India's Hydro Power Potential has been estimated at about 250,000 MW. Most of this is located in Himalayan region and involve hundreds of kilometers of tunneling. Tunnels constitute substantial percentage of the overall cost of the project and are generally on the critical path in the overall execution of the project. Tunneling through adverse geology of Himalaya, the world's loftiest and youngest mountain is a challenging task for the planners, engineers and geologists. A number of hydro-electric projects in India have been delayed by several years due to encountering of faults, thrusts, shear zones, heavy water ingress, hot temperature conditions, emission of poisonous gases etc. during tunneling. The paper presents the challenges of tunneling experienced under adverse geological conditions and the adopted solutions and remedial measures along with case studies.

1 Introduction

The total estimated hydro power potential of India is 2, 44,000 MW including Medium & Major Conventional Hydro (1, 50,000 MW), Pumped Storage Schemes (94,000 MW) but excluding Small, Mini & Micro (15,000 MW). The present installed capacity of hydro power including pump storage schemes as on 31.01.2015 is of the order of 41,000 MW being less than 16% of the total installed capacity of 2,58,701.45 MW including thermal, nuclear, hydro and renewable energy (Sharma 2015).

The construction of tunnels and underground civil structures is a big challenge to engineering skill, when these are located in the weak and fragile rock mass under shear zone. More than 75% of hydro power potential in India is located in the Himalayan hill states of Jammu & Kashmir, Himachal Pradesh, Uttarakhand and North-Eastern states. The world's highest and the youngest mountain belt of Himalaya is a classic example of an orogenic system created by continent -continent collision of Indian and Sino-Tibetan plates. During the Eocene-Oligocene period the convergence of Indian and Sino-Tibetan plates resulted in the crustal shortening that was largely accommodated by south directed deformation resulting in tectonic transport and thrusting all along the arcuate length of the Himalayan range and eastward extrusion through strike slip faults (DeCelles et al. 2001, Joshi & Tiwari 2009).

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