Clay Minerals Contributing to Creeping Displacement of Fracture Zone Landslides in Japan

Abstract

Various investigations on tectonically-induced landslides in Shikoku in west Japan have been carried out, most of which conclude at tectonic activities through the major fault lines and enhanced rock mineral decomposition as being mainly responsible for the landslide occurrence. Little work is found, however, on the mechanism of their creep activation and role played by the expansive clay minerals. This paper aims at looking into strength parameters of the landslide clays from mineralogical point of view. In addition, the strength behavior is analyzed from inclusion of weaker clay minerals such as smectites. It is found that the drop from peak to residual friction angles for the tested samples reaches as high as 20°. In addition, the residual strength of the landslide clays was found to decrease with higher amount of expansive clay minerals, which was estimated as being relative to chlorite mineral from the XRD patterns. Moreover, the presence of non-crystalline clay materials was found to considerably lower the friction angles of the landslide soils.