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.

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Safety on Site: Diaphragm Wall Construction by Heritage Infraspace

Apart from being the pioneers of diaphragm wall construction for deep basements, what makes Heritage Infraspace Pvt Ltd (HIPL) rank as the one of the top construction company in India is their approach to safety on site. Safety on construction sites protects the workers and keeps the public safe.

The construction sites commissioned to HIPL are typically congested locations in bustling cities with high pedestrian and vehicular traffic. Inadequate safety procedures could lead to mishaps involving construction employees, heavy equipment and onlookers, placing them in severe and sometimes life-threatening danger.

Here are some of the steps HIPL follows, as a responsible diaphragm wall construction company in Ahmedabad, India, to ensure the safety of workers and general people around the site, right from implementing a health, safety and environment plan to an internal checklist of to-dos by the safety team of HIPL.

General Workers’ Safety

Every member on the ground, including the labourers and engineers, is provided with reflective safety jackets, standard safety helmets and safety shoes with steel toes.

Those working in reinforcement get hand gloves, and shoulder pads as they carry heavy and long rods of steel bars and welded wire fabrics.

Welders are provided with a proper faceguard, gloves and safety aprons, to protect them from the sparks flying off the metal during the process.

Teams working with concrete in Diaphragm wall construction are also provided with special gum boots and hand gloves.

Site Safety Protocols

At every HIPL construction project site, a safety officer assists the project manager in implementing safety guidelines and reviewing risk assessment. Together they conduct multiple levels of safety inspections at site on a continuous basis, making on-the-spot corrections.

Before the beginning of any project operations, the safety officer and the project manager conduct a safety meeting with all staff members. This session educates everyone involved in the project about the various steps to be taken to avert any untoward incident that might put anyone in danger or cause loss of property.

Hard Barrication is done prior to construction commencement. Clear and visible signages like Deep Excavation, Non PPE Zone, Active Drilling in Process, Electrical DG Set Zone, Cage Making in Progress etc are placed to ensure site identification.

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