Abstract: Landslides in residual soil layers are one of the major geological hazards in southeastern China. To investigate the potential failure modes and triggering mechanisms of such large-scale landslides and explore effective monitoring and early warning solutions, this paper takes the Yaoshan landslide in Quanzhou, Fujian Province as a case study. It analyzed the material composition, structural characteristics, and hydraulic conditions of the slip zone within the landslide mass, and systematically conducted engineering geological surveys and deep displacement monitoring. The deformation and propagation process of the slide mass along the shear zone under rainfall-induced conditions was captured. Using stress path tests, the deformation and failure process of the slip zone due to increased pore water pressure was examined. The results showed that the residual soil layer where the Yaoshan landslide is located exhibited a layered structure, with the slip surface developing within a sandy clay layer relatively rich in clay content. The interplay of internal and external stresses drove the Yaoshan landslide to display progressive failure. Under extreme rainfall and rapid groundwater level rise, increased pore water pressure and strain localization in the slip zone accelerated fracture propagation, leading to an increased displacement rate of the slope. If the fracture surface fully connects, the slide mass may undergo accelerated sliding. In the design of a monitoring and early warning system, parameters such as the hourly displacement of the landslide, cumulative rainfall over the preceding 7 days, and hourly rainfall can be selected as early warning indicators.