PROBLEM TO BE SOLVED: To provide shield-excavation technique, by which branch-line shield machines can be started from a plurality of branch spots of a main truck tunnel, and a shield machine, which has a short machine length and a simple structure and by which curving performance can be ensured. ;SOLUTION: The shield machine 1 has a front drum 2, an outer drum member 3, a main-body frame 4, a cutter disk 5, a cutter driving motor 6, a plurality of shield jacks 7, a sludge removal facility 8, an erector device 9, etc. The outer drum member 3 is externally fitted slidably to the front drum 2, the dront drum 2 and the outer drum member 3 are formed in a double structure and a main truck tunnel is excavated, and segments are constructed to the internal surface of the outer drum member 3 and a branching starting port is formed while sections excepting the outer drum member 3 in the shield machine 1 are forward moved relatively to the outer drum member 3 as excavating the main truck tunnel. The outer drum member 3 is drawn near to a front to the front drum 2, the shield machine 1 is moved forward from the branching starting port, and the branch-line shield machine is started from the branching starting port. A plurality of branching excavation can be conducted.;COPYRIGHT: (C)1999,JPO
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