A recent excavation along Rideau Street hit a pocket of silty clay that turned into a sticky mess after two days of spring rain. The contractor had moisture content data, but no one knew the plasticity index, and the structural fill specification suddenly looked impossible to meet. That is exactly where our Atterberg limits testing in Ottawa becomes the difference between a delayed project and one that stays on schedule. Ottawa’s post-glacial Champlain Sea clays, especially in low-lying areas near the Rideau River, can swing from stiff to soft with small changes in water content. We run liquid limit, plastic limit, and plasticity index under ASTM D4318 using calibrated Casagrande cups and a rolling device that replicates the exact thread-rolling technique the standard demands, giving the design team a defensible number for soil classification and compaction control. For projects where the fines content points to potential shrink-swell behaviour, we often pair the Atterberg analysis with a grain size distribution test to lock down the full USCS classification before the earthworks begin.
A plasticity index above 30% in Ottawa’s Champlain Sea clay is a red flag for volume change, and we flag it the same day the test finishes.
