Imaging And Characterizing Fractures Ahead Of Tunnel Face Using In-Tunnel Hsp Method

A new method for imaging and characterizing fractures ahead of a tunnel face has been<br>developed and successfully applied to field measurements. The fundamental technique of the<br>method, we named in-tunnel HSP ( Horizontal Seismic Profiling ), is featured as an<br>combination of that being employed in VSP and reflection seismic method. The measuring<br>process of in-tunnel HSP is basically the same as refraction seismic survey. In-tunnel HSP can<br>provide 2-D sections for in-line and backward portions as well as the portion ahead of a tunnel<br>face, which enables us to verily the certainty of seismic events in the 2-D sections by<br>correlating them with actual fractures cropped out in a tunnel and characterize them<br>geotechnically prior to the prediction of undriven section.<br>We have applied in-tunnel HSP to 29 survey lines in 15 tunnels in Japan until now.<br>Field application of the method and engineering evaluation of the results has proved in-tunnel<br>HSP is quite practical to delineate and characterize fractures ahead of tunnel face and to<br>ensure the safety through the focused tunneling based on the prediction.