## Calculations - Landslide Runout

The Val Pola landslide, Crosta et al., 2003, was the most destructive and expensive landslide occurred recently in Italy. The 28 July Val Pola landslide in Lombardy, northern Italy claimed 27 lives and total cost of about 400 million euros including destruction of villages, road closure, monitoring and warning systems, construction of permanent outlet tunnels and earth movements. Between June and July 1987, Valtellina was hit by an exceptional meteorological event. About four times the average rainfall for the area felt between the 15 and 22 of July, while the 0 grad isotherm remained between 3500 and 4000 m a. s. l. causing rapid glacier melting. On 28 July, a volume between 34 and 43 millions of cubic meters detached from the slope. It moved rapidly down the western valley flank to reach the valley bottom. Maximum avalanche deposit thickness was about 90m and the materials was characterized by hummock surface, lobate forms, large blocks at the deposit surface and fine grained materials within the accumulation body.

In our calculation the groundwater from reality was included. Initially the pore pressures follow from a specified phreatic level. When the sliding mass runs down, the groundwater is more or less entrapped and moves together with the sliding mass downwards. Due to consolidation effects the groundwater builds very high pressures at the point of changing inclination of the Val Pola hill ; these high groundwater pressures significantly influence the overall velocity of the sliding soil + water mass. The water pressure pictures below nicely show the build of of groundwater pressures.

In the Vajont landslide 300 million cubic meter soil volume slided into the Vajont river. A soft clay layer formed the principal sliding surface. Separate material layers in the landslide can be seen with different colors in the plots below. Please realize that our numerical scheme allows for such variations over the height of a sliding mass, as apposed to depth averaged methods which cannot take into account variations in depth direction. In the picture on the left, the initial layers can be seen. The picture on the right shows the slides layers, as settled in the end stage in the Vajont river.

The analysis of the Arvel slide in Switzerland shows the capabilities of our numerical scheme to model erosion of a sliding mass on other soil layers. The picture below show this erosion process at separate time points. The downward moving slide erodes the initially loose deposit material at the bottom of the domain. To obtain realistic soil material properties we found it to be necessary to include plasticity softening in the sliding mass elasto-plasticity law.

The analysis of the Arvel slide in Switzerland shows the capabilities of our numerical scheme to model erosion of a sliding mass on other soil layers. The picture below show this erosion process at separate time points. The downward moving slide erodes the initially loose deposit material at the bottom of the domain. To obtain realistic soil material properties we found it to be necessary to include plasticity softening in the sliding mass elasto-plasticity law.