RESIDUAL SHEAR STRENGTH OF INFILLED ROCK JOINTS OF MEDIUM STRENGTH ROCK

Abstract

Determination of shear strength of infilled discontinuities is perhaps one of the complex problems faced by geotechnical engineers. The main difficulty is due to the large number of variable parameters, which influence the shear strength of infilled jointed rock masses. The rock mass contains discontinuities and is 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 characterization of discontinuity or a shear zone is not possible merely by visual examination of a specimen or 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 equilibrium. In the present work, an attempt has been made to study the influence of gouge thickness on the residual shear strength of infilled joints. Triaxial tests have been conducted on rock joints filled with gouge of various thicknesses ranging from 5-30mm.China clay has been used as infilled material. The joints considered are rough and smooth. The inclination of joints has been kept at 30° to the horizontal. The consolidated undrained tests have been carried out both for rough and plane joints filled with gouge. The confining pressures varied from 100 to 300 kPa .the discontinuities have been moulded with cement sand mortar of (4:1 ratio).For joints the asperity is taken as 30° with mean roughness amplitude of 4mm.The results show decrease in shear strength with decrease in roughness.