TUNNEL TIMBERING PATTERN SELECTING METHOD

PROBLEM TO BE SOLVED: To clarify a timbering pattern change standard. SOLUTION: A seismic exploration is made prior to excavating an unexcavated part of a tunnel 10. In the case of making the seismic exploration, an oscillating hole and a receiving hole are excavated. Elastic wave emitted from the oscillating hole is propagated to the unexcavated natural ground on the working face side and reflected by the natural ground at a boundary of different texture, and the reflected elastic wave is received by an accelerometer installed in the receiving hole. In this seismic exploration, a large number of reflection surfaces 16a-16e appear, and parts indicated by dotted lines are reflection surfaces where rock texture changes from soft to hard, while a part indicated by a two-dot chain line is a reflection surface where rock texture changes from hard to soft. In the appearing status of the reflection surfaces 16a-16e, the reflection surfaces where rock texture changes from soft to hard are dominant, and the reflection surface 16b with largest reflection energy also changes from soft to hard, so that the natural ground in front of the working face is predicted to be better. In an execution timbering pattern, a timbering pattern CI is therefore changed to simpler CII in correspondence with natural ground classification C.