Federation Square, Melbourne, decking over the railway

To ease some of the worst urban traffic congestion in the USA, the Central Artery Project (C/AT) in Boston, Massachusetts, involves relocating much of the city’s main highway network underground. Known locally as the ‘Big Dig’, it is a landmark project in urban infrastructure redevelopment1,2. It is scheduled for full completion in 2005 but with many of the new sections now operational it is already revitalising the city and establishing a more sustainable future for its citizens. It was essential to minimise disruption during construction and the alternative of tunnel jacking provided a key solution to this need. The jacked tunnels comprise by far the largest, most complex project of this type in the world, with each box structure well over 10 times the size of any jacked tunnels previously attempted in the USA. Introducing a wide range of innovation, the tunnel jacking has delivered a low maintenance, robust construction while adding important environmental advantages and contributed to over US$300m in construction savings3. From concept to completion of the tunnel jacking in 2001, required over a decade of sustained development and close teamwork. The official opening of the section of interstate highway section that includes the jacked tunnels was celebrated on 17 January 2003. This paper provides an overview of the tunnel jacking and focuses on the key structural aspects and the innovations involved. Alan Powderham, FREng, FICE, MIStructE Mott MacDonald Steve Taylor, MICE, MIStructE, PE (Structural) Hatch Mott MacDonald Derek Winsor, MICE, MIStructE, PE (Structural) Mott MacDonald