Analysis on the Result of Slope Deformation Observation in Todoroki Area, Hokudan-cho, Awaji Island

Abstract

Observation of slope deformation using thirteen extensometers being set continuously and investigation by a portable penetration test apparatus were done on a slope which consists of weathered granodiorite in Todoroki area, where the Nojima Fault appeared at the toe at the time of the 1995 Hyogoken-Nanbu Earthquake. Analysis of the result of extensometer observation suggests that slope deformation is composed of two different types of ground movement; one is creeping movement of surface layer, and the other is movement of soil block which displaces as one body. Positive correlation between rate of surface layer creeping and rainfall intensity can be seen during precipitation but the creeping lasts for a long period (more than ten days) after rain stopped. Two active soil blocks are found; one is across the Nojima Fault and the other is uphill of it. Their movements begin almost one day after a precipitation and show stick-slip type displacement. Result of the penetration test shows structure of resistance which agrees with the result of analysis on slope deformation stated above.