Stepwise application of horizontal seismic profiling for tunnel prediction ahead of the face

摘要

Prediction of geologic boundaries ahead of the tunnel face is of major importance for safe and economic tunneling, especially in Japan's complex geology. The Japanese Islands are on an active tectonic boundary and subduction zones that contain 86 active volcanoes and more than 2000 active faults. Consequently, many weak, fractured, and faulted zones are encountered when excavating long-spanned tunnels in Japan. Horizontal drilling from the face can detect weak zones directly. However, it is time-consuming and often interferes with tunneling works. Fan shooting and seismic tomography were tried in 1985 for delineation of weak zones in surrounding rocks but had limited success. Field experiments expanded in 1992 to include the use of VSP to predict ahead of tunnel face. After this technique was reoriented, it was renamed in-tunnel horizontal seismic profiling (HSP).