With the rapid growth of urbanization, the wide gap between demand and supply of power in the country has necessitated putting an increased thrust towards development of hydroelectric projects particularly in geologically complex Himalayan terrain. Tunnelling in Himalaya is undoubtedly the most challenging activity in hydro power construction. The hydropower tunnelling works in India were mostly accomplished by conventional drilling and blasting methods resulting in time and cost overruns. Now, while the focus is on faster completion of projects, need for an advanced technology more particularly in tunnelling is being felt. As a consequence, use of TBM has gained importance in hydropower tunnelling for being a more dependable alternative to drill & blast method. However, the ability of TBM to cope with varying ground conditions in Himalaya has posed a question mark in utility of this machine. The weak, jointed, sheared/fractured rock mass of Himalaya, under high stresses and potential confined aquifers, pose a major challenge to tunnelling engineers. The initial experience with TBM in Dulhasti Project (India) was not encouraging as TBM got submerged and ultimately buried which was partly attributed to unexpected ingress of water. Similarly, in Parbati-II and Tapovan Vishnugad Projects (India), excavation of HRT by TBM faced severe difficulties. However, success was achieved in excavation of inclined pressure shaft by a double shield TBM in Parbati-II Project. Presently, successful construction of 14.7km of HRT in Kishanganga Project (India) by double shield TBM has established TBM technology as a viable alternative for execution of long tunnels in Himalayas.

The paper presents a brief account of the geological and geohydrological problems faced in some of the TBM driven hydropower tunnels in India, lessons learnt from them and prospects and the future challenges to be faced in TBM driven Himalayan tunnels.

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