IT’S midday and the sky is partially overcast. Standing on a concrete deck four km from the shore and some 40 metres above the surging waters, one is besieged by the howling wind. It is as if a sea-storm is brewing and the howling is a constant reminder that unless one latches onto something, one might be blown away!
The guide reads the apprehension in your eyes.
“The sea is relatively calm today and the wind-speed at this moment is barely 40 kmph. This is pretty normal,” he says in a reassuring voice, making you wonder about the challenges of working 24x7 in these conditions to build the Mumbai Trans Harbour Link (MTHL) – India’s longest sea-bridge. It will connect India’s commercial capital, Mumbai, to the distant outskirts of Navi Mumbai.
The challenges are many. In May, when cyclone Tauktae lashed over Mumbai at 114 kmph, about 300 metres of the temporary access bridge (TAB) at the project site were damaged. This, after several vessels, including a 6,000-MT capacity ship anchored mid-sea, drifted due to the cyclone and hit the TAB at expansion joints. A TAB is a low-height facility constructed along the alignment of a proposed bridge and is used for ferrying men and material for construction work.
“It was a raging cyclone and the rough waves surged furiously through the night. It felt like everything would get blown away,” recalls Mr Prabhuswamy, a senior deputy general manager who is in charge of launching girders in the inter-tidal section of the sea-bridge. “Notwithstanding the damages to the TAB, we take pride in the fact that the cyclone couldn’t inflict any damage to the nearly 3-km length of the sea-bridge that had been constructed by then. It took us about 15 days to restore the TAB and then the work restarted full-swing,” he adds.
MTHL is a 21.8 km sea-bridge that takes off at Sewri in south Mumbai and, on crossing over the Thane Creek north of the famous Elephanta Island, terminates at Chirle near Nhava Sheva in Navi Mumbai. It’s a 27-metre-wide two-way bridge with three lanes each direction.
The owner of the project – Mumbai Metropolitan Regional Development Authority (MMRDA) – has split the job into three parts. Package-I starts from the shore at Sewri and runs 10.38 km into the sea, Package-II starts mid-ocean and runs for another 7.8 km, landing on the shore at Chirle. Package-III picks up from there and runs another 3.61 km on the shore, linking MTHL to the Mumbai Pune Expressway at Navi Mumbai.
L&T, together with Japan-headquartered IHI, won the contract for MTHL-I, L&T alone MTHL-III, and a consortium of Daewoo-Tata bagged the contract for MTHL-II.
From the operational point of view, L&T has divided MTHL-I into three parts – the 5.9 km Sewri interchange section (with eight-ramps), the 4.1 km inter-tidal section and the 5.8 km marine section. As of October, while the superstructure works in the inter-tidal section are almost complete, overall, 57% of MTHL-1 is completed. “If COVID and the cyclones hadn’t happened, our progress would have been much more,” says Mr Sanjay Digambar Patil, L&T’s deputy project director for MTHL-I.
CHALLENGING THE CHALLENGES
Constructing a sea-bridge of this magnitude is anything but a cakewalk. More so because, firstly, it is coming up in an eco-sensitive zone frequented by flamingos and several other migratory birds; secondly, mid-sea there are sub-surface oil pipelines of ONGC and a crucial navigation channel for ship movement. And last but not the least, a highly sensitive establishment, the Bhabha Atomic Research Centre (BARC), is in the vicinity.
At MMRDA’s behest, L&T is addressing these challenges by adopting several innovations. These include a noise-barrier in the bridge’s inter-tidal section to shield the flamingos from the hubbub of speeding traffic, a view-barrier in the marine section to shield the BARC from public view and the use of an unusually long orthotropic steel deck (OSD) for unhindered movement of ships under the bridge.
“This is the first-ever instance of using an OSD in India. We are using a couple of OSDs in this project, with the longest running 180 metres and weighing a massive 2,300 MT,” says Mr Yung Mook Na, L&T’s project director for MTHL-I. Mr Na, a South Korean, is an engineering expert in OSD.
The interesting part is that the OSD has been fabricated in as many as four countries – Japan, Taiwan, Vietnam, China – and then shipped to Mumbai by sea. The OSD is now being assembled onshore at the MTHL-I project site at Sewri and will be subsequently shipped on a barge as a single piece to be placed on the piers mid-sea. To put it in perspective for a layman, the barge is as large as a football ground and has a capacity to ferry a load of up to a massive 35,000 MT.
“We are giving the finishing touches to the OSD now and hope to launch it by the end of November,” Mr Na adds. According to deputy PD Mr Patil, a comparatively easy alternative to OSD would have been a cable-stayed bridge. But this idea was discarded as the cables would have hindered the flight of the migratory birds in this eco-sensitive zone.
The unique materials being used include flow-filled epoxy-coated strands that have high resistance to chloride attacks, high corrosion protection, enhanced durability and excellent resistance against fretting fatigue. Then there is high-performance concrete qualifying Chloride Migration Coefficient Testing (CMCT) < 2×10 -12 m2/s. This effectively means that the concrete is of a quality superior to that used to construct nuclear reactors.
INTERESTING INNOVATIONS
MTHL-I’s has 536 piers – 228 in the interchange, 146 in the inter-tidal and 162 in the marine sections. In the inter-tidal section piling, the piers and superstructure jobs are almost complete. In the marine section, while piling is over, pier and segment launching works are in progress.
L&T has adopted the strategy of precasting the concrete segments and box girders on the shore, and then installing them on the piers standing – at a height of 26 metres, on an average, above the sea level. The piles, on the other hand, go as deep as 45 metres below the seabed. Thus, stepping onto the onshore project site at Sewri, one comes across rows of stacked precast segments and precast box girders waiting to be shipped for installation.
As regards the marine section, witnessing the work is a thrilling experience. Batching plants, cranes, material feeders, etc. are all mounted onto barges from which workmen are either carrying out piling or casting piers, surrounded by the choppy waves. At some places in the sea, batches of workmen are busy giving finishing touches to the pier-caps to make them ready for installation of the precast segments. The workmen are ferried every morning to these locations, which look like vertical mid-sea islands.
Due to the presence of critical utilities and facilities such as high-voltage electric cables, oil pipelines, railway tracks and roads, meticulous planning is required for the works pertaining to the Sewri interchange which will connect the sea-bridge to the Eastern Freeway. One wrong move could lead to a total power outage in Mumbai city, leakage of oil or massive traffic disruptions. L&T has been able to manage all these through careful diversion of routes, sequencing of works and adoption of innovative construction techniques.
AMAZING FACTS
Many aspects of the bridge will astound anyone. For instance, the 600,000 Cu. m concrete that is being used in this project to lay 400,000 transit-mixer km is akin to undertaking a road trip to the moon, 12 Eiffel Towers can be erected with the 90,000 MT rebar that has been requisitioned and three Howrah Bridges can be built with the 90,000 MT structural steel being used.
PATH TO PROGRESS
The initial deadline for commissioning the MTHL was September 2022 and the work was progressing expeditiously since commencement in 2018. But the unprecedented COVID-19 pandemic hampered the work to some extent, which led the MMRDA to revise the deadline to September 2023.
But no matter whether the sea-bridge is commissioned as per the revised deadline or takes a few more months due to reasons beyond the control of the project team, what is sure is that, once commissioned, it will slash the travel distance between Mumbai and Navi Mumbai to a mere 20 minutes. Using the Airoli and Vashi bridges, which are the current road links between the twin cities, takes up to 1.5 hours, depending on the traffic.
Moreover, once the bridge is ready, many people living and working in Mumbai will opt to live in the greener environs of Navi Mumbai, helping decongest the Maximum City. The bridge will also provide faster connectivity to the Jawarharlal Nehru Port and the upcoming Navi Mumbai International Airport, ensuring higher mobility and business growth. No wonder the Maharashtra government is taking keen interest in getting the sea-bridge completed expeditiously. In fact, Chief Minister Mr Uddhav Thackeray and his minister-son Mr Aditya Thackeray visited the MTHL-I project site twice in the recent past.
In the field of construction, there are projects that become landmarks over time. Then there are a select few that transcend the status of a mere showpiece and become a path to progress. MTHL is poised to become the latter.
