“Plagioclase solution degree index”: a new index to evaluate the weathering degree of granite

Abstract

The weathering degree of rocks has an adverse influence on their strength and deformability characteristics, which in turn influences the industrial uses of rock. The need to develop a weathering index that reveals their mechanical and engineering geological behaviors is thus pertinent to enable the building of more accurate models for forecasting geological hazards. Granite weathering in the Ma On San, Shek Kip Mei and Kwun Tong areas of Hong Kong was studied using scan electron microscope (SEM) images to observe mineral shapes for detailed identification of the weathering degree of completely decomposed granite (CDG). Plagioclase images captured from the SEM were subsequently analyzed and processed with the use of a microstructural image processing system. The results of the analyses indicate that plagioclase, though sensitive to weathering, still remains in CDG and is preserved at different weathering degrees. Hence, it provides a possibility for evaluating the weathering degree more accurately. Thus, a new index referred to as the plagioclase solution degree index is proposed to evaluate the weathering degree of granite.