Three-dimensional landslide evolution model at the Yangtze River

Abstract

Continuous river incisions, heavy precipitation events, reservoir water-level fluctuations, and changes in groundwater flow are the main driving factors of extensive landslide activities in the Three Gorges area of the Yangtze River in China. Although the triggers for these major landslide events can be technically detected, predicting and mitigating them remains challenging. This is especially the case where ancient, deep-seated, multi-stage landslides have created complex geological structures that make it difficult to uncover their evolutionary processes and to determine slip surfaces. This study, based on elaborate investigation of the Outang landslide in the Three Gorges Reservoir area, proposes a general framework for analyzing the spatial and temporal evolution of a multi-stage riverbank landslide. The framework applies three-dimensional geological modeling to integrate large amounts of data from earth surface investigations, subsurface explorations, in-situ monitoring and geological dating. The results indicate that the Outang landslide has a total volume of 8.3 × 107 m3 and a maximum thickness of 114 m. It consists of four individual sliding bodies that have been formed consecutively since 130 ka BP. Furthermore, the original slip surfaces of the sliding bodies are found to be interconnected, forming one large active landslide continually creeping towards the Yangtze River. While the entire landslide is in motion, the western, eastern and up-slope portions of the sliding mass are moving at a faster velocity of up to 12.6 cm per year. Our analysis of the Outang landslide reveals that its evolution can be subdivided into three sliding modes. These modes could serve as a reference for analyzing the spatial and temporal evolution of similar multi-stage landslides along riverbanks.