| 摘要 |
PROBLEM TO BE SOLVED: To shorten a time required for forming an invert in the base ground of an existing mountain tunnel. SOLUTION: In order to form an invert 18 in the base ground 14 of an existing mountain tunnel 10, the following processes are applied sequentially to each of one half part 26 and the other half part 32 in the direction of the width of the base ground. By cutting the base ground, the base 34 of the side wall of lining is exposed and a space for forming the invert which extends in the transverse direction of the tunnel is formed. During the cutting of the base ground, subsequently, a plurality of support means 38 for supporting the side wall are disposed, spaced from each other, under the exposed base of the side wall, Lastly, concrete is placed in the space 18 for forming the invert.
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