The St. Lawrence Lowlands didn't just give Quebec City its dramatic cliffs—it left behind thick deposits of loose, saturated silty sands across the Sainte-Foy plateau and parts of the Limoilou flats. When you're dealing with these compressible soils and a 5% probability of exceedance in 50 years per NBCC 2020 for seismic design, vibrocompaction design stops being a routine checklist item and becomes a critical mitigation strategy. Our team has worked on densification plans for sites within a kilometer of the river, where the water table sits barely 1.5 meters down in spring. We combine in-situ testing with numerical settlement analysis to target a relative density over 70%, which is often the threshold for acceptable post-liquefaction settlement in the Charlevoix seismic zone. Getting the vibrator energy and probe spacing right before mobilization saves weeks of rework.
In Quebec City's seismic environment, skipping pre- and post-CPT verification turns vibrocompaction design into guesswork—and guesswork fails at the building permit stage.
