Enhanced and Systematic Classification System for Rock Types in Tuen Mun and Tin Shui Wai Area, Hong Kong

Abstract

Classification of rock type is one of the most important factors in rock engineering. However, it is always perceived to be the least important factor in the industry. Engineers would like to focus on knowing the strength and the deformation properties of the rock with little attention paid to understanding the mineral constituent, chemical composition, mode of occurrence as well as the depositional environment of a particular rock type, that inherently affect greatly its weathering profile and the rock mass load/deformation behavior. In engineering practice, logging geologists will usually classify rock type solely based on visual inspection of core samples, which might not be adequate in many cases. In Hong Kong, in areas that are underlain by carboniferous sedimentary rocks, there are statutory regulations where extensive ground investigation and special foundation design would be required to overcome potential problem of cavities and sinkholes. Volcanic tuff breccia has been misidentified as carboniferous conglomerate or meta-siltstone with marble clast; the consequence of this had increased the foundation cost and ground investigation cost substantially. A systematic classification system for rock type in the Tuen Mun and Tin Shui Wai areas of Hong Kong would therefore be very crucial for all practitioners to follow in order to minimize any chances of misidentifying a particular rock type. In this paper, the importance of both geological and engineering classification of rock are described and are recommended for adoption in the future for rock found in the Tuen Mun and Tin Shui Wai area of Hong Kong.