Analysis of the landslide triggering mechanism during the storm of 20th–21st November 2000, in Northern Tuscany |
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Authors: | N Casagli S Dapporto M L Ibsen V Tofani P Vannocci |
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Institution: | (1) Earth Sciences Department, University of Florence, Florence, Italy |
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Abstract: | A severe rainstorm of high intensity occurred on 20th–21st November 2000, in the region of Pistoia, Tuscany, Italy, which
triggered, within the entire province, over 50 landslides. These landslides can be broadly defined as complex earth slides—earth
flows, originating as rotational slides that develop downslope into a flow. In this paper, two such landslides have been investigated
by modelling the process of rainwater infiltration, the variations in both the positive and negative pore water pressures
and their effect on slope stability during the storm. For both sites, results from morphometric and geotechnical analyses
were used as a direct input to the numerical modelling. A modified Chu, 1978 approach was used to estimate the surface infiltration
rate by adapting the original Green and Ampt, 1911 equations for unsteady rainfall intensity in conjunction with the surficial
water balance. For transient conditions, a finite element analysis was used to model the fluctuations in pore water pressure
during the storm, with the computed surface infiltration rate as the surface boundary condition. This was then followed by
the application of the limit equilibrium Morgenstern and Price, 1965 slope-stability method, using the temporal pore water
pressure distributions derived from the seepage analysis. From this methodology, a trend for the factor of safety was produced
for both landslide sites. These results indicate that the most critical time step for failure was a few hours following the
rainfall peak. |
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Keywords: | Landslides Infiltration Unsaturated and saturated flow Seepage analysis Stability analysis |
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