Numerical study on the evolution process of a geohazards chain resulting from the Yigong landslide
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Gordon G. D. Zhou I Pamela Jessica Cacela Roque I Yunxu Xie I Dongri Song I Qiang Zou I Huayong Chen
Numerical study on the evolution process of a geohazards chain resulting from the Yigong landslide
Abstract Geohazard chain processes in mountainous areas generally entail a landslide, followed by a dammed lake, a dam breach, and then outburst flooding. These chains have greater destructive power and a larger area of coverage than a single process, of which a representative event is the April 2000 Yigong landslide in Tibet, China. In this study, a two-part, numerical back-analysis of the entire chain process is carried out. Enhanced one-layer SavageHutter models, which incorporate a multiscale, empirical friction model (velocity-weakening) and appropriate erosion mechanics, are solved using a non-staggered central differencing scheme. A reasonable reproduction of the geohazard event chain was obtained. Results show that the use of the multiscale friction law is able to reproduce the dynamic process of the landslide with acceptable accuracy. In addition, the variation of soil shear resistance along the dam depth (against the water flow above) during the dam breach is considered in the study, in which the outburst flooding process is better modeled. The numerical results, validated by field measurements, provide reliable assessment and interpretation of the actual event. Keywords Yigong landslide . Geohazard chain . Numerical simulation . Velocity- weakening friction . Dam breach Introduction Mountain-hazard chains are catastrophic chain reactions in which one or even several hazards are triggered by an antecedent disaster under certain conditions in a mountainous region. Typical disaster chains, including landslides, debris flow, landslide dam and dammed lake, and outburst flooding, are influenced by topography, geomorphology, amount of precipitation, and other factors (Pei et al. 2017). Since in a mountain-hazard chain, one subdisaster is triggered after another, like a domino effect, the time scale at which the chain occurs greatly exceeds that of a single disaster and affects a greater amount of area. Particularly, earthquake-induced sub-disasters result in high casualties, structural damages, and significant financial losses (Han et al. 2019). Among all of the mountain-hazard chains that occurred in China within the past century, the Yigong hazard chain, which initiated in southeast of Tibet (Fig. 1), has received the most global attention. This mountain-hazard chain event can be divided into two phases with four processes: the granular mass flow and dam formation in the first phase, and the landslide dam failure and resulting outburst flooding in the second phase. A significant amount of work has already been devoted in studying the landsliding process up to the formation of the landslide dam (e.g., Xu et al. 2012; Zhou et al. 2013, 2015a, b; Delaney and Evans 2015; Liu and He 2018). Previous works have modeled the motion of the Yigong landslide using the Coulomb (Liu and He
2018) and Voellmy (Xu et al. 2012;
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