Flowslides In Pyroclastic Soils: Transition from “Static Liquefaction” to “Fluidization”

Flowslide triggering is usually considered well distinct from subsequent propagation; however the lesson learned from some study cases from a wide hilly area of the Campania Plain, repeatedly struck in the past by catastrophic flowslides involving initially unsaturated granular soils of pyroclastic origin and triggered by severe and longlasting rainfall, is that differentiation between triggering and run-out phases may not completely be warranted, as triggering itself, instead of being represented by a single event, should better designate the accomplishement of an evolutive process, starting from an instability situation – where instability develops in the form of inability to sustain the current deviator stress (static liquefaction) - and culminating in a fluidized state, sustained by continuously generated pore pressure excesses. Laboratory triaxial and flume tests, assisted by a convenient theoretical interpretation, revealed to be sufficiently suitable to adequately investigate the phenomenon.