## Slope stablility

Val Pola - Italy (1987) |
For slope stability studies there are two different types of analyses relevant. First, an initial instability calculation gives insight in the start of the slope instability. Soil parameters, typically think of the friction angle and material cohesion, can be lowered to the level where instability occurs in the calculation. The ratio of real parameters and lowered parameters defines the so-called 'Safety Factor', measuring how much the slope is away from initial failure. Second, after initial failure, runout of material may occur over long distances; soil and rocks get disposed far from there initial location. |

Las Colinas - El Salvador (2001) |
Fast moving landslides are one of the most significant danger coming from slope instabilities. The Santa Tecla-Las Colinas landslide (El Salvador, Central America) resulted in almost 500 casualties and can be considered one of the most destructive landslides ever known. This landslide involved a total volume of 183000 cubic meter of stratified volcanic deposits. |

We first computed the factor of safety. Degradation of material proprieties, friction angle and cohesion, has been performed on all the materials contemporaneously up to instability. Slope failure is triggered by decrease in resistance of the weak paleosoil layer where plastic deformation accumulates progressively. The geometry of the failure surface is well simulated by the numerical model with a sharp increase in displacement and velocity vectors starting from 23.5 m behind the initial position of the slope crest. This observation is in excellent agreement with field observations concerning the failure surface geometry and the presence of tension cracks. This picture shows displacement vectors. |