UAV-Based Photogrammetry and Geophysical Methods for Rockfall Hazard Assessment in Karst Terrain (Thung Nham, Vietnam)

Abstract

Rockfall is a hazardous geological phenomenon frequently occurring in steep limestone cliff terrains, posing significant risks to infrastructure and human safety. In the Thung Nham heritage area of Ninh Binh province, the expansion of transportation networks through mountain-slope cutting, combined with natural geological anomalies, has exacerbated the instability of rock masses. This study aims to decode the complex five-stage rockfall mechanism and quantify the scale of potential sliding masses to provide a scientific basis for mitigation. An integrated research methodology was employed, combining traditional field investigations with modern non-contact and penetrating technologies, specifically Unmanned Aerial Vehicle (UAV) photogrammetry for high-resolution terrain modeling and Natural Electric Field (Self-Potential) profiling using the S150 instrument. The geophysical results successfully delineated an extensive subterranean karst system characterized by large-scale cavities and deep-seated fractured zones infilled with water-saturated clay and poorly consolidated debris. The study quantifies a significant potential sliding mass with a high kinematic tendency to obstruct the transport corridor. These findings facilitate the proposal of four specialized engineering solutions, ranging from geotechnical reinforcement to protective galleries, ensuring a balance between absolute safety and the preservation of the original natural landscape.