Strain monitoring in steel rock bolts using FBG sensor arrays

Rock bolts replace timber sets and steel arcs in securing the structural stability of underground cavities in order to reduce the volume of excavation. Rock bolts used in the mining industry are made of steel allowing up to 20% relative elongation of the bolt. Strain measurements using Fiber-Bragg-Grating (FBG) are limited to relative strains in the order of 1%. In order to allow measurements of up to 20% relative strain, special arrangements of the FBG sensors had to be found to extend their measuring range.