Highlights of some construction processes witnessed on site -

BOTTOM UP

In the bottom-up method, the retaining wall is constructed along the station or tunnel box boundary prior to excavation. Excavation is carried out to a certain depth and then the strutting system is installed to support the retaining walls during excavation and construction of the station. After installation of strutting, a system is completed and final formation level is reached, the base slab is cast, then going from the bottom upwards the concourse slab is cast in accordance with normal procedure.

COFFERDAM

A cofferdam method, which comprises of an open cut excavation with suitable lateral support system such as secant pile wall/diaphragm wall with the lateral support system, is carried out to facilitate the construction of station box.

NATM

The tunnel is typically advanced by road header or drill and blast methods, sequential excavation is normally adopted i.e. top heading, bench and invert. The bench is excavated simultaneously to the top heading behind the excavation face, providing a ramp for access to the heading.
Some distance behind the bench, the invert is excavated. If the ground condition is unfavorable, an invert will be provided to close the lining, forming a complete ring.