The influence of the grain-size, mineralogical and geochemical composition on the Verdesca landslide

Abstract

Abstract. Silty sands and clayey silts taken from a landslide in the Agri Valley have been analysed in order to study the role of sediment composition in the slope stability and the development of a slip zone. A geognostic hole was used to collect samples and monitor movements. A slip zone at a depth of about 14 m was identified. Compositional and physical-mechanical characterisation of samples was carried out. Some compositional characters, such as a 32-2 µm grain-size fraction, clay mineral content, cation exchange capacity and total nitrogen, increase in the slip zone. Some correlations have been found between geotechnical properties (residual shear strength and residual friction angle) and the same compositional characters, which can therefore be considered possible factors influencing slope stability.

The Verdesca landslide in the Agri Valley (Basilicata, southern Italy): a new geological and geomorphological framework

“…Silty levels affected by dark nodules and blackish saline concretions can also be observed, respectively due to oxidation phenomena and solution-precipitation processes favored by groundwater circulation. These stratigraphic logs are consistent with that of the S1 borehole, described by Summa et al (2015). The clastic component increases with depth, anticipating the appearance of sandstone strata at about 40 m depth in borehole R1.…”

“…A pre-existing geognostic borehole (S1), equipped with an inclinometer tube, provided indications of a slip zone, as reported by Summa et al (2015) in this issue. However, the break of the inclinometer tube did not allow for further monitoring.…”

“…Recent movements involving a road tunnel, retaining walls and other manmade structures cracked an inclinometer tube in a pre-existing borehole at 14.3 m depth located near the road tunnel, allowing for the identification of a slip zone at that depth (Summa et al, 2015).…”

“…Lucanian Apennines tectono-stratigraphic units are derived from the Afro-Adriatic paleomargin deformation and are tectonically layered as follows: the Liguria-Piedmont Ocean units of the Liguride and Sicilide complex, from Cretaceous to Oligocene; Apennine Platform carbonate units, from Late Triassic to Tertiary; and the Lagonegro Basin units, from late Paleozoic to Tertiary (e.g., Scandone, 1967;Ogniben, 1969;D'Argenio et al, 1975;Mostardini and Merlini, 1986;Carbone et al, 1991;Roure et al, 1991;Monaco et al, 1998;Cello et al, 2000a;Menardi Noguera and Rea, 2000;Lentini et al, 2002;Tavarnelli and Prosser, 2003;Piedilato and Prosser, 2005). Thrust sheet top siliciclastic deposits (e.g., Gorgoglione Flysch) are emplaced by Tertiary upon tectonostratigraphic units indicated above (Carbone et al, 1991;Butler and Tavarnelli, 2006, and references therein).…”

“…In the upper sector this landslide is a rotational slide, evolving, in the lower part, into a translational slide (Varnes, 1978;Cruden and Varnes, 1996). The landslide foot has been affected by further superficial movements, due to the continuous erosion of the Scazzera stream, whose course is diverted in relation to the zone accumulation.…”