Liquefaction, building settlement, and residual strength of two residential areas during the 2016 southern Taiwan earthquake

Abstract

On February 6, 2016, a moment magnitude (Mw) 6.4 earthquake struck southern Taiwan and devastated the Tainan area. Although the intensity of ground shaking was only moderate (peak ground acceleration, ~ 0.2 g), widespread damage associated with liquefaction (e.g., settlement and tilt of residential buildings) was observed. In this study, soil liquefaction in two residential areas during the Meinong earthquake was assessed comprehensively via field investigation and thorough numerical analysis. Liquefaction triggering analysis using field measurement was performed initially to identify the liquefied layer. The agreement between the gradation of ejecta and in situ soil sample corresponding to the liquefied layer confirmed the analysis results. The liquefied layer is shallow, and the damage level (i.e., settlement) is highly correlated to the distance between the footing and liquefied layer. In the second part of the study, a simplified numerical analysis was proposed to simulate the interaction between the shallow footing structure and liquefied soil. By gradually reducing the soil strength of the liquefied layer in the analysis, the residual strength of the liquefied soil was found to be 10–20% of the original one to reproduce the observed building settlement. The obtained residual strength is compatible with the previous study based on the back analysis of embankment or slope failures.