Rail Vikas Nigam Ltd (RVNL) has embarked on a pivotal phase of the New Garia-Airport Metro project, commencing the construction of the underground stretch for the Orange Line. This 29-kilometre corridor, integral to Kolkata’s expanding metro network, is currently operational for a 5.4-kilometre elevated segment from New Garia to Ruby crossing.
The line transitions underground as it approaches the Jai Hind metro station at the airport, necessitating a sophisticated tunnelling endeavour. The traditional cut-and-cover technique has been chosen for constructing approximately 500 metres of twin tunnels. An RVNL engineer elucidated that this method involves excavation or trenching before casting a base slab and covering the tunnel with an overhead concrete structure. This approach is particularly cost-effective for short and shallow tunnels compared to the deployment of high-tech tunnel boring machines (TBMs), which were utilised for the East-West Metro project.
Despite its cost advantages, the cut-and-cover method presents significant engineering challenges, particularly as the project nears the airport. The final 125-metre section, which lies beneath the airport’s approach road, necessitates an alternative technique to avoid disrupting passenger access. Here, the box-pushing method will be implemented. This technique, as explained by the engineer, is optimal for creating underpasses or subways where traditional open-cut systems are impractical due to continuous traffic flow.
The box-pushing method involves constructing reinforced concrete boxes adjacent to the road and then incrementally pushing them into place using hydraulic jacks. This approach ensures minimal surface disruption, a critical requirement given the high volume of airport traffic. The successful implementation of these tunnelling methods underscores RVNL’s commitment to enhancing Kolkata’s urban mobility infrastructure. Once completed, the Orange Line will significantly bolster connectivity between New Garia and the airport, promising a seamless transit experience for the city’s commuters. This project not only exemplifies the use of innovative construction techniques in urban infrastructure but also reflects the strategic planning required to execute large-scale public transportation initiatives in densely populated areas.
