A TEAM LED by Mott MacDonald has been shortlisted for the UK's biggest engineering prize, the Royal Academy of Engineering MacRobert Award, for the three huge jacked tunnels on the Boston Central Artery project (below).
The tunnels form the interchange between the I-90 and I-93 interstate roads (GE July 1999).
Weighing up to 30,000t and up to 100m, they were slid beneath seven rail lines carrying more than 40,000 passengers in and out of Boston's South Station every day. Conventional cut and cover methods would have meant relocating the railway five times.
'The ground was one of the biggest problems, ' said Mott MacDonald transportation director Alan Powderham. 'It is very soft and full of the artefacts from 200 years of harbourside development, which became major obstacles for the tunnels. The site is right by Boston harbour and is crossed by a waterway as well as the railway lines.' Ground freezing was used around the tunnel zone to create 200,000m 3of 'artificial tundra'. A new anti-drag system using steel ropes was developed to ease jacking. Jacking was completed in February 2001 and the Central Artery project is due to be finished by 2005.
The shortlisted team consists of Powderham, Stephen Taylor of Hatch Mott MacDonald, Chris Howe of Skanska Construction, Douglas Allenby of Edmund Nuttall and John Ropkins of John Ropkins. The winner of the MacRobert gold medal and £50,000 will be announced in November.