The St. Lawrence River carves a deep channel past the cliffs of Quebec City, but it is what lies hidden beneath the surface that dictates every foundation decision here. Post-glacial Champlain Sea deposits dominate the lowlands—soft, sensitive clays that lose strength when disturbed. Up on the Promontory of Quebec, shale and sandstone bedrock sits beneath a thin, erratic mantle of dense glacial till. Standard penetration testing often struggles to capture the fine layering in these formations. We deploy electric friction-cone CPT rigs capable of pushing through stiff crusts and measuring pore pressure in real time, which is essential for identifying thin silt seams that control slope stability along the Côte de Beaupré. For projects near the Old Port, where historical fill overlies marine clay, the continuous data stream from a CPT test eliminates the blind spots that traditional boreholes leave behind.
In Quebec City, a CPT pore pressure spike isn't noise—it's often the only warning of a thin silt seam in the Champlain clay that will double the consolidation settlement timeline.
