| With the in-depth implementation of China’s national strategies such as “the Belt and Road Initiatives” and the western development,all kinds of infrastructure in the western region are facing the threat of geological disasters.Landslide dams,as a typical and widespread disaster in mountainous area,are mostly formed when the mass movements triggered by earthquakes or rainfall block the rivers and valleys.The consequences of landslide dams induce inundating upstream and potentially flooding downstream areas,causing huge losses and damages to people’s lives and properties.According to the material composition of the landslides and the characteristics of dam formation,dams formed by highly fragmented debris are usually featured by poor stability and large degree of failure,making them more dangerous.The morphology and structure of such dams directly depend on the properties of the debris itself and the process of its movement and accumulation,and greatly affect the stability and failure of the dams.Aiming at the formation process of landslide dams formed by highly fragmented debris,the dam formation mechanism and dam characteristics were systematically studied under the action of multiple factors including the properties of debris itself,slope topography,and valley shape,by using model tests,numerical simulations and statistical analysis.The influence of dam morphology and structure on its stability and breaching process was analyzed by considering the formation and failure of landslide dams as a whole process.The main research contents and results are as follows:(1)A model test equipment for the whole process from the formation to failure of landslide dams was developed,and a series of model tests were conducted under the influence of the combination of three factors,namely,debris gradation,sliding path width and valley shape.It is found that the wide graded debris containing gravels shows obvious grain segregation during the flow process,while the fine-grained debris has apparent characteristics of fluidization motion.The debris in the U-shaped valley and V-shaped valley shows the accumulation modes of “collisional diffusion accumulation”and “pushing and climbing accumulation” respectively.The final dam is irregular in shape and inhomogeneous in particle distribution.(2)Based on the formation characteristics of the dam in the tests,the influence of dam morphology and particle distribution on dam failure is explored through the analysis of its failure mode and failure parameters.The key factors affecting dam failure and the failure mechanism of landslide dams are revealed.(3)The discrete element method is used to analyze the dam formation process under different conditions.Combined with model tests,the crest surface frontal angle is defined to describe the location of the overflow point and the morphology of the dam crest,and the parameters characterizing the dam structure are proposed.The geometric shape and particle distribution of landslide dams are analyzed from the macro-meso scale.The effects of debris composition,debris volume,slope angle,slope height,sliding path width,and valley shape on the morphological and structural characteristics of landslide dams are revealed.(4)The key factors affecting the morphological characteristic parameters and structural characteristic parameters of landslide dams are determined by considering the properties of debris itself,slope topography,and valley shape.The dam height is greatly affected by the valley shape,debris volume,slope height and sliding path width;the crest surface frontal angle is closely related to the slope angle and debris material;the up/downstream slope is mainly affected by the debris material,valley shape,slope angle and sliding width.In the U-shaped valley,the main factors affecting the grain size distribution(GSD)in different parts of the dam are the width-depth ratio of the valley,sliding width,slope height and debris material,while those in the V-shaped valley are the bank slope of the valley,slope angle,debris material and volume.(5)Based on the multivariate regression method,the prediction models for the morphological and structural characteristics of landslide dams in U-shaped and Vshaped valleys are established respectively using the key influencing factors of the dam morphological and structural characteristic parameters.The validity and applicability of the prediction models are verified by the model test data and two real landslide dam cases. |
