When you are working on a roadway or parking lot in Ottawa, the Ontario Provincial Standard Drawings (OPSD) and the City of Ottawa’s supplemental specifications aren't just paperwork—they are a survival guide. The capital’s pavement structures face a brutal annual cycle: deep frost penetration reaching 1.8 meters in an average winter, followed by a messy spring thaw that saturates the silty Leda clay subgrades so common across the region. A standard flexible pavement design that works in Toronto fails here because the bearing capacity of the moisture-sensitive subgrade can drop by over 60% during the thaw-weakening period. In our experience, integrating a solid CBR road test early in the investigation phase is the only reliable way to quantify that seasonal strength loss and avoid premature rutting. We also cross-reference these results with Atterberg limits to predict the volumetric instability of the native glacial sediments before finalizing the asphalt and granular base thickness.
In Ottawa, the pavement structure must be a drainage system first and a structural section second—because Leda clay doesn't forgive standing water.
