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诱发的大规模泥石流。但是，由于目前还没有一个预测模型，因此无法预测这种泥石流的流量和危险区域。本文提出了一个滑坡粘性泥石流的预测模型，无论泥石流是在收缩性土壤中还是在膨胀性土壤中产生，都需要不同的供水方式来填充泥石流颗粒之间的空隙。通过在滑面附近出现饱和土层，假设滑坡发生在膨胀土块体中，在陡槽中制备了含水量丰富的膨胀土试件，并将其释放至坡下。下饱和层发生剪切液化，以泥石流形式留在土块后面。土块沿坡面向下运动时，其厚度逐渐变薄，所形成的泥石流体积逐渐增大，并给出了土块液化速度与含水量和剪切速率的函数关系，得到了描述土块运动的方程组。通过与实验结果的比较，验证了理论的正确性。得到了不仅能预测土块运动而且能预测土块停止后泥石流运动的另一方程组。利用该理论对典型的滑坡型泥石流--折原川泥石流进行了数值模拟。

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.