With a population hovering around 550,000 and a metropolitan area that climbs the cliffs of Cap-Diamant, Quebec City presents a fascinating geophysical challenge. The promontory itself, rising over 90 meters above the St. Lawrence, is underlain by Ordovician sedimentary rock, but the lower town and Saint-Roch areas sit on thick sequences of post-glacial marine clays and deltaic sands. These abrupt transitions—from bedrock to compressible Champlain Sea deposits—mean that a standard geotechnical borehole can only tell part of the story. We run vertical electrical soundings (VES) to map these contrasts across a site in a matter of hours, giving project owners a continuous profile of subsurface resistivity before they commit to excavation or foundation design. It is a tool we have applied on everything from university expansions to port-side infrastructure in the Old Capital, and it consistently reveals hidden lenses of soft clay that would otherwise complicate a build.
A well-executed VES survey in the Quebec City region can pinpoint the depth to bedrock within 10% accuracy, cutting through the ambiguity of Champlain Sea sediments.
