花岗岩风化程度的化学指标及微观特征对比——以香港九龙地区为例

据香港九龙3个不同工程场地取得的149件不同级别的风化花岗岩样品的化学分析结果,用统计学方法,从反映岩石风化程度的18项化学指标中选取9项进行了分析计算.对其结果及其与风化程度分级的关系的研究表明有4种指标比较理想.通过对样品微观特征的观察研究和矿物成分、微孔隙率以及综合显微岩石指标(Ip)进行了描述和定量分析,发现其中一些指标有一定相关性.这些化学指标和微观特征相关的统计值在一定程度上可定量表征花岗岩的风化程度,即:随风化作用进行,碱、碱土金属组分逐渐淋失,脱硅、富铝铁化作用逐渐加强;相应地,先是钠长石风化成高岭石,其次为云母和钾长石的风化.粘土矿物所占体积百分比随风化程度增高而变大,至残积土(Ⅵ级)时已达50%左右;Ip指标值下降,微孔隙率增高.文章综合出各个风化级别的指标变化范围及平均值供花岗岩分布区花岗岩风化野外调查和研究工作参考.

Comparison of chemical indices and micro-properties of weathering degrees of granitic rocks - a case study from Kowloon, Hong Kong

According to the analytic data of 149 samples from 3 sites of Kowloon Peninsula, Hong Kong, a series of statistic values of chemical proportions and weathering indices are calculated, and their relations with the weathering grades are discussed. Then the micro-properties involving mineral constituents, micro-fracture contents and sophisticated micropetrographic index (I_p) are also quantitatively described, some of them are related with each other to an extent. The statistic values corresponding to the chemical, mineral and micro structural properties quantitatively depict the material weathering grades of granitic rocks. With the progressive weathering, the alkalis and alkaline earth leach out, and finally eliminate. The content of silica decreases while that of sesquioxide goes up. Accordingly, the plagioclase diminishes and the potash feldspar the next. The clays are formed more-and more-and reached 50% in grade Ⅵ. The I_p gradually goes down and the microfractures merge more-clearly. To sum up, the total statistic values of various kinds are listed, which is perhaps of referential for the regional geotechnical engineering investigation and research works.