Relief well as liquefaction mitigation option in Mpanau, Sigi, Central Sulawesi, Indonesia

Abstract

The liquefaction disaster that occurred in Central Sulawesi in September 2018 was not only in the form of flow liquefaction but also a sand boil. Sand boils are caused by excess pore water pressure (PWP) which causes sediment ejecta due to water pressure within the ground. This research focuses on the use of relief wells to relieve excess PWP. During the 2018 disaster, the research location in Mpanau, Sigi, Central Sulawesi, had many sand boil points and the emergence of new water springs after the earthquake. At this point, the increase in PWP presumably resulted from a leaking groundwater basin, thus providing additional pressure. The method used was calculating the Ejecta Potential Index (EPI) and modelling with Seep/w. This calculation determined the amount of PWP that could be released to maintain the comparison between PWP and effective stress. This comparison is also known as the PWP (Ru) ratio and should be kept at less than 0.8, indicating the absence of liquefaction in the layer. This analysis was carried out with the initial conditions without wells and after the presence of wells, then assessing the distance of the wells to eliminate artesian pressure. It was concluded that this mitigation method is appropriate for areas that have groundwater basins with layers prone to aquifer leakage to reduce additional PWP.