The Influence of Claystone Type on Landslide Hazard: A Case Study

The landslide is more common in locations with steep slopes and is unstable. Developing an early warning system is the aim of this study, which focuses on Nanggulan, Yogyakarta Special Region-Indonesia. The Nanggulan has a wavy shape with a minor slope and is made up of Eocene sedimentary rocks. The landslide indicators, such as curved walls, cracked roads, fractured building walls, subsided building floors, sinkholes, and the creation of crown scarps, were discovered at various sites. X-Ray Diffraction (XRD) analysis and soil index properties of rock and soil samples, were used in the research. The XRD examination revealed the presence of smectite-group clay minerals (monmorillonite and saponite). Calculating the soil index parameters yielded that the soil has a specific gravity of 2.173–2.62, water content of 18.207–47.653%, liquid limit of 45–77%, plastic limit of 21–43%, plasticity index of 18–42%, cohesiveness of 1–91 kPa, and a friction angle of 10°–54°. The direction of the slope is more than 20°, so there is little possibility of planar failure, and the Nanggulan is stable. However, from the smectite-group clay minerals, the plasticity index and the liquid limit value indicate that the rock is cohesive and easy to move when it is wet. This form of landslide typically occurs on gently sloping terrain, is controlled by expansive lithology, has a relatively slow movement rate, and indicates that the landslide type was creep.