MUMBAI: Motorists travelling between Kandivli and Malad will eventually be able to use a four-lane underground road tunnel in each direction, as part of BMC’s plan to extend the Coastal Road through the western suburbs. Work on the 3.9-km twin tunnels, which will pass about 40 metres below ground, has moved a step closer, with the giant tunnel boring machines (TBMs) that will excavate them undergoing their first major round of testing in Chennai.Coastal Road (North), or Versova Dahisar Link Road (VDLR), will be a 22km alignment including roads on land, elevated sections and stilts as well as a cable-stayed bridge and a cut-and-cover tunnel beneath a creek. The TBMs will take on the most important task. With a cutterhead diameter of 15.6 metres, these are among the largest of their kind to be deployed for a road tunnel project in India. A team of BMC officials visited the Herrenknecht India Private Limited plant in Chennai recently to conduct a factory acceptance test (FAT) on one of the two machines. The geological conditions along the alignment are also expected to pose challenges. Mumbai’s underlying Deccan Trap formation consists of basalt, a dense volcanic rock formed by the cooling of ancient lava flows. The rock can be extremely hard and abrasive, with variations in its composition and degree of weathering affecting excavation.
The BMC has appointed Megha Engineering & Infrastructures Ltd (MEIL) as the contractor for this stretch. “We inspected all the machine parameters, including the rotation of the cutterhead, functioning of the shield, grouting system, pressure levels and thrust jacks that propel the TBM forward, as well as the segment-lifting mechanism,” said an official. The team also checked the mechanical and electrical systems, ventilation, air pressure, operator cabins and the control cabin, which monitors pressure across the machine.The TBM components were shipped from Germany to Chennai in parts and assembled at the factory. The fully assembled machine is 87 metres long. While the factory acceptance test checks the functioning of the machine and its various systems, a second round of site acceptance tests will be conducted after it is transported to the tunnel-launching site. This is because actual ground and operating conditions cannot be replicated at the factory, the official said. The machine will undergo these checks before tunnel boring begins.Work on the launch shaft at Charkop, spread across a 31m x 120m site, began in August. The TBMs are scheduled to be launched in May 2027. The finished diameter of each tunnel will be 14.2 metres. The scale of the machines sets the project apart from Mumbai’s existing road tunnels (see graphic).The two tunnels are being constructed under Packages C and D, each covering a 3.9-km stretch. Approximately 3 km of each tunnel will be excavated using TBMs, while the remaining 900 metres will be constructed using the rectangular cut-and-cover method.Package C comprises the northbound tunnel between Mindspace, Malad, and Charkop Creek, while Package D covers the southbound tunnel between Charkop Creek and Mindspace, Malad. Together, the twin tunnels will form part of the proposed signal-free Versova-Dahisar corridor.Transporting the massive machines to Mumbai presents a logistical challenge of its own. Manufactured in Germany and currently assembled in Chennai, the TBMs will be transported to Mumbai in disassembled form on an estimated 95 to 100 trailers. Their components will be brought in phases, in coordination with the excavation progress of the launching shaft.“There is little space to store the machines’ large components along the alignment. This differs from the south Coastal Road project, where reclaimed land provided some room to handle and store construction material,” a BMC official said.The alignment passes through creek and mangrove areas, where space constraints, difficult ground conditions and unexpected geological findings have added to the complexity of design and construction, the official said.Coastal Road (North) is expected to ease suburban traffic. Dhaval Shah of Lokhandwala Oshiwara Citizens Association said it would cut travel time and ease congestion on Western Express Highway. But environmentalist Mili Shetty flagged the impact on mangroves. Of the 60,000 in the project’s influence zone, 45,000 will be impacted and around 9,000 permanently felled. She fears the lost green cover will be replaced by noise and pollution. Civic officials said compensatory afforestation would be undertaken in Bhayander and Chandrapur near Tadoba forest.
