Kinematic Behavior Analysis of a Deep-Seated Landslide Prone Area: A Case Study of Laiyi Village, Taiwan

This study investigates the kinematic behavior of a deep-seated landslide prone area in Laiyi Village, Pingtung County, Taiwan, through a comprehensive in-situ monitoring system. The instrumentation array includes surface dual-axis tiltmeters, piezometers, Global Navigation Satellite System (GNSS) for surface displacement, borehole inclinometers, and rain gauge, with data transmitted in real-time at 10-minute intervals. Spanning from 2023 to 2025, the monitoring data reveals a significant non-linear coupling between slope displacement and intense rainfall events. Notably, during Typhoon Gaemi in 2024 and the heavy rainfall events in late July 2025, GNSS-derived displacement rates exhibited a stepwise escalation, with peak velocities exceeding 90 mm/day. During the torrential rain event on July 28 (the 0728 event), the maximum cumulative displacement surpassed 600 mm, accompanied by surface tilt variations exceeding 600 arc-seconds.

Conversely, piezometric monitoring indicated only minor fluctuations in groundwater levels (rising 1~ 4 m) across multiple rainfall events, suggesting that the groundwater elevation is not the primary driver of slope instability in this area. Instead, rainfall infiltration serves as the dominant triggering mechanism. The analysis identifies a critical threshold where slope mobility significantly intensifies when the 72-hour cumulative rainfall exceeds 600 mm. Furthermore, such kinematic activity is observed to decelerate and cease within approximately 10 days following the cessation of the rainfall event.