High intensity rainfall leads to slope failures that are initially unsaturated. Rainfall is the main triggering factor for the slope failure; however, the denseness of the soil with associated soil properties has not received adequate attention on the stability of the slopes. In this study, the finite difference analysis of transient water flow through unsaturated–saturated soil is carried out to study the effects of rainfall intensity and duration on pore pressure generation, degree of saturation, slope stability and shear strain increment during rainfall event. A parametric sensitivity analysis is performed considering three rainfall intensities applied over the soil slopes consisting of three different soil states namely loose, medium and dense. Results indicate that the rainfall affects the stability of loose and medium soil slopes much as compared to the dense soil slope. The rain-induced instability is much more in loose soil slope as compared to the medium soil slope. © 2017, © 2017 Informa UK Limited, trading as Taylor & Francis Group.