CHENNAI: More than 80 pillars, girders and 50 spans have already been constructed/placed in a Rs 621-crore flyover being built on one of Chennai’s busiest roads, but it has hit a major engineering roadblock.The 3.2-km Teynampet-Saidapet flyover on Anna Salai was to have been finished by September 2026, but the state highways department has had to redesign it midway through construction. The new deadline is February 2027, but officials themselves say the new target may be difficult to reach.The problem is in the Nandanam-Teynampet stretch, where the original plan was to use the existing Metro foundations for the central pillars. Later officials found that the Metro foundations in this stretch were not straight. If the flyover’s pillars were constructed on those foundations, the elevated road itself would be skewed and curved.The problem was found after construction had advancedIt is the size of the problem that makes the development important. The project was started in January 2024 and the design change was approved when the construction was well advanced. More than 80 pillars, girders and 50 spans were constructed or placed on the Saidapet-Nandanam side.The department has now approved a change of scope to substitute the central pillars with portal pillars on the affected section. Under the revised arrangement, 45 pillars will come up at the Teynampet and Nandanam Metro stations. The Chennai Metro Rail Ltd will provide foundation support on station walls.The re-design is also about the varying width of Anna Salai. The width of the road is only 28 meters near Cenotaph Road and 32 meters near Arivalayam as against 36 meters at DMS and 40 meters at Saidapet. But officials said putting central pillars in the narrower sections could seriously disrupt traffic.Why the project is technically challengingThe flyover is unique because it is being built over an existing Metro tunnel. The project utilizes prefabricated steel structures that can be installed using foundations from the Metro stations, a method to reduce construction time and reduce impact on the road below.But the design has to take into account at the same time underground Metro infrastructure, existing foundations, utility networks and a heavily congested arterial road. The latest problem shows the costly and time-consuming differences between a detailed project report and actual site conditions once construction is underway.The project already costs Rs 621 crore for 3.2 km. It is expected to reduce travel time between Teynampet and Saidapet and decongest several major junctions along Anna Salai.Next stepsOfficials said their immediate priority is to redesign the affected section without adding to the project cost. But it is not certain that the new deadline will be met, as the work has to be organized around the new structural arrangement.The delay will continue to cause diversions and disruption to the commuters on Anna Salai. The project was meant to change how people transit one of the city’s busiest corridors. But the latest engineering conundrum raises a bigger question for big city infrastructure: How well are existing underground infrastructure and site conditions being captured before construction starts?That question matters far beyond Chennai. With Indian cities putting up more flyovers, Metro lines and underground utilities in the same crowded corridors, coordination between the various infrastructure systems is becoming as important as the construction itself.
