Geotechnical Challenge Solved with Lightweight Fill

by Joe Kowalewski, Norlite LLC

This past summer, Karl’s Excavating was awarded the contract to handle the excavation and site work on the MedExpress Urgent Care Building in Hadley, Massachusetts. The site had soft soils that posed a geotechnical challenge in supporting the weight of the new building.

Stephen Lanne, P.E. of Terracon, the geotechnical engineer, proposed site surcharging with an alternate of utilizing lightweight aggregate (LWA) fill as an option to remedy the site issues. After evaluating the options, the final decision was made to utilize 3/8 x #8 LWA geotechnical fill. The use of LWA allowed the facility to be occupied sooner than the surcharging would have allowed. The LWA fill option required less excavation resulting in a significantly reduced load on the underlying soft clay layers. The LWA fill consisted of expanded shale with a unit weight of approximately half that of typical fill materials (under 65 pounds per cubic foot in place).

The project plans included placing up to 3 feet of LWA fill to raise grade within and around the new building. The foundation excavation was extended 5 feet beyond each side of the foundation wall before sloping up to the surrounding grade. Inside the building footprint, existing soils were removed to the bottom of the footing level. Soil subgrades were then satisfactorily proof-rolled with soft or unstable areas removed and replaced with compacted structural fill. LWA was then placed in ten-inch compacted lifts up to the bottom of the slab/pavement base course elevation.

Karl’s Excavating stated, “The lightweight aggregate fill was very easy to work with and they are very pleased with the installation.”

The medical facility began serving the community in September of 2017.

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