| 摘要 |
PROBLEM TO BE SOLVED: To provide a segment ring structure which does not hinder construction of a width-spread portion of a tunnel, satisfies necessary performance at each portion of the tunnel, and is economical. SOLUTION: The width-spread section of the tunnel is constructed by removing a part of mutually facing portions of the two or more existing tunnel segment rings which are adjacent to each other, and connecting a newly constructed inner structure to the remaining segments. In a cross section of the tunnel width-spread portion, the segment ring structure is formed of the plurality of segments in the single segment ring, and the removed segment 1 is different in structure from the remaining segment 2. Further, at the time of formation of the segment rings, appropriate strength is imparted to each of the segments, corresponding to a location in the tunnel.
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