Kinematics and Internal Deformation of Granular Slopes

Abstract: Flow-like mass movement is the most destructive landslide and causes loss of lives and substantial property damage throughout the world every year. This thesis focuses on the spatial and temporal changes of the mass movement in terms of velocity and displacement within the failure mass, and the spatial and temporal distribution of the three dimensional internal deformation of the granular slopes using discrete element method, physical experiments, and natural landslides. We have also studied the effect of weak horizons on the kinematics and internal deformation of granular slopes. Numerical model results show the following features related to a failure mass. The failure mass flows downwards in an undulating pattern with a distinctive velocity heterogeneity. Dilatation within the failure mass is strongly dependent on its mechanical properties. A larger mass moves downslope and the mass moves faster and further in the model with lower internal friction and cohesion. The presence of weak horizons within the granular slope strongly influences displacement, location of the failure surface, and the amount of the failure mass. In addition, results from analogue models and natural landslides are used to outline the mode of granular failure. The collapse of granular slopes results in different-generation extensional faults in the back of the slope, and contractional structures (overturned folds, sheath folds and thrusts) in the toe of the slope. The first-generation normal faults with a steep dip (about 60º) cut across the entire stratigraphy of the slope, whereas the later-generation normal faults with a gentle dip (about 40º) cut across the shallow units. The nature of the runout base has a significant influence on the runout distance, topography and internal deformation of a granular slope. Good agreements are found between models and nature for the collapse of granular slopes in terms of the similar structural distribution in the head and toe of the failure mass and different generations of failure surfaces. The presence of a weak horizon within the granular slope has a significant influence on the granular failure and three dimensional internal deformation of the failure mass.