| 摘要 |
PROBLEM TO BE SOLVED: To maximally restrain vibration and rolling without a large wall block being produced in such a case that a concrete material wall forming a parts of a cylinder, is cut so as to form a branch tunnel started from a large shield excavator at a right angle. SOLUTION: A branching shield excavator 5 is incorporated in a large diameter shield excavator 1 having a branch excavating opening formed in a part of a cylindrical shield plate 10 and blocked by an arcuate concrete material wall 4 having a large wall thickness. The cylindrical shield plate 10 is provided at its front end face with a semispherical cutter disc 6 having its center part projecting outward, corresponding to an arcuate longitudinally sectional shape of the concrete material wall 4, for cutting the concrete material wall 4. |
