Mechanics of a tectonized soil slope: influence of boundary conditions andrainfall

The Vadoncello landslide was mobilized in December 1993 and is still active . it involves highly tectonized soils and is the reactivation of a landslid e dragged by a larger landslide at the toe of the slope soon after the 1980 Irpinia (Southern Italy) earthquake. investigations and monitoring of the Vadoncello landslide were carried out, between 1994 and 1996, within an EC funded research project. The slope has been found to be formed of chaotic s uccessions of soil and rock strata which have been grouped into soil comple xes. The soil mechanical properties are shown to be very poor, the deep soi ls being prone to large plastic straining even due to relatively small load ing changes. The soil displacements show that a shallow fast rotational sli ding has occurred at the top of the slope acid a shallow earthflow has deve loped downslope, both lying above deeper soils involved in a mechanism of s low and long-lasting irrecoverable movements. These slow deep movements are considered to be consequent to the plastic flow of the clayey soils, They can be activated by the effects of seasonal rainfall, of low-medium intensi ty seismic events and by the effects of the morphological changes resulting from the slow movements themselves. The landslide reactivation in 1993 is seen to have been the combination effect of a low return-period rainfall ev ent and the slow movements active at depth in the slope.