A New Sensing System for Pre-Excavation Subsurface Investigation for Tunnels in Rock Masses. Volume I. Feasibility Study and System Design.

摘要

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. Pilot tunnel costs as with all subsurface construction are rising at rates much higher than the economy,thus the use of borehole site investigation has potentially very high benefit/cost characteristics. The prototype system designed is a highly mobile geophysical measurement (data acquisition) system. The system will take electromagnetic radar measurements,pulsed acoustical measurements,and multi-spaced array resistivity measurements. The sensors will be used in traverses along the borehole,and data will be taken and stored on magnetic tape for subsequent reduction and analysis at a computational center. The system could reduce accidents,reduce bid contingencies,and reduce other factors contributing to rapid escalating costs of subsurface excavation. Volume I describes the feasibility study and system design. Volume II contains the Appendices A-R.