The paper investigates the initiation mechanism of debris flow through the survey with detailed analysis for several field debris flow events. The field investigation shows that the debris flow evolution includes distinct three stages: the soil structure changes and forms slide debris, slide debris mobilizes into debris flow, and the debris flow slips a long distance along the slope. In order to reappear and explain the aforementioned phenomenon existing in the initiation procedure of debris flow, the vane shear rheometer device is developed to test the shear rheology properties of debris source. Subsequently, the shear rheological tests with water drained out are performed utilizing the fine sand as tested material. A series of tests are performed and experimental data are obtained including the shear strain, negative pressure, water content, shear velocity, shear resistance, pore water pressure, and line displacements on the shear surface. Based on the changes of water content and negative pressure, the unsaturated permeability coefficients are obtained to explain the water-free infiltration process in the tests. According to the changes of shear velocity and experimental phenomena, the debris flow evolution is divided into three stages including the antecedent rainfall stage, accelerated initiation stage, and long-distance movement stage, which is similar to the three corresponding stages existing in the filed debris flow events. According to the analysis of test results, the mechanics of the debris flow initiation could be explained as the following: the debris source’s shear strength decreased to the value of yield shear strength, the peak shear strength available during undrained loading of a saturated, contractive, sandy soil, after a long period of antecedent rainfall infiltration. The tiny cracks expended to form connecting crack surfaces in the debris source interior, and then the debris source moves rapidly under the continuous rainfall, indicating the debris flow initiation. During the long-distance movement stage, the particles of debris source on the shear surface rearrange and form a smooth slide surface as the values of water content and pore water pressure increase. Therefore, the increase of water content and the decrease of negative pressure caused the soil shear strength decaying, and that is the major reasons of debris flow initiation. In addition, the other key reason is the particles rearranging on the initiation surfaces. The vane shear rheometer apparatus and corresponding test results have provided a more concrete and rational mechanism interpretation for debris flow initiation.

中文翻译：

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泥石流引发的实验研究

本文通过调查研究泥石流的引发机制，并详细分析了几个现场泥石流事件。野外调查表明，泥石流的演化过程包括三个阶段：土壤结构变化形成滑屑，滑屑动员成泥流，泥流沿边坡滑移了很长一段距离。为了重现和解释在泥石流引发过程中存在的上述现象，开发了叶片剪切流变仪装置以测试泥土源的剪切流变性质。随后，利用细砂作为被测材料进行排水流失的剪切流变测试。进行了一系列测试，并获得了包括剪切应变，负压，水含量，剪切速度，抗剪切力，孔隙水压力和剪切面上的线位移。根据含水量和负压的变化，获得了不饱和渗透系数，用以解释试验中的无水渗透过程。根据切变速度和实验现象的变化，泥石流演化分为前期降雨阶段，加速启动阶段和长距离运动阶段三个阶段，与场状碎屑中存在的三个对应阶段相似。流事件。根据测试结果的分析，泥石流引发的机理可以解释如下：泥石源的剪切强度降低到屈服强度，在长期降雨降雨渗透后，不排水的饱和，收缩，沙质土壤中可获得的峰值剪切强度。微小的裂缝扩展成碎片源内部的连接裂缝表面，然后碎片源在连续降雨下迅速移动，表明碎片流开始了。在长距离运动阶段，随着水含量和孔隙水压力值的增加，剪切面上的碎屑源颗粒会重新排列并形成光滑的滑动面。因此，含水量的增加和负压的减少引起土壤抗剪强度的下降，这是泥石流引发的主要原因。另外，另一个关键原因是粒子重新排列在起始表面上。