Instrumented cable bolts developed at the Spokane Research Laboratory of the National Institute for Occupational Safety and Health were used in conjunction with existing ground control to monitor rock mass loads at various field sites (FMC Granger, Getchell, Meikle, SSX, K-2, and Stillwater). Axial and shear loads were determined by strain gauges to levels of instrument accuracy of ±5 N or ±5 microstrain as these loads were transferred to the instrumented cable bolts. These gauges were 12.5 mm long and embedded into a remanufactured king wire that replaced the conventional king wire. Cable bolt performance, quality of grout, and installation techniques were also assessed. By using instrumented cables, a mine operator can determine axial load along the cable at predefined gauge locations. By monitoring load on and displacement of the rock mass, more effective ground support can be selected and installed, which will lead to safer working conditions for miners.
Until recently, external measurement devices such as the tensmeg or resistance wire cable strain cell gauges (Hyett et al. 1997) were used to determine load on cable bolts, In 1996, the "stretch measurement to assess reinforcement tension" (SM,A.R.T) cable was developed and patented by researchers at Queens University (Hyett et al. 1997). This system replaces the king wire of a cable bolt with multipoint extensometers (MPBX''s) enclosed in a tube to measure cable elongation, thereby enabling deformation and load to be determined (Bawden et al. 1998),