Pore pressure variations in a post-glacial marine clay slope at Saint-Vallier, Quebec, Canada

Clay slopes susceptible to landslides are widespread in southern Quebec. In some cases, their stability is closely monitored due to the significant risks involved. The hydraulic head is a key parameter in assessing the effective stress of the soil, and consequently, the slope stability. However, during slope stability calculations, hydraulic heads are often simplified with assumptions such as steady-state conditions, when, in fact, hydraulic head varies throughout seasons. Yet these variations in Quebec’s clay slopes are poorly documented. This study aims to characterise the hydraulic head variations and their spatial distribution by the analysis of meteorological and piezometer data at a Saint-Vallier (QC) clay slope. Thus, a statistical approach using generalized additive models is used to study the seasonal cycles of hydraulic head, quantify the amplitude of the variations and study the long-term trends. Preliminary results show that annual variations in hydraulic head slightly exceed 1.5 m near the surface, but decrease rapidly with depth, reaching values below 0.3 m in some piezometers installed at depths greater than 29 m. However, at the base of the slope, variations are similar at all depths and are around 0.8 m. These variations are likely related to seasonal variations of the river at the bottom of the slope.