Contractors on the £1.4bn Delhi Metro project in India are using the New Austrian Tunnelling Method (NATM) to accelerate excavation after unexpected ground conditions delayed progress of the tunnel boring machines (TBMs). Three TBMs have been used on the project but unexpected mixed face conditions, where the strata are made up of both hard and soft rock, have made tunnelling difficult. Engineers were changing the cutters more often than anticipated. NATM is being used at several locations to make up time. The tunnel forms the second line of the three line metro system and will run 11km from Vishwavidalaya in the north of the city to the Central Secretariat in the south.
Completion is scheduled for June 2005.