City of Somerville - Owner
Suffolk Construction - General Contractor
The Dow Company - Site Contractor
The expansion of Somerville High School—the most expensive high school construction project in Massachusetts history—required a combination of micropiles and soil nailing. Hub used underpinning to shore up the existing 1895, five-story brick building, supporting the soil laterally for a depth of up to 25 feet below the foundations.
This project was originally intended to start in late summer, which provides ideal weather conditions for the shotcreting portion of the work. However, after an adjacent building wing was demolished, exploratory test pits discovered the presence of contaminated soils and the presence of a dry rubble stone foundation in the section that had to be underpinned. The original micropile/soil nailing design could not be used to support the rubble stone foundation. A drilled soldier pile, shotcrete, and tieback system was designed to provide support to the structure in this section. Delays resulting from this changed condition extended the start date to last week in December. Hence, construction of the soil nail and soldier pile walls would be done in severe winter conditions.
Hub was directed by the owner to accelerate this work with both additional crews and longer work hours. The latter proved to be very difficult due to the short winter days and cold temperatures. Despite these challenges, Hub’s crew persevered and completed this entire scope by the beginning of April.
Extensive instrumentation was included to monitor both vertical and lateral movements of the existing structures and the lateral support systems. The maximum vertical movement of the adjacent existing structures was only one-eighth inch, which was well below the project requirement of one inch. The maximum lateral movement of the excavation support systems was four tenths of an inch, which was less than the six tenths project requirement.