CMRL corridor 4: Steel portal beams erected in Porur, Poonamallee
Weighing several hundred tonnes, the fabricated structures were transported in modules from Raipur, Chattisgarh, to Chennai in two modules.
The steel portal beams erected in Porur, as a part of the ongoing phase 2 Metro Rail construction works
CHENNAI: The corridor 4 in the phase II Metro Rail construction in the city has been a priority project for the Chennai Metro Rail Limited (CMRL), especially where the construction of the stretch between Light House and Poonamallee is currently underway.
The CMRL has been expediting the project as it’s likely that the stretch will be the first to be operational around November 2025 among all the corridors in phase II.
As part of the works, it has recently completed strenuous tasks of erecting two steel portal beams (an element of viaduct), one in Porur junction and other in Poonamallee bypass. Officials recount this as a significant milestone, as it required many re-designs. One location was towards Poonamallee from Kodambakkam, which crosses MGR flyover at Porur junction.
“The positioning of the portal structure in Porur had many challenges for the designers and construction engineers with utilities on either side of the service road. Foundation on the extreme side of the service road was infeasible due to the large span length. After much deliberation among the authorities and designers, the right fit of foundation was derived with four piles of foundation in a single row adjacent to the Porur flyover,” said T Archunan, director (projects), CMRL.
For the right fit, the spans (the centre to centre distance between two piers) between the two foundations were also minimised to 22 metres at the Porur junction.
Some of the other challenges were narrow working space and congested area to design the foundation, shifting of wet utilities and halting of traffic in both Porur and Poonamallee,
“The foundation of the steel portal beam in Porur was coming in the junction of two water pipelines of 1.5 metres and 1.2 metres – one towards Manapakkam and another branching towards Kodambakkam,” he pointed out. “We shifted the two wet utilities 25 metres away from the pile foundation in collaboration with Metro Water authorities and city traffic police.”
Officials also noted that they had opted for the steel portal beams in both locations due to lack of space, high vehicular movements and utilities. Some of the other challenges were narrow working space and congested area to design the foundation, shifting of wet utilities and halting of traffic in both Porur and Poonamallee.
“The steel portal beam was chosen in both locations as pre-stressed concrete (PSC) or reinforced concrete (RCC) structures will be required for supporting arrangements on either side of the flyover in Porur and also in Poonamallee. This would have necessitated blocking of roads,” the official added.
Hence, to overcome these challenges, the high-grade steel structure in Porur weighing 145 tons was designed with a 22 metre span.
“The steel portal beam was fabricated in a Research Design and Standards Organisation (RDSO)-approved plant in Raipur, Chattisgarh. The structure was then transported to Chennai in modules, and erected in just 5 hours on July 27,” the official added. “This achievement demonstrates the project team’s expertise and commitment to finding innovative solutions to complex challenges.”
Meanwhile, a similar steel portal beam was also erected at Poonamallee bypass on two different days at night in June. “The assembled beam of 380 tonnes was transported to site using a specialised puller in two segments in which one segment is 23.85-metre long weighing 240 tonnes, and the other is 12.5-metre long weighing 140 tonnes,” he noted.
