| On 14-16 November 2002 the North Italy was affected by an
intense rainfall event: in the Albaredo valley (Valtellina) more than 200 mm
of rain fell triggering about 50 shallow landslides, mainly soil slips and
soil slip-debris flows.
Landslides occurred above the critical rainfall thresholds computed by
Cancelli and Nova (1985) and Ceriani et al. (1994) for the Italian Central
Alps: in fact the cumulative precipitation at the soil slips initiation time
was 230 mm (in two days) with a peak intensity of 15 mm/h.
A coupled analysis of seepage and instability mechanisms is performed in
order to evaluate the potential for slope failure during the event. Changes
in positive and negative pore water pressures during the event are modelled
by a finite element analysis of water flow in transient conditions, using as
boundary condition for the nodes along the slope surface the recorded
rainfall rate. The slope stability analysis is conducted applying the limit
equilibrium method, using pore water pressure distributions obtained in the
different time steps by the seepage analysis as input data for the
calculation of the factor of safety. |