Processes and mechanisms governing the transition of slides in tectonized clays and clay shales into rapid earthflows

Rapid earthflows are widespread in the tectonized clays and clay shales which outcrop along the Apennines chain in Italy. Investigations carried out mostly in UK and in Italy show that the building up of high positive excess pore pressures induced by mechanisms of undrained loading is a trigger of such special slope movements. This interpretation deserves further investigation in the case of tectonized clay shales; in fact, accounting for nature and stress history of such overconsolidated deposits, rising of high positive excess pore pressures is not an expected effect of undrained loading.The paper tries to give an interpretation to this not secondary aspect of the matter, presenting experimental data which stress the high susceptibility of these soils to a dramatic deterioration caused by chemical changes in the pore fluid.