The 2018 Sulawesi earthquake of magnitude Mw 7.5 triggered large-scale flow slides and ground liquefaction in the Palu Valley at multiple locations on a ground of very gentle gradient. Findings of the post event forensic geotechnical investigation conducted by the authors of this research highlighted the presence of silty clay or sandy clay layers sandwiched between sandy or sandy gravel layers at multiple locations in the flow slide zones. These sandwiched layers tend to have low permeability as compared to overlying and underlying layers sandy strata. To study the contribution of these sandwiched layers on the triggering of flow slides, a preliminary research was conducted using 1D soil column with clay and non-plastic fines sandwiched between sand layers. The findings highlighted that the excess pore water pressure reached its peak value by an instant shock. A thin interlayer water called water film is easily formed below the clay and non-plastic fines seam on impact. The influence of water film on pore pressure dissipation and overall soil settlement was studied. Water film formed beneath the clay and non-plastic seam permits the soil layer above it to float, with continuous deformation in soil due to change in equilibrium condition.