Ian McFeat-Smith
Charles Haswell & Partners (Far East)

G.K. Nieuwenhuijs
W.C. Lai
Electronic & Geophysical Services, Ltd., Hong Kong

Application of seismic surveying, orientated drilling and rock classification for site investigation of rock tunnels

Abstract
This Paper outlines the merits and limitations of various site investigation techniques for rock tunnels at portals, areas of low cover, urban areas and for sub aqeuos crossings. A model is presented which includes the integrated use of seismic refraction surveying, the drilling of vertical and orientated boreholes and collation of the data obtained in terms of a simple rock classification system.

This approach has been tried and tested in Hong Kong's sedimentary and igneous rocks on a number of tunnel projects involving the excavation of some 60kms of rock tunnels from 20 portals and shafts. Emphasis is given to the use of geophysical methods to locate rockhead and zones of potentially difficult tunnelling ground.