Drilled Shaft Installation Under Polymer Slurry: A Case Study in Barrie, Ontario

ABSTRACT: Drilled shaft foundations for Ministry of Transportation Ontario (MTO) projects have traditionally been installed using casing to ensure sidewall stability during construction. However, site access, subsurface conditions, and caisson sizes can result in construction challenges related to laydown area, equipment size demand and installation efficiency. At the Highway 400/Essa Road Overpass Replacement Project in Barrie, Ontario, 20 m long, 1.5 m diameter drilled shafts have been installed in silty sands with a high groundwater table. The use of full-depth temporary casing was considered but was found to be impractical due to the extremely limited working footprint in the roadway median adjacent to live traffic lanes and existing infrastructure, and the risk of basal instability. Hence, a polymer slurry drilling system with short surficial casing was selected by the Contractor as the preferred method for stabilizing the shafts in these challenging geotechnical and site conditions. Polymer slurry testing, base cleaning, concrete mix design and testing, and pile integrity testing were completed to support the construction and quality control.