Importance of Diaphragm Walls in Metros — A Case Study
India’s first metro rail started back in 1984 in Kolkata (then Calcutta), West Bengal . Ever since, India has seen a rapid expansion of metro rail in various cities, with Delhi leading, and other cities catching up like Ahmedabad, Bengaluru, Gurugram, Kanpur, Kochi, Lucknow, Mumbai and now even Agra.
India being a country with densely populated cities, building metro railway lines and stations is nothing short of a challenge. Heritage Infraspace Pvt Limited has assisted and provided metro diaphragm wall construction services to many metro contractors in India. Here, we break down the importance of diaphragm walls in the construction of metro railways, as an interesting case study.
Types of stations built by metro contractors in India
There are majorly two types of metro stations: elevated and underground stations.
An elevated metro railway station or elevated train station is a railway platform alongside the tracks above street level on a viaduct or other elevated structure, usually constructed from steel, cast iron, concrete, or bricks by metro contractors in India.
An underground metro railway station is where the platform is built multiple levels beneath the ground as deep basements. The metro rail tracks run parallel to these stations, with a bustling city above it.
Elevated railways are normally found in urban areas where there would otherwise be multiple level crossings. Usually, the tracks of elevated railways that run on steel viaducts can be seen from street level.
Underground metro stations are generally proposed in older, dense parts of the cities where roads are narrow and sharp turns do not allow elevated rail alignment without major demolitions.
Importance of diaphragm walls for underground metro stations
Diaphragm walls are sturdy underground structures that can act as a permanent structural wall. Diaphragm walls can be installed to deeper depths, which helps in building multi-basement stations.
Compared to construction of a station on an elevated metro corridor, underground metro diaphragm wall construction services require less temporary propping. The top-down construction method can be applied in building an underground metro railway station.
The diaphragm wall is a rigid structure, hence the ground movement induced by basement excavation for underground metro is lesser compared to usage of flexible retaining walls. Diaphragm walls act as a strong guide wall for the launching shaft for metro stations.
Challenges faced by HIPL Ground Team
A major challenge HIPL faces as a commercial construction company in India working on various underground metro projects is accurately/precisely identifying the quality of the soil. With urbanisation, soil quality cannot be determined with a single inspection, and as the excavation takes place, the teams come across various forms of soil, which affects the metro diaphragm wall construction to a great extent.
The other challenges are as below:
Metro construction area sees a lot of activity and hence securing an entire stretch for the excavation work and diverting the traffic is a challenge.
Transportation of various construction materials, utilities, machinery, etc. is a big challenge, as urban areas have constant and heavy flow of vehicular and foot traffic in congested spaces.
