Structure and kinematics of a landslide in a complex clayey formation of the Italian Southern Apennines

This paper describes the geometrical structure and the main kinematic features of an ancient and active landslide which develops in structurally complex formations of the Southern Apennines (Italy): a scaly clayey formation in the medium and lower part of the slope, and a stratified marly–calcareous rock formation in the upper part. The landslide 3D geometry was reconstructed by using topographic data, stratigraphies from continuous coring boreholes and inclinometer data. The analysis of the kinematic features was based on the measurement of deep and superficial displacements. Laboratory tests were carried out to evaluate shear strength parameters. It was found that in each investigated transversal section of the landslide channel the displacements can be considered uniform, and that the decrease of the displacement rates, from upslope to downslope, mostly depends on the increase in the areas of transversal sections, the “soil discharge” variations being slight. Stability analyses confirmed that shear strength close to the residual value is available on the slip surface. The large difference between residual strength and peak strength of the landslide material is consistent with the displacement uniformity. ►The inclinometer profiles provide uniform displacements above the slip surface. ► Residual strength, much lower than the peak one, is available on the slip surface. ► So, the displacements can be considered uniform in each entire transversal section. ► The evaluated “soil discharge” in the landslide channel results roughly constant. ► The displacement rate thus depends fundamentally on the transversal sections’ areas.