In a bid to save time and due to paucity of space, the Delhi Metro Rail Corporation (DMRC), which is assisting the Mumbai Metropolitan Region Development Authority (MMRDA) in executing Metro projects, has decided to erect precast concrete girders for platforms during construction of Metro 2A corridor. Known as ‘pi-girders’, due to their resemblance in shape to the mathematical ‘pi’, the girders have been earlier used in Lucknow and Delhi Metros.
“Generally, platforms for Metro stations are constructed in-situ. But here, we will be precasting the girders and erecting them on to the station for platforms. This will help us save time and also overcome the challenge of space issues,” said an MMRDA official, who is implementing the project.
In other cities, platforms have generally been constructed by setting up beams on either sides and then laying a slab. However, construction speeds up when the girders are precast and launched on to the elevated viaducts, said the official.
Currently, these pi-girders are being cast at the Bandra casting yard. Again, due to space constraints, the girders will be erected in two parts at some of the stations. “In some places, there is not enough space to launch the girder as a whole. So, for convenience of construction, we will be splitting it,” he added.
The platforms will be 185 metres in length and cater to rakes with eight cars. Meanwhile, unlike stations of Metro 1, which rest on three piers, these stations will be constructed on a single pier. “There is not enough space on Link Road to accommodate three piers for a station. We would have needed more land on either side of the road. So, we worked on the design and changed it to single piers,” the official said.
Two cantilever beams are placed on either side of the single pier and are connected by pre-stressing bars through a process called ‘stitching’. The concourse levels of the station are constructed on the beams. During construction, the beams are propped up by support beams and are removed once they are completed.
Over the concourse level, another 20.5-metre precast beam will be launched, on which the platform will be constructed. This is currently being cast at the Malvani casting yard and Mumbai is likely to be the first city to have the beams precast. In other Metros, this is generally constructed in-situ. It is on this beam that the two U-girders for the rail tracks are erected and on their either side the pi-girders are placed for platforms.
The 18.5-km corridor will connect Dahisar and DN Nagar and will have 17 stations. The corridor will be connected with Metro 1 at DN Nagar and Metro 7 at Dahisar. email@example.com