Modelling the transient groundwater regime for the displacements analysis of slow-moving active landslides

Active slow-moving landslides in clayey soils exhibit continuous movements generally related to changing ground water levels. This paper highlights the importance of groundwater modelling for the prediction of these types of movements through the analysis of a well-documented case history: the Porta Cassia landslide on the Orvieto hill in central Italy (e.g. Tommasi et al. 2006). The analysis uses recorded rainfall and pore pressure data to define a reliable model of the transient groundwater regime in the slope, which is then used to derive the time-dependent shear stresses along the main slip surfaces. The displacements at selected points along the slip surface are then computed using a relationship between the local factor of safety and the displacement rate at those points.