Bengaluru, July 30 : Karnataka Chief Minister B. S. Yediyurappa has launched the Bengaluru Metro Phase II tunnelling operations in the city, an official said on Thursday. "Yediyurappa has set in motion one tunnel boring machine (Urja) on Thursday. Urja will be tunnelling the northbound tunnel between Cantonment and Shivaji Nagar stations," a Bengaluru Metro official told IANS. Under Phase II, the project will consist of a 13.9 km underground corridor from south ramp near Jayanagar Fire Station to north ramp near Nagawara underground station, consisting of 12 underground stations and 10.37 km of twin tunnels. The entire underground work has been divided into four sections -- namely RT01, RT02, RT03 and RT04. "The expected geology in tunnel section is about 250 m in hard rock, 350 m in mixed ground conditions and about 255 m of soil," said the official. Larsen and Toubro (L & T), the contractor for Bengaluru Metro, has procured two slurry tunnel boring machines (TBM) to complete the tunnelling work. Both the machines, Urja and Vindhya, reached Chennai sea port to be later transported to Bengaluru. /IANS