Compositional characterization of fine sediments and circulating waters of landslides in the southern Apennines - Italy

Several studies in the last several years have shown that slope stability and the physical-mechanical properties of sediments can be influenced by their granulometrical, chemical and mineralogical characters and circulating water chemistry, which highlights the importance of studying these processes using a multidisciplinary approach. Two landslides, in a well-known geological area in the Southern Apennines impacted by many landslides, were studied to integrate geological and geomorphological surveys and geotechnical tests with the compositional characterization of the sediments and circulating waters and through a careful definition of the tipology and intensity of the weathering processes. Pliocene clays and Oligocene slates affected by the studied landslides were characterized for mineralogical, chemical and grain-size composition and these compositional characters were compared with their physical (Atterberg limits, plasticity, activity) and mechanical (friction angle, cohesion, residual shear strength) properties. These properties were determined using distilled water, waters circulating in the landslide sediments and saline solutions that amplify seasonal chemical variations. The compositional and physical-mechanical properties of the sediments were compared with the slip and low deformation zone positions, detected in situ from inclinometer measurements, in order to identify any anomalies in the weak zones along the stratigraphic column. The results showed some correlations between the compositional characters of sediments (grain size, mineralogy and geochemistry) and the slip zone position, and highlighted that the chemistry of the circulating waters can modify certain physical-mechanical behaviours. However, the magnitude and modalities of such influences depends strongly on the geological history and lithotypes involved in the sliding. The Pliocene clay landslide was found to have several slope instability risk factors, such as kaolinite content and water salinity, while the physical-mechanical properties of the Oligocene slates were demonstrated to be less sensitive to sediment and water compositional characters. Finally, significant correlations were detected between the position of the slip zone and the degree of sediment chemical alteration using a new weathering index specifically designed for the sediments studied. These results demonstrate that the study of landslides must not ignore the compositional characterization of the sediments and waters, as certain chemical or mineralogical features can represent important risk factors contributing to the worsening of the slope stability and the triggering of the slip.