METHOD FOR PREDICTING DANGER IN CONSTRUCTING OF TUNNEL

摘要

PROBLEM TO BE SOLVED: To prevent blows resulting from a leakage of compressed air and oxygen deficiency in the air by mixing a tracer gas in the compressed air, feeding the mixture into a tunnel, and checking the presence/absence of the tracer gas by a tracer gas detector at the ground surface. ;SOLUTION: When a tunnel is built, compressed air of a predetermined pressure with helium gas mixed is sealed from an upper air lock 3 into a working chamber 2 and the ground is excavated downward in the working chamber 2. In this case, it is enough to mix the helium gas with the compressed air approximately by 1%. A gas in the periphery of a caisson body 1 is sucked at the ground surface by a helium leak detector 6 which is loaded on a cart 7 and thus freely movable. The presence/absence of the helium gas is thus detected. If the compressed air with the helium gas mixed leaks in a stratum 5, the helium gas penetrates the stratum 5 faster than the air and scatters at the ground surface. Therefore, by checking the presence/absence of the helium gas by the helium leak detector 6, a leakage of the compressed air from the tunnel can be detected before the compressed air leaks to the ground surface.;COPYRIGHT: (C)1998,JPO