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, thehydraulic properties that drive groundwaterflow along the slope remain poorly understood. Moreover, landslidedeposits are often characterized by layering andfissures that cause high heterogeneity in the distribution ofhydraulic properties. This heterogeneity leads to great uncertainty in the prediction of groundwaterflow paths.This study aimed to improve understanding of hydraulic and transport properties of deep earth slides and toidentify preferentialflow directions inside the landslide body. A dye tracer test was used to estimate transportparameters and characterize groundwaterflow paths. The results indicate that in the studied landslide, twogroundwaterflow types exist and are related to the presence offissured rock blocks and debris horizons em-bedded in afine matrix. The estimated low groundwaterflow velocity has rarely been estimated in other studiesof this landslide type. The groundwaterflow direction appears to be mainly influenced by the failure surfaceshape and differs from the sliding direction. Our results differ from those in other landslide studies and improveour knowledge of groundwaterflow properties in deep earth slides; furthermore, they offer a new contribution toslope stability analyses and formula, and to the effective design of mitigation strategies.