Abstract
Surface slip on slopes of slightly consolidated sand beds is considered to be one of the important types of failures which occurs most frequently on the natural slopes.
In this paper, the authors described at first, an example of detailed field inspection data on the failures arose in Narita sand group (Pleistocene) and they concluded that the slip plain is situated in the zone of loosened sand laid under the sand zone which is much loosened but reinforced by the roots of plants. They added the field observation of loosening speed on the cutted slopes in similar sand beds and the results of laboratory experiments: strength reduction accompanied with increment of water contents and sharp change of cohesion when void ratio excess 1.0-1.2.
The authors also concidered on the microscopic structure model of these semi-consolidated sand and explained about the process of weaking and surface slip by the microscopic process of loosening.
