Simulation of water film formation during the 2018 Sulawesi earthquake, Indonesia

The water film effect is considered a key factor in triggering large-scale flowslides on gently sloping terrain in highly stratified, liquefiable sandy soils during the 2018 Sulawesi earthquake in Indonesia. The mechanism of water film formation under multiple less permeable soil layers (capping layers) with different plasticity characteristics is evaluated using one-dimensional (1D) soil model tests under impact loading and their 1D response analysis. As observed, a water film can form under both plastic and non-plastic capping layers under the influence of the impact load. The influence of the number of capping layers, as well as their plasticity, on water film formation and the dissipation of excess pore water pressure is evaluated. In addition, the resulting vertical and lateral deformation of the soil layers, together with the stresses generated under sinusoidal loading, inducing a water film effect are 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 in, if not being completely responsible for, triggering flowslides by forming a low-friction interface under the capping layer.