| 摘要 |
PURPOSE:To make it possible to simultaneously excavate a main tunnel as well as a preliminary tunnel. CONSTITUTION:A preliminary tunnel 3 is excavated at the outside of an expected excavating section of a main tunnel so that a part thereof sticks out and long size materials 6 such as electric wires, communication lines, air ducts, water pipes, etc., necessary for digging the preliminary tunnel are inserted in the protrusion and further, a shelter 10 protecting the long size materials from the impulse of blasting is provided therein as well. Hence, the long size materials 6 can be surely protected when blasting for expanding to the main tunnel 1. In this way, time preliminary tunnel can be excavated regardless of the expanding excavation of the main tunnel. Since the expanding excavation of the main tunnel can be carried out without transferring the long size material, excavation of the preliminary tunnel and expanding excavation of the main tunnel can be easily and safely conducted at the same time. Accordingly, the whole construction period can be greatly reduced. |
