The Delhi Metro Rail Corporation (DMRC) is close to completing tunneling for its second phase of construction, with less than 2 kilometers left out of 35 km, following the completion of India’s longest tunnel in an urban area built using the New Austrian Tunneling Method (NATM). The 2.85-km-long tunnel is part of the 22.7-km Airport Express Line, which will connect the Delhi city center to the international airport when completed in the summer of 2010.
NATM has been used to build long tunnels in nonurban areas, including the Konkan Railway, but the metro tunnel is the longest so far in an Indian city. Construction of the tunnels, at a depth of 17 to 27 meters, began in late 2007 with the sinking of three access shafts.