EFFECT OF BEDDING AND SHEARING PLANE ON SHEAR BEHAVIOUR OF SEDIMENTARY ROCK

Abstract

Shear strength is an important criterion while designing a structure over rock mass. This shear strength is significantly affected by the presence of joints or cracks. In sedimentary rocks there are discontinuities due to deposition of subsequent layers while formation. These discontinuities are called bedding planes and being the plane of weakness; these have a significant effect on the strength and deformation criterion. By keeping the above information in mind an organized laboratory investigation was planned to analyze the effect of these bedding planes on strength and deformation of rock mass. In this project, laboratory tests were performed for characterization of rock material, Kota sandstone, brought from Dabi mines, Kota, Rajasthan. Physical properties were evaluated by using the Indian Standards test procedures. Anisotropic effect due to presence of bedding plane was estimated by testing rock samples at different orientations, bedding planes being at angle to the loading direction. Oblique shear tests were performed for inducing fracture in rock sample and for estimating shear strength due to shear failure along a predetermined failure plane. Field shear tests were carried out on Kota sandstone to estimate shear strength due to sliding friction failure between fractured surfaces. This project mainly focuses on effect of a single parameter in particular affecting the strength: the angle between bedding plane and loading plane. Brazilian tensile strength tests were carried out to know the effect of tensile stresses on the mode of failure of rock material. Rock core samples were used for estimating physical properties and various strength tests were performed by following standard test procedures. Field shear tests were performed under constant normal load condition. Tests were conducted on air dried samples at room temperature for at least 15 days.