Landslide Investigation and Monitoring at Ciloto, West Java, Indonesia

Abstract

Ciloto is one of the most active landslide areas in West Java. Landslide has occured since 1982 until now (2013). Landslide occured especially in the rainy season. This area is important because connected Cianjur and Jakarta (Capital City). Landslide destroy not only environment, property and infrastructure, but usually also cause deaths. Therefore, landslide mitigation and monitoring is very crucial and should be done properly. Monitoring of the Ciloto landslide by using GPS has been conducted periodically. The result in 2012 showed the displacements to the southeast with velocity 2 × 10−7–4 × 10−6 mm/sec. Horizontal displacements of landslide area are in between 4.8 cm and 13.65 cm to the southeast. Vertical displacement has downward trend −0.3 to −13.82 cm, and upward trend 4.8–13.65 cm. The benchmarks horizontally active BA1, BA2, and BAT which are located at the body of landslide, while G27 at the foot of the landslide area. Based on estimation of strain from horizontal displacement shows that the maximum shear strain is the highest at the bottom of the crown until the upper part of the landslide’s body with a value of 15 × 10−4. The result of slope stability analysis shows that the slope is in stable condition but the safety factor is very small, only 1.06. Groundwater rise or heavy rain in a long is significantly control the slope stability. Based on the simulated critical condition occurs when there is an increase of 0.48 m water table decreasing slope stability (safety factor <1). During 5 h heavy rainfall on December 2012, crack has occured in the road and settlement area.