滑坡碎屑流持速效应机理研究

The granular flow transformed from landslide can always travel a long distance at a high speed and lead to a calamity, therefore, it is very necessary to study the mechanism that leads to the high speed and long run-out of the granular flow. Speed maintaining effect, which means the capability to maintain the flowing speed, is one of the most important reasons leading to the high speed and long run-out , while the shear strength at its bottom is the key factor that affects the speed maintaining effect. But because of the complexity of the granular flow itself, the shear strength parameter at its bottom during flowing has not been obtained so far. The research project plans to study the changing law and mechanism of the shear strength at the bottom of granular flow during its flowing through the longitudinal sections in the deposits of granular flow transformed from the Wenjiagou and the Niumiangou landslides triggered by 2008 Wenchan earthquake. First, the structure, grain size distribution and mechanical parameters of the deposits along the section are analyzed to study the structure of the granular flow and mechanical status, fragmentation, movement laws of the grains during the flowing course, which gives the clues to study the changing mechanism of shear strength at the bottom of the granular flow. Then the grain material will be sampled at the bottom of the deposits and tested with large-scale direct shear and ring shear tests, through which shear strength parameters and its changing laws along the longitudinal section and as shear distance increasing will be obtained. Meanwhile, distinct element method will be used to model the dynamic course of granular flow to analyze the the changing law of the microscopical dynamic parameters during its flowing. The parameters obtained from numerical modeling ,in-situ research and geotechnical tests can be proofed and complemented from each other. Based on the above research results, the changing law and mechanism of the shear strength at the bottom of the granular flow are studied, the mechanism of the speed maintaining effect is revealed.

滑坡碎屑流具有高速远程的运动特征，往往造成灾难，对其高速远程机理进行研究极为必要。滑坡碎屑流的持速效应，即由于摩擦阻力减小而保持高速运动的能力，是其能够高速远程的重要原因之一，而碎屑流流动过程中底部的剪切强度又是持速效应的关键。但是由于滑坡碎屑流自身的复杂性，目前还没有获取碎屑流底部剪切强度参数的报道。拟利用文家沟和牛眠沟滑坡碎屑流堆积物出露的纵向剖面，分析剖面上碎屑物的堆积特征、颗粒级配和力学性质变化，研究碎屑流运动过程中的内部结构和颗粒的受力、破碎、运动规律等细观动力学参数，进一步研究剪切强度变化机理；取底部碎屑物质进行粗粒土大直剪试验和环剪试验获取碎屑流底部剪切强度及变化规律；利用颗粒流数值模拟再现滑坡碎屑流的动力学过程，分析剪切强度和细观动力学参数变化规律，结果与堆积物现场和试验研究相互补充和验证。通过上述研究获取滑坡碎屑流流动过程中底部剪切强度变化规律及机理，揭示其持速效应机理。

在我国西南山区，高速远程滑坡碎屑流引起的群死群伤事件频繁发生，但是目前国际上对滑坡碎屑流的高速远程机理即持速效应机理还没有定论，难点在于获取碎屑流运动过程中的微观动力学参数。本项目以牛眠沟、文家沟和武隆鸡尾山滑坡碎屑流为研究对象，利用现场调查和遥感影像，建立了典型高速远程滑坡碎屑流的地质模型，查明了它们的宏观动力学过程；利用文家沟滑坡碎屑流堆积物中被泥石流和雨水径流切割形成的纵剖面，查明了碎屑流堆积物的堆积结构；利用室内环剪试验模拟了碎屑流的长距离流动剪切过程，利用离散元数值方法模拟了武隆鸡尾山滑坡碎屑流失稳破坏至碎屑流流动的全过程，获取了碎屑流流动过程中颗粒的受力、破碎和运动规律，获取了粒间及碎屑流底部的剪应力变化机理与规律，获取了碎屑流流动过程中动能、应变能和重力势能的转化与变化规律。研究认为，滑坡碎屑流的持速效应机理包括以下2个方面：（1）碎屑流流动过程中，颗粒碰撞和剪切破碎导致颗粒级配减小，进一步导致颗粒间以及碎屑流底部与地面之间的摩擦阻力下降，粒间摩擦阻力下降可以使碎屑流更容易向平面上扩展，且减小摩擦耗能；碎屑流底部与地面之间的摩擦阻力降低，可以促进碎屑流的整体运动；（2）颗粒之间发生碰撞和能量传递，前部颗粒接受后部颗粒传递的动能从而能够运动得更远。本项目的研究结论对国内外该领域的研究具有一定的指导意义，同时，可以为我国西南山区的高速远程滑坡碎屑流致灾范围预测提供理论依据。本项目在国内外权威期刊上公开发表论文4篇，其中3篇被SCI收录，1篇被EI收录，研究成果获得国内外同行的好评。