STRENGTH AND DEFORMATION BEHAVIOUR OF JOINTED ROCK

Abstract

Most of the rational approaches to the design of the structures on or in a rock mass are based on the strength and deformation response of the rock mass. The present investigation is undertaken to understand the strength and deformation behaviour of jointed rock. Rock mass are heterogeneous containing cracks, fissures, joints, faults and bedding planes with varying degree of strength along these planes of weakness. These discontinuities or plane of weakness which are often present in a rock mass, control its strength behaviour to a large extent. The presence of joints, always makes a rock mass, weaker and more problematic. Apart from the frequency of joints, the orientation of joints with respect to the loading direction assumes greater significance from the stability point of view. Another significant aspect concerning the joint is the strength along these joints. Estimation of Reliable strength and deformation behaviour of jointed rock is necessary to evolve safe and economical designs for tunnels, open pits, dam foundations and underground chambers In current thesis, an attempt has been made to study the strength and deformational behaviour of Phyllite, obtained from Tehri Dam Project Site in terms of compressive strength and deformational response in Uniaxial and in Triaxial compression at varying confining pressures 5 MPa,10 MPa ,20 MPa ,30 MPa and 50 MPa and at Schistocity angle ((3=0°,15°,30°,45°,75° and 90°) with respect to action of axial stress. The test data was used to fit the existing strength criterion. The laboratory investigations on phyllite rock revealed that, its ultimate strength varies nonlinearly in both confined and unconfined states at different orientation and different confining pressure. This confirms that phyllite is an anisotropic rock. Increase in the confining pressure causes an increase of the rock strength in all cases of Schistocity angle.