Hydraulic and earth engineering – Underground passageway – e.g. – tunnel – Boring
299 33, 405138, E21D 1302
TECHNICAL FIELD OF THE INVENTION
This invention relates to a method of forming an underground cavern, and more particularly, to a method of building an underground cavern of a large scale at a very deep place, and a tunneling machine suitable for use in a part of the process of building an underground cavern.
BACKGROUND ART OF THE INVENTION
Underground caverns of a large scale built at very deep places of the kind mentioned above are extremely big caverns having a depth of about 100 meters and inside dimensions of about 100 meters, and are utilized for underground power stations and natural resources storing depots, etc. Such underground caverns are generally built in hard rock beds.
However, with the development of high-degree utilization of underground space of late years, there are strong demands for building such caverns of a large scale at very deep places in soft grounds even in urban communities.
In the case of building such caverns in soft grounds, two methods have so far been used. One method is to build earth retaining walls "a" so as to surround a required space and then excavate earth and sand within the space, as shown in FIG. 1; this is called, "Continuous Wall Building Method" (Open Excavating Method). Another method is to excavate a tunnel "b" of a large diameter during which lock bolts "c" are driven from the inner surface of the tunnel into the ground simultaneously with injection of a grout, and then form a concrete wall "d" on the inner surface by spraying cement mortor; this is called, NATM method.
Of the above-mentioned prior art methods, the former is disadvantageous in that, if a cavern or a tunnel is to be built at a very deep place, then the thickness of the earth retaining walls "a" must be increased, resulting in an increase in the earth retaining wall building cost. At the same time, the latter is a method which has been developed of late years for use in building tunnels in mountainous districts. In the case of the latter method, if the scale of the tunnel to be built is large, then the thickness of the rock beds to be reinforced becomes large, and reinforcing work is effected while excavation of the tunnel is being made. Therefore, there occur losses in time due to changes in arrangement of operations and uncertainty in ensuring safety during excavation.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned deficiencies in the prior art, and has for its object to provide a method of building an underground cavern, which enables an underground cavern of a large scale to be built safely and economically at a very deep place in soft ground, or in a soft rock bed, and also provide a tunneling machine suitable for use in carrying out the aforementioned method of building an underground cavern.
To achieve the above-mentioned object, according to a first aspect of the present invention, there is provided a method of building an underground cavern, comprising the steps of forming a ground reinforcing zone around a portion to be hollowed out prior to excavating the underground cavern to be formed, and then excavating the interior of the ground reinforcing zone thereby forming the underground cavern.
According to a second aspect of the present invention, there is provided a method of building an underground cavern as set forth in the first aspect, wherein the ground reinforcing zone forming step further comprises the steps of forming the ground reinforcing zone around the portion intended to be hollowed out; digging a vertical shaft from the ground surface to the uppermost portion of the ground reinforcing zone; providing a starting station at the lower end of the vertical shaft where a tunneling machine is started; taking the tunneling machine into the starting station; starting the tunneling machine from the starting station so as to advance in the ground reinforcing zone to thereby dig out a spirally extending tunnel around the portion to be hollowed out; digging out a plurality of a holes by means of a ground reinforcing unit mounted on
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Baumaschine & Bautechnik, BMT, vol. 29, No. 6, Jun. 1982, pp. 302-307, Wiesbaden, DE; A. Eber et al, "Bauverfahren fur das Auffahren sehr grosser untertagiger Raume", p. 305, col. 2-p. 307, col. 2, FIGS. 2, 3, 5.
Kabushiki Kaisha Kematsu Seisakusho
Kananen Ronald P.
Taylor Dennis L.
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