This book outlines the stability analysis and rock support optimisation of headrace tunnel of Mai hydropower project in Nepal. The geology and the geo-technical parameters are comparatively poor at the project area as the headrace tunnel lies in Siwalik zone of Nepal consisting of Mudstone, Siltstone, Sandstone and shear zones. And also, Rock support defined during feasibility study of the project was inadequate for which this work has suggested some improvements in the support system of the headrace tunnel. The main objective of this study were to analyse the engineering geology and geotechnical parameters of the alignment and subsequently verify the stability and rock support design using two dimensional numerical modelling program "Phase2" with other two supporting software called "UNWEDGE" and "Rock Data". The tunnel alignment was divided into eight different sections considering the rock type and rock overburden. The two dimensional model was created representing each section in the alignment to analyse the elasto-plastic behaviour of Rockmass. Further, hydraulic fracturing assessment has also been carried out to know the effect of water pressure inside the tunnel.