全风化花岗岩孔径分布-颗粒组成-矿物成分变化特征及指标相关性分析

Variation features of pore radius and particle diameter distributions and mineral content of completely decomposed granite and correlation of parameters

孔径分布、颗粒组成和矿物成分是全风化花岗岩微观和结构特征的3个主要方面,也是决定其工程地质性质的关键因素。理论研究和实际工程中,常用大、中小和微孔隙、角砾、砂粒和粉粘粒、三大矿物(石英、长石和粘土矿物)含量等指标表征这3方面的特征。3方面指标在一定范围上变化幅度多大?数值间相关性及作为土结构模型组份因子,它们相对权重多大?通过对香港九龙两处边坡51件全风化花岗岩试样压汞测试、颗粒分析和X射线衍射(XRD)等微观结构特征分析,结果表明:两处边坡粗粒和细粒结构全风化花岗岩有明显区别,前者主要属于砾石土和砂砾土,部分为含砾土,大孔隙多,石英和粘土矿物多,而后者部分属含砾土,部分为细砂土和亚砂土,微孔隙多,长石多;两者长石和粘土矿物含量变化正好相反。借助于多因素关系矩阵法,对3方面共9个指标作相关分析发现,相关性较好的指标是:角砾和砂粒 (0.948);大孔隙和微孔隙(0.846);石英和长石(0.827);长石和粘土矿物 (0.747)。从土结构因子角度考虑,权重从大到小指标是:微孔隙、长石、粘土矿物、砂粒、角砾、大孔隙、中小孔隙、粉粘粒和石英。其分析结果可为该类土微观结构特征细化及分类提供依据,为其微结构力学研究提供基础材料。

The three aspects with respect to micro-properties of the completely decomposed granite (CDG) as the distribution of pore radius, particle diameters and mineral content play a major role in determining the engineering geological features of the CDG. In theoretical study and engineering practice the following parameters are used to describe the characteristics in the three aspects: large, middle and small, micro-pores, gravel, sand, silt and clay particles, three major mineral components (quartz, feldspar and clay minerals), etc. How large of the variation range of these indices in one certain size of trial pits and blocks? How about the correlation of the indices in the three parts? As factors of soil structure, how large of their weight ratios once the soil structure is to be under considerations? In this paper, a total of 51 nos. specimens from 18 nos. blocks from three trial pits of two slopes in Kowloon, Hong Kong, were taken as examples. The test is carried out by means of the mercury injection, particle size distribution and X-ray diffraction. After preliminary analysis, it is found that the CDG with coarse particle portions is very different from that with fine particle portions. The former belongs to gravel soil and sandy gravel soil, and some of it is gravel-bearing soil, with more big pores, more quartz and clay minerals. The latter belongs to gravel-bearing soil, some is fine sandy soil and sub-sandy soil, with more micropores, more feldspars. Variations of feldspar and clay mineral contents are inverse to each other. Furthermore, the interaction matrix is applied for analysis of the correlation of the 9 indices. As a result, it is found that the correlation coefficient varies to a great extent. According to the value of the correlation coefficient, those indices with larger ones are: gravel and sand particles (0.948), big pores and middle-small pores (0.846), quartz and feldspar (0.827), feldspar and clay minerals (0.747). If the soil structure factors are under considerations, the 9 indices are in sequence of weight ratio from large to small: micro-pores, feldspar, clay minerals, sandy particles, gravel, large pores, middle-small pores, silt and clay particles, quartz. These indices, quantified after their correlations and weight ratios, provide bases for the study of micro-features in detail and classifications of the CDG, and perhaps act as one of the basement for the constitution equations of microstructure mechanics of soils to be built.