In 2012, a new 6.65 m (21.8 ft) Robbins EPB will tackle mixed ground conditions in densely urban Chennai. The city is a rapidly growing technological and industrial centre. Owner Chennai Metro Rail (CMRL) has commissioned two new rail lines to help with traffic congestion, totaling 45.1 km (28.0 mi) in length. The Robbins EPB will excavate two 1 km (0.6 mi) tunnel sections of Lot UAA-01 on Line 1, extending from the Washermanpet area toward Chennai International Airport.The EPB, for contractor Afcons Infra?structure, will excavate variable ground consisting of granite, sand, silt, and clay with boulders up to 300 mm (12 in) in diameter. The mixed ground EPB design will utilize a combination of 17 inch diameter disc cutters as well as soft ground tools.Specialised, small grippers located around the circumference of the machine's shield will allow for cutterhead stabilisation in harder ground, and in addition will react the forces needed to pull the cutterhead back from the face.