NHESS Natural Hazards and Earth System Sciences NHESS Nat. Hazards Earth Syst. Sci. 1684-9981 Copernicus Publications Göttingen, Germany 10.5194/nhess-6-1025-2006 Infiltration, seepage and slope instability mechanisms during the 20–21 November 2000 rainstorm in Tuscany, central Italy Tofani V. 1 Dapporto S. 2 Vannocci P. 1 Casagli N. 1 Earth Sciences Department, University of Florence, Italy Regione Toscana, Sistema Regionale di Protezione Civile, Italy 12 12 2006 6 6 1025 1033 Copyright: © 2006 V. Tofani et al. 2006 This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 Generic License. To view a copy of this licence, visit https://creativecommons.org/licenses/by-nc-sa/2.5/ This article is available from https://nhess.copernicus.org/articles/6/1025/2006/nhess-6-1025-2006.html The full text article is available as a PDF file from https://nhess.copernicus.org/articles/6/1025/2006/nhess-6-1025-2006.pdf

On 20–21 November 2000, a storm of high intensity, with a estimated return period of more than 100 years, triggered over 50 landslides within the province of Pistoia in Tuscany (Italy). These failures can be defined as complex earth slides- earth flows. One of the documented landslides has been investigated by modelling the ground water infiltration process, the positive and negative pore water pressure variations and the effects of these variations on slope stability during the rainfall event. Morphometric and geotechnical analyses were carried out through a series of in-situ and laboratory tests, the results of which were used as input for the modelling process. The surface infiltration rate was initially simulated using the rainfall recorded at the nearest raingauge station. Finite element seepage analysis for transient conditions were then employed to model the changes in pore water pressure during the storm event, using the computed infiltration rate as the ground surface boundary condition. Finally, the limit equilibrium slope stability method was applied to calculate the variations in the factor of safety during the event and thereby determine the critical time of instability. For the investigated site the trend of the factor of safety indicates that the critical time for failure occurs about 18 h after the storm commences, and highlights the key role played by the soil permeability and thickness in controlling the response in terms of slope instability.

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