Tunnels for the Chennai Metro were drilled using Tunnel boring machines (TBMs) brought from Russia and China. In December 2011, two TBMs were shipped to Chennai from China. A total of 12 TBMs were deployed from July 2012, 8 from Germany, 2 from China, and 1 each from the United States and Japan. The first tunnel work commenced in July 2012 from Nehru Park to Egmore for a distance of 948 meters. By December 2017, upon completion of the tunneling work of the Chennai Metro, all the machines were shipped backed to their origin countries. Each TBM weighed 850 tonnes and was able to drill hard surfaces, creating tunnel passages to connect underground stations. The length of the TBMs was about 85 to 90 meters. Tunnels were bored 50 feet below the surface, and each kilometer of tunneling cost 3,000 million. The average length of tunneling was 6 to 8 meters a day.