The effect of joint frequency on a discontinuous rock mass under experimental compressive strength testing conditions

The dominating parameters of a discontinuous rock mass are joint orientation, joint frequency and joint strength. Under experimental testing conditions, these parameters can individually influence rock mass strength, elastic properties and the mode of failure. This study aimed to assess the effects of joint frequency on rock mass properties, particularly in a confined stress state, as a review of the literature identified a lack of experimental information on the topic. A total of 24 uniaxial and 87 triaxial compressive strength tests were undertaken using intact and discontinuous, jointed sandstone core specimens, the latter having saw-cut joints orientated across the longitudinal axis of the core. Based on the results, several conclusions have been made concerning the Anisotropic Effect factor, the Joint Factor method and the mode of rock failure. First, the Anisotropic Effect factor can be adjusted for joint frequency. Second, the joint strength parameter of the Joint Factor method can also be modified and finally, a single shear failure plane was observed as the dominant mode of failure for both intact and jointed rock specimens under confinement. These conclusions provided and insight into the effects of joint frequency in a discontinuous rock mass.