With reference to two slow earthflows in structurally complex clayey formations of the Italian southern Apennines, this paper shows the results of a long-term displacement monitoring using integrated systems of inclinometers and GPS, and their comparison with PSInSAR data. A fixed-in-place and traversal inclinometer system, first installed in 2004, recorded both the shear displacements along the slip bands, and the internal deformations of the landslide masses. A GPS network of permanent stations and benchmarks, installed in 2006–2007 in 23 strategic points of the slope, allowed for the temporal continuity of displacement monitoring. The two long series of data allowed to evaluate the factor scaling of the PSInSAR COSMO-SkyMed data, although the component of the displacement vector along the line of sight (LOS) was small. PSInSAR data allowed for the monitoring extension to houses and rigid structures that acted as reflectors. The joint data analysis allowed for the comprehension of the main features of the landslides’ kinematics.
To analyze the response to hydrological conditions of an instable slope in a structurally complex clay formation, the hydraulic conductivity of the subsoil was estimated and pore water pressures were monitored. Two types of field tests were carried out: falling head tests in the Casagrande piezometers and localized seepage measurements in test boreholes. The experimental data show that in a narrow band around the slip surface, the hydraulic conductivity is higher—more than two orders of magnitude—than that of the landslide body and of the stable formation. Furthermore, the data of a long-term monitoring by Casagrande piezometers and vibrating wire cells show that the response of pore water pressures to the site hydrological conditions along the shear band is far faster than in the landslide body and in the stable formation. The slip band seems largely connected to the atmosphere, and the water pressures in the band are correlated with the deep displacement rates of all the inclinometers crossing the active slip surface.
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