Study on the Phenomena of Liquefaction Induced Massive Landslides in 28 September 2018 Palu-Donggala Earthquake

Liquefaction Induced Mass Landslide in Palu Donggala Earthquake on 28 September 2018 was one of the rare and biggest event on these types of landslides in the world. The phenomena was the most complete occurence since all mechanism of liquefaction and liquefaction induced landslides were represented. On these particular event, the author has conducted study on the liquefaction mechanism based on field observation including running drone in several areas, conducting soil investigations, work on analysis and collect as much as data from local people. This paper discusses Liquefaction Mechanism in these unique and spectacular sites (mainly in four areas: Balaroa, Petobo, Jono Oge and Sibalaya) because the earthquake seems to trigger liquefaction by multidirectional vibration and of particular interest is because the earthquake are near faults with shallow earthquake focus of about 10 km below the city. The extraordinary distance of liquefaction flow and lateral spreading is one of unique phenomena which is believed to be caused by the existence of initial artesian pressure and significant vertical acceleration causing the soil loosing contact stress. Layers of sands and clays or silts might have caused significant force to the liquefied sands and flow laterally. Instead of surface phenomena, the main objectives of this paper is also to discuss the results of CPTu tests conducted for analysis and fact findings on liquefaction phenomena. Each data of CPTu yields liquefaction potential index which is used to characterize the severity of ground damage and discuss mitigation and risk reduction in the future.