d-REBAR Instrumented Rock Bolt

How it works

The d-REBAR uses miniature inductive displacement sensors (long base-length strain gauges, 300-2000 mm) recessed into a 3.2 mm groove milled into the bolt. Stretch of the bolt shifts a precision coil relative to its high-permeability core, changing the frequency of a resonant circuit that the on-board microcontroller measures and temperature-compensates.

Every bolt undergoes multipoint calibration, with the coefficients written into microcontroller memory and a calibration report supplied with each unit.

Configuration

Up to six strain gauges can be fitted in two diametrically opposed slotted channels, in either staggered or stacked arrangements, so the sensor layout can be matched to a fully grouted rock bolt's load distribution. The instrument is designed to be spun in resin using a standard rock drill, with the electronics head either detachable during installation or permanently encapsulated in a stainless steel tube.

Data and connectivity

Readings can be taken with a handheld manual readout unit or logged continuously with a data logger. Data is provided as strain rather than load, since the strain gauges can follow deformation up to 5% - well beyond the roughly 0.5% range of a typical foil resistance gauge.