The surface roughness of unfilled rock discontinuities has a major influence on the hydro-mechanical behaviour of discontinuous rock masses. Although it is widely recognized that surface roughness is comprised of large-scale (waviness) and small-scale (unevenness) components, most investigations of surface roughness have been restricted to small fracture surfaces (<1m2). Hence, the large-scale components of roughness are often neglected. Furthermore, these investigations typically define roughness using two-dimensional profiles rather than three-dimensional surfaces, which can lead to biased estimates of roughness. These limitations have led to some contradictory findings regarding roughness scale effects. This thesis aims to resolve some of these issues. The main findings indicate that discontinuity roughness increases as a function of the sampling window size contrary to what is commonly assumed. More importantly, it is shown that the estimated roughness significantly decreases as the resolution of surface measurements decrease, which could lead to the under estimations of roughness and, consequently, discontinuity shear strength.

The surface roughness of unfilled rock discontinuities has a major influence on the hydro-mechanical behaviour of discontinuous rock masses. Although it is widely recognized that surface roughness is comprised of large-scale (waviness) and small-scale (unevenness) components, most investigations of surface roughness have been restricted to small fracture surfaces (<1m2). Hence, the large-scale components of roughness are often neglected. Furthermore, these investigations typically define roughness using two-dimensional profiles rather than three-dimensional surfaces, which can lead to biased estimates of roughness. These limitations have led to some contradictory findings regarding roughness scale effects. This thesis aims to resolve some of these issues. The main findings indicate that discontinuity roughness increases as a function of the sampling window size contrary to what is commonly assumed. More importantly, it is shown that the estimated roughness significantly decreases as the resolution of surface measurements decrease, which could lead to the under estimations of roughness and, consequently, discontinuity shear strength.

Discontinuity surfaces generally consist of undulations termed as roughness. It is well known that surface roughness plays an important role on the shear strength and shear behavior of discontinuities. However, the effect of roughness will not be the same when the direction of shearing changes. This effect causes variation of shear strength with shearing direction or in other words anisotropy on shear strength. In this thesis, an experimental study was performed to investigate the effect of roughness and anisotropy on shear strength. For this purpose, joint samples were prepared using a model material and direct shear tests were conducted at different normal stress levels and shearing directions.