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

Abstract

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.