Fibre Optic Instrumented Rock Bolt Fibre Rebar

Rock bolts are subjected to a combination of axial and shear loading. Over the life cycle of the excavation, rock movements may transition from distributed to discrete as cracks and shear zones localise.

Accurately monitoring the strain profile of fully grouted rock bolts reveals much about rock mass behaviour around an excavation and about the rock bolts. Optical Strain Sensing represent the perfect solution for strain monitoring for most bolt types.

An optical fibre is embedded along 3 grooves machined along the length of the rock bolt. The delta 120° arrangement allows excellent resolution on axial strain and shear vector.

An optical connector is mounted at the end of the bolt. This connector is protected by a metal cap during both shipping and Installation

The optical bolt is installed with standard methods. The cap is removed for connection to the optical cable coming from the optical analyser. A new cap is mounted to permanently protect the optical connector and cable if shotcrete is not used.

The optical analyser can be located several hundreds of meters away from the bolts in a safe zone meaning this solution can be adopted in hazardous and explosive environments such as coal mines.

APPLICATIONS

– Suitable for rock mines, storage caverns, road and rail tunnels and coal mines

– Inherently safe and IS certifiable optical rock bolts

– Measurement of strain profile rather than localized strains

– Measurement of shear and axial longitudinal strain

– Spatial resolution from 5cm down to 1mm

– Operational accuracy better than +/-10 microstrains

– Instrumented optical bolt cost minimized

– Suitable to a variety of rock bolts : rebar, threadbar, NMX, CT, AT & AX grade bolts

– Clusters of bolts that can be monitored simultaneously