滑坡碎屑流中碎屑颗粒的变形破碎与能量转化及其宏观动力学效应

The catastrophic event induced by rock avalanche occurs frequently in the western China. Mechanisms of deformation and failure, and laws of energy transformation of grains are the key factors to reveal the transport mechanisms of rock avalanche. This study plans to use the sections exposed in the deposit of rock avalanche and some regular exploration methods to analyze the deposit structure, use scanning electron microscope to analyze the section morphology of grains, and use numerical modeling to obtain the dynamic parameters of grains. The results of above three methods could be comprehensively analyzed to study mechanisms of deformation and failure of grains during movement. Multi-cyclic loading and unloading test with triaxial apparatus is introduced to obtain energy transformation curves under different confining pressure and loading rate of grains acted by compressive stress. SHPB test in the field of rock dynamics is used to obtain energy transformation curves and dynamic impact strength curves under different strain rate of grains acted by impact load. The laws of energy transformation under above two kinds of loads could be analyzed using the curves obtained. With the results obtained from triaxial compression tests and SPHB tests, PFC discrete element method is improved to model the transport course of rock avalanche and energy transformation course of grains in it, through which the transport mechanisms of rock avalanche could be revealed. The conclusions of this study could be the theoretical basis of forecasting the hazardous zone of rock avalanche.

滑坡碎屑流导致的群死群伤事件在我国西部山区频繁发生，碎屑颗粒的变形破碎机理及能量转化规律是揭示其高速远程机制的关键因素之一。利用碎屑流堆积物中出露剖面辅以勘探手段，分析其堆积结构，利用扫描电镜分析碎屑颗粒的断面形态，利用数值模拟获取碎屑颗粒的动力学参数，通过对三者结果的综合分析，揭示滑坡碎屑流运动过程中碎屑颗粒的变形破碎机理；利用多循环加卸载三轴压缩试验获取岩石三向受压时，不同围压和加载速率下的能量转化曲线，引入岩石动力学领域的SHPB试验，获取岩石受冲击荷载时不同应变率下的能量转化曲线和动态冲击强度曲线，分析上述能量转化曲线，揭示滑坡碎屑流运动过程中碎屑颗粒的能量转化规律；利用岩石三轴和SHPB试验所得结果改进PFC离散元数值方法，再现滑坡碎屑流的运动过程和其中碎屑颗粒的能量转化过程，揭示滑坡碎屑流的高速远程机制。研究成果可以为高速远程滑坡的致灾范围预测提供理论依据。

我国西部高速远程滑坡碎屑流频发，对西部城镇和重大工程建设造成严重威胁。碎屑流流动过程中颗粒的破碎与能量转化是影响高速远程滑坡致灾范围的主要因素之一,揭示颗粒的破碎和能量转化机理，是对高速远程滑坡进行预测预报和风险评价的前提。本项目以鸡尾山和大光包高速远程滑坡碎屑流为研究对象，通过无人机影像、现场简单勘探、调查与统计等，揭示了滑坡碎屑流堆积物的物质组成、堆积结构、颗粒级配分布等堆积特征与规律，结果显示，在横剖面上，碎屑流堆积物除了表面约10m为大块石层，主要堆积结构为倒序堆积；在纵剖面上，碎屑流堆积物保持了源区地层的相对顺序，且从近端到远端颗粒级配逐渐减小。利用环剪试验和数值模拟，获取了滑坡碎屑流运动过程中颗粒的受力、变形和破碎特征，以及颗粒破碎的机理、影响因素和规律，揭示了滑坡碎屑流运移过程中颗粒主要受剪应力作用，颗粒破碎主要为剪切破碎，颗粒变形过程中聚集的弹性能量在破碎瞬间集中释放，能够引起颗粒之间的摩擦系数急剧减小。通过改进UDEC和PFC2D离散元数值方法，可以使它们模拟高速远程滑坡启动过程中滑面上和碎屑流流动过程中碎屑流内部的摩擦系数降低以及对高速远程滑坡宏观动力学过程的影响。以鸡尾山高速远程滑坡为例，利用改进的UDEC和PFC2D数值方法模拟其失稳、启动、凌空飞行、碎屑流运移的全过程，结果表明，由剪切弱化导致的滑带上摩擦系数降低可以使其剪出速度增加88.8~311.5%，位移增加4.9~64.2%；碎屑流运动过程中颗粒之间摩擦系数的降低，可以使其位移增加395~711m；因此，滑面上和碎屑颗粒间的摩擦系数减小是滑坡碎屑流高速远程效应的主要原因之一。通过上述研究，揭示了滑坡碎屑流运移过程中颗粒的破碎机理，并从颗粒破碎和能量转化角度揭示了滑坡碎屑流的高速远程机理，研究结论可以为高速远程滑坡的预测预报、风险评价与防治提供理论支撑。