Degree Name

Doctor of Philosophy


School of Civil, Mining and Environmental Engineering


Shear behaviour of rock discontinuities filled with weak layers plays a significant role in rock mass and mining stability. The water content and saturation conditions of the infill material can vary dramatically in the field. In fact, the infill material remains partially saturated in many cases. Compared with fully saturated conditions, the unsaturated infill material tends to increase the shear strength of the discontinuities. While researchers have attempted to study the shear behaviour of discontinuities filled with unsaturated materials, constant normal load boundary or triaxial conditions are usually adopted. However, the Constant Normal Stiffness (CNS) conditions are more realistic in many situations, especially in underground mining applications. In addition, the hydraulic/mechanical parameters of the infill material (i.e. void ratio, degree of saturation and matric suction) will vary during the discontinuity shear. Yet the shear strength models for the unsaturated-material-filled discontinuities proposed so far failed to capture these variations. Also, it is known that the infilled discontinuities have “two-stage” shear behaviour when the infill thickness to average asperity height ratio (t/a) is relatively low. While researchers and engineers are more focused on the behaviour after discontinuity asperities come to contact (i.e. “second stage”), the “first-stage” behaviour is more vital when the shear movement before asperities contact is large enough to cause engineering damage. Moreover, the infill lateral confinement conditions may significantly influence the infilledjoint behaviour of direct shear tests. However, related studies are rare.

In this research, A series of undrained CNS direct shear tests were performed to study the shear behaviour of unsaturated-material-filled discontinuities, with the infill water content ranging from 11% to 27.3% ...



Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.