Tunnelling in the Himalayas: Risk Assessment and Management for Tunnelling in Extreme Geological Conditions

This paper draws upon experience gained from a series of major tunnel projects undertaken in the Himalayas and several others worldwide that identify specific engineering risks being encountered in extreme geological conditions in developing mountainous terrain. A state of the art Risk Management Plan and Matrix is presented and used to demonstrate appropriate methodology for identification and management of such hazards and risks as well as appropriate mitigation measures to be undertaken for effective control of the works. Experience is drawn from a series incidents encountered in major rock tunnels where severe access constraints, unstable and snow bound portals, large water inflows, silt flows, rock bursts, squeezing ground, wide fault zones, hard abrasive quartzies, schistose metamorphic rocks, soft youthful sandstones have been, and are currently being excavated by drill and blast, roadheader, open type and double shielded TBMs. Means of minimizing such risks and their impact on contracts are identified together with improved practices for the Indian Tunnelling Industry. Indicative international costs for tunnelling in such conditions are also provided.