This paper delineates the examination of the time dependent behaviors of landslides observed at two sites by focusing on the saturation of sliding surface clays.
We also study a relationship between test conditions and actual phenomenon by conducting mechanical tests with boring cores, since we consider that mechanical characteristics of sliding surface clay give large impact on landslide speed.
In conclusion, we suggest that it is important to consider the degree of saturation of sliding surface clay as one of the reason to cause landslide on designing landslide prevention works.