The Mumbai Metro Rail Cooperation (MMRC), has begun tunnelling a 153 meters long tunnel below the Mithi river.

The 153-metre long tunnel is dug using the New Australian Tunnelling Method (NATM) between Dharavi and Bandra-Kurla Complex (BKC). The proposed BKC station will be underwater, and the works are expected to be completed by August 2020.

The 33.5 km Metro 3 line will reportedly be the second Metro in the country to have tunnels under the riverbed, where the first was constructed under Hooghly river in Kolkata, reported Times of India.

“The BKC Metro station, that will come up below Mithi river will have two island platforms instead of one island platforms as is being constructed at the other 25 underground stations,” S K Gupta, MMRC Director (Projects) was quoted saying by TOI.

According to the report, the BKC station would be crucial intersection point as it is being designed as a three-line station with two main platforms and a cross-over line, which will connect to either side of the mainline.

The MMRC had reportedly carried out extensive study and detailed planning before tunnelling beneath the water body.

“The presence of soil and weak rock under the riverbed increases the risk of instability of the excavated opening before proper support is installed,” said Gupta.

Layers of soil and broken rocks under the riverbed will be strengthened by grouting to reduce permeability and the ingress of water. An ‘umbrella’ of steel bars will be created above the excavation area for safety, and there will be a constant check on the soil/rocks during excavation, the TOI report quoted MMRC officials saying.

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