Mumbai Trans Harbour Link (Atal Setu): Enhancing Connectivity and Development
Introduction
The Mumbai Trans Harbour Link (MTHL), named as Atal Setu, is a transformative infrastructure project in Mumbai, India, designed to significantly improve transportation connectivity and alleviate congestion in one of the country’s largest metropolitan areas. This ambitious project aims to bridge the gap between Mumbai and its satellite city of Navi Mumbai, fostering economic growth, social development, and urban expansion in the region. With its strategic importance and vast scale, the MTHL has garnered widespread attention as a crucial artery for the city’s future development.
Project Overview
It is the India’s Longest Sea Bridge and one the Longest Sea Bridges of the World. It seamlessly connects Sewri on Mumbai Island and Nhava Seva on the mainland (Navi Mumbai) to reduce the travel time between Mumbai and Navi Mumbai from 1.5 hours to 20 minutes.
The Main Bridge of the sea link is 21.80km marine viaduct with 1 interchange at Sewri on South Mumbai side and 2 interchanges at Shivaji Nagar and Chirle on Navi Mumbai side. The MTHL is a 6-lane freeway (and two emergency lanes), with a dual carriageway of 14.8m total width each.
The project passes through eco-sensitive Sewri Mudflats, Ship Navigation Channels and sensitive installations like Crude Oil Jetty, Oil Pipelines, railway lines, operational flyover etc.
The Atal Setu project has opened for public on 12th Jan 2024. Despite the inherent complexities of a large-scale infrastructure and Covid Pandemic, the project was completed in record time. This disciplined approach underscores the team’s commitment to delivering a high-quality project while managing constraints effectively.
Economic and Social Impact
The Mumbai Trans Harbour Link is poised to have far-reaching economic and social implications for Mumbai, Navi Mumbai and the surrounding regions. By enhancing connectivity between these two major urban centers, the project is expected to catalyze economic growth, attract investments, and create employment opportunities across various sectors.
Improved accessibility to Navi Mumbai is witnessing a spur in real estate development, commercial expansion, and industrial activities in the region. Businesses are getting benefit from better logistics and transportation linkages, facilitating the movement of goods and services. Additionally, the project is reducing the congestion on existing roadways, thereby reducing travel time, fuel consumption, and vehicular emissions.
From a social perspective, the Mumbai Trans Harbour Link is fulfilling the promise of fostering greater social inclusion and integration. Residents of Navi Mumbai are gaining easier access to employment, education, healthcare, and recreational facilities in Mumbai, expanding their horizons and improving their quality of life. Likewise, commuters from Mumbai will have access to a wider range of opportunities and amenities in Navi Mumbai, fostering greater regional cohesion and harmony.
Environmental Considerations and Sustainability
While the Mumbai Trans Harbour Link is delivering significant benefits in terms of connectivity and development, it has essentially addressed the environmental concerns and prioritized sustainability in its implementation. The project traverses sensitive ecological zones, including mangrove forests and marine habitats, raising apprehensions about potential environmental degradation and habitat loss.
To mitigate these concerns, stringent environmental safeguards and mitigation measures have been incorporated into the project design and execution. Environmental impact assessments (EIAs) have been conducted to evaluate the potential ecological repercussions of the project and identify appropriate mitigation strategies. Measures such as mangrove transplantation, habitat restoration, and pollution control have been undertaken to minimize the project’s ecological footprint and preserve the region’s biodiversity.
Furthermore, the Mumbai Trans Harbour Link is being developed with a focus on sustainability and resilience. Efforts were made to minimize the project’s carbon footprint through the adoption of green construction practices, energy-efficient technologies, and sustainable materials.
Project Highlights:
Many first-of-its-kind technical features in India like
- Ortho-tropic Steel Deck (OSD) – Spans with Steel Superstructure of upto 180 meters long and 2300 MT weight
- ORT (Open Road Toll System) for seamless travel where vehicles need not stop or slow down at the toll plaza.
Project Challenges
While the MTHL is a testament to engineering excellence, its construction presented numerous challenges. The significant challenges encountered, and the innovative mitigation measures employed to overcome them.
Presence of sea-bed pipelines
- The presence of seabed pipelines necessitated staggered pier placement at the project site, required a different approach for erection of Orthotropic Steel Deck (OSD) spans at those locations, as the standard rectangular barge couldn’t navigate these obstacles
- To address this, we specially fabricated an H-shaped barge was designed to navigate the staggered piers and avoid the seabed pipelines.
Close proximity of foundation to sea-bed pipelines
- The pile foundations of 2m diameter in groups of 4 or 6 were planned at a minimum of 15m from the sea-bed pipelines.The pipeline locations identified in the actual survey overlapped with the planned locations, necessitating a design change to restrict the safe distance from the pipelines.
- To address this, we designed to use 3m diameter piles in groups of two at 10m from the sea-bed pipelines and executed the same with Reverse Circulation Drilling (RCD) method. This approach, a first in India for such large diameter piles, was chosen by ensuring precise installation of the pile lines using the GPS data for accommodating the revised design requirements.
Pile Cage lowering of 3m dia
- To handle 3m dia Pile cage having weight approximately 65 T is a major constraint in marine conditions. The existing 250 T barge crane in floating condition, which was being used for 2m dia pile works, can lift 35T only at 15m radius. Availability of high-capacity (400T) crane in floating condition is a major constraint.
- We designed an innovative solution by utilizing the Permanent pile liner as support for the trestle and the strand jack on top of trestle. Hence any additional machinery and equipment requirement was eliminated. Safe access and walkway was provided at 3 levels for ease of movement and operation.
Submerged Pile Caps at Navigational Spans
- For Navigational span, pile caps were to be provided in tidal zone i.e., submerges during high tides. These are 6 pile group pile caps of size of 14.3 x 9.5 x 4 m present at the longest spans of 180m. Construction of such huge pile caps that get submerged is a major constraint.
- We designed & built a Precast Shell at CD +4.5m above tide level, weighing 320T, and lowered it by 2m, using 4 Nos of 180T capacity Strand jacks. This solution enables to keep the Navigational channel operational at all the times during the construction. This eliminated the requirement of using coffer dams, which is the traditional method of constructing this type of pile caps, saving a lot of construction time.
Orthotropic Steel Deck (OSD) Erection
- OSD done for the first time in India. Spans of upto 180m and 2600MT to be erected in Sea at heights of 30mtr. Spans are slightly curved due to the alignment requirement of the bridge and launching it on barges with erection towers requires high precision. The depth of water available at the erection location varies from 2.5m to 6.5m depending on the tides leading to requirement of faster erection methodology
- Special Barges designed & fabricated – India’s largest barge and a special H-Shaped barge . Special construction methods developed using advance survey equipment and Computer operated Strand Jack lifting systems. Self-Propelled Modular Transporters (SPMTs) were used to handle the spans on land. Detailed hourly planning was done for launching and erection activities to match with the tides and water depth availability.
Conclusion: Towards a Connected and Vibrant Future
The Atal Setu (Mumbai Trans Harbour Link) stands as symbol of progress, connectivity, and aspiration, heralding a new era of urban transformation and prosperity for the people of Mumbai and Navi Mumbai alike. It is iconic and monument structure in the region.