The document discusses the design of excavation support for ventilation towers constructed as part of the Big Dig project in Boston. The towers had footprints of 200 ft by 100-150 ft and were 150 ft deep, requiring a system of struts and whalers made of over 20,000 tons of steel to support each excavation as it increased in depth and the towers were built upwards. The struts comprised of paired and welded deep W sections to support compression from surrounding soil, while continuous W sections served as whalers spanning the length of each pit. Inflatable jacks pumped with high-pressure grout were used to put the struts into compression as excavation progressed.

1. Musaddeque Hossein PE
Email: musahossein@hotmail.com; Phone: (703)-629-3463
Support of excavation design
10908 Adare Drive, Fairfax, VA 22032
PROJECT: BOSTO DE TRAL ARTERY A D TU EL PROJECT
MASSACHUSETTS
Architect: NA
Engineer of Record: LeMessurier Consultants
Contractor: Walsh / O’Donnell, Boston
Project Manager: Massachusetts Highway Department
Estimated Project Cost NA
Project Description:
The Central Artery and Tunnel project, also known as the “Big Dig”, comprises of immersed
tube tunnels, cut and cover tunnels, ramps and other transportation structures constructed in
downtown Boston to ease traffic congestion. To provide airflow and fire suppression in the
tunnels, several ventilation towers were constructed. The foot-print of the towers were roughly
200 ft in length, 100 ft – 150 ft in width and 150 ft deep. To support the excavation for the
construction of such towers a system of struts and whalers were installed as the excavation
increased in depth. The struts and whalers were subsequently removed as the construction of the
towers progressed upwards towards finished grade from the bottom of the pit.
Design Highlights:
• Struts comprised of deep W sections paired and stitch welded to support the compression
loads from the unexcavated soil around the pit. Whalers comprised of continuous W
sections spanning the length of the pit. Inflatable jacks (inflated with grout pumped in
under high pressure) were use to put the struts into compression. Over 20,000 tons of
steel was used in each pit to support the excavation.