Engineering behaviour of phyllites: Fid-Bau Portal

Engineering behaviour of phyllites

Ramamurthy, T. / Rao, G. Venkatappa / Singh, J.

Abstract The physico-mechanical behaviour of intrinsically anisotropic rocks cannot be assessed through common engineering experiences due to a number of governing intrinsic factors, e.g., variation of mineral assemblage, fabric and physical and mechanical properties. The study of such rocks under the stress conditions existing within the drilling reach of the earth's crust, has not been given due attention, not even in laboratory-simulated conditions. Therefore, it seemed worthwhile to undertake a comprehensive study using three varieties of intrinsically anisotropic phyllites, obtained from the vicinity of the Chamera hydroelectric project site in the Himalayan region. Attention has been paid to their petrographic and petrofabric analyses through thin-sections, X-ray diffraction and scanning electron microscopy, and the physical and geotechnical properties with special reference to their anisotropyp ]Compression tests were run from unconfined to a maximum confining pressure (σ3), of 70 MPa for the three phyllites at specified orientation angles, β (angle between the plane of weakness and the direction of the major principal stress, (σ1), of 0, 15, 30, 45, 60, 75 and 90°. Thus, the physico-mechanical response of the phyllites as a function of confining pressure and the orientation angle has been determined and the degree of anisotropy could be quantified in terms of physically measureable parameters.