After years of legal delays, monsoons, heavy lifting and a lot of fancy formwork, the Bandra-Worli Sea Link, a 4.7- kilometer viaduct with two cable-stayed spans, made its final connection on April 20 and is slated to open to traffic in mid-May. When it does, the bypass over the sea will cut the time of a trip across Mahim Bay in Mumbai, India, from about 40 minutes to just six.
Drivers who had to suffer through 23 traffic lights to make the trip from Bandra in north Mumbai to Worli in the southern part of the city will face only four on the new route, planned by the Maharashtra State Road Development Corp.
Hindustan Construction Co. (HCC) started work on the project in 2000. It faced a one-year delay because the developer could not gain access to the site. An original 1998 design by Jacobs Sverdrup called for the original cable-stayed span’s twin decks to share pylons. This design was modified in 2003 by Dar al-Handasah Shair and Partners, London. MSRDC had decided to build one of the twin decks ahead of the other, hoping for an earlier start for toll revenue, so Dar al-Handasah revised the structure so that each deck was independently supported by its own pylon.
But more delay was ahead. The Bandra cable-stayed section was planned so that fishing boats from the Mahim fishing village could pass below the bridge without getting shattered by monsoon waves. The original design had only one 500-meter-long cable-stayed section, with 50-m transition spans on both sides. Then, after the contract was awarded to HCC, the Worli fishing village at the other end protested. Villagers went to court claiming they should not be forced to go all the way to Bandra to pass through the channel. The courts agreed, and the design was significantly altered by adding the second cable-stayed bridge, which is 350 m long, including transition spans. Environmental objections to the project also went all the way to India’s Supreme Court, resulting in moving the alignment 200 m farther away from shore.
Through all this, HCC stuck with the job, its leaders say, not just because they had invested so much in specialized equipment. “Apart from investing our money, we had invested our heart and soul. We are confident we will be long remembered for having brought ease to Mumbai’s commuters,” said Jimmy Mogal, HCC’s vice president of corporate communications.
Rough Seas
The work then faced its natural challenge: the tides and storms of India’s west coast on the Arabian Sea. Santosh Rai, HCC planning manager, says the contractor had to plan the job around monsoons, where winds range from 70 or 80 kilometers per hour up to 120 kmph. The bridge is designed to withstand 264 kmph winds at the top of the towers and 150 kmph at the bridge deck level. At some parts of the site, “we had to stop work during every monsoon for five months,” Rai says, because the authorities do not allow navigation during monsoons. Workers, materials and equipment move out to the farthest piers each day by boat. Work also faced the daily challenge of the area’s high tides. To overcome this problem, HCC built a temporary bridge and used it to move crews, materials and equipment out to the pylon area.
HCC chief engineer D.K. Sharma says this is the first cable-stayed bridge built under sea conditions in this part of the world. “We had storms where we did have to stop work,” he adds. During a storm last September, for example, HCC had to send crews into refuge areas built into the piers. “For three days, we were able to provide food, water and facilities, but we could not get them out,” he says. Boats got close enough to throw in supplies but could not land without damaging the structures.
Even in calmer weather, logistics were a huge issue. HCC had to transport 10 or 12 segments per day and supply materials to 30 different work locations. Crews worked in shifts, with 800 to 900 workers dispatched to different locations each morning. “Then, through the day, food had to be supplied to each and every person, giving tea breaks, for example. We had to arrange so many things for so many locations,” Rai says. Equipment on-site at the peak of construction included 22 barges, four tugboats, five jackup platforms, 34 smaller cranes and seven tower cranes.
Exposed Rock.
K.R. Visvanath, HCC’s vice president of construction, says the job also faced highly variable geotechnical conditions and a highly uneven foundation bed of basalts, volcanic tuffs and breccias overlain by completely weathered rocks and residual soils. The strength of the rock varied from extremely weak to extremely strong, complicating foundation work. “The intertidal zone on the Worli side was all exposed rock at low tide,” he said. Foundations included more than 600 large-diameter piles, with a rock-socketed length up to 34 m. Tests for the piles were conducted using the Osterberg load-cell method, with test loads of up to 5,600 tonnes.
The pylons for the cable-stayed towers were challenging to construct both above and below the bridge deck. Sharma says the inspiration for the shape of the pylon was the traditional Indian greeting, or “namaste,” where hands are put together with forearms forming an inverted V. He adds that the shape “also provides stability.” The 129-m-tall towers have a curving profile, which makes them even more human-like. The bridges have two four-legged pylons. The legs are inclined toward one another above the bridge deck until they merge into a single tower head at 98 m.
To cast the inclined upper tower legs, HCC worked with automatic climbing formwork experts from Doka to customize a system for the job that could be adapted to the varying cross sections and angles of inclination. It has several different platform levels, allowing rebar to be placed a casting section ahead of the pouring operation. Merging the legs into the tower head took extra attention “to keep the forms from colliding with one another,” Sharma adds, and to reconfigure the climbers to the new cross section. The forms also had to produce the pylons’ fluted architectural finish and be stripped without damaging it. Anchorage boxes were fabricated on-site in halves with tolerance on the main plates of only 0.125 degrees. The assembled units were transported and installed atop the towers.
The pylon legs converge again below the bridge deck in one plane, creating a diamond cross section; installing the 140-ton precast segments for these lower legs was particularly tricky. HCC devised a construction method that used a pier table so workers could lift segments from bobbing barges in rough water and set them with 5-millimeter tolerances. The system used a lifting boom to pick up a segment inside a steel frame. Pins were fixed below the segment, allowing workers to slide it out onto a trolley and transfer it into position. “It took us four months to test the prototype.” Rai says.
The cable-stayed deck sections were built using the balanced-cantilever method. The central pier supports spans on either side. VSL Singapore Pte. Ltd. partnered with HCC early in the job to design the launching truss, able to carry precast box girders that weigh up to 2,000 tonnes. One of the bigger challenges was moving the launching truss across the Bandra channel for the second span. This was done during a favorable high tide using a barge-mounted crane called the Asian Hercules, brought in from Singapore, which can lift up to 1,600 tonnes.
Second Link
The second phase of the Western Freeway Sea Link is expected to start only after India’s general elections in mid-May. Called the Worli-Haji Ali Sea Link Project, it will be a continuation of the existing sea link. The extension will involve a 3.2-km-long precast segmental viaduct with 50 m spans, connecting Worli and Haji Ali.
At Worli, connectors in a cloverleaf formation over the sea will facilitate access to and from the bridge. The sea-link extension will have a bored-pile foundation and precast segmental superstructure. “No large spans are envisaged for this project,” says Sharma.
The second phase will be let as a build-operate-transfer project, and bids have been received from only two bidders: HCC and Reliance Infrastructure. Reliance, whose bid is expected to be significantly lower, already is the contractor on a section of the Mumbai metro. The Haji-Ali link is expected to take 42 months from start of construction. The winner of the concession will pay Maharashtra State Road Development Corp. $327 million toward the cost of all five work packages of the overall sea-link project. The concession period is 40 years, and tolls will be collected to recover the cost of acquiring the first phase and the construction of the second.
The Bandra-Worli Sea Link Project and later phases of the Western Freeway have the potential to bring about enduring changes in the travel patterns of the area, linking the island city of Mumbai to its western suburbs. A third phase is also planned to take the sea link across Back Bay to Nariman Point. But that area’s prominent hotels and famous views have prompted MSRDC to study a combination bridge-and-tunnel option.
