Sweet success formetro-3:mmrc builds270-metretunnelundermithi

Of the 1.18-km tunnels between BKC and Dharavi, the 270-m stretch toughest as water flows continuously, rest marshy land, mangroves

MUMBAI: City’s fully underground Metro-3 corridor from Colaba to Seepz has crossed the Mithi river’s main water channel. Of the 1.18km tunnels being built between the Bandra-kurla Complex (BKC) and Dharavi station, 270 metres (m) come under an active river channel, which has been crossed, said Mumbai Metro Rail Corporation (MMRC) officials on Thursday during a media visit to the BKC and Cuffe Parade Metro stations. The remaining work is expected to be completed by the end of March.

“Of the two tunnels, one tunnel has achieved 87% progress, while another has achieved 65% progress. However, we have already crossed the active river channel. We are also tunnelling almost 10m every day, so we aim to finish the rest of the work in a month’s time,” said SK Gupta, director (project), MMRC.

By active river channel, he was referring to the portion of the river where water continuously flows, making it the most challenging part to tunnel under. The remaining area above the tunnels includes marshy land and mangroves, which get flooded during high tide.

The 33.5 km Metro-3 corridor (Colaba-andheri-seepz) will be the second Metro in the country to have tunnels under a riverbed. The first one is being constructed in Kolkata under Hooghly river.

To prevent water seepage between the segments of the tunnels, MMRC is using special gaskets that swell when they come in contact with water. A segment is used to form the rings of the tunnel. Each ring has about six segments in it.

At present, the business hub of BKC, which is not connected with existing suburban lines, will be the largest station along Metro line 3 (474m in length). This station will be a crucial intersection point as it will be a three-line station with two main platforms, a cross-over line which will connect to either side of the mainline, and two stabling lines.

The cross-over line is being constructed using the new Austrian tunnelling method (NATM), a more conventional method of tunneling. As of January, 40% of the station works in BKC was completed.

BKC TO CUFFE PARADE WILL BE FASTER

With BKC being a crucial intersection station with reversal facilities, it will also offer better frequency of less than four minutes between two trains, officials said. MMRC is looking at making the line operational in two phases – Aarey to BKC by December 2021 and BKC to Cuffe Parade by mid2022. The frequency between Aarey and Cuffe Parade is expected to be around 6-8 minutes, officials said.

The New Austrian Tunnelling Method (NATM) is a modern tunnelling method appropriate for congested spaces.

It is a European method that was also used for the construction of the Delhi metro

In Mumbai, the technology will be used in seven stations, to widen the tunnels by using mining and equipment like breakers

For tunnels with variable

geometry and in mixed ground conditions, NATM is more cost effective, flexible and safer

tunnels

of 1.18km length each, 12.5m below the city’s Mithi riverbed, between Dharavi and BKC ( to be dug using tunnel-boring machines)

cross-line tunnel to be dug using NATM

will

m South-end of BKC station

be underwater

The TBMS are huge

machines being used to drill underground tunnels in the city. The 17 highly- mechanised machines being used for Mumbai

Metro-3 have been named after the rivers of Maharashtra