Seismic Refraction Surveys in a Bored Tunnel at White Pine Copper Mine: Fid-Bau Portal

Seismic Refraction Surveys in a Bored Tunnel at White Pine Copper Mine

J. J. K. Daemen / C. Fairhurst

One of the aims of this research was the study of the influence on support requirements of different excavation methods, specifically drilling and blasting as compared to tunnel boring. The purpose of making seismic refraction surveys of tunnel walls in blasted and in bored tunnels was to obtain a quantitative comparison of the overall rock properties. This was done at the White Pine Copper Mine where development tunnels were being bored and blasted in the same geological formations. Seismic refraction surveys were carried out with a Bison Signal Enhancement Seismograph. Two types of measurements were made: traverses along the tunnel and cross-sectional surveys. An isometric view of the tunnel with the locations of the surveys is included. Measurement results are presented under the form of a series of tables and of traveltime vs. impact distance plots. The tables are computer printouts of straight line least square fits. Contrary to expectations no broken zone was observed. A broken zone around the tunnel, i.e. a zone where the mechanical properties of the rock have been changed markedly would show up in the measurements as a low velocity layer. Results were inconclusive, since there are no results reported as yet from a blasted tunnel.