Mechanism and discharge prediction of the debris flow that is induced by a landslide

近年来，日本经常发生由滑坡引起的大规模泥石流。但是，这种泥石流的排放和危险区域是无法预测的，因为目前还没有预测模型。本研究旨在建立滑坡产生的粘性泥石流的预测模型。不论是在收缩土还是膨胀土中诱发泥石流，都需要不同的供水方式来填补泥石流颗粒间的空隙。根据滑坡面附近饱和土层的出现，假定滑坡发生在膨胀性土块中。在一个陡峭的实验水槽中准备了一块含有大量水分的膨胀土，并将其释放，使其沿斜坡向下移动。下饱和层被剪切液化，以泥石流形式留在土块后。随着土块向坡面下移，土块逐渐变薄，留下的泥石流总量逐渐增大。将液化速度作为含水率和剪切速率的函数，得到了描述土块运动的方程组。通过与实验结果的比较，证明了该理论的有效性。得到了另一个既能预测土块体运动又能预测土块体停止后泥石流运动的方程组。哈里哈拉河泥石流是一种典型的滑坡泥石流，本文将利用新发展的理论对其进行数值模拟。

Recently in Japan, large scale debris flow that is induced by landslide often occurs. But, the discharge and the hazardous area of that kind of debris flow cannot be predicted, because, at the moment, there is no predictive model. This investigation aims to present a predictive model of viscous debris flow generated by a landslide.Whether the debris flow is induced in contractive soils or in dilative soils may require different way of water supply that is necessary to fill up the void space among particles in debris flow. Here, the landslide is assumed to occur in dilative soil block by the appearance of saturated soil layer near the slip surface.A test piece of dilative soil that contains plenty of water was prepared in a steep experimental flume, and it was released to move down slope. The lower saturated layer was liquefied by shearing, and it was left behind the soil block as debris flow. The soil block becomes thinner and thinner with its advance down the slope, and the total volume of debris flow left behind increases.The speed of liquefaction was given as a function of water content and shearing rate, and a system of equations that describes the motion of the soil block was obtained. The validity of the theory was proved by comparing the theoretical results with experiments. Another system of equations that is able to predict not only the motion of soil block but the motion of debris flow even after stoppage of the soil block is obtained. The Harihara River debris flow that is a typical landslide induced debris flow will be reproduced numerically using the newly developed theory.