Abstract
Landslides in the Izumi Group are usually caused by rainfall as well as by excavations such as open cuttings. Some of the landslides with clear morphology, however, are in stable over a long period of time. In this paper, we investigate two types of landslides including seven unstable cases and three stable cases. Then, the characteristics of the landslides in the Izumi Group are discussed.
The stability of the landslides is basically dependent on two angles. One is the angle of slip surface of the landslides, and the other is the average angle of the ground surface. It is shown that the stability of the landslide is higher if the two angles are less than 22 degrees. It is also shown that the landslide may slide along a small fault or a layered fracture zone for a dip slope, whereas for an opposite slope, the sliding may occur in a weak zone in which creep was fully developed over a long period. Consequently, the landslides are concentrated on the neighborhood of the Median Tectonic Line because large tectonic movements have taken place in this region. In addition, the stability of the landslides is strongly affected by groundwater. The infiltration of surface water into an opening crack may generate sufficient pressure of water to induce a landslide to slide.
