Ottawa’s downtown core sits on a deep deposit of sensitive Champlain Sea sediments, primarily Leda clay, over limestone bedrock. An excavation deeper than 3 meters in this material demands more than a generic shoring plan. The clay’s low remolded strength can trigger progressive failure if the wall system doesn’t limit deformation early. We combine CPT soundings with laboratory triaxial testing to define undrained shear strength profiles for staged excavation analysis. This data feeds directly into wall deflection predictions and strut load calculations. The Rideau Canal locks and several Parliament Hill parking structures were built through these exact soils, and the lessons from those projects shape our current design approach. A reliable excavation monitoring program validates the design assumptions during construction, which is critical when neighboring heritage buildings are only meters away.
In Ottawa’s Leda clay, wall stiffness matters more than soil strength for controlling excavation-induced settlement.
