Marble is not very common in Hong Kong, it accounts for only 3% of the geological area. Despite this fact, marble and the cavities associated, play an important role within the building strategies of the city, being located in areas crucial for the development of new residential areas in Hong Kong. In order to better understand the issue, boreholes from Area 90 in Ma On Shan have been studied. This paper aims to study cavity distribution, size and location along with the rock profile and to provide an overview of the engineering problems associated with this geology. Ma On Shan Formation can be classified according to the current literature along with the risk that might pose to future civil engineering projects.

1 Introduction

Karst landscapes are characterized by fluted and pitted rock surfaces, shafts, sinkholes, sinking streams, springs, subsurface drainage systems and caves. The unique features and the three-dimensional nature of karst landscapes are a result of a complex interplay between geology, climate, topography, hydrology and biological factors over long time scales (Stoke T. et al. 2010).

During the Carboniferous, Guangdong Province developed into a platform-flat facies characterized by medium to thick-bedded, lenticular cross-bedded, bioclastic micro-fine crystalline limestone, argillaceous limestone, carbonaceous and calcareous shale and dolomitic limestone sequence.

Carboniferous rocks are present through the north-western part of Hong Kong. The oldest rocks do not occur at outcrop, but have been penetrated in boreholes principally in the Yuen Long and Ma On Shan areas (Sewell R.J. et al. 2000).

From the boreholes, the marble consists of bluish grey to creamy white, dolomite to calcite marble with thin (<10mm) interbeds of dark green to black meta-siltstone and is steeply dipping (70-80°) to the South East (Sewell R.J. 1996 and Sewell R.J. et al. 2000). The Ma On Shan Formation has a minimum thickness of 200m. No fossils have been recovered from the marble and contact formations are not known (Sewell R.J. et al. 2000). Joints, commonly parallel to the foliation planes, are frequently coated with chlorite. Clasts of black siltstone within the marble have been detected in some boreholes together with weak pyritization along foliation planes (Sewell R.J. 1996).

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