HR: 0800h
AN: H51C-0651    [Abstracts]
TI: A Probabilistic Analysis of the Impact of the Topography on Slope Stability
AU: * Simoni, S
EM: silvia.simoni@ing.unitn.it
AF: Civil and Environmental Engineering Department, University of Trent, via Mesiano 77, Trento, 38050, Italy
AU: Rigon, R
EM: riccardo.rigon@ing.unitn.it
AF: Civil and Environmental Engineering Department, University of Trent, via Mesiano 77, Trento, 38050, Italy
AU: Cordano, E
AF: Civil and Environmental Engineering Department, University of Trent, via Mesiano 77, Trento, 38050, Italy
AB: This work investigates the influence of topography on hillslope stability in partially saturated soils, by using a distributed hydrological model, GEOtop [Rigon et al., 2006] coupled to a simple geo-mechanic model, GEOtop-FS [Simoni et al., 2007], which includes the theory of Lu and Likos, [2004]. GEOtop is a dynamic hydrological model, and describes the transient infiltration by solving Richards equation; GEOtop-FS uses the pore pressures computed by GEOtop to return, for every time step, probabilistic stability classes for any point in the catchment. Three variables are defined for each cell of the analyzed catchments: P_FS = P[ FS < 1] [Duan and Grant, 2000] represents the stability range expressed in terms of failure probability; it can assume one of the following ranges of values 0-20% (very low probability of failure), 20-40% (low), 40-60% (moderate), 60-80% (high), 80- 100% (very high); α is the slope angle and mrph represents one of the three basic morphological attributes, convergent, divergent and planar, as derived from the planar curvature of the sites. We investigate the probability that a given range of stability/instability, in a given morphology, mrph, occurs at a slope angle α, which is given by p(α | P_FS, mrph). In order to assess whether the slope angle is really a discriminant factor for slope stability, it is necessary to correlate the information provided by p(α | P_FS, mrph) with the one provided by p(P_FS | α , mrph), which describes the probability that a cell characterized by an α slope angle and by a morphology mrph, falls within a certain range of P_FS. The analysis is performed using different, representative, soil types and three assumptions on soil depth: a uniform soil depth distribution, a soil depth calculated based on the topography derived from field geophysical measurements and a soil depth derived from the application of simple theories on soil-sediment evolution. The analysis shows that in partially saturated soils, where rainfall infiltration occurs mainly in the vertical direction, topography does not influence hillslope hydrology at local scale. However, when lateral redistribution occurs as a consequence of water table rise, some effects are evident at the catchment scale. The analysis suggests that planar and divergent sites tend to be stable, whereas for convergent sites instability seems to be evenly distributed among different stability ranges for slope angles close to soil internal friction angle.
DE: 1816 Estimation and forecasting
DE: 1826 Geomorphology: hillslope (1625)
DE: 1838 Infiltration
DE: 1866 Soil moisture
DE: 1873 Uncertainty assessment (3275)
SC: Hydrology [H]
MN: 2007 Fall Meeting