Tunnel and construction method thereof

Abstract

To provide a tunnel and a construction method thereof capable of suppressing increases in the amount of excavation of the ground, the thickness of the lining concrete, and the amount of steel in a steel support, and eliminating the trouble of identifying a point of a support structure that protrudes most into the tunnel by measurement.SOLUTION: A tunnel 80 has a support structure 70 and a lining concrete 50. The support structure 70 has a primary shotcrete 11, a steel support 20 made of H-shaped steel, a secondary shotcrete 12 having a concave surface 10a recessed toward the ground between adjacent steel supports 20 spaced apart, and a rock bolt 30 having a bolt body 31 driven into the ground G at the concave surface 10a and an anchoring body 32. The lining concrete 50 is formed while wrapping a surface 22a of a pit inner flange 22 and the anchoring body 32. Both a head 31a of the bolt body 31 and the anchoring body 32 are accommodated in a step between the surface 22a of the pit inner flange 22 and the concave surface 10a.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a tunnel and a construction method thereof. [Background technology]

[0002] In the construction of tunnels (mountain tunnels, etc.), the following method is generally applied: excavate the ground by blasting or other means, lay sprayed concrete and steel supports, then drive multiple rock bolts into the ground from the surface of the sprayed concrete to secure it to the ground and construct a support structure; this process is repeated in the axial direction of the tunnel, and then a lining concrete of a specified thickness is laid on the inside of the support structure to construct a tunnel of a specified length. Shotcrete includes primary shotcrete and secondary shotcrete. The primary shotcrete is applied promptly after the ground is excavated, steel supports are installed on the surface of the primary shotcrete at intervals in the axial direction of the tunnel, and the secondary shotcrete is applied so that the steel supports are wrapped around the surface of the primary shotcrete. Rock bolts are then driven into the ground from the surface of the secondary shotcrete. A support structure including rock bolts provides a support structure with high structural stability against natural ground that is at risk of collapse or excessive deformation, for example.

[0003] Here, Patent Document 1 proposes a rock bolt end fixing device that fixes the protruding end of a rock bolt that is driven into the natural ground around a tunnel to the tunnel wall surface. This fixing device includes a pressure plate that has an insertion hole for the protruding end and is in contact with the tunnel wall surface, a nut screwed onto the protruding end, and a color-changing member made of resin or rubber that is sandwiched between the pressure plate and the nut and changes color depending on the pressure applied. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-80732 Summary of the Invention [Problem to be solved by the invention]

[0005] Conventional rock bolts, including the rock bolt described in Patent Document 1, have a pressure plate (washer) and a nut that protrude significantly from the surface of the shotcrete, and the head of the bolt body of the rock bolt protrudes further from the nut. This can lead to various problems.

[0006] These challenges will now be explained with reference to Figure 1, which shows an enlarged cross-sectional view of a portion of an example tunnel equipped with a conventional support structure including rock bolts.

[0007] Shotcrete C1 is applied to an excavation surface Ga created by excavating natural ground G. In the illustrated example, after a welded wire mesh (not shown) is installed on the excavation surface Ga, a primary shotcrete C2 with a thickness t2 that forms the shotcrete C1 is applied, and steel supports D made of H-shaped steel are installed at intervals u1 in the axial direction of the tunnel, and a secondary shotcrete C3 with a thickness t2 is applied on the surface of the primary shotcrete C1 so as to wrap around the steel supports H. The thickness t1 of the shotcrete C1 is the sum of the thicknesses t2 and t3.

[0008] After the shotcrete C1 is applied, a borehole H is drilled into the natural ground from the surface Ca of the shotcrete C1, and the inside of the borehole H is filled with grout M such as mortar. Then, the bolt body B that forms the rock bolt R is driven into the borehole H, and the head Ba of the bolt body B is made to protrude from the surface Ca of the shotcrete C1. Next, the washer W is installed while the head Ba is inserted into the bolt hole Wa of the washer W, the nut N is tightened, and the grout M is allowed to cure, thereby fixing the bolt body B to the natural ground G. In this way, the washer W and nut N that fix the bolt body B to the natural ground G form an anchorage E. The thickness of the washer W is t6, the thickness of the nut N is t7, and the protruding length of the head Ba from the nut N is t8, and the sum of these is t9. The tunnel T equipped with the support structure F is constructed by constructing the lining concrete C4 so as to wrap around the anchor E and the head Ba of the bolt body B.

[0009] In calculating the lining thickness t10 of this lining concrete C4, when the head Ba of the bolt body B protrudes further into the tunnel than the tunnel inner flange D1 of the H-shaped steel D as in the illustrated example (height t9 is greater than the height t5 from the surface Ca of the lining concrete C1 to the tunnel inner flange D1: t9>t5), it may be required to construct the lining concrete C4 with a lining thickness t10 greater than the design value from the head Ba. In such a case, the thickness t1 of the sprayed concrete C1 must be constructed so as to meet the design value, and then the lining concrete C4 with a lining thickness t10 greater than or equal to the design value must be constructed from the head Ba of the bolt body B, which inevitably creates the problem of an increase in the amount of excavation of the ground G.

[0010] In addition, a space (protrusion space S) with height t9 is formed between the surface Ca of the sprayed concrete C1 and the lining concrete C4, which is the sum of the thickness t6 of the washer W, the thickness t7 of the nut N, and the protrusion length t8 of the head Ba of the bolt body B. This protrusion space S needs to be filled with concrete and blocked when the lining concrete C4 is constructed, so that the lining concrete C4 must be constructed at height t9, which is the sum of thicknesses t8 and t7. As the height t9 increases, the lining thickness of the lining concrete C4 increases, which creates the problem of an increase in the amount of concrete in the lining concrete C4.

[0011] In addition, since the surface of the covering concrete C4 is set back toward the ground by the height t9 of the protruding space S, as the height t9 increases, the cross-sectional dimension (diameter) of the steel support becomes larger, resulting in a problem that the amount of steel used in the steel support increases.

[0012] Furthermore, it is necessary to determine through measurement control whether the thing that protrudes most into the inside of the tunnel is the head Ba of the bolt body B or the inside of the tunnel flange D1 of the steel support D, and to construct the lining concrete with the point that protrudes most into the inside of the tunnel as the starting point of the lining thickness t10 of the lining concrete C4, which creates the problem that measurement control and the construction of the lining concrete based on measurement control require time and effort.

[0013] The present invention aims to provide a tunnel and its construction method that can suppress increases in the amount of excavation of the ground, the thickness of the lining concrete, and the amount of steel in the steel support structure, and eliminates the hassle of measuring to identify the point of the support structure that protrudes most into the tunnel. [Means for solving the problem]

[0014] In order to achieve the above object, one aspect of the tunnel according to the present invention is as follows: A tunnel having a support structure and a concrete lining, The support structure includes: A primary shotcrete layer formed on the inner wall surface of the excavated tunnel; On the surface of the first sprayed concrete, steel supports made of H-shaped steel are installed at intervals in the axial direction of the tunnel; A secondary shotcrete is formed on the surface of the primary shotcrete while wrapping the entire area of ​​the H-shaped steel except for the surface of the inner flange of the H-shaped steel, and has a concave surface recessed toward the ground between the adjacent steel supports at the intervals; and a rock bolt including a bolt body that is driven into the natural ground at the concave surface and a fixing body that fixes the bolt body to the natural ground, The lining concrete is formed by wrapping the surface of the inner flange of the hole and the anchoring body, The present invention is characterized in that both the head of the bolt body and the anchor are housed within a step between the surface of the borehole inner flange and the concave surface.

[0015] According to this embodiment, the secondary sprayed concrete which forms the support structure has a concave surface recessed toward the ground between adjacent steel supports which are spaced apart, and both the head and anchor of the bolt body of the rock bolt which is driven into the concave surface are contained within the step between the surface of the inside flange of the steel support and the concave surface. Therefore, the component of the support structure which protrudes most into the inside of the tunnel is determined to be the inside flange of the steel support, and the lining concrete can be constructed using the inside flange as the starting point of the lining thickness. This makes it possible to reduce the amount of excavation required for the ground, the thickness of the lining concrete, and the increase in the amount of steel required for steel supports when constructing mountain tunnels and other tunnels, and also eliminates the hassle of measuring to identify the point of the support structure that protrudes furthest into the tunnel.

[0016] Here, "both the head of the bolt body and the anchor are housed within the step" means that the construction is based on a design that allows both to be housed within the step. The head of the rock bolt may be either in a form that protrudes from the nut and is screwed into the anchor, or in a form that is not protruding from the nut and is screwed into the anchor. In the former form, the sum of the thickness of the anchor and the protruding length of the head is usually set to be equal to or greater than the diameter (1D) of the bolt body, but by setting it to less than 1D, the protruding length of the components of the rock bolt from the concave surface can be further shortened, which is preferable.

[0017] In addition, with regard to the configuration in which "the secondary shotcrete is formed by wrapping around the entire area of ​​the H-shaped steel except for the surface of the flange on the inside of the tunnel," a certain amount of concrete adheres to the surface of the flange on the inside of the tunnel during application of the secondary shotcrete, but since this concrete adheres in this way is not a component of the secondary shotcrete of a specified thickness, it may be considered not to be included in the secondary shotcrete in this specification. In reality, the concrete adhering to the surface of the flange on the inside of the tunnel will be removed by scraping. Furthermore, since the secondary shotcrete is applied by spraying concrete while forming a concave surface, there are two types of secondary shotcrete: one in which the secondary shotcrete is formed so as to fill in the side of the H-shaped steel flange inside the tunnel, and one in which the secondary shotcrete is formed so that the side of the flange inside the tunnel is exposed.

[0018] In another aspect of the tunnel according to the present invention, A male thread is provided on at least the outer periphery of the head of the bolt body, The fixing body is a nut having a head body and a shaft having a planar dimension smaller than that of the head body, the nut being provided with a continuous female thread extending from the head body to the shaft; a washer through which the shaft is inserted and which has an insertion hole having a planar dimension smaller than that of the head body; The male thread is threadedly engaged with the female thread in a state where the male thread does not protrude from the head body.

[0019] According to this aspect, the fixing body that forms the lock bolt has a nut that has a head body and a shaft with a female thread inside them, and a washer that has an insertion hole through which the shaft is inserted and in which the head body is engaged, and the male thread provided on the outer periphery of the head of the bolt body is screwed into the female thread without protruding from the head body, thereby making it possible to further shorten the protruding length of the components of the rock bolt from the concave surface of the secondary sprayed concrete.

[0020] In another aspect of the tunnel according to the present invention, A male thread is provided on at least the outer periphery of the head of the bolt body, The fixing body is A nut comprising a head body and a shaft having a planar dimension smaller than that of the head body, and a continuous female thread is provided from the head body to the shaft, The head body is a flange that spreads in a flat plate shape, The male thread is screwed into the female thread in a state where it does not protrude from the head body.

[0021] According to this embodiment, the fixing body that forms the lock bolt is a nut that has a head body consisting of a flat flange and a shaft, with a female thread provided inside thereof, and the male thread provided on the outer periphery of the head of the bolt body is screwed into the female thread without protruding from the head body, thereby making it possible to further shorten the protruding length of the components of the rock bolt from the concave surface of the secondary sprayed concrete.

[0022] Another aspect of the tunnel according to the present invention is The height of the H-shaped steel is 125 mm, The thickness of the area of ​​the concave surface of the secondary shotcrete into which the rock bolt is driven is 100 mm; The step is characterized in that it is 25 mm.

[0023] According to the present embodiment, in a support structure in which a steel support made of H-shaped steel (H-125) of a similarly typical height of 125 mm is applied to a secondary sprayed concrete of a typical thickness of 100 mm, both the head and the anchor of the bolt body are contained within this 25 mm step difference, which is preferable in that it can achieve the various effects described above in a tunnel having a support structure suited to the actual construction.

[0024] In addition, one aspect of the tunnel construction method according to the present invention is to A process includes applying a primary shotcrete to the excavated surface of the ground, installing steel supports made of H-shaped steel at intervals in the axial direction of the tunnel on the surface of the primary shotcrete, applying a secondary shotcrete to the surface of the primary shotcrete between the adjacent steel supports at the intervals while wrapping the entire area of ​​the H-shaped steel except for the surface of the inner flange of the H-shaped steel, with a concave surface recessed toward the ground, drilling a borehole into the ground from the concave surface, injecting grout into the borehole, driving a bolt body forming a rock bolt into the borehole, attaching an anchor to the bolt body forming the rock bolt, curing the grout, and anchoring the bolt body to the ground, thereby constructing a support structure; and a step B of constructing a lining concrete while wrapping the surface of the inner flange of the hole and the anchoring body, The process A is characterized in that both the head of the bolt body and the anchor are accommodated within the step between the surface of the borehole inner flange and the concave surface.

[0025] According to this embodiment, the secondary sprayed concrete which forms the support structure is applied between adjacent steel supports spaced apart so as to have a concave surface recessed toward the ground, and when a rock bolt is driven into the ground from the concave surface, both the head and anchor of the bolt body are contained within the step between the surface and concave surface of the inside-hole flange of the steel support.This means that the component of the support structure which protrudes most into the inside of the tunnel is determined to be the inside-hole flange of the steel support, and the lining concrete can be applied using the inside-hole flange as the starting point of the lining thickness. This makes it possible to reduce the amount of excavation required for the ground, the thickness of the lining concrete, and the increase in the amount of steel required for steel supports when constructing mountain tunnels and other tunnels, and also eliminates the hassle of measuring to identify the point in the support structure that protrudes furthest into the tunnel. Effect of the Invention

[0026] According to the tunnel and its construction method of the present invention, it is possible to suppress the increase in the amount of excavation of the ground, the thickness of the lining concrete, and the amount of steel in the steel support structure, and to eliminate the trouble of measuring to identify the point of the support structure that protrudes most into the tunnel. [Brief description of the drawings]

[0027] [Figure 1] FIG. 1 is an enlarged cross-sectional view of a portion of an example tunnel with a conventional support structure including rock bolts. [Diagram 2] FIG. 2 is an enlarged cross-sectional view of a portion of an example tunnel according to an embodiment. [Diagram 3] FIG. 13 is an enlarged cross-sectional view of a portion of another example of a tunnel according to an embodiment. [Figure 4] FIG. 11 is an exploded perspective view of an example of a rock bolt applied to another example of a tunnel according to an embodiment. [Diagram 5] FIG. 13 is an exploded perspective view of another example of a lock bolt. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, a tunnel and a construction method thereof according to an embodiment will be described with reference to the accompanying drawings. In this specification and the drawings, substantially the same components are designated by the same reference numerals, and duplicated explanations may be omitted.

[0029] [Tunnel according to the embodiment and its construction method] An example of a tunnel and a construction method thereof according to the embodiment will be described with reference to Figs. 2 to 5. Here, Fig. 2 is a cross-sectional view of an enlarged portion of an example of a tunnel according to the embodiment. Fig. 3 is a cross-sectional view of an enlarged portion of another example of a tunnel according to the embodiment, and Fig. 4 is an exploded perspective view of an example of a rock bolt applied to the other example of a tunnel according to the embodiment. Note that in each drawing, illustrations of welded wire mesh in the primary shotcrete and reinforcing bars in the lining concrete are omitted.

[0030] The tunnel 80 in the illustrated example is a mountain tunnel, and its construction method is to first excavate the natural ground G by blasting or the like, and then apply the primary shotcrete 11 to the excavation surface Ga of the excavated natural ground G. The thickness t2 of the primary shotcrete 11 is set to, for example, about 50 mm.

[0031] Next, steel supports 20 made of H-shaped steel are installed on the surface of the primary shotcrete 11 at intervals u1 in the axial direction of the tunnel. This interval u1 is set to, for example, about 1 m. The ground-side flange 23 of the arc-shaped H-shaped steel 20 abuts against the surface of the primary shotcrete 11, and the surface of the inside-hole flange 22 on the inside of the tunnel is erected facing the inside of the tunnel via the web 21. For example, two halved arc-shaped H-shaped steel pieces are grasped and erected by a construction machine (erector), and the upper ends of each H-shaped steel are bolted together to erect the arc-shaped steel supports 20.

[0032] After erecting a plurality of steel supports 20 at intervals u1 in the axial direction of the tunnel, the entire area of ​​the H-shaped steel 20 except for the surface of the flange 22 on the inside of the tunnel is rolled up, and the secondary shotcrete 12 is applied while forming a step 10b recessed toward the ground G on the surface of the primary shotcrete 11, thereby forming a shotcrete 10 consisting of the primary shotcrete 11 and the secondary shotcrete 12. The thickness t3 of the secondary shotcrete 12 is set to, for example, about 100 mm. Therefore, the thickness t1 of the shotcrete 10 is, for example, about 150 mm. Here, the shotcrete can also be called the primary lining concrete, and the lining concrete described below can also be called the secondary lining concrete.

[0033] The depression 10b of the secondary shotcrete 12 is provided with a concave surface 10a that is as flat as possible, and the thickness of the step 10b between the surface of the flange 22 inside the hole and the concave surface 10a is t5. For example, when the thickness t3 of the secondary shotcrete 12 is set to about 100 mm and H-shaped steel of H-125 is used for the steel support 20, the thickness of the step 10b is 25 mm.

[0034] Next, in the central region (or approximately the central region) of the concave surface 10a between the pair of steel supports 20, a borehole 35 of a predetermined length extending to the ground G is drilled, grout 36 is injected into the borehole 35, and then the bolt body 31 forming the rock bolt 30 is driven into the borehole 35.

[0035] After the bolt body 31 is driven, the anchor 32 forming the rock bolt 30 is attached to the head 31a of the bolt body 31, and the grout 36 is allowed to cure (wait for it to harden) to anchor the bolt body 31 to the natural ground G. More specifically, the anchor 32 has a washer 33 with an insertion hole 33a and a nut 34 with a female thread 32a, and a male thread 31b is provided on at least the outer periphery of the head 31a of the bolt body 31.

[0036] The head 31a of the bolt body 31 is inserted into the insertion hole 33a, and the nut 34 is screwed and tightened while the female threads 32a of the nut 34 are screwed into the male threads 31b of the head 31a. The grout 36 hardens, thereby fixing the bolt body 31 to the ground G.

[0037] 2, the rock bolt 30 is driven in so that both the head 31a of the bolt body 31 and the anchor 32 are contained within the thickness t5 of the step between the surface 22a of the inside flange 22 of the steel support 20 and the concave surface 10a. In other words, the bolt is designed so that both the head 31a of the bolt body 31 and the anchor 32 are contained within the thickness t5 of the step, and the rock bolt 30 is installed based on this design.

[0038] In the illustrated example, the total t14 of the thickness t11 of the washer 33, the thickness t12 of the nut 34, and the protruding length t13 of the head 31a of the bolt body 31 from the nut 34 is set to be less than or equal to the step thickness t5.

[0039] Through the series of construction steps described above, the support structure 70 is constructed (this is referred to as Process A). Process A, which includes a series of construction steps from drilling holes in the ground G by blasting or the like to constructing the support structure 70, is carried out over a predetermined length section in the axial direction of the tunnel, and by carrying out this process multiple times in the axial direction of the tunnel, a tunnel equipped with the support structure 70 of a predetermined length is constructed.

[0040] Next, reinforcing bars (not shown) are arranged on the inside of the tunnel on surface 22a of inner tunnel flange 22, and lining concrete 50 is constructed while wrapping surface 22a and anchor 32, thereby forming support structure 70 in the drilled hole in natural ground G, and constructing tunnel 80 with lining concrete 50 formed on the inside of the tunnel of support structure 70. Here, construction of lining concrete 50 can be carried out using, for example, a centering cart (not shown) or the like (the above is step B).

[0041] According to the tunnel 80 and its construction method shown in the figure, the secondary sprayed concrete 12 forming the support structure 70 has a concave surface 10a recessed toward the ground G between adjacent steel supports 20 at an interval u1, and both the head 31a and anchor 32 of the bolt body 31 of the rock bolt 30 driven into the ground G from the concave surface 10a are contained within the thickness of the step 10b between the surface 22a of the inside flange 22 of the steel support 20 and the concave surface 10a.As a result, the component of the support structure 70 that protrudes most into the inside of the tunnel is determined to be the inside flange 22 of the steel support 20, and the lining concrete 50 can be constructed with the surface 22a of the inside flange 22 as the starting point of the lining thickness t10.

[0042] This makes it possible to reduce the amount of excavation of the ground G, the lining thickness of the lining concrete 50, and the increase in the amount of steel in the steel support structure 20 during the construction of the mountain tunnel 80, and eliminates the hassle of measuring to identify the point of the support structure 70 that protrudes most into the tunnel interior.

[0043] Here, as described above, an example can be given in which the height of the H-shaped steel 20 is 125 mm (H-125), the thickness of the area of ​​the concave surface 10a of the secondary shotcrete 12 into which the rock bolt 30 is driven is 100 mm, and therefore the step is 25 mm. In this embodiment, in a support structure 70 in which a steel support 20 made of an H-shaped steel (H-125) of a similarly general height of 125 mm is applied to a secondary shotcrete 12 of a general thickness of 100 mm, both the head 31a of the bolt body 31 and the anchor 32 are accommodated within this step of 25 mm, and therefore the various effects described above can be achieved in a tunnel 80 having a support structure 70 suited to actual construction.

[0044] Tunnel 80A shown in Figure 3 has a different configuration from tunnel 80 in that the anchors 42 of rock bolts 40 that form its component support structure 70A are different from the anchors 32 of rock bolts 30 that form the support structure 70 of tunnel 80.

[0045] As shown in Fig. 4, the rock bolt 40 has a bolt body 41 and an anchor 42. Grout 48 is injected into a borehole 47 drilled in the natural ground G from the concave surface 10a, and the bolt body 41 is inserted into the borehole 47. A male thread 41b is provided on at least the outer periphery of the head 41a of the bolt body 41.

[0046] The fixing body 42 has a nut 43 and a washer 46. The nut 43 has a head body 44 with a maximum planar dimension d1 and a shaft 45 with a planar dimension d2 smaller than that of the head body 44, and is provided with a female thread 43a with a length t20 that continues from the head body 44 to the shaft 45.

[0047] The washer 46 has an insertion hole 46a through which the shaft 45 is inserted and whose planar dimension (diameter d3) is smaller than that of the head body 44.

[0048] Of the male threads 41b provided on the head 41a of the bolt body 41, a length t21 of a threaded region 41c that threadably engages with the female threads 43a is set shorter than a length t20 of the female threads 43a (t20>t21).

[0049] 3, the head 41a of the bolt body 41 does not protrude from the nut 43 but remains inside the female thread 43a of the nut 43, so that the protruding length from the concave surface 10a of the step 10b is the total t17 of the thickness t15 of the washer 46 and the thickness t16 of the head body 44 of the nut 43, and the total t17 is set to be equal to or less than the thickness t5 of the step. Here, although the head 41a of the bolt body 41 remains inside the female thread 43a of the nut 43, the threaded region 41c of the male thread 41b is threaded into the female thread 43a that continues from the head body 44 to the shaft 45, so that the head 41a of the bolt body 41 and the nut 43 are joined with a sufficient threaded length.

[0050] As is clear from a comparison with Figure 2, the only things that protrude from concave surface 10a are washer 46 and head body 44 of nut 43, and head 41a of bolt body 41 is not included, which is preferable as it makes it possible to further shorten the protruding length of the components of lock bolt 40 from concave surface 10a.

[0051] It is also possible to use a lock bolt 60 having an anchor 62 without a washer, as shown in FIG.

[0052] 5 has a bolt body 61 and a fixing body 62. At least the head 61a of the bolt body 61 is provided on the outer periphery with a male thread 61b.

[0053] The fixing body 62 is a nut having a head body 63 consisting of a flat flange and a shaft 64 having a smaller planar dimension than the head body 63, and is provided with a female thread 62a of length t22 that continues from the head body 63 to the shaft 64.

[0054] Of the male threads 61b provided on the head 61a of the bolt body 61, a length t23 of a threaded region 61c that threadably engages with the female threads 62a is set shorter than the length t22 of the female threads 62a (t22>t23).

[0055] Therefore, head 61a of bolt body 61 does not protrude from nut 62, but remains inside female thread 62a of nut 62, so the protruding length from concave surface 10a of step 10b is only the thickness of head body 63, and the thickness of head body 63 is set to be equal to or less than (or less than) thickness t5 of the step. Therefore, similar to lock bolt 40, the protruding length of the components of lock bolt 60 from concave surface 10a can be further shortened, which is preferable.

[0056] In addition, the present invention is not limited to the configuration shown here, and may be implemented in other embodiments in which other components are combined with the configurations and the like of the above-mentioned embodiment. In this regard, the present invention may be modified within the scope of the gist of the present invention, and may be appropriately determined according to the application form. [Explanation of symbols]

[0057] 10: Sprayed concrete 10a: concave 10b: Step (depression) 11: First sprayed concrete 12: Secondary sprayed concrete 20: Steel shoring (H-beam) 21: Web 22: Inside hole flange 22a: Surface 23: Ground side flange 30: Rock bolt 31: Bolt body 31a:Head 31b: Male thread 32: Fixing body 32a: Female thread 33: Washer 33a: Through hole 34: Nut 35: Borehole 36: Grout 40: Rock bolt 41: Bolt body 41a:Head 41b: Male thread 41c: Threaded area 42: Fixing body 43: Nut 43a: Female thread 44: Head body 45: Shaft 46: Washer 46a: Through hole 47: Borehole 48: Grout 50: Lining concrete 60: Rock bolt 61: Bolt body 61a:Head 61b: Male thread 61c: Threaded area 62: Fixing body (nut) 62a: Female thread 63: Head body (flange) 64: Shaft 70, 70A: Support structure 80, 80A: Tunnel (mountain tunnel) G: Natural ground Ga: Excavation surface

Claims

1. A tunnel having a support structure and a concrete lining, The support structure includes: A primary shotcrete formed on an excavation surface where the ground is excavated; On the surface of the first sprayed concrete, steel supports made of H-shaped steel are installed at intervals in the axial direction of the tunnel; a secondary shotcrete which is formed on the surface of the primary shotcrete while wrapping the entire area of ​​the H-shaped steel except for the surface of the flange on the inside of the tunnel, and has a concave surface recessed toward the ground between the adjacent steel supports at the interval; a rock bolt including a bolt body that is driven into the natural ground at the concave surface and a fixing body that fixes the bolt body to the natural ground, The lining concrete is formed by wrapping the surface of the inner flange of the hole and the anchoring body, A tunnel, characterized in that both the head of the bolt body and the anchor are contained within a step between the surface of the inner hole flange and the concave surface.

2. A male thread is provided on at least the outer periphery of the head of the bolt body, The fixing body is a nut having a head body and a shaft having a planar dimension smaller than that of the head body, the nut being provided with a continuous female thread extending from the head body to the shaft; a washer through which the shaft is inserted and which has an insertion hole having a planar dimension smaller than that of the head body; 2. The tunnel according to claim 1, wherein the male thread is screwed into the female thread in a state where the male thread does not protrude from the head body.

3. A male thread is provided on at least the outer periphery of the head of the bolt body, The fixing body is A nut comprising a head body and a shaft having a planar dimension smaller than that of the head body, and a continuous female thread is provided from the head body to the shaft, The head body is a flange that spreads in a flat plate shape, 2. The tunnel according to claim 1, wherein the male thread is screwed into the female thread without protruding from the head body.

4. The height of the H-shaped steel is 125 mm, The thickness of the area of ​​the concave surface of the secondary shotcrete into which the rock bolt is driven is 100 mm; 2. A tunnel according to claim 1, characterised in that the step is 25 mm.

5. a step A of applying a primary sprayed concrete to the surface of the excavated natural ground, installing steel supports consisting of H-shaped steel on the surface of the primary sprayed concrete at intervals in the axial direction of the tunnel, applying a secondary sprayed concrete to the surface of the primary sprayed concrete while wrapping the entire area of ​​the H-shaped steel except for the surface of the inner flange of the H-shaped steel, with a concave surface recessed toward the natural ground between the adjacent steel supports at the intervals, drilling a borehole into the natural ground from the concave surface, injecting grout into the borehole, driving a bolt body forming a rock bolt into the borehole, attaching an anchor to the bolt body forming the rock bolt, curing the grout, and anchoring the bolt body to the natural ground, thereby constructing a support structure; and a step B of constructing a lining concrete while wrapping the surface of the inner flange of the hole and the anchoring body, A tunnel construction method characterized in that in step A, both the head of the bolt body and the anchoring body are accommodated within the step between the surface of the inner hole flange and the concave surface.

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