| 摘要 |
PURPOSE: To enable long-distance drilling by advancing a preliminary gage cutter in the predetermined direction from an initial position inside the drilling diameters of gage cutters by operation of a thrust means. CONSTITUTION: In an initial position a preliminary gage cutter 52 is positioned inside the drilling diameters of a double edge type gage cutter 38 and a single edge type gage cutter 44, and is advanced by means of a hydraulic motor 32 and a shield jack 20 while drilling the natural ground ahead. When the wear of the gage cutters 38, 44 is detected, pressure oil is supplied to the oil passage 90 of the piston rod 60 of each preliminary cutter device 50 via piping 86. This pressure oil flows into a front chamber 96 consisting of a cylinder tube 58 and a piston 94, to move the cylinder tube 58 forwards and to advance the preliminary gage cutter 52 diagonally forwards via a bracket 66. With the head of a stopper pin 78 fitted into the pin hole 82 of a locking member 84 and the preliminary gage cutter 52 held in that position, the preliminary gage cutter 52 is used in place of the gage cutters 38, 44 to drill the natural ground ahead and the natural ground in the circumferential direction. |
