全风化花岗岩全岩和粘粒中粘土矿物含量变化对比

Comparison of clay mineral content variations in clay-size portions and bulky completely decomposed granite

工程实践和理论研究中常用全岩和粘粒中粘土矿物绝对和相对含量。对同一样品探求两者关系,便于数据对比,有利于工程应用。以采自香港九龙的2处边坡3个探坑中51个全风化花岗岩样品为例,作者用同一套仪器、测试方法,先后采用了颗分法测粘粒质量百分比、物理化学方法测比表面积、XRD方法测矿物成分,分别得出了全岩和粘粒中粘土矿物的绝对含量和相对含量,以及用粘粒质量百分比乘以相对含量得出的换算含量。另外还将全岩XRD矿物成分同薄片统计结果进行了相关分析。对粘土矿物绝对含量基本为20%～45%的全风化花岗岩,对比分析不同含量结果表明:全岩中的某些粘土矿物,如高岭石、蛭石的绝对含量远大于换算含量;不同样品中高岭石和蛭石的相对含量变化幅度远大于它们在全岩中绝对含量变化,两者变化呈现某种一致性;全岩中粘土矿物含量远大于粘粒(粒径<2μm和<5μm两个界限)的含量。后两者相对而言变化基本一致,差值不大;同全岩中粘土矿物含量相关性较好的是比表面积;同薄片统计结果相比,全岩XRD粘土矿物含量受对风化矿物处理不确定性的影响,结果往往偏大。

How about the relationship between clay mineral contents in bulky soils and in clay-size portions, respectively? Taking 51 nos. samples of completely decomposed granite (CDG) from 3 trial pits in 2 slopes of Kowloon, Hong Kong, as an example, the study is carried out with the same instrument, approaches and analyzers. In this procedure, the sampling pipette is adopted to measure the weight proportion of clay-size particles, the physicochemical method is used to test the specific surface area, and the X-ray diffraction (XRD) is applied to measure mineral contents in bulky rocks and clay minerals in clay-size portions. Furthermore, the correlation of statistic results from thin section with those from XRD is analyzed.For these CDG with clay minerals contents in a range of 20%～45%,it is found that:(a)In bulky rocks, clay minerals, e.g. kaolinite, vermiculite, are with a higher absolute content than the calculated content from clay-size portions percent timing the relative content of clay minerals in the portions; (b)The variation of relative contents of kaolinite and vermiculite is more prominent than that of the absolute content in bulky rocks, and these two with similar varying features; (c)The absolute content of clay minerals in bulky rocks is far larger than the clay-size portions (two limits of particle size: <2μm and <5μm). The portions within the two limits are with an concordant variation; (d)The specific surface area value is closely connected with the absolute content of clay minerals in bulky rocks; (e)Compared with results from thin section, the clay mineral content from XRD is usually bigger due to its uncertainty in identification of feldspars under weathering as clay minerals or not.