Overstressing of the rock surrounding a tunnel can result in either brittle fracture of the intact rock or shear failure along pre-existing discontinuities such as joints or shear zones. These two types of failure can co-exist and the extent to which the failures ...

A discussion on the use of the geological strength index (GSI) for the characterisation of tectonically undisturbed but lithologically varied sedimentary rocks rock masses is presented. Two GSI charts are proposed for estimating the mechanical properties ...

A review of underground openings, excavated in varying rock mass types and conditions, indicates that the initiation of brittle failure occurs when the damage index, Di , expressed as the ratio of the maximum tangential boundary stress to the laboratory unconfined ...

Stress-strain curves for brittle rocks show three characteristic stress levels: crack initiation, long-term strength, and peak strength. Damage-controlled testing at low confining stresses has shown that the long-term and peak strengths are sensitive to the ...