Last spring we were called to a site off Rue Notre-Dame where a contractor had opened a 4.5-meter cut for a triplex foundation. The slope face stood near-vertical for three days before a rain event triggered a shallow failure that took out the south formwork. Repentigny’s residential expansion pushes deeper into the terraces flanking the L'Assomption River, and those cuts expose the sensitive silty clay that defines the Champlain Sea deposit. A proper slope stability analysis before excavation would have identified the critical height and the required bench width. Our approach integrates in-situ permeability testing to quantify pore pressure buildup during the spring thaw, because that is what turns a stable winter cut into a mid-April slide. When the stratigraphy suggests interbedded sand lenses, we also run CPT soundings to map drainage paths that concentrate seepage at the toe.
A factor of safety of 1.3 means nothing if the pore pressure input comes from a textbook instead of a piezometer reading in April.
