Abstract
An infilled rock joint is likely to be the weakest plane in a rock mass. The most pronounced effect of the presence of infill material is to reduce the friction of the discontinuity boundaries (i.e. rock to rock contact of the joint walls). The thicker the infill the smaller the shear strength of the rock joint, and once the infill reaches a critical thickness, the infill material governs the overall shear strength and joint walls (rock) play no significant role. However, some infilled joints may gain strength over time due to consolidation mechanisms, but may be weakened upon subsequent joint movements. Several models have been proposed to predict the peak shear strength of infilled joints under both constant normal load (CNL) and constant normal stiffness (CNS) conditions, taking into account the ratio of infill thickness (t) to the height of the joint wall asperity (a), i.e. t/a ratio. CNS models provide a much better accuracy of the infilled joint behaviour in the field but none of these models have focused on the overconsolidation effect of the infilling material. This paper presents a critical review on the existing models and a series of laboratory investigations carried out on idealised saw-toothed rock joints at the University of Wollongong in order to verify the effect of overconsolidation. The tests show how the overconsolidation ratio (OCR) influences the shear strength. The critical thickness, i.e., t/acrit, decreases with increasing OCR. A revised model for predicting the peak shear strength of rough infilled joints considering the effect of OCR is presented on the basis of the laboratory tests performed
Publication Details
This conference paper was originally published as Indraratna, B, Oliveira, DAF & Jayanathan, M, Revised Shear Strength Model for Infilled Rock Joints Considering Overconsolidation Effect, Proceedings of the 1st Southern Hemisphere International Rock Mechanics Symposium SHIRMS 2008, Perth, 16-19 September 2008. Original conference information available here