Kolkata: The Kolkata Metro has started using boxes the size of three train coaches to create a Metro Rail tunnel at the city airport.
According to Rail Vikas Nigam Ltd (RVNL), the implementing agency of the New Garia-Airport Line, the 14 concrete and reinforced cement boxes are being used to build the 135 m tunnel in the last leg of this Orange Line corridor.
This box-pushing method is being used for the first time to create a Metro tunnel in Kolkata. This method helps make small tunnels under railway tracks and busy roads without disrupting traffic on the ground.
Each box is 14.85m wide, 7.35m deep, and 9.6m long, giving it a dimension of 1047 cubic m. The standard size of an LHB coach used in a long-distance train of Indian Railways is 308 cubic m.
The boxes are being cased and then pushed forward with the help of hydraulic jacks. As the boxes move forward, a cutter excavates soil to make way forward. This cutter is fixed at the head of each box.
This tunnel is being built after the Orange Line enters the airport premises, turning right from VIP Road. It starts near the airport flyover and goes up to the Y junction of the airport station near the post office on the approach road to the terminal building.
The Y junction is an interface between the Orange Line and the Noapara-Airport corridor or the Yellow Line. It is about 400 m from the Biman Bandar station.
Box-push tunnel construction was the only viable method in this case. Neither the cut-and-cover method nor the tunnel boring method could be used.
Thr vehicles could not be stopped on the road as it is the main approach to Kolkata airport’s integrated terminal building. Tunnel boring machines cannot be used for such a short length of construction.
However box-pushing method takes more time than tunnel boring machines or the conventional cut and cover method.
