India’s longest Sea-link Notching Many Firsts

The 22-km Mumbai Trans-Harbour Link is on track to meet the December 2023 deadline, o icials say. It’s also raising the bar by using technologies that have not been seen before in India

Manasi Phadke

Last Wednesday afternoon, the 2,300-metric tonne deck was lowered between Pier 184 and 185 of the under-construction SewriNhava Sheva Mumbai TransHarbour Link (MTHL). It was a milestone, not just for the showpiece project or Mumbai but also generally for India’s engineering and construction prowess.

The 22-km MTHL, touted as India’s longest sea link, will connect Sewri in peninsular South Mumbai to Nhava Sheva in mainland Navi Mumbai. By offering speedy transit between the two parts of the city, it promises to unlock the commercial and residential potential of the mainland, and will be a key connector to the under-construction Navi Mumbai International Airport.

The Rs. 17,843-crore link is inching closer to completion, span by span, towards its December 2023 deadline. And in the process, it is marking many firsts in India’s construction sector, the engineers and officials involved in the project say. One of these firsts, for India at least, is the use of orthotropic steel decks (OSDs).

These special steel decks enable a span, or distance between two piers, that’s up to three times longer than the norm, and are being used in stretches that are navigational channels for large ships. The humongous pink slab that reached its final destination this week was, at 180 metres, the longest OSD used yet, making its precise launch even more significant, engineers working on the project said.

“About 85 to 90% of the civil work (structural work) is complete and we are on track to meet the December 2023 deadline,” S.V.R Srinivas, commissioner at the Mumbai Metropolitan Region Development Authority (MMRDA), the state government agency in charge of the project, told The Print.

“Many of the engineering technologies used in this project have been deployed in India for the first time, and for everything, we have had to exercise a lot of caution. Even one small error can be colossal and set the project back,” he added.

The MTHL was first conceived nearly two decades ago as a link across the Mumbai harbour that could spur development on the mainland by improving its connectivity with the island city — much like Kowloon across the Victoria Harbour in Hong Kong. But the construction eventually started in 2018.

One span at a time

The OSDs are fabricated in panels of 12 metres each in Japan, South Korea, Vietnam, and Myanmar before they are brought to the Karanja Port at Uran in Navi Mumbai for assembly. The longer spans that these decks give are important for large ships to be able to pass through navigation channels without difficulty.

While a regular span on the MTHL is 60 metres, with the use of OSDs, the MMRDA has planned for spans ranging from 80 to 180 metres. Every few days, a barge carrying an OSD sets sail from Karanja Port, pulled by a tug boat. “We can move the barge only in high waters, so we have to be very careful about the tide timings. We take advantage of the tide pushing us whenever possible and move at a very slow speed,” a marine logistics expert advising on the project told The Print.

Even if the engineers catch the favourable tide, it takes about seven or eight hours for the barge to reach the site location, he said. “We should be able to finish launching all OSDs by August. On the remaining 18 km too, we have finished launching 90% of the girders,” Srinivas said.

After this, contractors will install crash barriers along the entire length, vision barriers at the part of the sea link along the sensitive Bhabha Atomic Research Sector, noise barriers at certain places, and then top the road with bitumen and install a tolling system before the MTHL is fully ready to be commissioned for public use.

Crash barriers are the metal fences found at the side of roads to reduce the risk of serious accidents. Vision barriers are uninterrupted structures also found along the side of roads to help block the line sight on either side of the road. The tolling system is likely to be an Open Road Toll (ORT) without any boom barriers to prevent long queues, Chief Minister Eknath Shinde, who went to the site of the OSD’s launch Wednesday, told reporters.

A project of firsts

The country’s longest sea link has clocked a lot of firsts besides the complex-to-launch OSDs. For years environmentalists were at odds with the MTHL proposal fearing that the raucous construction activity would drive away the migratory flamingos that make an annual appearance at the Sewri mudflats from December to May.

For this, the MTHL tea