Rainfall-induced reactivation of deep-seated landslides is commonly governed by delayed groundwater recharge and progressive deformation near deeply buried shear zones. However, the temporal relationship among rainfall, groundwater variation, deep deformation, and local slope stability remains difficult to quantify using rainfall records alone. This study investigates the locally reactivated zone of the Wangjiayuan deep-seated landslide in Hubei Province, China, by integrating rainfall, groundwater-level, borehole-displacement, and surface-inclination monitoring. Depth-dependent displacement and displacement-gradient profiles were used to constrain the probable local shear zone near borehole ZK02. A slope-corrected Green–Ampt model was employed to estimate wetting-front advancement, while a monitoring-constrained equivalent hemispherical model was used to evaluate temporal variations in local stability. Borehole displacement exhibited three successive stages: rapid growth during May–June 2023, relatively limited variation from July 2023 to April 2024, and renewed acceleration after May 2024. Pronounced displacement gradients between depths of 13 and 16 m, together with the observed soil–bedrock interface, indicate a probable shear zone at approximately 15–16 m. Surface inclination remained small but spatially heterogeneous, suggesting slow overall deformation accompanied by persistent local activity. During representative rainy periods, groundwater rise was generally followed by increased displacement rates at depths of 13 and 15 m, demonstrating an apparent delayed hydro-mechanical response. The calculated factor of safety varied from 1.48 to 2.16 and decreased by approximately 31.5% after prolonged rainfall and rapid groundwater rise. Short rainfall events that affected only the shallow wetting zone had limited influence on stability. The results indicate that groundwater variation near the basal shear zone is more closely associated with deep deformation than individual rainfall peaks. The proposed framework provides a practical indicator of relative stability changes in the local reactivated zone, although the calculated factor of safety should not be interpreted as a deterministic failure threshold for the entire landslide.

Deep-seated landslide,local reactivation,borehole monitoring,groundwater response,rainfall infiltration,time-varying stability