Abstract
Different soil cover saturation has a significant effect in influencing slope stability conditions of weathered covers under earthquake-induced shaking. Here we analyze the Montecilfone, Italy (2018), case history, an Mw 5.1 earthquake that revealed an exceptionality in the spatial distribution of the surveyed earthquake-induced shallow landslides. This feature can be justified as intense rainfall occurred in the epicentral area before the seismic event, contributing to increasing the saturation and the weight of the soil covers. To verify the effective influence of antecedent rainfall as a preparatory factor in the earthquake triggering of soil covers, stability conditions for both static and dynamic scenarios were validated by reconstructing different saturation conditions related to a rainfall event that occurred before the earthquake. Soil cover surveying was performed within a 150 km2 area to output its spatial distribution in terms of their compositional features and thickness, whose variability was constrained through empirical models. Based on laboratory test results, 1D infiltration numerical models were performed through the Hydrus-1D free domain software to estimate the saturation degree of the soil cover and the water infiltration depth, taking as a reference the intensity of the rainfall event. Soil cover sequential charts of water content were obtained at different depths and times up to those recorded at the time of earthquake occurrence by the performed numerical modelling. Safety factors (SFs) of the slope covers were quantified assuming an unsaturated condition in the slope stability equation. The outputs reveal that pore pressure spatial distribution in the unsaturated medium infers on the earthquake-induced scenario of shallow landsliding, demonstrating its role as a preparatory factor for earthquake-induced shallow landslides.
Highlights
Large scale occurrence of slope failures can be verified either when the equilibrium between forces acting on the slopes and their own resistances are imminently unbalanced through the action of short term forcings or progressively through the cumulative and repetitive action of inner or external forces [1,2].Periodic fluctuations of the hydraulic pore pressures can drive slope deformations toward failures
As the value of H, we considered and fixed different depths within the soil cover to assess the in-depth distribution of Safety factors (SFs) and weight the contribution of capillarity in the slope stability
The results obtained demonstrate the suitability of the applied analytical approach for the reconstruction of seismic landslide scenarios, at basin scale, in hydraulically controlled conditions
Summary
Periodic fluctuations of the hydraulic pore pressures can drive slope deformations toward failures These processes are responsible for medium- to long-term variation in strength and can be considered preparatory factors for slope instability. Changes in hydraulic and physical conditions can instead statically predispose the action of short-term forcings since they control the mechanical strength and the bulk density of the geological layering. In this regard, the role of covers, which derive from vertical weathering profiles of the soil, in the predisposition to shallow landslides when triggering events, such as intense rainfall and earthquakes, are concurrent is not fully constrained. Such uncertainty arises from the objective difficulties in spatializing the thickness that the alteration covers have on the slopes as well as in the reconstruction of the geometries through which they are connected to the alluvial or debris at the valley floor
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