Transition from Creeping to Rapid Landslide Movement and its Precursor

Abstract:

Despite the landslides and, in particular, rock slides are well investigated and classified, several aspects are still not clear (Hungr, 2014). For example, in spite of self-stabilizing nature of rotational slides there are several cases, where these landslides occurred with extreme speed. Extremely rapid rock avalanches have been observed in such cases as 1915 Great Fall of Folkestone Warren, the Roccamontepiano landslide in Central Apennines, and 2010 Maierato landslide in Calabria. Inspired by these observational data, which expose significant potential for environmental damage, we developed a new analytical model which incorporates post-failure strain-softening into elasto-plastic and visco-ferma (Kelvin) rheology for the shear layer of the rock avalanches. The model is developed for two different cases: rotational and translational landslides. As it turns out, the strain-softening behavior itself is necessary but not sufficient for the transition from smooth creeping movement to the rapid “slide-quake” rock avalanche. The condition of onset of “slide-quake” is obtained. It includes rock parameters such as elastic shear modulus, uniaxial compressive stress, as well as the post-failure stress-strain curve parameters, and the slope angle. The model shows that despite gravitational self-stabilization of rotational landslide, the rapid slide instability is possible, and provides condition for initiation of rapid slide. Due to self-stabilization, the total displacement of rapid slip turns out to be finite so that the landslide stops after the slip. The magnitude of the rapid slide displacement significantly depends on the shape of post-failure stress-strain curve. A precursor of rapid slide is formulated for the strain-rate as a function of increasing gravitational load (either due to precipitation or additional debris load). In a simple case of linear dependence of the load as a function of time, the strain-rate diverges as a power function of temporal proximity τ = (t_c -t) while approaching the time of rapid slide, t_c, which is the time of reaching the critical gravitational load. A similar precursor has been obtained in the past in the framework of a different earthquake model as of instability at a frictional fault under smooth external forcing (Geilikman, in “Computational Seismology and Geodynamics”, 1994).