The Town of Concord, Massachusetts is completing the construction of a new $80 million, 250,000-square-foot, 4-story high school. The new school is being constructed behind the existing school which will remain functioning until the new school is completed and can be demolished.
The new building is designed to meet the educational and community needs with energy and environmental elements for long-term sustainability. The new school will be solar ready and will use high performance operable windows and a high performance building envelope consisting of four floors instead of the current sprawling building. The landscaping incorporates environmentally green elements such as bike paths and rain gardens.
Nobis provided both feasibility and schematic design phase geotechnical services that assisted the town in determining the new school’s final location and layout. Nobis completed final design services in 2012 for the approved location of the new school. To support the construction of the new school, Nobis completed 24 test borings up to 80 feet deep and 5 test pits. Recommendations included foundation type, bearing capacity, settlement, groundwater controls for building and site walls, lateral earth pressures, retaining wall design, seismic parameters, slope stability, stormwater design support, pavement design, foundation and pavement subgrade preparation procedures and other earthwork activities.
The building site is underlain by deep loose to medium dense sands and/or varved silt and clay deposits. Nobis evaluated liquefaction susceptibility of the saturated sand deposits in accordance with Massachusetts State Building Code and estimated consolidation settlement of the varved silt and clay deposits. Using historic 1950 construction drawings, Nobis was able to determine that up to 15 feet of soil had been removed in the 1950s under portions of the proposed building; therefore the clays in these areas are highly over consolidated (i.e., the clays have been under greater pressures in the past), enabling Nobis to reduce the estimated settlements below portions of the building.
Nobis determined the estimated consolidation settlement of the varved silt and clay under the load of up to 20 feet thick new fill beneath the finished floor of the new school was excessive in one portion of the building and recommended a preload that would mitigate the post-construction settlement in this area. Nobis has also been providing subgrade inspections, preload evaluation, soil re-use support and other geotechnical related services during earthwork activities and foundation construction.