Engineers start work on 568m curve for EMB-Salt Lake Bypass viaduct
Times of India | 2 January 2025
Kolkata: The New Garia-Airport Metro will negotiate a 568m curve at Chingrighata to zip between Salt Lake Bypass and Eastern Metropolitan Bypass. This will be one of India's sharpest viaducts and will pass over both EM Bypass and the right-turn flyover at Chingrighata. The radius of this viaduct loop is 302m, with the curve starting from pier 310 opposite Captain Bheri on EM Bypass and terminating at pier 329 opposite Jal Vayu Vihar on Salt Lake Bypass.
In May 2023, Rail Vikas Nigam Ltd (RVNL), which is executing the 29km New Garia-Airport (Orange) line, acquired the Chingrighata site to construct the Metro pillar (318) at the centre of the crossing after pursuing with the state administration for six years. Last week, girder-launching began to bridge the final 568m gap in the Orange Line's second phase. The agency is chasing a March deadline to launch the 8km Ruby-Sector V section. The corridor now operates 5.4km from New Garia to Ruby.
Engineers are proceeding cautiously to bridge the Chingrighata gap. "The construction of the viaduct, which overlaps with the Chingrighata flyover, is exceptionally challenging. The viaduct was designed to circumnavigate the flyover. The lengths of the 19 spans vary between 28m and 32m to achieve the curve," a Railways engineer explained. The viaduct will be 5.5m higher than the flyover. Around 100m of the curve will encroach inside the flyover's carriageway. "The viaduct will be substantially above the flyover and will not cause any hindrance to vehicular traffic," the engineer said.
Girder-launching for a bridge or a Metro viaduct (the elevated concrete or steel structure on which tracks are laid) involves machinery (weighing no less than 400 tonnes) to hoist heavy precast segments or concrete spans and position them sequentially to assemble a continuous structure. Officials indicated that the "balanced cantilever" method will be implemented to construct the viaduct owing to the heavy traffic flow on the Chingrighata crossing.
Among the other sharp bends on Metro tracks is the 228m ‘Kardashian' curve of East-West Metro's underground section in Howrah. " Nine years ago, constructing the loop beneath the Brabourne Road flyover was challenging because the entire task was underground. There's a curve limit for a tunnel boring machine (TBM) that burrows and builds underground tunnels. The radius for a TBM cannot exceed 228m," recalled an engineer from Afcons, which constructed the East-West Metro's under-river section.
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