Liquefaction index ratio analysis for the 2018 Sulawesi Earthquake: Simplified and dynamic numerical method evaluation

The 2018 Sulawesi Earthquake induced extensive liquefaction cases across several sites in Indonesia, resulting in large-scale flow slide at Balaroa, Jono oge, and Petobo. This unprecedented ground failure phenomenon caused severe damage and losses. Liquefaction assessment in Indonesia is commonly based on simplified methods using the standard penetration test (SPT) to estimate the liquefaction potential index (LPI). However, these methods do not account for seismic duration and time effects, nor do they capture the excess pore water pressure ratio (r u ) or changes in effective stress of the ground. This research investigated the liquefaction index ratio using simplified methods and dynamic analysis which considers earthquake motion input from the deconvolution process performed by the DEEPSOIL program. Furthermore, the effective stress decreasing ratio (ESDR) analysis was conducted using numerical analysis through LIQCA 2D as a fully coupled method of two-phase theory. The analysis employed the elastoplastic constitutive model with horizontally layered ground, utilizing finite element simulation. The liquefied layer from the time history was examined as part of the back analysis of earthquake induce-liquefaction, yielding liquefaction resistance index (LRI) from 9 boreholes. Even though there are differences in results due to the scheme and basic concepts of analysis, the outputs showed a strong connection index for examining the maximum and minimum index ratios. ESDR analysis provided the LRI with strong interconnection dynamic parameters, such as the small value r u which did not reach the 0.9 value that correlated with lower ESDR. The highest ESDR value from each layer did not always produce the highest LRI. This research highlights the significant contributions of detailed and complex dynamic methods in providing realistic liquefaction simulations, while also emphasizing that simplified methods can serve as standard practice for engineers in Indonesia. Both approaches are adequate models for assessing the liquefaction ratio value.