ABSTRACT
The paper reporte on various validation tests and improvements on a spiral strain gtage originally introduced in 1987 to monitor the load or the strain on cable bolts used as ground support. The original 70 cm long gauge has been further evaluated and modified in terms of many objectives: smaller overall diameter of the gauge, better waterproofing, assessment of temperature variation influence, reduction in the drift occurring immediately after installation, development of gauges of various lengths (18 cm to 3 m) in order to measure either local strains or average strains along the length of the instrumented cable and finally, rugger construction of the gauge to accompany slippage movements of the instrumented cable in the borehole. Experience accumulated over the years in various instrumentation programs involving the spiral strain gauge is also reported in the paper. It includes instrumentations in underground and open pit mines together with laboratory testing in which the basic properties of the spiral strain gauge together with its applications in other types of instrumentation such as in reinforced concrete, cable bolt slippage assessment, load transfer assessment in pull-out tests and in shear testing of reinforced rock joints, average strain assessment in steel cables, nutcage and birdcage cable bolt instrumentation and dynamic loading of cable bolts are evaluated.
