| 摘要 |
PROBLEM TO BE SOLVED: To easily enlarge a diameter in a part of propelling pipe tunnel section or the like having a curve section. SOLUTION: An initial form divided into a plurality of arc section pieces in the circumferential direction and assembled in the circumferential direction has a diameter of a cylindrical shape approximately the same as that of the adjoining propelling pipe in the direction of about the axis in a tunnel, a recess is formed in a part of the inside circumferential surface and, at the same time, segment pieces 11 forming specific tapered surfaces on the inside circumferential surface of the end in the direction of the axis and a sheet-like body stored inside of the recess in the segment pieces 11 and closing a space made between the neighboring segment pieces 11 in the circumferential direction are included. The circumferential space between the segment pieces 11 is enlarged to enlarge an outside diameter in the direction of the tunnel section by thrust in the direction of the axis in the tunnel transferred through the tapered surfaces 12 from the end of the propelling pipe buried contiguously in the direction of the axis when the segment pieces 11 are assembled.
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