Past submarine landslides are often uplifted by tectonic movements and appear on land. The layer of the past submarine landslides are mechanically weaker than the surrounding strata and may cause landslides. The stability of a past submarine landslide is affected by (i) a load of overlying strata, (ii) pore pressure acting on the past submarine landslide surface, and (iii) the shear strength of the surrounding rock including the submarine landslides surface.
In this paper, we conduct a direct shear test and rebound hardness test to study the mechanical characteristics of past submarine landslides. The samples used in this study are tuffaceous sandstone (white pumiceous volcaniclastic material) and mudstone next to the weak surface of past submarine landslide in the Pleistocene Kiwada Formation of the Kazusa Group along the Isumi River in Otaki-cho, Chiba Prefecture, central Japan. We study the effect of the saturation of rock samples on friction strength and the relationship between hardness distribution and the weak surface was investigated. The proposed experimental approach shows that the present mechanical properties of the past submarine landslide surface can be used to evaluate the reactivation of the weak layer.
