PURPOSE:To prevent damaging quality of direct placed concrete by orderly placing concrete in the rear part of a shield excavator as a closed shield machine is self-run and pushed as a reaction force is exerted only on an outer peripheral natural ground. CONSTITUTION:Upon the starting of operation, a whole gripper 67c is thrust in a natural ground through grip opening parts h1 and h1' and a rack is pressed against a resistance force for engagement therebetween. The gripper 67c being a first arcuate plate piece is contracted, and an arcuate plate button is released to stretch a thrust jack J1 for the first arcuate plate piece by means of a resistance frame 6 serving as a reaction force. After excavation of an outer and an inner pipe is completed, a whole shield jack J3 is contracted to pull the resistance frame 6 to a front. After the shield excavator is self-run for excavation, concrete is placed. Through expansion of a concrete press jack J7, concrete is pressed through the medium of a spreader face plate.
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