| 摘要 |
PROBLEM TO BE SOLVED: To provide an entrance ring which contributes to positive construction of a branch tunnel from a narrow main tunnel via which only a front trunk of a shield machine can be carried in, and is advantageous to improve branch tunnel construction efficiency. SOLUTION: The entrance ring 16 consists of a front section 30 and a rear section 32 both formed of a steel, and peripheral surfaces of the front and rear sections are arranged so as to extend along a single cylindrical surface. Right and left side surface portions 30B and notches 30C of the front section 30 are formed such that the entire areas of edges of the right and let side surface portions 30B abut on a cylindrical internal peripheral surface of a tunnel wall 14 of the master tunnel 12. The rear section 32 is formed such that a circumferential portion 32A thereof is detachable from the remaining portion 32B, and when the detachable circumferential portion 32A is detached, the remaining portion 32B has an opening 32C formed therein in a manner opening sideways. The entire internal surface of the rear section 32 has a water cutoff member 34 attached thereto, for elastically abutting on a trunk body of the shield machine to seal groundwater. COPYRIGHT: (C)2008,JPO&INPIT
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