EXCAVATION METHOD OF TUNNEL

PROBLEM TO BE SOLVED: To perform placing of long steel tube forepiling at the minimum angle near parallel without excessively performing widening and excavation by using a guide supporting inserting and fixing a guide pipe on an H-shaped steel web. SOLUTION: A guide supporting 3 matches H-shaped steel to the design cross section of a tunnel, bending processing is performed at prescribed curvature, and a guide pipe 4 is inserted and fixed in a hole provided in a web. The guide supporting 3 is set at a design position nearest to heading, a protection pipe 5 is inserted to perform spraying of concrete, and a steel tube 7 integrated with a rod 61 attached to a drill jumbo 6 and a diameter widening drill bit 62 is inserted into the protection pipe 5 and punched to place the steel tube 7. Only the supporting just before the guide supporting 3 is made a camber supporting 31 for avoiding interference with the drill jumbo 6. I-shaped steel, a lattice girder and the like can be used except for the H-shaped steel. Thereby placing of the long steel tube forepiling can be performed at the minimum angle without widening and excavating.