Testing of rock joints filled with gouge using a triaxial apparatus

The rock mass contains discontinuities and its instability depends on the geometry of these discontinuities and the slope and orientation of the excavated face. One of the most important factors is the shear strength of potential failure planes. The characterisation of a discontinuity or a shear zone is not possible merely by visual examination of a specimen nor by subjecting it to conventional laboratory testing. The combined effects of the shear zone, its stress–strain history and the resulting strength deformation relation modulate the behaviour of rock mass, particularly when it approaches the state of limit equilibrium.This paper presents a testing technique for rock joints filled with gouge of various thicknesses (t=5–30 mm), dip angle (β=5–50°) and at strain rate (e=5–80 mm/h) in a triaxial testing system. The results of unconsolidated undrained tests carried out in triaxial conditions both for undulating and planar types of joints filled with gouge are reported. Extensive experimental results provided an insight into the development of a constitutive relation to predict strength criteria of discontinuous rock masses.