| 摘要 |
PROBLEM TO BE SOLVED: To install bent steel pipes as supports to improve the ground even in the ground of weathered rocks and crushed rocks and to exchange bits for excavation according to changes in the ground. SOLUTION: A top heading 2 is provided at the planned part of a large- section tunnel ceiling. A propelling device carriage on which a bent steel pipe propelling device is mounted is moved to a predetermined location in the top heading 2. Bent steel pipe units in which hole enlarging bits and blade tips to be connected to down-the-hole hammers are built in at the tip parts are joined to one another by a steel pipe joining device provided for the propelling device. Then the planned surface 3 of the large-section tunnel ceiling is excavated, and the bent steel pipe units are propelled along the planned surface 3 by the propelling device. After propelling the bent steel pipes by a predetermined length, augers, universal joints, the down-the-hole hammers, the hole enlarging bits, and the blade tips inside the bent steel pipes are recovered through the steel pipes to leave only the steel pipes to be supports 1.
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