The primary role of the bolt reinforcement is to minimise displacement of the existing fractures by providing confining stress to the fracture surfaces. In some cases, rockbolts may minimise some residual fracture formation within the moving strata. Rockbolts installed across the bedded, jointed or fractured strata is capable of resisting axial and shear deformation (Figures 13 and 14). The fully grouted bolt function can be classified into three separate categories: the axial resistance of the rockbolts subjected to tensile load; the shear resistance of the bolts installed across a potential shear plane and the combination of both axial and shear resistance of the bolts undergoing pull and shear loads.
Hence, there are three types of rockbolt failure mechanisms: the axial failure where bolts fail due to significant axial load; the shear failure where bolts yield due to large shear load; the combined axial and shear failure due to both axial and shear load. Figure 2.14 shows two bolts in an underground mine yielded due to a combination of pull (joint opening) and shear at rock joints.