Mechanics of the granular rapid subaerial flow(pyroclastic flow and snow avalanche)

点击翻译按钮获取中文摘要

This research aims to present the unified theory of the flow of both the pyroclastic flow and the snow avalanche and to make possible to numerically simulate the actual phenomena.First, the constitutive equations for the granular flow which take the inelastic collision, the kinetic momentum transport and static skeleton stress into account are deduced. Then, those equations are extended to a resistance to flow formula to explain the characteristic behaviors of the experimentally obtained laminar, laminar/dispersive and dispersive type flows.This theory is applied to the Merapi type pyroclastic flow that occurred at the Fugendake, Unzen volcano. The processes of breaking the fallen lava dome into fragment and the flow of those pyroclastic material are satisfactory explained. Quantitative mechanism of formation, flow behaviors and the stoppage of the main basal fluidized layr and the nue 'ardent' part upon the basal layr which are the characteristic structure of the pyroclastic flow are made clear. A numerical simulation model based on the theory can explain the actual limits of flow as well as the distribution of the thickness of deposit within the area.Processes of snow ball formation and the effects of snow balls to the characteristics of the flow are quantitatively explained by the granular flow theory. Moreover, the effect of the snow temperature to the formation of snow balls and the process of erosion and deposition are taken into account in the numerical simulation model. The model is applied to the 1986 Maseguchi snow avalanche (powder snow avalanche) and the 1992 Hakubadake avalanche (we snow avalanche) and the reporductions of both two phenomena are very good.