ABSTRACT
Laboratory tests for determining the shear strength of bolted rock joints indicate that peak values of strength are developed when a grouted bolt is installed at an angle of about 35–50° to the plane of the joint. This range of angles generally corresponds to the peak, post-peak, or pre-residual region of behavior. Solution of practical problems, such as the bolting of unstable slopes or of major wedges in underground caverns, indicates that minimum bolt capacities are required when the bolt is angled perpendicular to the frictional resultant, corresponding to the arctangent of (τ/σn) relative to the joint, as above. Methods are described for generating appropriate shear force-displacement curves for rock joints so that a bolt of a given stiffness can be installed at the appropriate angle of mobilized friction. Bolts of lower stiffness require smaller installation angles and correspondingly increased capacity. The use of bolts of lower stiffness, for example partly grouted bolts, may be justified if displacements are irresistable, or if other components of support are of reduced stiffness. Bolt design should always be compatible with the expected deformation.
