Hydrological responses and stability analysis of shallow slopes with cohesionless soil subjected to continuous rainfall

Understanding the hydrological and physical responses of shallow slopes subject to rainfall events is vital for the efficiency of a warning system setup. In this research, a series of experiments were undertaken to evaluate the hydrological responses of shallow slopes of varying steepness and when subjected to varying intensities, periods, and inter-storm periods of rainfall. An analysis of infinite slopes was also undertaken to develop a fundamental understanding of rainfall-induced shallow slope failure characteristics. The hydrological and physical responses were characterized in the infiltration and saturation phases. During the infiltration phase, the maximum magnitude of water content was found behind the wetting front, termed as the water content behind the wetting front (theta(wb)). For a certain soil type, the magnitude of theta(wb) was found to be dependent on the magnitude of rainfall intensity, regardless of the slope gradient and initial water content. Based on the relative depth of the failure plane, the failure can be categorized by three prime modes: (i) along the impervious layer mode, (ii) shallow depth mode, and (iii) transitional mode. These modes can be characterized by the magnitude of a stability index termed as tan phi'/tan beta ratio. An infiltration index, termed as i/k(s) ratio, was found to play a role in the depth of the failure plane only for the transitional mode.