Experimental and numerical simulation on water film formation during the 2018 Sulawesi Earthquake

The water film effect is considered a key factor in triggering the large scale flowslides on gently sloping terrain in highly stratified, liquefiable sandy soils during the 2018 Sulawesi Earthquake. The mechanism of water film formation under multiple less permeable soil layers (capping layers) with different plasticity characteristics is evaluated using 1D soil model tests under impact loading and their 1D response analysis. As observed, the water film can form under both plastic and non-plastic capping layers under the influence of impact load. The effect of number of capping layers, as well as their plasticity, on the water film formation and the dissipation of excess pore water pressure is evaluated, as well as the resulting vertical and lateral deformation of the soil layers, together with the stresses produced under a sinusoidal loading, inducing a water film effect is studied. From the results, it can be concluded that the configuration and the plasticity of the capping layer which controls its permeability characteristics, have a significant influence on the stability of the water film. Moreover, the water film effect plays a key role, if not the completely responsible for triggering the flowslides by forming a low-friction interface under the capping layer.