Monitoring and analysis of an earthflow in tectonized clay shales and study of a remedial intervention by KCl wells

This paper describes the behaviour of an earthflow in a marine origin clay shale of the Southern Italian Apennines, and analyses the first results of an experimental remedial measure of soil improvement based on KCl wells. The main features of the structure and kinematics of the earthflow have been evaluated on the basis of geomorphologic analyses, geotechnical laboratory and field investigations, monitoring of deep/superficial displacements and pore water pressures, and modelling by phenomenological and physically-based approaches. The results of the study show that the landslide movement corresponds to a very slow sliding on a deep shear surface, along a fault line, in the residual shear strength conditions. Internal viscous strains also occur locally, above all in the weathered and softened soil, and contribute to the constancy of soil discharge along the channel. The average yearly rate of displacement, over the past ten years, has been in the order of few cm/year in the head zone and one/two orders of magnitude lower in the accumulation. The seasonal rate variations are apparently influenced by rain which can influence, besides pore pressures, pore fluid composition. The pore fluid is a composite saline-sodic solution, the concentration of which decreases dramatically from the stable soil to the landslide body and to the uppermost soil horizon. Laboratory results show that with sodium concentration decreasing, the shear strength decreases and the shear displacement rate under constant effective stresses increases. On the other side, the laboratory results show that exposure to potassium chloride solutions makes the soil shear strength increase greatly and permanently. First results of a chemical treatment by KCl wells in the head zone of the earthflow show that, locally, the ion transport in the surrounding soil is rather fast.