JPH04198593A - Construction of half tunnel and construction method thereof - Google Patents

Abstract

PURPOSE:To prevent an accident of a landsliding and to promote safety by providing shorings along internal wall surfaces of an overhang-shaped excavation section formed in a bedrock, etc., and laying struts at a certain interval between the shorings and open ends of a subgrade. CONSTITUTION:An overhang-shaped excavation section 4 is excavated from the surface of a bedrock 5 having a steep slope in a mountainous district, and beam-like shorings 11 having an approximate dog legged shaped section along internal wall surfaces of the excavation section 4. After that, struts 12 are provided along the wall surfaces at a certain interval so that they are laid between the shorings 11 and open ends of the surface of the bedrock of a subgrade. The strut foundation 13 for increasing strength is formed on a part of the subgrade of the struts 12, and a half tunnel A is constructed. According to the constitution, the deformation of the bedrock 5 around the internal wall surfaces can be suppressed by the shorings 11 and struts 12, the struts 12 can be arranged while preventing the bedrock 5 from falling, and safety and execution efficiency can be promoted.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to the structure and construction method of a half tunnel constructed to pass a road, etc. along a slope or cliff in a mountainous region or an 11σ bank, etc. It is something.

<Conventional technology> In recent years, road networks are being developed in mountainous areas and along coastlines, and when roads are routed along rock slopes or cliffs in these areas, conventionally the slopes or cliffs are used to secure the road surface. Drill as
The ``cutting method'' is carried out by forming a long slope, the ``Rock Sierra I method'' involves excavating an area large enough to secure the road surface and installing a lock shet to prevent rockfall accidents, and the ``Rock Sierra I method'' involves cutting through an I tunnel. -Nnerue method" etc. were practiced.

<Problem to be solved by the invention> However, for example, although the conventional cutting method is advantageous in terms of construction cost, it has problems with ease of construction due to the slope inclination and cutting slope. Due to this, the slopes are often long and the area of rock excavation becomes large, making construction difficult. In addition, in terms of maintenance and management, it is difficult to maintain the integrity of the slope because it is a long slope, and secondary disasters are likely to occur because it promotes weathering. becomes. Furthermore, from the point of view of land acquisition, as the road becomes a long road, the width of the road becomes wider, making it necessary to widen the scope of acquisition. It is also likely to induce landslides along geological weakening.

The Rock Sheet method also allows for a smaller excavation area compared to the Cut-1 construction method, but there remains the risk of rockfall accidents. In particular, it is still fresh in our memory that recently in Fukui Prefecture, a rock shed constructed using the same method was destroyed by falling rocks and trees, resulting in the loss of human life, and the problems with the 11th method have been brought into focus. , and according to I. Nnerue's method,
Since there is no long slope, the above-mentioned problems are solved, but there are problems such as increased construction costs (and even higher maintenance costs for internal lighting, etc.).

Therefore, the present invention has good workability by reducing the excavation area, is suitable for maintenance and management of safety measures such as preventing accidents caused by falling rocks, and requires less land acquisition. The purpose of this project is to develop structures for passing roads, etc. on rocky slopes (J cliffs) of mountains, etc., as well as methods for moving them upstream.

Means for Solving the Problems> Therefore, the present invention firstly aims to improve the interior of an overhang-shaped excavated portion having a roadbed and an inner wall surface formed by excavating into the surface of a rock slope or cliff. A half-tunnel structure consists of a support installed along the wall surface and supports placed at regular intervals between the support and the open end side of the roadbed. Shoring is installed along the inner wall surface of an overhang-shaped excavated part that has a roadbed and inner wall surface formed by excavating against the surface, and the rock behind the shoring is driven into the shoring. A half tunnel structure consists of rock bolts buried in the ground, and supports placed at regular intervals between the support and the open end of the roadbed. On the other hand, an overhang-shaped excavation part having a roadbed and an inner wall surface is formed, and a shoring is installed along the inner wall surface of the excavated part described in -1-, and a temporary structure that supports the shoring near the open end of the roadbed The above objective is achieved by a method of constructing a half tunnel in which supports are erected and the supports are then passed between the supports and the open end side of the roadbed at a constant interval.

<Function> In other words, in the present invention, an overhang-shaped excavation part is formed in the rock, etc., and the support T installed along the inner wall surface of the excavation part and the open end side of the support and the roadbed are formed. Since the pillars are placed at regular intervals in between, deformation of the rock near the inner wall surface A1 is effectively suppressed. In particular, if rock bolts are buried in the bedrock behind the shoring, deformation of the bedrock is further suppressed.

When constructing the half tunnel structure of the present invention, an overhang-shaped excavation section is first formed, and shoring is installed along the inner wall surface of the excavation section where l = f.
Since temporary supports will be erected at 'iii, the supports can be placed at regular intervals while effectively preventing rock collapse.

According to the half tunnel of the present invention, since a long slope is not formed, the excavation area is small, and the excavation is performed in an overhanging manner, thereby eliminating the risk of an accident due to a fall.

<Example> In order to further clarify the gist of the structure of the half tunnel of the present invention and its construction method, examples will be described below using drawings.

As shown in Figures 1 and 2, the half tunnel A shown as the first embodiment is constructed by excavating an excavation section 4 that overhangs the surface of a rock 5 on a steep slope in a mountainous area.
A beam-shaped shoring 11 having a substantially doglegged cross-sectional shape is installed along the inner wall surface 2 of the excavated portion 4, and extends between the shoring 11 and the open end of the rock surface of the roadbed 3. As shown in FIG. 1, pillars 12 are provided at regular intervals along the wall surface, and pillar foundations 13 are formed on the apparent roadbed portion to increase strength. Since the half tunnel A is constructed as described above, there is no need to form a long slope, and therefore the area of rock excavation can be reduced, and the second part of the half tunnel is free from falling rocks and rock. Even if it falls, it will not be crushed by the fall as in the case of the lock sheet construction method. In addition, the width in front of the road may be narrow, making land acquisition easier.

This half-tunnel Δ is performed according to the procedure shown in FIG. Specifically, horizontal construction is carried out using the following method. 3. Excavation section First, the excavation section 4 is formed by excavating the surface of a rock slope or cliff. In other words, the excavation portion shown in FIG. 4 is performed. This excavated portion 4 is obtained by excavating to have an overhanging cross-sectional shape as shown in FIG. 5, and has a roadbed 3 and an inner wall surface 2. Book#'t
In the 6 construction method, the target ground is usually medium-hard rock to hard rock, so the excavation is mainly done by blasting. However, with blast excavation, there is a risk of loosening other piles, so great care must be taken during construction.

In recent years, I/N tunnel excavation by N A "T" M has become popular, and mechanical excavation technology has improved compared to blast excavation due to the original purpose of NΔTM, which is not to damage the ground. A hard rock excavation method using a hole-drilling machine, in other words, a slot I/drilling machine is used to drill slots on the outer circumference and face of the tunnel to form a free surface, and the blocks surrounded by the free surface are subjected to high-hydraulic fracturing. Break the rock using equipment, expandable crushing materials, hydraulic wedges, etc., and then break the rock with a hydraulic breaker.
There is a method for excavating hard rock without blasting by crushing it by impact.

In addition, the boom excavator uses T, B, and M (+-nel polling machines) to excavate the entire cross section of the rock at once, and there are few success stories in Japan, where the geology is subject to rapid changes and there are many springs. On the other hand, it is inexpensive, flexible and adaptable to changes in construction methods, and there are no restrictions on the shape of the cut cross section.
It has the advantage of being easy to move and install in a short time.

■Erection of shoring Next, as shown in FIGS. 4 and 5, shoring 11 is installed along the inner wall surface 2 of the excavated portion 4. The shoring is provided in the form of a beam. In the case of the Honji method, it is advantageous to use highly rigid supporting materials in order to suppress the deformation of the ground.

The standard material for shoring is H-shaped steel with a pitch of 1.0m. !
5ox 1.50 or 200 x 200.

■Erecting temporary supports Subsequently, as shown in FIG. 5, temporary supports 15 are erected.

This is done before installing the supports 12, and since the arch effect cannot be expected like in a tunnel, temporary supports are always required. The second support should be made of net and connected to the temporary support. The temporary supports will be removed after the branch office is constructed. The standard members of the temporary support are I-T section steel 300 with a pitch of 1.0m.
x 300 or 400 x 400.

■Construction of the branch As shown in Figure 5, construct pillars at a certain interval between the shoring and the open end of the roadbed. The pillars meet the architectural limits after construction, and are aesthetically treated by widening the pitch of the temporary pillars. As shown in Figure 5, the upper beam and foundation work are integrated. After the construction of the pillars is completed,
The safety of the pillar is of paramount importance, and if the foundation of the pillar is unstable, it is necessary to reinforce it with anchors, etc.

■Construction of lining Lining is performed for the aesthetic treatment of the excavation surface, shoring, etc., protection against small collapses on the excavation surface, protection against spring water, etc., and is performed using covered concrete, precast lining, etc. Do it with consideration.

Next, a half tunnel B (not shown as a second embodiment) has approximately the same configuration as the first embodiment, but as shown in FIG. Bolts 14 are driven into the bedrock on the back side of the ceiling 111 of the shoring 11. The Rockhol I.1
4 are driven into the ceiling portion 111 from the top to the 1τ portion at appropriate intervals, and are arranged at regular intervals along the inner wall surface 2. If the Rockholt 14 is provided in this way, the deformation of the rock in the ceiling part is suppressed and there is almost no deformation, as can be seen from the analysis shown in T'The.

Next, a half tunnel based on the above structure will be analyzed. The analysis was performed using FEM (finite element method), which is a numerical analysis often used for tunnel deformation problems, etc., and this allows us to understand the form of deformation due to excavation, changes in stress state, etc. can. Furthermore, if the physical property values of the ground can be specifically obtained, the amount of deformation can be estimated. The main theme of this construction method is how to suppress the amount of deformation without damaging the ground, and for this reason, deformation analysis using FEM plays an important role in determining whether or not this method can be adopted. In this analysis, the ground is assumed to be a perfectly elastic body as a test case.

Here, when performing elastic analysis in FEM analysis,
The physical property values to be set are: 111th volume ρ (t/m"); 2. Elastic modulus (yank modulus) T (t/m"); and 2. Poisson's ratio ν.

Here, regarding the physical properties of rocks, the density ρ is in the range of ρ-20 to 3.0 (t/m'').Furthermore, the elastic modulus Eu is generally higher in igneous rocks than in sedimentary rocks. Poisson's ratio is C0
It is in the range of 2-03.

Furthermore, the relationship between the -axial compressive strength σ and the rock's elastic modulus E l (E, , = 303Xσ) is based on existing data.

can be read.

In addition, the correlation between YR stone physical properties and rock physical properties is E=i,
i]3×E,, 09130 E・Modulus of elasticity of rock (kg/cm2) El,: Modulus of elasticity of rock (kg/cm2).

In addition, the relationship between rock physical properties and elastic wave velocity is: density
11 (t/m”) ρ=2.06dV +,”IL
J"8・-axial compressive strength σ (kg/cm2) σ-22,8
3Vp2=07・Elastic modulus E (kg/cm2) E=
8.156X] OV i, “””'-,-] ],
- Poisson's ratio ν C0. /1501(]/V
,,)038''.

It is necessary to evaluate the physical properties of the rock based on the correlation of each physical property, such as -lr, and to set appropriate physical property values.

It should be noted that it is necessary to judge whether the amount of deformation obtained by FEM analysis will lead to the destruction of the entire structure. NA
In designing and constructing TMI tunnels, the NΔTM concept will be useful as the excavation will proceed while managing deformation.

For example, a method has been proposed in which the ground t, I-+ strain is calculated backwards from the results of displacement measurements such as tunnel interior displacement, crown subsidence, underground displacement, etc., and the safety of the tunnel is quantitatively evaluated based on the magnitude of the strain. ing. What is introduced here is the concept of "critical strain." If the fracture strain is the strain at which a rock breaks, the critical strain takes a value smaller than the fracture strain, which is a dangerous state for safety. This is thought to be due to strain. Here, the critical strain is defined as follows.

ε. =σc/E Here, ε. , limit strain LJc・-
The axial compressive strength, E elastic modulus, and ocular field strain are quantities that are not significantly affected by discontinuous surfaces such as joints. That is, if the unconfined compressive strength decreases due to the influence of the discontinuous surface, the elastic modulus also decreases, and the degree of decrease is almost the same. This indicates the possibility of estimating the critical strain of rock from rock core values.

An actual analysis will be performed based on the method of setting physical property values and evaluating the analysis results as described above. The analysis is performed according to the procedure shown in FIG. The cross section of the actual analysis was as shown in Figure 7, and the physical property values were set based on the assumption that the rock in the depth direction is hard rock, and the ground was set to layer a as shown in Figure 7. The physical property values were set for four layers: , 1 layer, C layer, and d layer. The physical property values of each layer were set as described above.

(The following is a blank space) In addition, in FIG. 7, in the conventional cut-up method, excavation is performed as shown by the two-dot broken line.

In order to grasp the effect of supporting rock bolts, the following load conditions were set to calculate the deformation.

1. Deformation due to excavation 2. Deformation due to excavation when there is shoring 3. Deformation due to excavation when there is rockhole I/Shoring
-) is set by combining the following commands.

GRAV Gravity load (initial stress state) EXCΔ:
Excavation (excavation of elements) BANK: Mounding (addition of elements such as shoring) DLOA
D In the case of distributed load (load due to rock bolt) 1G
GRΔV for RAV-EXCA 2 → GR for BANK-IEXCA3
The analysis results performed under the following conditions are as follows: Δv-4BΔNK-IDLOAD→EXC8.

The deformation form near the excavation surface is shown in Figure 8 (△) for each load condition.
~(I3). In Fig. 8, the broken line shows the state before deformation, and the solid line shows the state after deformation.
) is the deformation due to excavation only, (B) is the deformation with shoring, and (C) is the deformation with shoring. The figure shows the deformation form and degree of deformation under each load condition when a rock bolt is applied.

In FIG. 8, the deformation diagram is scaled based on the maximum displacement amount, so the displacement scale is different for each load condition. However, the state of deformation can be compared. The matters obtained from the modified form are summarized as follows.

■In the case of deformation due to excavation, the amount of deformation is greatest at the open part at the large end of the excavation, but it can be seen that this amount of deformation is kept small when shoring is provided.

■Furthermore, when Rockholt beads were applied, the deformation of the top plate that was present when only shoring was used was suppressed, and the structure was almost completely free of deformation.

■If shoring is provided, the amount of deformation will be greatest at the bottom plate. Since this was an elastic analysis, it is thought that the deformation was suppressed by the shoring, or that the deformation affected the bottom plate.

If we summarize the amount of deformation near the excavation surface (=1), the amount of deformation of the contact number not shown in Fig. 9 is shown in Table 1 for the vertical direction and Table 2 for the horizontal direction.

(Margin below) Table 1 Amount of change in y direction (cm) Table 2
Amount of change in direction (cm) -1- By comparing the amount of change due to each load case, we can find the following trends: deformation due to excavation only, deformation with shoring, and deformation with shoring. It will be done. In particular, the second shoring works effectively against the deformation of the ceiling. For example, the degree of deformation at node number 106 is approximately 4.0 mm when there is shoring, whereas 2 [if there are 2, approximately 1/20 such as 0 and 2 mm
can be suppressed to It is thought that the effects of Rockpol I will play a major role in the stability of the woodworking method if the design is designed to suppress deformation based on the measurement results of the magnitude and direction of Rockpol I force.

It should be noted that the present invention is not limited to the present examples (but may be arbitrarily defined within the scope of the purpose, operation, and effects described below of the present invention, and these changes do not change the gist of the present invention in any way. Needless to say, this is not something you can do.

<Effects of the Invention> In the present invention configured as follows, there is provided a support that is installed along the inner wall surface of an overhang-shaped excavation portion formed on a board, etc., and a link between the support and the roadbed. Since the supports are placed at regular intervals between the open end sides of the support structure, deformation of the rock near the inner wall surface can be effectively suppressed by the supports and support supports. This is also recognized from the above-mentioned analysis results.

In particular, if Rockholt is buried in the bedrock of the support work, deformation of the government demand can be further suppressed.

In addition, when constructing the half tunnel structure of the present invention, first an overhang-shaped excavation section is formed, and after 1- installing the support along the inner wall surface of the excavation section, before installing the supports. Since temporary supports are erected, the supports can be placed at regular intervals while effectively preventing the rock from collapsing, making it possible to prevent accidents such as front placement, thereby increasing safety.

According to the half tunnel of the present invention, since a long slope is not formed, the excavation area can be reduced, and construction efficiency can therefore be improved, and maintenance is also easier compared to the cutting method. Become. In particular, since the excavation is performed in an overhanging manner, the risk of an accident due to the fore-end falling is also eliminated.

In addition, in terms of land acquisition, since only overhanging excavation is required, the acquisition area can be kept small and unobstructed.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a perspective view of a half tunnel, FIG. 2 is a cross-sectional view of the half tunnel, and FIG. , Figure 4 is a flowchart showing the construction method, Figure 5 is an explanatory diagram showing the construction method, Figure 6 is flowchart 1 showing the analysis method, and Figure 7 is a cross-sectional view showing the shape of the ground used in the analysis. , Figures 8(A) to (C) show deformation due to excavation only;
FIG. 9 is an explanatory diagram showing the degree of deformation in each case of deformation with shoring and deformation with shoring and rockpol I. FIG. 9 is an explanatory diagram showing node numbers. A: Half tunnel B Half I tunnel 11: Shoring 111 Ceiling section 112: Side section
12. Strut 13: Strut foundation 140 Kholt 2° inner wall surface 3 Subgrade 4 Excavation part: 5. Bedrock

Claims (1)

[Claims] 1) Along the inner wall surface of an overhang-shaped excavated portion (4) having a roadbed (3) and an inner wall surface (2) formed by excavating into the surface of a rock slope or cliff. Shoring installed along the road (11
), and struts (12) extending at regular intervals between the shoring and the open end side of the roadbed. 2) Shoring installed along the inner wall surface of an overhang-shaped excavated portion (4) that has a roadbed (3) and an inner wall surface (2) formed by excavating into the surface of a rock slope or cliff. (11
), a rock bolt (14) driven into the support and buried in the bedrock behind the support, and a pillar (12) inserted at a constant interval between the support and the open end side of the roadbed. )
A half tunnel structure characterized by consisting of. 3) An overhanging excavation section (4) having a roadbed (3) and an inner wall surface (2) is formed on the surface of a rock slope or cliff, and shoring ( 11) along the road and support the support near the open end of the roadbed (
15), and furthermore, a support (11) is inserted at a constant interval between the support and the open end side of the roadbed.