A 1.2 km section of the line between Bandra Kurla Complex and Dharavi stations will pass under the Mithi river. This will be the second under-river tunnelling for a mass transit project and metro rail tunnel in India after the similar subway tunnel construction beneath the Hooghly river on Kolkata Metro Line 2.
Underneath the riverbed at the mouth of the Mithi river in Mahim-Bandra Kurla Complex, precision engineering and all manner of precautions are in place as sophisticated machines set out this week to bore tunnels 10 metres below Mumbai’s mother drain. The structure of the Colaba-Bandra-Seepz Metro line, being constructed by the Mumbai Metro Rail Corporation Ltd (MMRCL), and runs from Prabhadevi beneath Mahim Causeway or Lady Jamshetjee Road before turning gently into the city’s suburbs at Mahim, where it will run beneath the Western Railway tracks, a patch of mangroves near Dharavi and the Sion-Mahim Link Road before turning into Bandra Kurla Complex. Here, a part of the BKC Metro station and a 170-metre section of tunnel will be constructed right under the Mithi river, only a little over a kilometre from where it empties into the sea.
New Austrian Tunnelling Method (NATM) is responsible to build a 153-metre section of the tunnels at BKC station, and a considerable part of which will be in the water body. This is a tunnelling system designed so as to use the strength of the soil or geological formation around the tunnel to support it. The BKC station, with a wider and longer box, is intended as a two-platform, three-line station where the third line is meant to provide stabling and sick-siding or emergency turnaround services. Work on the horseshoe-shaped tunnels has begun very slowly over the past few weeks but is expected to make real progress in the coming few days. The ceiling of these tunnels will be 8.5 metres to 12.5 metres below the riverbed.
Line 3 of the Mumbai Metro, or the Colaba–Bandra-SEEPZ line, is a part of the metro system for the city of Mumbai, India of which construction has been initiated. When completed, the 33.5-km long line will be the first underground metro line in Mumbai. The metro line will connect Cuffe Parade business district in the extreme south of the city to SEEPZ in the north-central with 26 underground and one at-grade station