Overview of Flowslide in Petobo during liquefaction of the 2018 Palu Earthquake

Abstract

Massive flowsides inducing deformation of about 1 km on gentle slope occurred in Petobo during liquefaction of the 2018 Palu Earthquake. The liquefaction mechanism attributed to this enormous lateral deformation is not fully understood yet. In fact, a comprehensive understanding of this phenomenon mechanism is crucial to mitigate similar disasters in the future. This manuscript describes the flowslide observations in Petobo based on geotechnical investigations, including trench, geophysical survey, CPT, boreholes, and laboratory testing. The investigation showed that the flowslide location consisted of a liquefaction layer with a cap layer on it. The liquefaction layer consists of two successive liquefied layers, the upper layer is finer and less permeable than that of the one below. With the upper layer less permeable, this may result in an increase in the void ratio due to void redistribution distributed in the liquefied upper layer. This study demonstrates that variations in liquefied layer conditions have a major effect on whether flowslide due to liquefaction occurs or not. The results of this study are expected to enrich our knowledge related to liquefaction-induced flowslide and can be used as a basis to evaluate flowslide potential in other locations.