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

近年来，日本由滑坡引发的大规模泥石流时有发生。但是，这种泥石流的流量和危险区域无法预测，因为目前还没有预测模型。提出了一种预测滑坡引起的粘性泥石流的模型，无论泥石流是在收缩土中诱发的，还是在膨胀土中诱发的，都需要不同的供水方式来填充泥石流颗粒之间的空隙。通过在滑动面附近出现饱和土层，假定滑坡发生在膨胀土块中，在陡峭的试验水槽中制备了一块含水较多的膨胀土试件，并将其释放下坡。低饱和层被剪切液化，以泥石流的形式留在土块后面。土块随着下坡的推进而变得越来越薄，留下的泥石流总量增加，液化速度是含水率和剪切速率的函数，得到了描述土块运动的方程组。通过理论计算结果与实验结果的对比，验证了理论的正确性。得到了既能预测土块运动又能预测土块停止后泥石流运动的另一组方程。Harihara河泥石流是一种典型的滑坡诱发泥石流，将利用新发展的理论对其进行数值再现。

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.