ABSTRACT:

Tunnelling through the fragile, weak and jointed rock masses of Himalaya is a challenging task. Almost in all the tunnelling projects of Himalaya some or the other type of tunnelling problems have been encountered and are still being faced; be it a face collapse, chimney formation, water inrush, squeezing, etc. Though it is not a welcoming situation, but there is a lot to learn from such conditions. The experiences of Himalayan tunnelling are briefly presented in the paper.

INTRODUCTION

The Himalayan region and its adjacent basins straddle a third of India"s land mass and support about half the country"s population. The 100 or more dams across its rivers and tunnels supply almost 50 per cent of the country"s power requirements and irrigate millions of acres. But geologically the Himalaya is among the most unstable mountain range in the world (India Today, 1993). Himalaya occupy a unique position internationally providing substantial power production from hydro-power projects, a highly cost-effective clean and renewable energy resource. Total annual energy potential of the fast flowing rivers has been calculated at roughly 80000 TWh, out of which the economically viable potential has been assessed at 10000TWh. Only about 25 per cent out of this potential has been tapped so far. Almost all the hydro-electric projects in Himalaya have an underground structure, be it a tail race tunnel, a head race tunnel, an adit, a cavern for turbines or transformer hall, shafts, etc. In the paper, the lessons from past and present tunnelling operations have been present in brief to highlight the challenges of tunnelling through Himalaya.

THE HIMALAYA

The Himalayan range, located to the north of the subcontinent, was formed by the collision of the Indian Plate with the Eurasian Plate.

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