泥石流堆积物的粒度分布及其分形结构

Grain-size distribution and fractal structures of solid grains in debris-flow deposits

关键词:  泥石流  堆积物  粒度分布  粒度分维  分形特征

Key words:  debris flow  debris-flow deposits  grain-size distribution  fractal dimension of grain size  fractal feature

摘要:

泥石流堆积物主要由砾石、砂砾、粉粒和粘粒组成,组成泥石流堆积物的颗粒级配变幅很大,从直径大于数十米的巨砾到肉眼难以看见的几微米的胶体微粒均有分布,大小颗粒粒径之比可达106~107。泥石流堆积物颗粒具有明显的自相似性和无标度区间。本文以小江流域多处泥石流堆积物为研究对象,采用图解法全面分析了泥石流堆积物的粒度组成特征,根据分形理论计算了泥石流堆积物颗粒的分维值,对泥石流堆积物的分形特征进行探讨,并与泥石流堆积物粒度特征相联系,发现分维很好的反映了泥石流堆积物颗粒组成及其粒度分布特征。将泥石流堆积物颗粒分维与泥石流的粘性、形成年代等性质相联系,以找出它们彼此之间的关系。

Abstract:

Debris flow can be seen as a two-phase rheological fluid with soil-fluid compositions,and the debris-flow deposits consist of mud,silt,sandy gravel,boulder,etc.,with grain sizes ranging from several microns to more than tens of meters.Consequently,solid grains in the debris-flow deposits display a marked self-similarity in geometrical shape and scale-invariance in size according to fractal theory.In this paper,various debris-flow deposits located in the Xiaojiang River basin were collected as studied samples,and the features of grain-size distribution of these deposits are examined through illustration method.Then fractal dimensions of solid grains in these deposits are calculated respectively with the dimension values between 2.5 and 3,showing obvious fractal features of grain-size distribution.Furthermore,the results of grain-size dimensions are consistent with the results obtained through the former method.So fractal dimension can be seen as such a parameter,which reflects the grain composition and grain-size distribution of the debris-flow deposits.Finally,the relationship between fractal dimension,and viscosity and accumulation ages of debris-flow deposits are discussed as more characteristics of debris flow are determined by grain composition and grain-size distribution.