Flowslide Due to Liquefaction in Petobo During the 2018 Palu Earthquake

The 2018 Palu Earthquake in Indonesia triggered liquefaction that was followed by many incidents, including in massive flowsides in Petobo. In this location, flowsides with deformations reaching 1 km occurred on gentle slopes. The liquefaction mechanism causing this enormous lateral deformation is not fully understood yet. In fact, a comprehensive understanding of this phenomenon mechanism can be used to mitigate similar disasters in the future. This study describes the flow slide observations in Petobo based on geotechnical investigations, including trench, geophysical survey, CPT, boreholes, and laboratory testing. The investigation showed that the flow slide location consisted of alternating layers with high and low permeabilities. The high permeability difference during pore water pressure dissipation in the liquefied layer resulted in void redistribution in layers overlain by low permeability layer. This void ratio increase triggered a significant shear strength loss in the corresponding layer. This study also shows that differences in the soil condition and the water table depth play important roles whether a location experiences a flow slide or not. The results of this study are expected to enrich our knowledge related to liquefaction induced flow slide and can be used as a basis to evaluate flow slide potential in other locations.