Numerical Investigation Of Internal Properties In Landslide Dam By DEM

Natural landslide dams may easily fail and result in catastrophic floods. In thisthesis, internal properties in a landslide dam are studied to help deal with the threat.Four aspects of current research are reviewed, including field investigation,experimental research, theories for segregation and numerical study. The discreteelement method (DEM) is found to be the most effective method for our research.The theory and background of PFC3D, a DEM program, is introduced. A numericalmodel based on PFC3Dis built to simulate the formation of a landslide dam on differentinitial conditions including varied slope angles and heights. Different sections, meandiameter distribution and solid fraction inside the simulated dam body are analyzed, anda segregation factor is proposed to measure the inhomogeneity degree. The conclusionsare as follows:Particle size distribution: The analysis shows that large particles tend to accumulatein the surface layer and the part close to the opposite slope. The deposit will becomeless homogeneous with smaller slope angle and larger slope height. The side walls havelittle effect on the particle distribution. When the slope is high enough, there may be twoparticle distribution forms.Segregation factor: Larger segregation value means that the dam body is moreinhomogeneous. The segregation factor value of large particles is higher than the valueof fine particles and the value of medium particles is lowest. When the slope is less high,the segregation factor value will increase rapidly with slope height. And it will reach astable value when the slope is high enough. For smaller slope angle, the stable value islarger.Compactness: The compactness of the surface layer is lower than the bottom layer.When the slope height is large, the part of the dam body close to the landslide source isless compact and there will be a relatively compact part in the middle of the dam body.Particle flow process: The flow regime in the front head and rear part of theparticle flow is more likely to be collision dominated than in the middle part. When theflow distance is less long or the slope angle is smaller, the segregation degree willincrease more rapidly with flow distance. And when the flow distance is long enough,the segregation degree will reach a stable value. For larger slope angle, the stable value is smaller.