Landslide at the Sangun Metamorphic Region

Abstract

A landslide occurred on a slope consisting of the Sangun metamorphic rock in Ube-shi, Yamaguchi Prefecture. The slope of the surface was 10-20 degrees. The area of the landslide itself was 25m wide and 80m long.We examined the slope from a geological, a petrological, and a soil engineering perspectives to identify the characteristics of this landslide. This research resulted in the following findings.The geological features of the slope included tremolite rock and serpentinite hornfels produced by the action of contact metamorphism caused by granite. The landslide occurred as a result of cutting at the end of the slope and heavy rainfalls. The base of the slope may have been easily weakend by the heavy rainfalls because the base primarily consisted of alternating strata of massive rock that had been finely ruptured, and weathered, sandy to silty soils with a relativily high permeability. The residual strength of the clay (chlorite) at the slide surface was almost the same as that obtained by the simple inverse analysis. The analysis of Skempton's residual factors for the three slide surfaces showed that the slide near the end of the slope occurred due to a reactivity movement of an older landslide, while the other two slides occurred first.