This report includes a feasibility study and system design for an initial prototype of a sensing system for pre-excavation subsurface investigation for tunnels in rock. Tunnels in rock are very expensive, and costs often rise far above estimates when unforeseen problems are encountered during excavation. New techniques in rapid excavation technology, such as the development of boring machines, have increased the need for improved site investigation. Possibilities for a new sensing system that will provide more complete data on subsurface conditions were investigated. Favorable results obtained from high-resolution geophysical sensing in boreholes have been combined with improvements in drilling of long, horizontal, precise boreholes in order to provide an economical alternative to pilot tunnel for subsurface investigation.

February issue includes Appendix entitled Directory of United States Government periodicals and subscription publications; September issue includes List of depository libraries; June and December issues include semiannual index