| 摘要 |
PURPOSE:To obtain usual excavation forces without weakening the excavating force by preventing the generation of great stress when excavating an excavating tube in a curved form. CONSTITUTION:A ringed tool 21 is inserted between the pressure-receiving back face of the receiving port of preceding excavation tube and the propulsive face of the insertion port of the following excavation tube. The width of the part 22 to be the inside of curve of the tool 21 during curved excavation is made wider in the crosswise direction than the other parts 23 and 24 in such a way as to increase the lapping margin between the propulsive face and the pressure-receiving face sufficiently. |
