Abstract
The 1963 Vajont landslide is a reference example of large rockslides involving clay interbeds emplaced in sedimentary rock masses in correspondence with the basal rupture zone (thinly stratified cherty limestone of the Fonzaso Formation dated to Middle–Upper Jurassic). The basal shear zone of the 1963 Vajont landslide was made up of a chaotic assemblage of displaced rock masses, limestone angular gravel, and spread clay lenses. The mineralogical investigations showed that the clays are characterized by complex assemblages of illite/smectite mixed layers (36–96%) admixed with variable amounts of calcite (4–64%) and quartz (0–6%). The clay layers show highly variable plasticity properties and shear strength characteristics. The samples with a large prevalence of clay mineral content (CM) (CM > 79%) are characterized by low values of the residual friction angle (6.7–14.9°), whereas clay materials characterized by a higher content of granular minerals (calcite and quartz) clearly show greater friction angle values (19.5–26.7°). The high permeability of the limestone angular gravel, which caused a rapid reservoir-induced inflow (1960–1963), together with the low friction angle of the clay layers were responsible for the overall shear strength reduction in correspondence with the basal rupture zone, thus favoring the huge sliding on 9 October 1963.
Highlights
Many large rockslides and large-scale slow-moving rock slopes, in both massive and closely stratified rock masses, are characterized by the occurrence of a deep-seated basal rupture zone where deformation and damage caused by shear stresses are concentrated
We present in this work the results of a geochemical, mineralogical, and geotechnical investigation performed on several clay samples collected from the Vajont landslide and from a comparable in situ Jurassic–Cretaceous sequence occurring in the surrounding area
The mineralogical investigations carried out for this study showed that the clay interbeds occurring
Summary
Many large rockslides and large-scale slow-moving rock slopes, in both massive and closely stratified rock masses, are characterized by the occurrence of a deep-seated basal rupture zone where deformation and damage caused by shear stresses are concentrated. Shear zones at the base of large rockslides or slow-moving rock slopes include fine-grained or clay materials [2,3,4,5,6,7]. These materials can have a different origin or formation process. Clay materials within basal rupture zones have a mechanical origin and occur as a Geosciences 2020, 10, 360; doi:10.3390/geosciences10090360 www.mdpi.com/journal/geosciences
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