Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 6 4 2006 10.5194/nhess-6-529-2006 http://www.nat-hazards-earth-syst-sci.net/6/529/2006/ http://www.nat-hazards-earth-syst-sci.net/6/529/2006/nhess-6-529-2006.html http://www.nat-hazards-earth-syst-sci.net/6/529/2006/nhess-6-529-2006.pdf 529 539 2006-06-14 Softening and instability of natural slopes in highly fissured plastic clay shales L. Picarelli G. Urciuoli A. Mandolini M. Ramondini Dipartimento di Ingegneria Civile, Seconda Università di Napoli, Aversa, Italy Dipartimento di Ingegneria Geotecnica, Università di Napoli Federico II, Napoli, Italy Softening is often considered to be the main cause of first-time slides in OC clay, but so far the mechanics of softening has not been satisfactorily explained. Bearing on laboratory data and field observations about landslides in tectonized highly plastic clay shales of Italian Apennines, the paper describes a process of soil weakening that could explain some failures of natural slopes.