Simple mechanisms for strength regain on the slip surface of stop-start mudslides.

A long -term field experimental work is at the base of this paper, wich refers of the mechanisms operating in many landsslides as well as of the artificial reproduction in laboratory of the phenomena observed in nature. Sophisticated test procedures allowed defining a base knoledge on the processes governing the landsliding. In other words, the occurrence in an intermittent clay mudslide of different thereshold piezometric values sufficient of making the landslide rapidly moving and the developing of counterbalancing viscous resisting forces capable to drammatically reduce the hight velocity peaks, wich may occur at the very initial movement srage, were ascertained by means of long-term monitoring. In contrast, only one threshold, clearly lower and corresponding to measured residual shear strenght, was identified to stop the movement. This finding induced the authors to delve inside the mechanism governing the phenomenon. Laboratory tests were carried out by means of modified shear apparatuses in order to reproduce as much as possible the in situ shear stress conditions. The results confirmed that a phenomenon of shear strenght regain is operative, both in situ and in laboratory.