Variations in sub-tropical deep weathering profiles over the Kowloon Granite, Hong Kong

Variations in the physical characteristics of the weathering profile over the Kowloon Granite in Hong Kong have been established using borehole records supported by field mapping. There is a strong correlation between topography of the weathered profile base and the main structural trends. Linear zones of deep weathering have been preferentially eroded to create valleys, which subsequently became sites of alluvial and colluvial accumulation. Variations in weathering patterns are primarily a function of the geometry and infilling of relict jointing, which together determine local hydrogeology and hence intensity of weathering. Magnetic susceptibility is a reliable indicator of material weathering grade in the Kowloon Granite. Corestones are generally restricted to weathered profiles over topographically high areas, the locations of which are controlled by regional joint spacing and orientation. Corestone-bearing profiles are rare, and more commonly, deeply weathered granite without corestones passes abruptly into relatively fresh rock. This has important implications for engineering ground models derived from borehole interpretation.