JPH0349356B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Industrial Application Field The present invention relates to a method for constructing supports in the shield construction method applied when excavating tunnels, etc. with a shield excavator, and particularly for tunnels with an oval cross section. This invention relates to a method for constructing supports in the shield construction method, which is suitable for use when excavating.

(b) Prior art Figure 8a is a cross-sectional view of primary support for a tunnel with an elliptical cross section constructed using the conventional support construction method, and b is a diagram showing the bending that acts on the primary support in the cross section shown in a. It is a bending moment diagram showing a moment.

Conventionally, when excavating a tunnel with a shield excavator, it has been common practice to assemble and use precast concrete segments as primary support, and to apply an inner wrap of concrete as secondary support.

(c) Problems to be solved by the invention When the cross section of the tunnel is circular, there is no need to provide any support after the primary support is constructed as the excavator excavates, until the secondary support is constructed. Although this was not done for the primary shoring (that is, the primary shoring alone was sufficient to resist the earth pressure), as shown in Figure 8a, when the tunnel cross section was made oval. , compared to a tunnel with a circular cross section, a large bending moment MS due to earth pressure acts on the primary support (see Figure 8b). Therefore, after the construction of primary support,
Unless some reinforcement measures are taken until the secondary shoring is constructed, there is a risk that the tunnel will collapse due to earth pressure. It is possible to counteract the bending moment by increasing the thickness of the primary support, but in that case, the thickness of the primary support would be extremely thick, which would be uneconomical and unsuitable for tunnels with the same excavation diameter. However, there was a disadvantage that the size of the part used for roads etc. was correspondingly smaller.

In addition, conventionally, a method has been proposed in which prestress is introduced into the primary support by installing prestressed steel wires or prestressed steel bars within the segment where the primary support is constructed; The installation work is extremely complicated, and there is a disadvantage that the internal structure of the segment becomes complicated due to the installation of PC steel wires and PC steel bars.

In order to eliminate the above-mentioned drawbacks, the present invention eliminates the need to install a PC steel wire or a PC steel bar within the segment,
This is an economical shield construction method that can reduce the thickness of the primary support while resisting the bending moment caused by earth pressure, and therefore allows for a larger portion of the tunnel to be used for roads, etc. in tunnels with the same excavation diameter. The purpose of this study is to provide a method for constructing support.

(d) Means for Solving the Problems That is, the present invention provides for a tunnel that is excavated by a shield excavator while constructing primary support by segments immediately after the shield excavator, and when constructing the primary support, As the shield excavator moves forward, the primary support comes into contact with the ground and before earth pressure acts on the primary support, a prestress introduction mechanism is provided between mutually opposing portions of the primary support in the internal space of the tunnel. is connected, and the prestress introduction mechanism applies a countervailing force to the primary support from the inner space side of the tunnel in a direction that cancels out the bending moment acting on the primary support due to earth pressure, and in this state, the primary support is brought into contact with the ground, and then a secondary shoring is constructed inside the primary shoring, and after the secondary shoring is constructed, the prestress introducing mechanism is removed and the earth pressure is applied to the primary shoring and the secondary shoring. It will be structured so that the burden will be paid jointly.

(e) Effect With the above configuration, the bending moment due to earth pressure acting on the primary shoring is canceled by the canceling force generated by the prestress introducing mechanism, so that the primary shoring is constructed and the secondary shoring is Until it is constructed, it acts to protect the primary support from collapse due to earth pressure.

(f) Embodiments Hereinafter, embodiments of the present invention will be described based on the drawings.

Figure 1 is a cross-sectional view of the primary support for a tunnel with an elliptical cross section constructed using the shield construction method, which is an embodiment of the present invention. FIG. 2 is a bending moment diagram showing the acting bending moment; FIG. 2 is a sectional view when primary support for a tunnel with an elliptical cross section is constructed by a support construction method in the shield construction method, which is another embodiment of the present invention; b is a bending moment diagram showing the bending moment acting on the primary support in the cross section shown in a, and Fig. 3 is a bending moment diagram showing the bending moment acting on the primary support in the cross section shown in a. A sectional view when the primary support of the tunnel is constructed, b is a bending moment diagram showing the bending moment acting on the primary support of the cross section shown in a,
Fig. 4 is a front view showing an example of the prestress introducing mechanism, Fig. 5 is a perspective view showing an example of connecting each segment and the prestress introducing mechanism with a PC steel wire, and Fig. 6 is a front view showing an example of the prestress introducing mechanism. FIG. 7 is a front view showing another example, and FIG. 7 is a partially enlarged front view showing details of the prestress introducing mechanism of FIG.

Tunnel 1 excavated by shield excavator
As shown in FIG. 1a, the primary support 2 is excavated by a shield excavator and constructed at that time, and the primary support 2 has an oval shape in cross section. The primary support 2 is usually composed of a plurality of precast concrete segments, and a prestress introduction mechanism 3 is provided in the center of the primary support 2 in the horizontal direction.
As shown in FIG. 4, the studs 5,
6. One end of studs 5 and 6 is
The segment 2a protrudes into a hole 2b bored in the outer periphery of each segment 2a, and is screwed into the nut 7 while penetrating the bearing plate 9 in the hole 2b. stud 6,6
is detachably provided with a tensioning mechanism 12 that constitutes the prestress introduction mechanism 3 described above, and the tensioning mechanism 12 is attached to a receiving girder 15, and the receiving girder 15 is connected to the stud 6 via a coupler 11. It has a plurality of connection bolts 13. A center hole jack 1 is connected to the support girder 15 via a ram chair air 16.
7 is provided, and the center hole jack 17
A ram 17a is provided on the ram 17a so as to be freely protrusive and driveable in the horizontal direction, that is, in the directions of arrows A and B. A tension bar 19 is screwed onto the ram 17a via a coupler 11, and the tension bar 19 passes through a hole 15a drilled in the support girder 15, and the other end is screwed onto the stud 5 via the coupler 11. ing. Note that the tension bar 19 has a lock bolt 19a.
are screwed together.

Since the tunnel 1 has the above configuration, the tunnel 1, which is excavated with an elliptical cross section by a shield excavator (not shown), is constructed by assembling the primary support 2 and a plurality of segments 2a in the excavator. The excavator continues the excavation work using the assembled primary support 2 as a foothold, but the segment 2a assembled into an elliptical shape inside the excavator is moved by the surrounding area as the excavator moves forward. Before coming into contact with the ground and receiving earth pressure,
In the interior space of the assembled segment of the excavator, ie the tunnel, a prestress introduction mechanism 3 is mounted.

That is, as shown in FIG. 4, the segment 2a is provided with studs 5 and 6 in advance, and when the segment 2a is installed at a predetermined position, the studs 5 and 6 located opposite each other in the tunnel are installed. and the tension bar 19 and connection bolt 13 of the prestress introducing mechanism 3 are connected using the coupler 11. The prestress introducing mechanism 3 is installed horizontally in the center of the tunnel 1, as shown in FIG.
Since the tunnel 1 has an elliptical cross section, the curvatures of each part are all different in the same cross section. Therefore, since the installation position of each segment 2a is uniquely determined from its curvature, the studs 5 and 7 are provided in the segment 2a having a predetermined curvature (that is, the segment 2a forming the side surface portion of the tunnel 1). By placing the prestress introduction mechanism 3 in the tunnel 1, the prestress introduction mechanism 3 can be easily set horizontally in the tunnel 1.

After the prestress introduction mechanism 3 is thus set, the center hole jack 17 is driven to pull the ram 17a in the direction of arrow B. Then,
The tension bar 19 is also pulled in the B direction via the coupler 11, and the stud 5 is also pulled in the B direction. In addition, due to the reaction, the stud 6 is pulled in the direction A via the support girder 15 and the connecting bolt 13, and as a whole, the tunnel 1 has a side portion inside the tunnel 1, as shown in FIG. A tensile force FT that pulls in the direction acts. This tensile force FT acts as a prestress for the primary shoring 2, since it is generated within the excavator, where the segments 2a are not yet in contact with the soil.

In this state, tighten the lock bolt 19a,
The tensile force FT is generated by the tension bar 19 and the connecting bolt 13 without passing through the jack 17.

In this state, when the primary support 2 is pushed out into the ground, the outer peripheral surface of the primary support 2 comes into contact with the ground and earth pressure acts on it. This earth pressure generates a bending moment MS on the primary support 2, but a tensile force FT is already applied to the primary support 2 by the prestress introducing mechanism 3, and the tensile force FT is different from the bending moment MS due to the earth pressure. Since a bending moment in the opposite direction is generated in the primary support 2, the resultant moment is equal to the bending moment MS (No. 8
See figure b. ) is an extremely small value compared to The bending moment MS distribution diagrams in Figures 1, 2, 3, and 8 are for the cross section of the right half of tunnel 1, and PRF in the figures represents the contour of tunnel 1. It is.

Further, in the above embodiment, the prestress introducing mechanism 3 is a case in which rod-shaped members such as the tension bar 19 and the connecting bolt 13 are stretched between the segments 2a, but the prestress introducing mechanism 3 is
Not limited to rod-shaped members, as shown in FIG. are assembled into one by a block 22 placed near the center of curvature of the segment 2a, and a tensile force is applied using a jack or the like.
It is also possible to configure it to give FT.

Furthermore, as shown in FIGS. 6 and 7, H is applied to segments 2a and 2a facing each other in the tunnel.
Steel materials 23, 23 such as shaped steel are embedded, and when constructing the primary support 2, the steel materials 23, 23 are buried.
Similarly, the steel materials 25, 25 and the steel materials 25, 25
A prestress introduction mechanism 3 consisting of a hydraulic jack 26 etc. bolted in series between the steel materials 25, 2
5. It is also possible to install it via the bolt 10, and in that state, drive the hydraulic jack 26 to pull it in the direction of arrow C, thereby applying a predetermined prestress to the primary support 2. Further, in the case of this embodiment, when a predetermined tensile force FT is applied by the hydraulic jack 26, a plurality of bolts 27 are installed between the brackets 25a which are provided in such a manner that the hydraulic jacks 26 are scissored to each steel material 25 and facing each other. death,
Of course, it is also possible to take over the tensile force FT from the hydraulic jack 26 by tightening the bolt 27 with the nut 29, and then remove the hydraulic jack 26 in this state. In such a case, similarly to the embodiment shown in FIG.
(In the case of Fig. 4, after tightening the lock bolt 19a, the center hole jack 17 is attached to the support girder 15.
Remove it and reuse it for constructing the next segment. ).

In addition, it is attached to the primary support 2 and has a predetermined tensile force FT.
The prestress introduction mechanism 3 that applies the prestress introduction mechanism 3 is used when the secondary shoring is constructed and the tunnel 1 is able to sufficiently resist earth pressure by the primary shoring and the secondary shoring. Configure to remove.

In addition, FIG. 2 shows a case where the prestress introduction mechanism 3 is not provided in the center of the primary support 2, but is provided in two locations, one at the top and one at the bottom of the cross section of the tunnel 1. Normally, a tunnel 1 having a circular or elliptical cross section has a public part such as a road built in its center, so the prestress introducing mechanism 3
By providing these above and below the tunnel 1, the prestress introduction mechanism 3 does not become an obstacle when constructing the part for use. FIG. 2b shows the state of the bending moment MS at that time.

Further, the prestress applied to the tunnel 1 may be applied in any manner as long as it acts in a direction to cancel the bending moment MS due to earth pressure.
As shown in the figure, provided in the vertical direction of the tunnel 1,
It is also possible to configure the prestress introduction mechanism 3 to apply an expansion force FE that pushes the upper and lower ends of the primary support 2 outwards. FIG. 3b shows the state of the bending moment MS at that time.

In addition, when removing the prestress introducing mechanism 3 after constructing the secondary support, as shown in FIGS. By matching the surface position X where the support 30 is constructed, the prestress introduction mechanism 3 can be easily removed after the secondary support 30 is constructed.

Further, in the above embodiment, the present invention was applied to excavating a tunnel 1 having an elliptical cross section, but the present invention is not limited to a tunnel having an elliptical cross section, but can also be applied to a circular tunnel. Of course.

(g) Effect of the invention As explained above, the tunnel 1 is excavated by the shield excavator while constructing the primary support 2 by the segment 2a immediately after the shield excavator.
When constructing the primary support 2, before the primary support comes into contact with the ground as the shield excavator moves forward and earth pressure acts on the primary support, the primary support is constructed in the inner space of the tunnel. A prestress introduction mechanism 3 is connected between mutually opposing parts of the tunnel, and the prestress introduction mechanism applies a tensile force from the inner space side of the tunnel in a direction that cancels out the bending moment acting on the primary support due to earth pressure.
A countervailing force such as FT or expansion force FE is applied to the primary support 2, and in that state, the primary support is brought into contact with the ground, and then a secondary support is constructed inside the primary support, and the secondary support is After the construction, the prestress introduction mechanism was removed and the earth pressure was jointly borne by the primary and secondary supports. Until the secondary shoring is constructed, the prestress introduction mechanism 3 changes to the secondary shoring and supports the earth pressure together with the primary shoring. Until this happens, it becomes possible to support earth pressure that cannot be supported by the thickness of the primary shoring alone. In addition, when the secondary shoring is constructed and the earth pressure can be jointly borne by the primary shoring and the secondary shoring, the prestress introducing mechanism 3 can be removed, so the prestress introducing mechanism 3 can be removed. does not occupy the internal space of the tunnel, making it possible to effectively utilize the internal space of the tunnel, and also allowing prestress to be introduced into the primary support by installing the prestress introducing mechanism 3 at any position in the tunnel. It becomes possible,
Flexibility in design and construction can be dramatically increased. In addition, conventional primary support 2
Compared to the method in which the secondary shoring is used as a mere decorative material, the present invention uses the secondary shoring as a structural member together with the primary shoring 2 after the secondary shoring has been constructed. The bending moment MS due to earth pressure, which was previously borne entirely by the primary support 2, can now be jointly borne by the primary support 2 and the secondary support, and the thickness of the segment 2a of the primary support 2 can be made thinner accordingly. Not only is it efficient and economical, but with the same excavation diameter, a larger area can be used for roads, etc.

In addition, by adjusting the canceling force generated by the prestress introducing mechanism 3, it is possible to create the operating state of the bending moment MS according to the conditions of the ground and the primary support 2, so that support construction work can be carried out on site. This can be done flexibly depending on the situation.

In addition, since the prestress introduction mechanism 3 is provided in the tunnel interior space, it can be placed inside the segment.
There is no need to install PC steel wires, PC steel bars, etc., which not only simplifies the structure of the segments that make up the primary support, but also eliminates the complicated work of installing PC steel wires, PC steel bars, etc. can do.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the primary support for a tunnel with an elliptical cross section constructed using the shield construction method, which is an embodiment of the present invention. FIG. 2 is a bending moment diagram showing the acting bending moment; FIG. 2 is a sectional view when primary support for a tunnel with an elliptical cross section is constructed by a support construction method in the shield construction method, which is another embodiment of the present invention; b is a bending moment diagram showing the bending moment acting on the primary support in the cross section shown in a, and Fig. 3 is a bending moment diagram showing the bending moment acting on the primary support in the cross section shown in a. A sectional view when the primary support of the tunnel is constructed, b is a bending moment diagram showing the bending moment acting on the primary support of the cross section shown in a,
Fig. 4 is a front view showing an example of the prestress introducing mechanism, Fig. 5 is a perspective view showing an example of connecting each segment and the prestress introducing mechanism with a PC steel wire, and Fig. 6 is a front view showing an example of the prestress introducing mechanism. A front view showing another example, FIG. 7 is a partially enlarged front view showing details of the prestress introduction mechanism shown in FIG. 6, and FIG. A sectional view when the support is constructed, and b is a bending moment diagram showing the bending moment acting on the primary support in the cross section shown in a. 1...Structure (tunnel), 2...Primary support,
3... Prestress introduction mechanism, 30... Secondary support, MS... Bending moment, FT... Cancelling force (tensile force), FE... Cancelling force (expansion force).

Claims (1)

[Scope of Claims] 1. In a tunnel excavated by a shield excavator while constructing primary support by segments immediately after the shield excavator, when constructing the primary support, as the shield excavator moves forward, Before the primary support comes into contact with the ground and earth pressure acts on the primary support, a prestress introduction mechanism is connected between mutually opposing parts of the primary support in the internal space of the tunnel, and the prestress introduction mechanism From the inner space side of the tunnel, a counteracting force is applied to the primary support in the direction of canceling the bending moment acting on the primary support due to earth pressure, and in this state, the primary support is brought into contact with the ground, and then the primary support is A secondary shoring was constructed inside the shoring, and after the secondary shoring was constructed, the prestress introduction mechanism was removed, and the earth pressure was jointly borne by the primary shoring and the secondary shoring. How to construct supports in the shield method.