India's First Underwater Metro Rail System Opened in Kolkata, West Bengal

Kolkata, India (Metro Rail Today): In a monumental achievement for Indian infrastructure, Prime Minister Narendra Modi inaugurated the country's first underwater metro services on 6th March 2024. The Howrah Maidan-Esplanade section, a marvel of engineering, stands as India's first metro tunnel beneath the Hooghly River, marking a significant milestone in Kolkata's transportation network. This triumph features the nation's deepest metro station, the Howrah Metro Station. Apart from the underwater metro rail corridor, two other lines were flagged off Line 3 (Joka to Majerhat) and Line 6 (Kavi Subhash station to Hemanta Mukherjee station) of the Kolkata Metro Rail Project.

Engineering Marvel and Trial Success

April 2023 marked a pivotal milestone for the Kolkata Metro, completing a trial journey through a tunnel that delves an impressive 32 meters below water level. The 4.8-kilometer stretch of the East-West Metro from Howrah Maidan to Esplanade, built for Rs 4,965 crore, reflects engineering ingenuity and a historic leap in India's metro infrastructure.

Kolkata's Underwater Metro

The East-West Metro Corridor encompasses a 520-meter tunnel connecting the IT hub of Salt Lake Sector V to Howrah Maidan, reducing travel time between Howrah and Sealdah to just 40 minutes compared to the 1.5-hour road journey. This not only offers a quicker commute but also aids in alleviating traffic congestion at both ends.

The Visionary Behind the Dream

Sir Harley Dalrymple-Hay, a visionary engineer from Birbhum, proposed the idea of an underwater railway in Kolkata as early as 1921. His dream materialized with the completion of the tunnel in 2021, executed by Afcons Infrastructure Ltd.

Project Overview

India's first underwater metro tunnel, proposed by Kolkata Metro Rail Corporation (KMRC) and executed by Afcons Infrastructure, began in 2015 and reached completion on Feb 13, 2020. Spanning a total of 16.6 km, the underwater tunnel measures 520 meters and traverses the Hooghly River.

Stages Of Construction Project

• Concept Of Project
• Design
• Planning
• Pre-Construction Stage
• Procurement Stage
• Construction Stage
• Post Construction Stage

Method Of Tunnel Construction

• Cut & Cover Method: Involving excavation equipment to dig a large trench, used for metro stations.
• Bored Tunnel Method: Digging a tube-like passage through the earth, used for underwater tunneling.
• Clary Kicking Method: Utilized in specific geological conditions.
• Shaft Method: Involves the construction of vertical or inclined passageways.
• Pipe Jacking Method: Involves the jacking of pipes to create tunnels.

Tunneling Method

• Cut & Cover Method: Involves digging a large trench, covered by a concrete deck, used for metro stations.
• Bored Tunnel Method: Involves digging a tube-like passage through the earth, used for underwater tunneling.

Technology Used in the Tunnel

The underwater metro tunnel beneath the Hooghly River utilized reinforced concrete segmental tunnel linings, ensuring water resistance.

Execution of Work

Engineers excavated over 5,400 meters of the tunnel using two tunnel boring machines (TBMs) named Rachna and Prerna. The 'cut and cover' method was employed for underground stations, involving digging a trench, lining it with concrete, adding a concrete roof, and sealing it.

Construction Management Techniques

1. Detailed Investigation
2. Case Studies
3. Planning
4. Design Consideration
5. Logistic Arrangements

Unique challenges, including tunneling beneath dilapidated buildings, railway offices, a busy railway yard, roads, bridges, and heritage monuments, required precise planning and innovative solutions.

Key Innovations

• Recruiting experienced tunnel crews
• Implementing safety measures in case of river water ingress
• Designing a 'soft eye' of Styrofoam for enhanced safety

India's first underwater metro tunnel in Kolkata is a testament to the nation's engineering prowess and commitment to progress. Beyond being a transportation solution, it symbolizes innovation and development. As India continues to invest in transformative infrastructure projects, the underwater metro tunnel stands as a beacon of a connected and efficient future.