Degree Name

Doctor of Philosophy


School of Civil, Mining and Environmental Engineering


Discontinuities such as fault planes, joints and bedding planes in a rock mass may be filled with different types of fine-grained material that are either transported or accumulated as gouge due to weathering or joint shearing. Behaviour of soil-infilled rock joints has significant importance with respect to the strength of fractured rock mass. The presence of even a small amount of fine grained infill material within a joint can reduce its shear strength considerably. Therefore, it is crucial to examine how the infill material can adversely affect the joint shear strength. Previous studies of infilled joints have mainly been focused on idealised regular joint patterns due to the simplicity and reproducibility in laboratory testing.

Depending on the degree of saturation and the thickness of the infill, the shear strength of the rock mass can be adversely affected. Previous laboratory studies have mainly examined the role of saturated infill that exhibits the minimum shear strength. However, in practice, the infill materials are mostly partially saturated generating matric suction within the joint that can contribute to increased shear strength. To the authors’ knowledge this is the first study to examine the influence of unsaturated infill on the joint shear strength. A series of laboratory triaxial tests on idealised model joints and imprinted natural joint profiles was carried out, with constant moisture contents of the infill being maintained. Based on the laboratory observations an empirical model for describing the infilled joint shear strength was developed in which the initial suction of the infill was based on the soil-moisture characteristic curve. As no current standards are available for such joint testing, it is anticipated that this laboratory attempt will provide a useful platform towards establishing a more accurate estimation of infilled joint strength in rock masses.