Tracer test to assess flow and transport parameters of an earth slide: The Montecagno landslide case study (Italy)

Subsurface water processes are principle triggering and driving factors during slope movements. However, the hydraulic properties that drive groundwater flow along the slope remain poorly understood. Moreover, landslide deposits are often characterized by layering and fissures that cause high heterogeneity in the distribution of hydraulic properties. This heterogeneity leads to great uncertainty in the prediction of groundwater flow paths. This study aimed to improve understanding of hydraulic and transport properties of deep earth slides and to identify preferential flow directions inside the landslide body. A dye tracer test was used to estimate transport parameters and characterize groundwater flow paths. The results indicate that in the studied landslide, two groundwater flow types exist and are related to the presence of fissured rock blocks and debris horizons embedded in a fine matrix. The estimated low groundwater flow velocity has rarely been estimated in other studies of this landslide type. The groundwater flow direction appears to be mainly influenced by the failure surface shape and differs from the sliding direction. Our results differ from those in other landslide studies and improve our knowledge of groundwater flow properties in deep earth slides; furthermore, they offer a new contribution to slope stability analyses and formula, and to the effective design of mitigation strategies.