The Undrained Behaviour of an Air-Fall Volcanic Ash

Abstract

Pyroclastic soils are widespread in the world. In particular, they cover a great part of Campania, a densely populated country of Southern Italy, where some distinct volcanic centers are present. In these soils, precipitations can trigger fast flow-like landslides causing destruction and loss of human lives. The movement style, the high velocity and the long run-out of these landslides are an indication of the occurrence, in the saturated soil mass, of mechanisms of undrained instability due to the inability of soil to sustain the deviator stress related to the slope condition. This paper reports the results of a wide experimental laboratory program carried out on a volcanic ash, which recently has been the seat of a killer landslide, stressing the factors that govern the undrained response of these materials.

Earthquake-Induced Flow-Type Slope Failure in Weathered Volcanic Deposits—A Case Study: The 16 April 2016 Takanodai Landslide, Japan

“…Geosciences 2022, 12, x FOR PEER REVIEW 11 of 21 [29]. Relatively high effective critical state friction angles (ϕCS' = 38°) were also reported by Picarelli et al [45] in triaxial compression tests on reconstituted (moist-tamped) specimens of sand-sized volcanic air-fall deposits from Italy which, analogously to the test on Kpfa pumice shown in Figure 7, exhibited undrained instability with a flow-type response.…”

“…Nevertheless, the Kpfa pumice specimen developed significant shear strains despite a high value for the effective friction angle mobilized during flow (at state Q) of φ Q = 42.6 • ; this value of φ is significantly larger than those mobilized by loose Toyoura sand during flow (at failure, φ F = 34 • ) and by medium-density Toyoura sand in the quasi-steady state (φ Q = 31 • ), with limited flow [29]. Relatively high effective critical state friction angles (φ CS = 38 • ) were also reported by Picarelli et al [45] in triaxial compression tests on reconstituted (moist-tamped) specimens of sand-sized volcanic air-fall deposits from Italy which, analogously to the test on Kpfa pumice shown in Figure 7, exhibited undrained instability with a flow-type response.…”

“…by Picarelli et al [45] in triaxial compression tests on reconstituted (moist-tamped) specimens of sand-sized volcanic air-fall deposits from Italy which, analogously to the test on Kpfa pumice shown in Figure 7, exhibited undrained instability with a flow-type response.…”

Mechanical and hydraulic properties of unsaturated layered pyroclastic ashes in landslide-prone areas of Campania (Italy)

“…Nonetheless, steep slopes covered with pyroclastic soils are often prone to landslides, where rapid movements frequently occur, causing catastrophic effects (Fiorillo et al 2001;Cascini et al 2008;Greco et al 2021). The soil behavior at failure looks similar over a relatively wide area, with the sliding surface within the layers of ashes for many of the studied landslides, such as in 1998 in Sarno (Cascini et al 2000;Bilotta et al 2005), in 1999 in Cervinara (Olivares and Damiano 2007;Picarelli et al 2020), and2005 in Nocera (Revellino et al 2013).…”

“…While the pumice strata are mostly gravelsized materials, the ashes are often well-graded silty sands. Along with a relatively high friction angle and permeability, these deposits are usually stable due to the action of soil matric suction under unsaturated conditions (Picarelli et al 2020). Nonetheless, steep slopes covered with pyroclastic soils are often prone to landslides, where rapid movements frequently occur, causing catastrophic effects (Fiorillo et al 2001;Cascini et al 2008;Greco et al 2021).…”