Degree Name

Doctor of Philosophy


School of Civil, Mining and Environmental Engineering - Faculty of Engineering


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 the reduction in 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. Once the infill reaches a critical thickness, the joint walls (rock) play no significant role in the overall shear strength. 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) boundary conditions, taking into account the ratio of infill thickness (t) to the height of the joint wall asperity (a), i.e. the t/a ratio. Models based on the CNS condition provide a much better accuracy of the infilled joint behaviour in the field, but only a limited number of studies have focused on the more realistic CNS stress-strain behaviour. This study presents a critical review of some of the earlier studies and the most recent advancement of a shear-strength model developed at University of Wollongong, Australia, supplemented with laboratory data for model validation. The effect of different factors on the shear behaviour such as the t/a ratio, infill friction angle, joint wall roughness, joint stiffness, and type of infill are presented. In addition the implication of soil-infilled joint on rock mass behaviour is investigated through extensive practical applications both analytical and numerical. The new set of proposed discontinuity strength and deformation relationships can be used as an alternative approach in design. Although the proposed soil-infilled joint model still suffers from inevitable limitations such as the empirical parameters that need further calibration with experimental data, the study vividly demonstrates its practical value with respect to underground excavation and slope stability in jointed rock mass.

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