A COMBINED HILLSLOPE HYDROLOGY STABILITY MODEL FOR LOW-GRADIENT CLAY SLOPES IN THE ITALIAN DOLOMITES/

The temporal trend of displacement of a landslide on a low-gradient cl ay slept in the Italian Dolomites as a function of precipitation was s imulated with a combined hydrological-slope stability model based on g roundwater and surficial displacement observations. Piezometric record s and lithological profiles from boreholes suggest the occurrence of p referential groundwater flow through a very permeable top layer of abo ut 1 m thickness, which overlies a less permeable, compact clay layer penetrated by dead-end cracks. To simulate groundwater levels in this system, a linear reservoir model with two outlets was applied, where t he upper outlet drains the permeable top layer, and the lower outlet d rains the dead-end cracks in the clay layer. The reservoir was assigne d a bottom boundary level varying in time. This was done to represent an inferred yearly fluctuation of a matric groundwater level due to re gional flow, which controls the thickness of the unsaturated part of t he clay layer absorbing water from the cracks. Groundwater output from the model was used in a visco-plastic stability model to simulate the velocity of landslide movement, taking into account a phenomenon of s trength regain that occurs in the clays along the slip surfaces. Calib ration and validation on 3 years of groundwater and displacement data showed that both models yield good results. Thus, good estimates of cu mulative landslide displacement were obtained as a function of precipi tation. The general concepts underlying the models offer possibilities for regionalization because from a geological point of view, this lan dslide is typical of many others in the Dolomites. (C) 1998 Elsevier S cience B.V.