Università degli studi di Modena e Reggio Emilia

A multidisciplinary approach focusing on the integration of diverse and non-invasive investigations is presented to define the hydrogeological conceptual model of the complex Fontana Cornia landslide in the Northern Apennines, Italy. The results of seismic refraction tomography and electrical resistivity tomography investigations indicate that the landslide has a curvilinear sliding surface dividing the shallow calcarenite debris layer from the deeper pelitic bedrock. The surface presents undulations in which water can be stored and supports the application of the fill and spill hypothesis that is seldom used in landslide studies. The joint interpretation of the geophysical outcomes and of the hydrogeological and hydro-chemical analyses of a spring located on the slope allows the definition of the landslide hydrogeological conceptual model. Four specific hydrologic stages with different groundwater flows though the landslide body were identified. The developed hydrogeological model may explain the displacements of the landslide that were detected with In-SAR monitoring. The isotopes analyses, the displacement monitoring, and the hydrogeological measurements confirm that periods with significant precipitations and snowmelt can cause an increase in landslide saturation that in turn triggers larger displacements. Conversely, the landslide slowly moves at a steady rate during periods with limited recharge water.

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.