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

本研究旨在提出火山碎屑流和雪崩流动的统一理论，并使数值模拟实际现象成为可能。首先，推导了考虑非弹性碰撞、动量输运和静骨架应力的颗粒流本构方程；然后，将这些方程推广为流动阻力公式来解释实验得到的层流、层流/色散和色散型流动的特征行为。这一理论被应用于云仙火山富根ake的默拉皮火山碎屑流。对熔岩穹丘破碎成碎片的过程和火山碎屑物质的流动进行了令人满意的解释。明确了火山碎屑流的主要基流化层和基流化层上的“热”部分的形成、流动行为和停止的定量机理，这是火山碎屑流的特征结构。基于该理论建立的数值模拟模型可以解释实际的流动极限以及区域内沉积物厚度的分布。用颗粒流理论定量地解释了雪球的形成过程和雪球对流动特性的影响。数值模拟模型还考虑了雪温对雪球形成和侵蚀沉积过程的影响。将该模型应用于1986年Maseguchi雪灾（粉雪灾）和1992年的Hakubadake雪灾（我们的雪灾），对这两种现象都有很好的描述。

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.