ABSTRACT
The Central Artery Tunnels (CA/T) in Boston, Massachusetts, constructed between 1991 and 2007, is a landmark project in the history of urban infrastructure redevelopment. The ground conditions beneath the railway presented an exceptionally challenging array of mixed face conditions for tunnelling. Original design concepts for the CA/T tunnels were based around traditional cut and cover construction techniques. Tunnel jacking beneath the railway as a potential alternative to cut and cover construction was presented at the bid stage for the design contract in February 1991. Jacked tunnels, particularly the longer ones, are typically constructed using several separate units. These tunnel elements are linked together by intermediate jacking stations and the tunnel is installed employing a ‘caterpillar’-like action. Tunnel jacking, in common with all tunnelling, requires adequate control of the tunnel face to prevent ground movement into the tunnel creating volume loss leading to ground settlement and lateral movement.
