JP5382432B2 - Excavation method of adjacent twin tunnel - Google Patents

Description

  The present invention relates to a method for excavating a proximity twin tunnel.

  Conventionally, a full section construction method with an auxiliary bench is known as a method for excavation of a mountain tunnel in a natural ground of a geologically poor part (see, for example, Patent Document 1). When early closing is used in combination with such an all-section method with an auxiliary bench, the distance from the face of the upper half section to the section closing by invert is, for example, about 6 to 7 m. This is a tunnel excavation method that can secure the mechanical stability of the tunnel support structure by closing.

  By the way, the mountain tunnel is the basis for the independence of the surrounding ground to ensure the stability of the tunnel, and the tunnel support structure is constructed by natural ground reinforcement within the range of about 0.3D (D: excavation width) from the excavation surface. The mechanical stability of is secured. In the case of a double-adjacent tunnel such as a two-lane road with a distance of about 6 m or less, the effect of the double-appearance appears in the tunnel support structure. In addition, improvement of injection and improvement of strength of the support structure of the preceding tunnel are performed.

The above-mentioned prior injection improvement in the natural area of the pillar part is performed in advance with respect to the natural area of the pillar part when the earth pressure acting from above and below exceeds the strength of the natural area of the pillar part. Improvements that are injected from the ground surface are common, and this is a method for ensuring the mechanical stability of the supporting structure of the adjacent twin tunnel.
In addition, when the strength of the supporting structure of the preceding tunnel is increased, the preceding tunnel is affected by the excavation of the succeeding tunnel, so the supporting structure of the preceding tunnel should have a higher strength specification than that of the succeeding tunnel. Adopting it ensures mechanical stability.

JP 2007-32490 A

However, in dealing with the influence of double installation in the conventional proximity double tunnel, there are the following problems.
In other words, in the case of making an improvement to inject in advance to the natural ground in the pillar part between tunnels, the injection work from the ground surface will be large and the excavation of the tunnel will be restricted by this improvement. There was a problem that the construction cost increased.
In addition, when the strength of the supporting structure of the preceding tunnel is increased, the cost of the members accompanying the increase in the strength is increased. In this method, when excavation of the trailing tunnel, the passive earth pressure on the side of the construction tunnel is unloaded, so when the preceding tunnel is constructed, repeated earth pressure of unloading and loading is received. The peak strength decreases and becomes plastic, which is not preferable from the viewpoint of ensuring long-term stability. In addition, since the support rigidity of the upstream and downstream tunnels is different, there is a problem that it is disadvantageous against external forces such as seismic force.
As described above, there is a need for a rational construction method that can secure the long-term stability of the adjacent double tunnel as well as shortening the construction period and the construction cost, and there is room for improvement in that respect. .

  The present invention has been made in view of the above-described problems, and can stabilize itself without performing injection improvement from the ground surface with respect to the ground of the pillar portion between adjacent tunnels, and the construction period and construction cost An object of the present invention is to provide a method for excavating a proximity double tunnel capable of reducing the above-mentioned.

  In order to achieve the above object, the excavation method for adjacent double tunnels according to the present invention is an excavation method for adjacent double tunnels in which the difference in the face position between adjacent tunnels is within 4 m in the tunnel axis direction. In tunnel excavation, a method of constructing a prior injection improvement by placing a short driven hollow bolt in advance in the ground of the pillar portion between adjacent tunnels, and smooth blasting within a predetermined range in contact with the pillar portion It is characterized by excavating by selecting the method to be performed by blasting by the Sting method according to the condition of the natural ground in the pillar part.

  In the present invention, when the pillar part between adjacent tunnels is a poor geological part, a short driving-type hollow bolt is placed in the pillar part to inject the rock consolidation agent. Drilling is performed by reinforcing the mountain, and when the pillar part is a hard rock part, blasting in a predetermined range in contact with the pillar part can be excavated by blasting by a smooth blasting method. As a result, the adjacent twin tunnel can be excavated while ensuring the soundness and independence of the natural ground in the pillar portion.

  In addition, by adopting a full-section excavation method with an auxiliary bench that can be closed early for excavation of each tunnel that constitutes a close-adjacent tunnel, it is possible to proceed simultaneously while keeping the difference in the face position of adjacent tunnels within 3 m. Can do. Therefore, the support structure of both tunnels can form a symmetrical structure that is advantageous in terms of mechanical stability in the three-dimensional stress field around the face, and the ground on the side of the pillar is A new stable field can be formed in the ground arch including both tunnels by a single stress redistribution while being restrained by the supporting structure and maintaining the triaxial stress field. Therefore, when one of the preceding tunnels excavates the other succeeding tunnel, the side passive pressure of the preceding tunnel is unloaded, and the influence of lowering the ground strength and plasticizing can be eliminated.

  Moreover, in the method for excavating a proximity double tunnel according to the present invention, it is preferable that the step of improving the receiving injection is performed for each face that has progressed in each tunnel.

  In the present invention, since the driving-type hollow bolt used for improving the receiving injection is short, by placing the driving-type hollow bolt for each face of the tunnel, the ground of the pillar portion adjacent to the tunnel area to be excavated next time is provided. The mountain can be reinforced reliably.

  According to the excavation method of the adjacent twin tunnel of the present invention, according to the state of the natural ground of the pillar portion, an excavation method of performing a receiving work for placing a short driving-type hollow bolt on the natural ground of the pillar portion; By excavating by any one of the excavation methods using the smooth blasting method for blasting within a predetermined range in contact with the pillar portion, it is possible to ensure the soundness and independence stability of the natural area of the pillar portion over the entire tunnel. Therefore, it is not necessary to improve the injection from the ground surface for the natural ground in the pillar part, and the supporting structure of both tunnels can be made to have the same specifications. Can be reduced.

It is sectional drawing which shows the structure of the proximity | contact double tunnel by embodiment of this invention. It is sectional drawing which shows the state which laid the short hollow volt | bolt in the natural ground of the pillar part. It is a fragmentary top view which shows the state which laid the short hollow volt | bolt in the natural ground of the pillar part. It is sectional drawing which shows the process of performing a smooth blasting construction method. (A), (b) is a figure which shows the construction order of the full-section excavation method with an auxiliary bench. (A)-(d) It is a figure which shows the construction order of the excavation method in a geological defect part.

Hereinafter, a method for excavating a proximity double tunnel according to an embodiment of the present invention will be described with reference to FIGS.
As shown in FIG. 1, the adjacent twin tunnel 1 according to the present embodiment is a mountain tunnel in which a first tunnel 1A and a second tunnel 1B are excavated in parallel at a substantially constant interval in the width direction. For example, it is a tunnel applied to a twin two-lane road tunnel.

  In the adjacent twin tunnel 1 shown in FIG. 1, the first tunnel 1A and the second tunnel 1B have the same supporting structure in the same cross section, and the distance d in the left-right direction is about 4 m, for example. Here, the first tunnel 1 </ b> A and the second tunnel 1 </ b> B include an upper half cross-sectional portion 11, a lower half cross-sectional portion 12, and an invert portion 13.

  And it is an area | region where the space | interval d between the 1st tunnel 1A and the 2nd tunnel 1B is narrow, Comprising: 45-60 degree | times toward the mutually opposing side from each top end 1c of the 1st tunnel 1A and the 2nd tunnel 1B Hereinafter, a region extending from a position inclined at a slant (shoulder portion at the upper side of the symbol θ shown in FIG. 1) to the bottom plate portion of each tunnel is referred to as a “pillar portion P”. The earth pressure F1 acts on the natural ground of the pillar part P from above and below, and the earth pressure F2 in the direction in which the side walls of the tunnels 1A and 1B are pressed acts. And this pillar part is the reinforcement range by the pre-filling injection | pouring improvement mentioned later, Comprising: It is the protection range of the blasting by a smooth blasting construction method.

  The excavation method of this adjacent twin tunnel 1 is based on the difference between the face positions 1a and 1b (see FIGS. 3 and 6A) of the adjacent first tunnel 1A and second tunnel 1B in the tunnel axial direction (extension direction). The excavation is performed by early closing of the full section excavation with an auxiliary bench that closes the section within 7 to 8 m from the face in each tunnel 1A, 1B so as to be within 4 m (details will be described later).

  Further, when excavating the tunnel, as shown in FIGS. 2 and 3, a short driving-type hollow bolt (hereinafter referred to as a short hollow bolt 2) is preliminarily placed on the ground of the pillar portion P between the adjacent tunnels 1A and 1B. Depending on the condition of the natural ground, a method of placing and improving the receiving injection and a method of performing blasting in a predetermined range in contact with the pillar part P by blasting by the smooth blasting method as shown in FIG. And drilling. That is, in this adjacent twin tunnel 1, either the excavation by the above-described advance injection improvement or the excavation by the smooth blasting method is performed according to the nature of the natural ground, so that the pillar portion P It is excavated to ensure the stability of natural ground.

  That is, when the pillar part P is the geological defect part G1, as shown in FIG. 2 and FIG. Specifically, excavation is carried out while using a pre-injection improvement work by placing a short hollow bolt 2 such as an injection type fore poling that injects a rock-solidifying agent into the pillar part P, which is to be reinforced if necessary. By doing this, the independence stability of the natural ground of the pillar part P until support construction is ensured.

  The tip-injection improver reinforces the short hollow bolts 2, 2,... At the end of one excavation of about 1 m, that is, at a predetermined driving angle from the face near the tunnel side wall excavated for each face toward the front outside. A plurality of spots are placed in the range (upper and lower half pillar portions P). The short hollow bolts 2, 2,... Are arranged at predetermined intervals along the circumferential direction of the tunnel. In the present tip injection improvement work, since the natural ground of the pillar P in contact with the tunnel region to be excavated next is reinforced, the collapse and damage of the natural ground of the pillar P during excavation can be suppressed.

  For example, a short hollow bolt 2 having a casting angle of about 15 degrees and L = 3 to 4 m is cast for each of the tunnel lengths D1 and D2 (about 1 m) shown in FIG. By this, the self-supporting of the excavation surface which touches the pillar part P is ensured. Thereby, even when the distance between the two tunnels 1A and 1B is 2 m or less, the short hollow bolt 2 driven from one tunnel can be constructed without reaching the other tunnel cross section. That is, for example, an injection-type long steel pipe fore-piling having a casting angle of about 9 degrees in the pillar portion P and a length L = 12.5 m reaches the tunnel section on the opposite side by construction. Not suitable for.

  In addition, as shown in FIG. 4, in the case where the natural ground of the pillar part P is the hard rock part G2, excavation is performed by a blasting method, but the smooth blasting method is adopted for the face in contact with the protection range of the pillar part P, The other face part uses the normal blasting method to suppress the explosion damage of the natural ground of the pillar part P, and blasts smoothly. Reference numerals 3, 3,... Shown in FIG. 4 indicate explosive loading positions according to the present smooth blasting method.

Here, the construction method of each tunnel 1A, 1B by the whole cross-section excavation method with an auxiliary bench is demonstrated based on FIG.
As shown in FIG. 5A, the cross section of the tunnel 1 is divided into an upper half cross section 11, a lower half cross section 12, and an invert section 13 and excavated in stages, and the face 12a of the lower half cross section 12 is excavated. Is excavated as a position away from the face 11a of the upper half section 11 by about 3 to 4 m (this is referred to as an auxiliary bench length L1). In the present construction method, the tip 13a of the invert portion 13 is positioned further 3 to 4 m behind the face 12a of the lower half cross section 12. Here, the symbol L2 shown in FIG. 5A is the distance from the face 12a of the lower half section 12 to the tip 13a of the invert portion 13 and is about 3 to 4 m as described above, and the symbol L3 is the upper half. The distance from the face 11a of the cross section 11 to the tip 13a of the invert part 13 is about 7 to 8 m.

  Then, the auxiliary bench length L1 is an area corresponding to one progression of the upper and lower half cross-section portions 11 and 12 (the hatched portions 11A and 12A shown in FIG. 5, for example, one engraving length D1 and D2 (see FIG. 3) is 1 m) The upper and lower half cross-sections 11 and 12 are excavated and sprayed concrete (not shown) in the circumferential direction of the tunnel with an appropriate support pattern according to the condition of the natural ground and a steel support shown by reference numeral 14 Establish such support. Specifically, the lower half section 12A is excavated immediately after excavating the upper half section 11A.

  After excavating the upper and lower half cross-section parts 11 and 12 and providing support, the invert part 13 is excavated to substantially the same position as the face 12a of the lower half cross-section part 12 as shown in FIG. Then, by installing a support (invert strut 15 or shotcrete) on the excavated invert 13, the tunnel cross-section is closed early within 8 m from the upper half face (a state where the support is applied to the entire wall surface of the tunnel 1). Finally, the invert part 13 is temporarily backfilled with excavated soil.

  In addition, in this tunnel 1, before the excavation of the entire cross-section excavation area, if necessary, the injection type is directed forward from the peripheral wall of the tunnel top end (the arch part from the top of the tunnel cross section to the side shoulders on both sides). Long steel pipe fore-pilling 16 is constructed radially outside the tunnel to prevent the top end from collapsing and loosening during excavation.

Next, the excavation method in the geological defect part G1 will be described in more detail based on FIG.
As shown in FIG. 6 (a), in the geological defect portion G1, first, the first tunnel 1A is set to 1 m, for example, with the upper half and the lower half being 1 m by the full-section excavation method with an auxiliary bench shown in FIG. 1 excavation length to be excavated (D1 shown in FIG. 6A indicates the excavation length of the upper half) and a support is installed. At this time, since the natural ground is the poor geological part G1, excavation is performed by a mechanical excavation method or the like. Moreover, since the pillar part P which contact | connects an excavation area | region is reinforced by the short hollow volt | bolt 2 in the self-supporting state, it can excavate without generating the loosening etc. of the pillar part P by excavation.
Next, as shown in FIG. 6B, a short hollow bolt 2 (referred to as 2A) is driven from the face near the side wall of the first tunnel 1A toward the front outer side, and the bolt 2A is Used to inject rock mass binder into the ground (see Fig. 2). As a result, the natural ground of the pillar portion P in the region to be excavated next to the first tunnel 1A (the reference numeral 1A ′ of the two-dot chain line) is reinforced, and can maintain a stable state, and is independent during excavation. It becomes possible.

  Next, as shown in FIG. 6 (c), one digging length (by a full-section excavation method with an auxiliary bench is provided so as to be substantially at the same position as the face of the first tunnel 1A dug in advance through the second tunnel 1B ( Excavation is performed only for the upper half of the sign D2 shown in FIG. 6C, and the support is installed (see FIGS. 5A and 5B). Thereafter, as shown in FIG. 6 (d), a short hollow bolt 2 (referred to as reference numeral 2B) is driven from the side wall portion of the second tunnel 1B toward the front outer side, and the bedrock using the bolt 2B. Inject the caking agent into the ground. This reinforces the natural ground of the pillar portion P in the region to be excavated after the second tunnel 1B (reference numeral 1B ′ of the two-dot chain line), can maintain a stable state, and is independent during excavation. It becomes possible.

As described above, in the present close twin tunnel 1, excavation is performed while the short hollow bolt 2 is previously placed in the ground of the pillar portion P between the adjacent tunnels 1 </ b> A and 1 </ b> B, and the advance receiving injection is improved. The excavation method for performing blasting in a predetermined range in contact with the pillar portion P by blasting by the smooth blasting method can be selected according to the state of the natural ground and excavated.
That is, when the pillar part P is the geological defect part G1, the ground part is reinforced and excavated by placing the short hollow bolt 2 on the pillar part P and injecting the rock mass binder, Moreover, when the pillar part P is the hard rock part G2, the blasting in the predetermined range which touches the pillar part P can be excavated by the blasting by the smooth blasting method. Thereby, the proximity twin tunnel 1 can be excavated while ensuring the soundness and independence of the natural ground of the pillar part P.

  In addition, by adopting a full-section excavation method with an auxiliary bench that can be closed early for excavation of each tunnel 1A, 1B constituting the adjacent twin tunnel 1, the difference in the face position of the adjacent tunnels 1A, 1B can be determined by the tunnel axis. It is possible to proceed simultaneously while keeping the distance within 4 m in the direction. Therefore, the supporting structures of both tunnels 1A and 2B can form a symmetrical structure that is advantageous in terms of mechanical stability in the three-dimensional stress field around the face, and the ground on the side of the pillar is A new stable field can be formed in the ground arch including both tunnels 1A and 1B by one time stress redistribution while being restrained by the tunnel support structures on both sides and maintaining the triaxial stress field. . Therefore, when one of the preceding tunnels excavates the other succeeding tunnel, the side passive pressure of the preceding tunnel is unloaded, and the influence of lowering the ground strength and plasticizing can be eliminated.

  Further, in the step of improving the receiving injection, since the short hollow bolt 2 is short, by placing the short hollow bolt 2 for each face of the tunnels 1A and 1B, it is adjacent to the tunnel area to be excavated next. The natural ground of the pillar part P can be reinforced reliably.

  As described above, in the excavation method of the proximity double tunnel according to the present embodiment, a receiving work for placing the short hollow bolt 2 on the ground of the pillar portion P is performed according to the state of the ground of the pillar portion P. By excavating by either the excavation method or the excavation method using the smooth blasting method for blasting within a predetermined range in contact with the pillar part P, the soundness and independence stability of the pillar part P over the entire tunnel line can be achieved. Can be secured. Accordingly, it is not necessary to improve the injection from the ground surface to the natural ground of the pillar part P, and it is possible to make the supporting structures of both the first tunnel 1A and the second tunnel 1B have the same specifications. Therefore, the construction period and construction cost can be reduced.

As mentioned above, although embodiment of the excavation method of the proximity double tunnel by this invention was described, this invention is not limited to said embodiment, In the range which does not deviate from the meaning, it can change suitably.
For example, in the present embodiment, the full-section excavation method with an auxiliary bench is adopted as the excavation method for the two tunnels 1A and 1B provided in parallel, but the present invention is not limited to this method. In short, it is only necessary that excavation can be performed while the difference between the face positions of the adjacent tunnels 1A and 1B is within 4 m in the tunnel axis direction.
Further, in the present embodiment, the method of performing the prior injection improvement for each face proceeding in each of the tunnels 1A and 1B is used, but the present invention is not limited to each face, and the length dimension of the short hollow bolt 2 is not limited. It is possible to place the short hollow bolt 2 at an appropriate timing according to the excavation progress length.
Furthermore, the installation range of the short hollow bolt 2 and the blasting position by the smooth blasting method can be arbitrarily set according to the region of the pillar portion P.

DESCRIPTION OF SYMBOLS 1 Adjacent twin tunnel 1A 1st tunnel 1B 2nd tunnel 2 Short hollow bolt (short driving type hollow bolt)
3 Explosive loading position by smooth blasting method 11 Upper half section 11a Face 12 Lower half section 12a Face 13 Invert part P Pillar part G1 Geologically defective part G2 Hard rock part

Claims (2)

A method for excavating adjacent twin tunnels in which the difference in the face position between adjacent tunnels is within 4 m in the tunnel axis direction,
In tunnel excavation, a method of constructing a pre-filling injection by previously placing a short driving-type hollow bolt in the ground of the pillar portion between adjacent tunnels, and
A method of performing blasting in a predetermined range in contact with the pillar part by blasting by a smooth blasting method,
Is excavated by selecting according to the state of the natural ground of the pillar portion.   The method of excavating a proximity double tunnel according to claim 1, wherein the step of improving the receiving injection is performed for each face that has progressed in each tunnel.

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