Shear strength parameter is a crucial in designing the rock mass structures such slope and tunnel. Stability of rock mass structure is affected by apparent joint sets and discontinuities present in the rock mass especially when the joint interfaces degraded and physically altered due to weathering effect. The weathered condition imposed on joint surface importantly play the role to control the shear strength characteristic and sliding behaviour. A comprehensive study and focussing on effect of weathering grade to the rock joint surface particularly for granite type of rock was introduced. A set of granite samples were collected from a quarry then been classified into respective grade of weathering based on surface hardness by using Schmidt rebound hammer and rock material density by using PUNDIT test. The standard laboratory testing of direct shear test that accordance to ISRM suggested method were carried out on jointed block samples with different grades of weathering. Detail assessment on rock joint samples were evaluated to characterize the physical appearance of different weathered joint surface condition. The rock joint surface assessment made based on Joint Roughness Coefficient (JRC) then been correlate with thin section petrographical results for justification with respect to mineral composition contents. As the result, the shear strength of weathered rock joint significantly influenced by the weathering grade due to changes of microstructure behaviour of the granite. Moreover, the lower grade of the granite sample has low frictional resistance force to against the sliding, hence indirectly produced low shear strength of the rock joint.
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