Development characteristics and failure modes of reactivated ancient landslides in the Sichuan–Tibet transportation corridor, China

The risk of reactivated ancient landslides in the Sichuan–Tibet transportation corridor in China is significantly increasing, primarily driven by the intensification of engineering activities and the increased frequency of extreme weather events. This escalation has resulted in a considerable number of fatalities and extensive damage to critical engineering infrastructure. However, the factors contributing to the reactivation and modes of destruction of ancient landslides remain unknown. Therefore, it is imperative to systematically analyze the developmental characteristics and failure modes of reactivated ancient landslides to effectively mitigate disaster risks. Based on a combination of data collection, remote sensing interpretation, and field investigations, we delineated the developmental attributes of typical ancient landslides within the study area. These attributes encompass morphological and topographic aspects, material composition, and spatial structure of ancient landslides. Subsequently, we identified the key triggers for the reactivation of ancient landslides, including water infiltration, reservoir hydrodynamics, slope erosion, and excavation, by analyzing representative cases in the study area. Reactivation of ancient landslides is sometimes the result of the cumulative effects of multiple predisposing factors. Furthermore, our investigations revealed that the reactivation of these ancient landslides primarily led to local failures. However, over extended periods of dynamic action, the entire zone may experience gradual creep. We categorized the reactivation modes of ancient landslides into three distinct types based on the reactivation sequences: progressive retreat, backward thrusting, and forward pulling–backward thrusting. This study is of great significance for us to identify ancient landslides, deepen our understanding of the failure modes and risks of reactivated ancient landslides on the eastern margin of the Tibetan Plateau, and formulate effective disaster prevention and mitigation measures.