 to form a support structure that is circular in front view. Once the pilot tunnel invert support structure 24 is formed, the pilot tunnel invert Id is backfilled.

[0023] In the main tunnel excavation process S4, the ground surrounding the pilot tunnel T1 is excavated and widened to achieve a predetermined cross-sectional shape. Figures 5(a) and (b) show the main tunnel excavation process S4. As shown in Figure 5(a), in the main tunnel excavation process S4, first, the steel support structure 22 and reinforcing plates 23 for the pilot tunnel T1 in the section corresponding to one construction cycle are removed. Next, temporary shotcrete is applied to the removed portion of the steel support structure 22 to suppress ground collapse. After that, as shown in Figure 5(b), the ground Gh surrounding the pilot tunnel T1 is excavated and widened. The excavation of the ground Gh may be done by blasting or by mechanical means.

[0024] In the main tunnel support process S5, as shown in Figure 5(c), the exposed ground surface Gh due to excavation in the main tunnel support process S5 is closed off by the main tunnel support structure 1. The main tunnel support structure 1 comprises sprayed concrete 11 applied to the ground surface, a plurality of main tunnel steel supports 12 provided at predetermined intervals, reinforcing steel members (linear members) 13 (see Figure 6) connecting adjacent main tunnel steel supports 12, and connecting members 14 (see Figure 6) horizontally installed between adjacent main tunnel steel supports 12.

[0025] In the main tunnel support process S5, first, a new steel support structure 122 is erected on the face side of the existing steel support structure 121, which is the existing steel support structure 12 for the main tunnel (support structure erection work). The steel support structure 12 for the main tunnel is formed by processing shaped steel (for example, H-shaped steel), and the erected steel support structure 12 for the main tunnel has an arch shape. In the support structure erection work, connecting members 14 are horizontally placed between the steel support structures 12 for the main tunnel. Figure 6 shows the connecting members 14 and reinforcing steel members 13. As shown in Figure 6, the connecting members 14 consist of steel rods with hooks formed at their ends, and the steel support structures 12 for the main tunnel are connected by engaging the hooks with sheath pipes 15 that are fixed to the steel support structures in advance.

[0026] Next, reinforcing steel members 13 (linear members) are welded to the existing steel support structure 121 and the new steel support structure 122 to fix the new steel support structure 122 to the existing steel support structure 121 (linear member fixing work). The reinforcing steel members 13 are made of L-shaped steel (equal-sided angle steel), and their ends are welded to the inner surface (internal surface) of the ground-side flange 12f of the main shaft steel support structure 12. The axial stiffness and bending stiffness of the reinforcing steel members 13 are both greater than those of the connecting members 14.

[0027] Figure 7 shows the main tunnel invert construction process S6. In the main tunnel invert construction process S6, as shown in Figure 7(a), first, the invert Ih is excavated behind the face of the main tunnel (tunnel T) which has been excavated to a predetermined length (for example, 3m behind the face). As the invert is excavated, the pilot tunnel invert support structure 24 is removed. Next, as shown in Figure 7(b), sprayed concrete is applied to the exposed ground surface due to the invert excavation, and steel support structures 16 for the invert are installed to form the invert support structure. The steel support structures 16 for the invert are formed by processing steel materials (for example, H-shaped steel), and a continuous support structure is formed by connecting them to the legs of the steel support structures 12 for the main tunnel. Once the invert support structure is formed, the invert Ih is backfilled.

[0028] According to the tunnel support structure and tunnel construction method of this embodiment, the steel supports (pilot tunnel steel supports 22 or main tunnel steel supports 12) arranged at the front and rear are fixed to each other by linear members (reinforcement plates 23 for the pilot tunnel and reinforcement steel members 13 for the main tunnel), thus suppressing axial displacement. Furthermore, even if there are locally weak ground, the settlement of the legs of the steel supports is suppressed, and the difference in axial displacement (increase in the distance between the front and rear steel supports) can be suppressed. As a result, shear strain occurring in the shotcrete can also be suppressed.

[0029] Furthermore, even if ground extrusion (loosening of the ground ahead) occurs at the tunnel face during ground excavation in the main tunnel excavation process, the axial displacement caused by the ground extrusion displacement can be suppressed because the steel supports arranged before and after are fixed to each other by linear members. When widening the pilot tunnel Td during main tunnel excavation, ground extrusion (loosening of the ground ahead) may occur, causing axial displacement towards the tunnel entrance, and tensile force acting in the axial direction of the tunnel may cause circumferential cracks in the pilot tunnel Td. In contrast, in the tunnel support structure of this embodiment, since the steel supports are fixed to each other by linear members within the pilot tunnel Td, the occurrence of circumferential cracks within the pilot tunnel Td can be suppressed by resisting tensile force in the direction of the tunnel entrance. Since the reinforcing steel members 13 are installed on the outside (ground side) of the internal flange 12f of the steel support structure 12 for the main tunnel, the internal cross-section of the tunnel T is not reduced by the reinforcing steel members 13.

[0030] In sections where locally weak ground is distributed, if there is a difference in axial displacement between the left and right sides, the shear force acting on the shotcrete may cause cracks. However, in the tunnel support structure of this embodiment, since the steel support structures are connected by linear members, integrity is ensured, the difference in axial displacement between the left and right sides is suppressed, and shear cracks that occur in the shotcrete can be suppressed. In addition, since the linear members (reinforcement plates 23) are fixed to the pilot tunnel steel support structure 22 of the pilot tunnel Td, loosening of the ground ahead is suppressed, and the amount of displacement during main tunnel excavation is reduced. The pilot tunnel T1 allows for an understanding of the geological structure, aquifer, and fragile layers before proceeding with the construction of the main tunnel, and also ensures stability before proceeding with the construction of the main tunnel Th.

[0031] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and each of the above-mentioned components can be modified as appropriate without departing from the spirit of the present invention. The main tunnel support structure 1 may include rock bolts as needed, and auxiliary methods such as pre-support methods (e.g., forepoling or pipe roofing) or ground improvement methods may also be employed.

[0032] Furthermore, in the above embodiment, the pilot tunnel Td is widened to construct the main tunnel Th. However, for example, the pilot tunnel Td may be widened to construct a second pilot tunnel before constructing the main tunnel Th, or the number of pilot tunnels Td may be increased depending on the ground conditions.

[0033] In the above embodiment, the case in which the reinforcing steel member 13 (linear member) is welded to the flange 12f of the main tunnel steel support structure 12 was described, but the reinforcing steel member 13 may also be welded to the web 12w of the main tunnel steel support structure 12. Alternatively, the reinforcing steel member 13 may be bolted to the main tunnel steel support structure 12. When bolting the reinforcing steel member 13 to the main tunnel steel support structure 12, as shown in Figure 8(a), a support member 17 made of L-shaped steel or the like is fixed to the main tunnel steel support structure 12, and the reinforcing steel member 13 is bolted to this support member 17. Alternatively, as shown in Figure 8(b), the reinforcing steel member 13 may be fixed to the flange 12f and web 12w using an auxiliary member 18 such as a round steel fixed to the corner of the flange 12f and web 12w of the main tunnel steel support structure 12.

[0034] In the above embodiment, reinforcing plates 23 were used as linear members in the pilot tunnel support structure 2, and reinforcing steel material 13 (L-shaped steel) was used in the main tunnel support structure. However, the materials constituting the linear members are not limited. For example, L-shaped steel or other steel materials may be used as linear members in the pilot tunnel support structure 2. In addition to steel plates and shaped steel materials, steel pipes and the like may also be used as linear members. [Explanation of Symbols]

[0035] 1. Main tunnel support structure 11. Sprayed concrete 12 Steel shoring for main shaft (steel shoring) 13. Reinforcing steel (linear members) 14. Connecting material 2. Tunnel support structure for pilot tunnels 21. Sprayed concrete 22 Steel shoring for shafts (steel shoring) 23. Reinforcement plate (linear member) G Ground T Tunnel Td advanced shaft Th main shaft

Claims

1. The sprayed concrete applied to the exposed ground surface due to tunnel excavation, A tunnel support structure comprising a plurality of steel support structures provided at intervals in the axial direction of the tunnel, A tunnel support structure characterized in that adjacent steel support structures are fixed to each other via linear members.

2. The tunnel support structure according to claim 1, characterized in that a connecting member is horizontally installed between adjacent steel support structures, separate from the linear member.

3. The tunnel support structure according to claim 1, characterized in that the linear member is a steel material welded to the inner flange of the steel support structure.

4. The tunnel support structure according to claim 1, characterized in that the linear member is a shaped steel welded to the steel support structure.

5. A tunnel consisting of an advanced pilot tunnel supported by a tunnel support structure for pilot tunnels, and a main tunnel supported by a tunnel support structure for main tunnels, The aforementioned tunnel support structure for the pilot tunnel is, The sprayed concrete applied to the exposed ground surface due to the excavation of the aforementioned pilot tunnel, Multiple steel support structures for the pilot tunnel are provided at intervals in the axial direction of the aforementioned pilot tunnel, It comprises a linear member for an advanced pilot tunnel that connects adjacent steel support structures for pilot tunnels, The aforementioned tunnel support structure for the main tunnel is, The sprayed concrete applied to the exposed ground surface due to the excavation of the aforementioned main tunnel, Multiple steel support structures for the main tunnel are provided at intervals in the axial direction of the main tunnel, A tunnel characterized by comprising a linear member for the main tunnel that connects adjacent steel support structures for the main tunnel.

6. The linear member for the pilot tunnel is a steel plate welded to the inner flange surface of the steel support structure for the pilot tunnel. The tunnel according to claim 5, characterized in that the linear member for the main tunnel is a shaped steel welded to the inner surface of the ground-side flange of the steel support structure for the pilot tunnel.

7. The tunnel according to claim 5, characterized in that a connecting member is horizontally installed between adjacent steel support structures for the main tunnel, separate from the linear members for the main tunnel.

8. The excavation process involves excavating the natural ground, A tunnel construction method comprising a support process in which the exposed ground surface due to excavation of the ground is closed off with support structures, and a tunnel formed by these processes, The aforementioned support structure comprises sprayed concrete applied to the ground surface and a plurality of steel support structures installed at predetermined intervals. In the aforementioned support process, The scaffolding construction work involves erecting new steel scaffolding on the face side of existing steel scaffolding, and A tunnel construction method characterized by performing a linear member fixing operation, in which linear members are welded to the existing steel support structure and the new steel support structure to fix the new steel support structure to the existing steel support structure.

9. A second excavation process involves excavating the surrounding ground of the tunnel, The tunnel construction method according to claim 8, further comprising a second support step of closing the ground surface exposed by the excavation of the ground in the second excavation step with a second support structure.

10. The aforementioned second support structure comprises a second sprayed concrete applied to the ground surface and a plurality of second steel support structures installed at predetermined intervals. In the second support process, The second steel support construction work involves erecting a new second steel support structure on the face side of the existing second steel support structure, and The tunnel construction method according to claim 9, characterized by performing a second linear member fixing operation, in which a second linear member is welded to the existing second steel support structure and the newly constructed second steel support structure to fix the newly constructed second steel support structure to the existing second steel support structure.

11. In the linear member fixing operation, the linear member made of steel plate is welded to the surface of the inner flange of the existing steel support structure and the surface of the inner flange of the newly installed steel support structure. The tunnel construction method according to claim 10, characterized in that, in the second linear member fixing work, the second linear member made of shaped steel is welded to the inner surface of the ground-side flange of the existing second steel support and the inner surface of the ground-side flange of the newly installed steel support.

Images