Direct by Design
DISCUSSION FORUM
Sustainability and its relevance to underground construction Shani Wallis, TunnelTalk
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ustainability – what does it mean? – actually? Other than a fashionable buzz word surrounded by vague platitudes and political soundbites, how does it actually relate to the underground infrastructure construction industry? These questions were discussed in detail at the Tunnelling Asia Conference in Mumbai, India, with some surprising, thought-provoking statements that took conventional understanding of the topic in different directions. In her keynote address, Ms Ashwini Bhide, Managing Director of Mumbai Metro Rail Corporation, introduced climate change as one of the urgent drivers of sustainability. • Maximum rainfall in Mumbai is 2,000-2,500mm/year. • In recent years, 35-40% of this has fallen in two or three unprecedented rain events. • From 2005 to 2015, sea level around Mumbai, which is built mostly on reclaimed land linking an archipelago of hard rock-outcrop islands, has risen by 3.6mm. • The current trend is for it to rise more and faster in the years to 2030. “Dealing with such realities, particularly for cities that demonstrate that their existing infrastructure cannot cope with the impacts, will require everybody, every public authority, every public infrastructure provider, to check-in” to contribute, collaborate, and shoulder the responsibilities collectively. This set the context for the first panel discussion chaired by Lt Gen Suresh Sharma, Senior Vice President of TAI, the Tunnelling Association of India, the host and organiser of the conference. In opening the session, Sharma described sustainability as “the ability to bounce back”. For infrastructure projects “consideration of the impacts of climate change must be part of their design and construction”, he said, and that there must be a greater regard for on-going “maintenance of infrastructure with an increased infusion of funding” for this specific process. Panellist Ms Bhide quantified water supply and sewerage infrastructure in Mumbai and metro construction across India. • Mumbai was the first city in India to excavate tunnels for water supply. • The first tunnel was built in 1956. • By 1971-72, the water supply network exceeded 7,000km. • The first TBM water tunnel was excavated in 1984.
December 2023 •
Today some 150km of water supply tunnels, in the 2.2m to 2.5m inner diameter range, are in construction with another 85km in planning and design. Similar statistics are there for the sewerage networks. The first three main outfall tunnels for the city were built in the 1990s and currently another five are under construction. Flood mitigation is a major responsibility for the water authorities and current projects provide underground stormwater storage facilities for low lying areas of the city. For metro works, India currently has • 700km of metro in operation, • another 1,000km in construction and • another 1,000km plus in planning and design with significant lengths underground, including in Mumbai where all of 33kms and 26 stations of Line 3 aligned underground with the depot and one station at the north end above ground. In his presentation to the conference, S K Gupta, Director (Projects) for Mumbai Metro Line 3, said that when opened in 2024, Line 3 will carry: • 14 lakh or 1.4 million riders/day, providing an • EIRR (economic internal rate of return) of nearly 18% and a • FIRR (financial internal rate of return) of 4.20%. By 2031, with additional trains and reduced headways, ridership is expected to increase to • 17 lakh or 1.7 million passengers/day and • by 2055 to 3.15 million/day. For an international and historic perspective, Jamal Rostami of the Colorado School of Mines in the USA Metro rail, particularly underground, can reduce traffic congestion as here in Mumbai where the all-underground Metro Line 3 will carry an estimated 14 lakh or 1.4 million riders/day when it opens in 2024
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