STRENGTH BEHAVIOUR OF ANESOTROPIC ROCKS

Abstract

In this study, an attempt has been made to study the anisotropic behavior 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 5MPa,10 MPa ,20 MPa ,30 MPa ,40 MPa , 50 MPa and 60MPa at Schistocity angle (P=00,150,300,450,750 and 90°) with respect to 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. The anisotropic curve is found to be of U-type. The maximum strength occurs at perpendicular to bedding plane (R =900) and minimum strength occurs at (3=30°.Tangent modulus (Et) is maximum when principal stress is parallel to bedding plane and minimum at orientation angle (i =30°.The deformation is maximum perpendicular (J3 =900) to bedding when compared to other orientations angle. By knowing c1; at P=00,300 and 90°, we can find the Major principal stress and Tangent modulus at any confining pressure and at any schistocity angle, without conducting triaxial tests At confining pressures at to 5OMPa both criteria matches well with the experimentation values except at high confining pressure of 60MPa,Where Hoek and Brown Criterion is more closer to the observed values The Tensile strength of phyllite has been determined by conducting Brazilian test at different orientations.