Use of Soldier Pile–Tremie Concrete Slurry Walls as Permanent Tunnel Walls

The analysis and design of soldier pile–tremie concrete (SPTC) slurry walls for the Massachusetts Highway Department's (MHD) Central Artery/Tunnel (CA/T) Project in downtown Boston are discussed. Unlike most slurry walls, which are used as temporary support for excavation during construction, these SPTC walls are designed also as the permanent wall system for the tunnels. The CA/T includes more than 6.1 km (20,000 ft) of slurry walls. Most of the walls are designed and are to be constructed as SPTC walls. Steel wide-flange soldier piles are installed at 1.21- to 1.83-m (4- to 6-ft) spacings in a slurry trench, and the tremie concrete is placed to form the concrete wall. The steel wide-flange piles form the primary support system for the wall. In most of the locations, the concrete is designed to act as “lagging” spanning between the structural steel members. The concrete base slab is rigidly connected to the SPTC walls, and the composite roof is pin-connected to the walls to form the tunnel. The following topics are discussed after an introduction to the project: geotechnical conditions, design concept of the SPTC slurry walls, design consideration, underpinning of the existing Central Artery, and low head-room construction.