To comply with the federal government policy of contracting work to private industry and to obtain feedback from field trials sooner, we had Geokon build (through Solinst, Canada) six vibrating wire rings according to CANMET specifications (size, profile). Geokon used its own vibrating wire-clamping method, exciter and amplifier circuitry. The Geokon units showed high-quality workmanship and did well during the monitoring phase. They failed during recovery, for which they were not designed. At the same time, CANMET tested its own prototypes. The field trials were in excess of 12 months and a total of 30 units have been evaluated. In addition to Geokon, the Millimeter Machine Shop and Richard Brancker Research of Ottawa, Ont., provided contract services for this program.
At the end of the period, CANMET had developed a strain (stress) sensor which is unique in regard to installation/retrieval, ruggedness, calibration stability, wire-clamping method and innovative circuitry (small size, low power consumption). Low-cost manual readout and in-the-hole data loggers are available.
We believe this instrument justifies some attention by the rock mechanics community because it fills a long-existing need for radial borehole monitoring in hard rock mines. Dr Gerhard Herget, Head, Instrumentation Section, and F. Kapeller, Technologist, CMTL/MRL/CANMET
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