Shear Strength Parameters of Granite Rock Mass: A Case Study

In situ shear strength parameters of rock mass are important design parameters required for design of structures founded on or constructed in rock mass. Block shear test method is quite popular among practicing engineers for determination of cohesion and friction angle of rock-to-rock and concrete-to-rock interface. Generally, at the stage of preliminary design, a value of desired shear strength parameters can be taken from available literature. However, such values must be used with proper engineering judgement. In case of rock mass, structural features of geology plays a very crucial role in affecting its engineering behavior. Same rock type may have significantly different shear strength parameters depending upon site-specific geological characteristics. In this paper, the variation in rock-to-rock and concrete-to-rock shear strength parameters of rock mass consisting of primarily granites is studied among three different geological variants, namely (a) western part of Himalaya, (b) Garo-Khasi Hills of Meghalaya, and (c) Eastern Ghat Belt of Andhra Pradesh. The variation in shear strength, cohesion, and friction angle is studied in terms of strength ratio, cohesion ratio, and friction angle ratio. These values are also compared with values for granites available in the literature. Site parameters supported with quantitative analysis of in situ data indicate that highest shear strength is expected at Eastern Ghat Belt and least shear strength at Garo-Khasi Hills.