Failure behaviors of rainfall-induced shallow landslides: insights from a novel large angle-adjustable plane shear apparatus

Rainfall-induced shallow landslides can occur rapidly after intense or prolonged heavy rainfall, especially in mountainous areas. In this study, failure behaviors of rainfall-induced shallow landslides are investigated using a novel large angle-adjustable plane shear (LAPS) apparatus. Details on the conception, features, and setup of the LAPS apparatus are first illustrated. Two series of tests are conducted with varying slope angles and water intensities to demonstrate the test processes. The results of the LAPS tests are analyzed according to the changes in displacement behaviors and water contents, as well as predictions of slope failure. The results show that the behaviors of rainfall-induced landslides were clearly observed during the LAPS tests, exhibiting three distinct stages: initial deformation, constant speed deformation, and accelerated deformation, which are consistent with the phenomenon from field cases. Moreover, the switch points of water content from stable to rapid growth stages gradually advanced with an increase in water intensity. The velocity behaviors observed in these tests displayed two distinct patterns, with earlier turning points observed as the slope angle or rainfall intensity increased. The LAPS apparatus provides a new tool for studying the failure behaviors of rainfall-induced shallow landslides.