A parametric study to characterize the impact of soil water retention curves on the seismic response of earth dams

Earth dams often exhibit partially saturated conditions throughout large sections of the embankment. The extent of these zones depends on the dam characteristics and stage of life. To reliably predict the dam response to static and seismic loads, it is essential to model the effects of partial saturation using coupled three-phase formulations to solve the boundary value problem. These formulations incorporate the soil water retention curve (SWRC) as an essential component. This property not only plays a key role in determining the hydraulic behaviour of the dam but also influences its stress and deformation response through hydro-mechanical coupling. However, the extent of this influence remains poorly understood. This paper presents a numerical study investigating how the water retention properties of construction materials affect the seismic response of a zoned earth dam. The study uses a commercial finite element code to solve a coupled three-phase approach, incorporating soil water retention curves and an advanced constitutive model for the soil skeleton. The dam geometry and soil parameters are based on a real dam to ensure a realistic context without aiming to interpret that specific case. The simulation of the static stages incorporates soil-water retention properties related to the actual grain size distribution of the dam materials, establishing pre-seismic suction conditions. For the seismic stages, the simulation considers different water retention properties, either those from the static stages or those induced by hypothetical scenarios involving erosion, transport, and deposition, which alter the grain size distribution of the core and shell materials. The parametric study shows that specific soil water retention patterns significantly impact the stress distribution and deformation mode of the dam embankment during seismic events.