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Landslides are a multifaceted phenomenon triggered by rainfall infiltration as a consequence of the decrease in effective stress upon the development of porewater pressure. Although many studies concentrated only on rainfall infiltration as the source of the primary hydrological regime, the impact of groundwater dynamics has been relatively underexplored owing to its elusive nature. Field investigations after the landslide incidents provide insight into the influence of groundwater dynamics and speculate its effect as a secondary hydrological regime is immense. Therefore, this paper uses centrifuge modeling and numerical simulations to study groundwater dynamics in rain-induced landslides. Instrumented model slopes made of silty sand were tested to examine the hypothesis of pre-existing groundwater flow levels and surcharged groundwater flow conditions in rain-induced landslides. It was observed that swiftly rising porewater pressure along the soil–bedrock interface triggered landslides more rapidly under high groundwater flow and immediate surcharged groundwater flow conditions. Deformation analysis confirmed that a voluminous landslide could be expected if the role of groundwater dynamics is higher. A two–dimensional coupled hydromechanical finite element simulation was performed to back–analyze the experimental results and to discuss the failure mechanism. Upon validation, numerical simulation emphasized how the failure was accelerated under low-intensity rainfall if high groundwater flow exists. Furthermore, the study identified that surcharged flow profoundly affects landslide initiation if the slope has a low pre-existing groundwater flow. The outcomes highlighted that groundwater dynamics should be an integral part of the temporal predictability of landslides as they can also govern the magnitude of landslides.
Jayakody et al. (Mon,) studied this question.