| 摘要 |
PROBLEM TO BE SOLVED: To prevent drilling efficiency from lowering even if cutter bits are worn, and improve safety and working efficiency, in the cutter head of a tunnel boring machine. SOLUTION: A plurality of first cutter bits 33 are fixed to the cutter spoke 32 of a cutter head 31, and a plurality of second cutter bits 43 are rotationally movably fitted adjacnt to a plurality of the first cutter bits 33. Usually, the second cutter bits 43 are held with receiving positions received in the cutter head 31, and when the first cutter bits 33 are worn, they are moved to projecting positions projecing from the front face of the cutter head 31 by a rotational jack 47. |
