Occurrences of carbonate rocks and buried karst in the northwest New Territories of the Hong Kong SAR significantly influence foundation design. The carbonate rocks include marble, dolomite, impure marble and marble clast-bearing rock. These different types of marble show varying degrees of karst development. Generally the extent of karst development increases with the calcium or magnesium carbonate content of the rocks. Based on a study of more than 3,500 boreholes, variations in the extent of karst development of the carbonate rocks can be described in terms of a five-fold classification of intensity, and in relation to three main lithological categories: Ma Tin, Long Ping and Tin Shui Wai marbles. The most intense karst development and the largest cavities occur in massive 'pure marble', in which the karstic zone can extend to depths of more than -127 mPD. development, with large cavities being rare and smaller-scale honeycomb weathering being The degree of karst development of impure marble is less than that of pure marble. Marble clast-bearing rock shows the least karst more typical. All of the carbonate rocks occur in fault-bounded outcrops and the faulting can further add to the difficulties in foundation design.
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