Ottawa sits on one of the continent’s most challenging foundation soils: Champlain Sea clay, commonly called Leda clay. This post-glacial marine deposit covers much of the urban area south of the Ottawa River and can lose over 90 percent of its strength when disturbed. In Kanata, Barrhaven, and the Greenbelt fringe, soft compressible clays extend 20 to 30 meters deep before hitting till or bedrock. A conventional fill-and-surcharge approach often takes too long or risks excessive settlement under new loading. Stone column design offers a practical alternative—installing compacted gravel columns through the soft zone to accelerate drainage and reinforce the matrix. The result is a stiffer composite ground that limits total and differential settlement while respecting the sensitivity of the native clay. Before committing to a Improvement scheme, we typically pair the design investigation with CPT testing to map layer continuity and undrained shear strength, and complement it with triaxial lab work when column confinement needs verification.
A well-executed stone column program in Leda clay can shift the site class from E to D under NBCC 2020, directly reducing seismic demands on the structure.
