ABSTRACT
In hard rock tunnelling, exploration techniques often only consist of probe drillings, which do not always contribute sufficiently well to the understanding of the spatial distribution of geological features. Reflection seismic investigations near the tunnel face are nowadays a valuable complement, as mechanical properties of the rock mass can be derived from the velocities of P- and S-waves. This enhances the understanding of ground conditions and enables the timely identification of hazardous zones. This study presents the application of the tunnel seismic technique during the excavation of an exploratory adit for the proposed Coire Glas Hydro Pumped Storage scheme, when the rock condition suddenly changed from moderate and very good rock quality to a highly fractured state. As part of a comprehensive characterization program, the seismic campaign yielded valuable information ahead of the face including in-situ seismic velocity values. The seismic results are compared with an 80 m long horizontal core drilling and subsequent tunnelling recordings.
