白龙江流域武都区段新发泥石流堆积物基本特征及颗粒级配分维研究

Study on the Basic Characteristics and Particle Gradation Fractal Dimension of New Debris Flow Deposits in Wudu Section of Bailong River Basin

白龙江流域是我国泥石流的高发地区,在强降雨的激发下沟谷内堆积的大量固体松散物质易形成泥石流。松散固体物质的颗粒级配影响着它的力学性能,进而对泥石流的启动产生较大影响。强降雨后,松散堆积体内大范围剪切破坏而转化为泥石流。以白龙江流域近期新发泥石流的16条泥石流沟为研究对象,取其具有代表性的堆积样品,通过室内土工实验,测试其基本物理力学参数。并通过筛分及激光粒度仪对样品的颗粒进行分析,采用统计图解法、粒度分维法和经验公式法对泥石流堆积物的特征、性质、粒度分形结构和颗粒级配关系进行分析。结果表明:1.区内泥石流堆积体粒度分布具有良好的分形特征,粒度分维值D为2.5~2.6,且粒度分维值D随黏粒含量Pc的增加而增大,二者满足关系式D=0.115 1ln(Pc)+2.509 8。2.通过经验公式、粒度分维计算、现场称重等方式确定了白龙江流域武都区段大部分泥石流为黏性泥石流。3.堆积物中的黏粒含量较多,但大都缺失中间粒径,级配不良,且堆积物的抗剪强度普遍不高。各泥石流堆积物的物理力学性质有着较大的差异,但其内摩擦角却大都在27°~30°变化。说明该区域泥石流堆积物的内摩擦角具有良好的相似性。通过研究新发泥石流堆积体的物理力学特性,依据分形理论,剖析粒度分维值与粒度组成、粘粒含量、黏粒级配等相关性,为泥石流防灾减灾提供基础数据支撑。

The Bailong River Basin is an area with a high incidence of debris flows in China. A large amount of solid loose materials accumulated in the valleys are prone to form debris flows under the excitation of heavy rainfall. The particle gradation of loose solid matter affects its mechanical properties which in turn have a greater impact on the initiation of debris flow. After great rainfall,large-scale shear failure in the loose accumulation body transforms into debris flow. Taking the 16 new debris flow ditches in the Bailong River Basin as the research objects,representative accumulation samples were collected,and the basic physical and mechanical parameters of the deposits were obtained through indoor geotechnical experiments. The particle gradation of the samples were analyzed by sieving and laser particle size analyzer,and the characteristics,properties,particle size fractal structure and particle gradation relationship of the debris flow deposits were analyzed by statistical graphic method,particle size fractal method and empirical formula method. The results show that:1. The geological environment of each channel is different,and the lithology is also different,but the particle size distribution of debris flow deposits in the area has good fractal characteristics. 2. The particle size fractal dimension D is between 2.5 and 2.6 and increases with the increase of the clay content Pc,and the two variables satisfy the relationship D=0.115 1ln(Pc)+2.509 8. 3. Through empirical formulas,particle size fractal calculations,on-site survey weighing,etc.,most of the debris flows in the Wudu section of the Bailong River Basin are proven to be viscous debris flows. 4. There are many clay particles in the accumulation,but the intermediate particle sizes are usually short. The accumulation generally has poor gradation and low shear strength. The physical and mechanical properties of various debris flow deposits are quite different,but their internal friction angle mostly varies between 27° and 30°,showing that the internal friction angle of debris flow deposits in this area has good similarity. In this paper,the physical and mechanical properties of new debris flow accumulations in the studied area were investigated,and the correlation between particle size fractal dimension value and particle size composition,clay content,particle gradation,and soon was accomplished based on fractal theory. This research can provide basic data support for debris flow disaster prevention and mitigation in the studied area.