PURPOSE: To expand and contract an excavated cross section during tunnel excavation by expanding and contracting each superposing section of an external cylinder, a partition wall and one half section and the other half section in the cross direction of an excavating cutter by a jack for shielding elongation and shrinkage. ;CONSTITUTION: A fixed number of shielding machines 1 are arranged, and the shielding machines for excavating corners are installed at the corner sections of a tunnel to be excavated. The external cylinders 2, excavating cutters 4 and partition walls 8 of each shielding machine 1 are shrunk in the cross direction in each superposing section 3, 5, 6. The external cylinders 2, the excavating cutters 4 and the partition walls 8 are held by jacks for shielding expansion and contraction in the shielding machines 1, a bedrock is excavated by the excavating cutters 4, and excavated soil and sand are carried and carried out by screw conveyors 17. Reaction is taken in segments constructed in parallel with excavation, a plurality of shielding jacks are elongated, and the shielding machines 1 are propelled. The superposing sections 3, 5, 6 of the external cylinders 2, the cutters 4 and the partition walls 8 are extended at the time of the spreading of an excavated cross section, and formed air gaps are sealed with grease, thus preventing the intrusion of foreign matters.;COPYRIGHT: (C)1995,JPO
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