Laboratory investigation of shear behavior of rock discontinuities based on shear rate, size and roughness characteristics

İşleyen, Ergin
Rock mass characteristics are significantly influenced by the presence of discontinuities. In order to develop safe rock engineering designs, factors affecting shear behavior of rock discontinuities should be carefully analyzed. In this study, effects of shear rate, sample size, roughness characteristics and co-dependency of these effects are investigated on rock discontinuity sample replicas. 3D models of the rock discontinuities are generated with close-range digital photogrammetry. Then, discontinuity models are obtained with a 3D printer, to be used as a mould to produce concrete discontinuity sample replicas for direct shear test. The suggested rock discontinuity sample replication methodology in the literature is adopted and found to be successful with accurate represantation of intended roughness level of the sample. The direct shear tests are conducted under three different constant normal load conditions with three different shear rates on two different sample sizes. The roughness degree of the samples are measured in terms of Z2, and it changes between 0.115 – 0.420. Experimental results indicated that, shear strength increases with increasing degree of roughness. Moreover, it’s revealed that effect of shear rate is a normal stress dependent property and it differs for high and low normal stress levels. Investigation of sample size effect showed contradictory results with the previous studies in the literature. It is observed that the shear strength of the small size samples is lower than the shear strength of the larger samples, even though the roughness is higher in the small samples. In addition, it’s revealed that the shear rate effect is co-dependent with the effect of the roughness and the effect of sample size. The shear rate effect becomes greater as the roughness degree decreases and the sample size decreases. 
Citation Formats
E. İşleyen, “Laboratory investigation of shear behavior of rock discontinuities based on shear rate, size and roughness characteristics,” M.S. - Master of Science, Middle East Technical University, 2017.