The present work is focused on investigating the potential role of capillary barriers on the stability of layered soil deposits laying upon high permeability steep slopes. In presence of capillary barrier effects, often possible on a soil stratigraphy characterized by contrasting hydraulic properties (pyroclastics deposit over pumices, silt upon fractured bedrock, silt over sand) failure might originate in less permeable layers, where unsaturated conditions might provide a crucial contribution to stability. Basic ideas and considerations have been drawn from a peculiar case study, the catastrophic landslide occurred in Campania, Southern Italy, on May 1998, which is discussed in this paper from a different perspective. The areal extent of failures’ distribution, their dense concentration at the steeper and higher slopes, the extremely high number of initial failures occurred within a relatively short time span suggest that the intimate cause of the event is related at some extent to the soil state rather than positive pore pressure pulses from water circulation in coarser layers or groundwater rising from bedrock. A widespread loss of soil strength related to saturation can likely explain such phenomena. Capillary barrier effects favour accumulation and lateral distribution of percolating unsaturated flow and possibly divert flowlines downslope, thus leading to localized increases in water content. Diversion of percolating waters facilitate lateral redistribution of soil moisture along the slope with possible further localized saturation, because more permeable layers may act temporarily as barriers and not as drains, as one could expect. Numerical 2-D infiltration models with parameters calibrated versus laboratory data show a relevant influence of capillary barrier effects on infiltration in layered slopes with vertically stratified variations of hydraulic properties and point out significant localized moisture accumulation with possible consequences on slope stability. Landslide initiation phenomena in layered covers might thus be due to the increase in saturation within the least permeable soil layers due to capillary barrier phenomena.
|Titolo:||On capillary barrier effects and debris slide triggering in unsaturated layered covers|
|Data di pubblicazione:||2012|
|Digital Object Identifier (DOI):||10.1016/j.enggeo.2012.07.003|
|Appare nelle tipologie:||1.1 Articolo in rivista|