Ottawa’s subsurface is a tale of two extremes—the highly sensitive, low-permeability Champlain Sea clays that blanket the lowlands, and the fractured limestone of the Trenton Group that lies beneath. When groundwater control makes or breaks a project budget, a lab permeameter reading simply won’t cut it. We run in-situ Lefranc and Lugeon tests across the National Capital Region because the anisotropy of these formations demands field-scale measurement. The clay can hold water like a sponge, while open joints in the limestone can drain a dewatering system faster than the design assumes. A single borehole Lugeon test in the bedrock often reveals packer test values that change the entire excavation support strategy, especially below the Rideau Canal escarpment where karst features are common. For projects near the Ottawa River, combining a Lefranc falling-head test in the overburden with deep excavation monitoring provides the baseline data engineers need to size wellpoints or cutoff walls before the first bucket of soil is moved.
A 5-stage Lugeon test reveals the difference between tight bedrock (<3 LU) and open conduits (>25 LU) that can drain a dewatering system in hours.
