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Debris flow is a prevalent geological disaster in Beijing, particularly in the Mentougou District, situated in the mountainous southwestern region of Beijing City. The past irrational exploitation of minerals has led to a substantial accumulation of slag, providing abundant loose materials for the formation of debris flow in the study area. Different from the traditional method of using hazard and vulnerability to carry out debris flow risk assessment, this paper proposes a debris flow risk assessment method based on (a) the possibility of debris flow occurrence, (b) the value of the disaster-affected object, and (c) the destructiveness of the debris flow. The possibility of 41 gully debris flows occurring was determined through theoretical calculations. Using the SFLOW model, the runout of the potential debris flow was simulated. On this basis, an investigation of the value of the disaster-affected objects was carried out. At the same time, according to the simulated movement information of debris flow, its destructiveness was determined. According to the results of the occurrence possibility of the debris flow, its destructiveness, and the value of the disaster-affected object, the risk levels of 41 potential debris flow gullies in the Mentougou District were obtained. The research results can guide the warning systems for debris flows in the Mentougou District of Beijing. [ABSTRACT FROM AUTHOR]

Abstract Catastrophic landslides occur frequently at large waste dumps, causing huge losses of lives and environmental degradation. In this study, Zhujiabaobao iron mine waste dump was surveyed and found to be unstable during a field investigation in April 2016. A failure potential assessment was undertaken for the waste dump; this is crucial for the prediction and mitigation of landslides hazards. Reconnaissance, geomorphological analysis, and laboratory experiments were carried out to provide basic data, and a three-dimensional waste dump model was constructed. To consider ground cracks in the waste dump and acquire information about potential sliding mass, an extended finite element model (XFEM) based on strength reduction technique was applied. An analysis shows that the factor of safety (FOS) of waste dump is 1.22, not very stable according to " The technical code for building slope engineering (GB50330-2013) " published by Chinese ministry of Housing and Urban-Rural Development, and the potential failure volume is 45 × 104 m3. Then, the potential landslide and debris flow due to slope failure were simulated using the software SFLOW based on a free-surface shallow water model (SWM). The landslide simulation considers different water contents of sliding mass, reflected in parameter C v (sediment concentration by volume), whereas debris flow simulation was designed for 20, 50, 100, and 200-year return periods. The results show that with the decrease in C v , the speed of sliding mass increases, and the run-out distance of landslide increases. However, even the farthest influence distance does not reach downstream buildings. The debris flow can pile up in front of gully mouth and even run into the Jinsha River. Therefore, once a landslide has occurred or when a lot of loose material is present, corresponding management measures (such as cleaning the material or setting the retaining wall) and a forewarning system should be developed to prevent huge damage caused by debris flow. Highlights • A method combining FEM and SWM for assessing waste dump failure potential. • The cracks have been considered in the model of stability analysis via XFEM. • The numerical model can fully consider real topographical conditions. [ABSTRACT FROM AUTHOR]