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This paper develops an improved three-dimensional sphere discontinuous deformation analysis (SDDA) model and uses UAV-based photogrammetry to enable SDDA to numerically analyze potential long-runout debris flows in Zheduotang area along the Sichuan-Tibet railway. First, the original SDDA is improved by proposing a sphere-sphere bonding algorithm to bond spheres with tetrahedral layout to form four-sphere clusters to approximate non-sphere particles in debris flow. Second, the capacity of the improved SDDA is verified by comparing modelling results with four groups of laboratory tests of granular flow. Third, UAV-based photogrammetry is used to obtain the real morphology of the extremely complex terrain surface of Zheduotang area which is finally transferred into a large number of triangular faces as the fixed boundary faces of SDDA. Then, three potential debris flow scenarios on this terrain surface are numerically studied, and some suggestions for engineering disaster prevention are drawn. Model performance shows that, the improved SDDA is a feasible tool to simulate debris flows. With the help of UAV-based photogrammetry, it shows significantly helpful for geohazard prevention for infrastructures in mountainous areas like the Sichuan-Tibet railway. • An improved sphere discontinuous deformation analysis model is proposed. • The validation of the improved model in debris flow simulation is verified. • UAV-based photogrammetry to parameterize the extremely complex terrain surface of mountainous area is used. • Engineering-scale long-runout debris flow simulations are carried out. [ABSTRACT FROM AUTHOR]

In 2008, the Wenchuan earthquake triggered many large landslides with rapid movement and long runouts, resulting in a great number of casualties. Although there have been many studies of the geographical features and initiation mechanisms of some catastrophic landslides, the movement mechanisms for many remain unclear. In this paper, we present a case study of a large landslide (debris avalanche) triggered by the 2008 Wenchuan earthquake in the Donghekou area, Sichuan Province, China. We made detailed field surveys of the geographical features of the landslide and carried out subsurface investigations of the landslide deposits using microtremor array measurement and electrical resistivity tomography (ERT). Based on the observed surficial features, shear-wave velocity (Vs) profiles and 2D electrical resistivity profiles of the landslide deposits, we estimated the possible thickness of landslide deposits at different locations, and also analyzed the possible landsliding mechanisms. We inferred that this landslide resulted from retrogressive failures on the source area, and the displaced landslide materials underwent transitional spreading with further entrainment of debris along the travel path. Multiple mud waves might have been formed in the substrate soil layers along the travel path due to the entraining of landsliding materials, and the landsliding materials might have presented channelized movements, indicating that different parts may have moved at different speeds. This kind of transportation mechanism may provide information for elevating the numerical simulation of landsliding, and also for reuse of deposit area of large landslides. • Donghekou landslide is a debris avalanches resulted from retrogressive failures. • The boundary between the landslide deposits and bedrock had been identified. • Main surges with mud waves on the bottom of landslide material had been identified. • Channelized sliding may have occurred within the landsliding materials. [ABSTRACT FROM AUTHOR]