Abstract: Based on the discontinuity data available up to detail project report (DPR) stage, a kinematic analysis using program "Unwedge3" was performed earlier for determining shape and size of potential wedges in machine hall cavern of Vishnugad Pipalkoti Hydro Electric Project (VPHEP) and thus optimizing the orientation of ma-chine hall cavern. Keeping various aspects in view, orientation of the axis of machine hall cavern of VPHEP was kept as N 320°. Thereafter additional investigations were done by exploratory drilling & drifting and hydro fracture test etc. The data on dis-continuities was updated by detailed geological logging of the drift. The hydro frac-ture test also revealed orientation of major horizontal principal stress along N 320°. Based on the latest assessment of data on discontinuity orientation and stress re-gime, a fresh kinematic analysis using program "Unwedge3" has been performed again for optimization of orientation of machine hall cavern. The kinematic analysis revealed that orientation of machine hall of VPHEP may be kept as N 305° instead of 320°, however in this case the cavern axis shall no longer be along the major horizon-tal stress. Therefore, 3D stress analyses for machine hall cavern has been done using program "Examine3D 4.0". The results pertaining to displacements, stresses & strength factor in both the orientation cases of the cavern are compared to arrive at conclusion for optimum orientation of the cavern. This paper provides an insight to the various aspects considered for kinematic analysis & 3-D stress analysis performed for optimization of orientation of the ma-chine hall cavern.
1 INTRODUCTION Vishnugad Pipalkoti HEP with installed capacity of 444 MW is one of the major on-going Hydro Electric Projects envisaged to harness the huge potential of river Alaknanda in district Chamoli of Uttarakhand State of India.