Considerations for selection of tbm in himalayan geology

Tunnels are the most important components of many a hydroelectric project. World over, mechanized tunneling by using TBM has become an integral part of excavation/execution of tunnels for speedy completion of the hydroelectric projects, though the same is still in the nascent stages of development in India. This paper discusses considerations for selection of a particular TBM in any hard rock underground excavation in preference to the conventional drill and blast method (DBM) especially in the context of hydroelectric projects. A comparison of different types of TBMs has been made from considerations of geo-technical constraints and excavation progress. The most widely accepted TBM performance prediction models have been described briefly in relation to various rock mass properties and mechanical parameters of TBM for framing technical specifications and contractual conditions for any tunnel excavation. Finally a case study of Parbati HE project Stage II, where TBMs are deployed in horizontal as well as incline excavations is presented. This shall give an insight of the type of TBMs adopted, their performance till date in lower Himalayan geological conditions of Parbati HE project Stage II.