Repentigny’s development along the northern shore of the St. Lawrence River traces back to the 17th century, but its modern expansion southward onto the lowlands has pushed infrastructure into some of the most challenging ground in the region. The area sits on thick deposits of post-glacial Champlain Sea clays — sensitive, compressible, and notoriously tricky for underground works. When a tunnel alignment is proposed beneath neighborhoods or beneath the Assomption River terraces, the geotechnical analysis for soft soil tunnels becomes the single most important step in the design process. We get called in early, often before the alignment is even finalized, because understanding the clay’s sensitivity and the local groundwater regime isn’t something you want to figure out after the TBM is mobilized. Our work in Repentigny has shown that even a few meters of variation in the clay’s plasticity index can radically change the required face pressure and the settlement trough at the surface. Before any cutterhead touches the ground, we integrate field data from cone penetration tests with laboratory testing to build a reliable ground model, and we often pair this with a CPT investigation to capture continuous profiles of tip resistance and pore pressure in the soft compressible layers.
The sensitivity of Repentigny’s Champlain clay demands a geotechnical model that goes beyond simple bearing capacity — we map the remolded strength loss that can turn a stable face into a running ground condition.
