The purpose of this study is to quantify the relationships between the grain size characteristics and physicomechanical properties of selected marble rocks from Ma On Shan, Hong Kong. The rock specimens can be subdivided into white, light grey and dark grey, depending on the amount of impurities of the original limestones before metamorphism takes place. A series of laboratory tests, including the point load test, Schmidh hardness test, and uniaxial compression test, have been carried out on the same set of core samples in accordance with the procedures given by ISRM. Also microscopic observations based on the double replica method have been made to quantify the microphysical characteristics, in particular the grain size. The results are statistically analyzed and some selected physical and mechanical properties of the marble rocks are plotted against each other in order to explore possible relationships. The study in particular examines the influence of gain size characteristics on the engineering properties of the chosen marble rocks.


The properties of rocks are influenced by the mineral composition, texture (grain size and shape), fabric (arrangement of minerals and voids) and the weathering state (Irfan, 1996). A number of petrographic techniques have been developed to document and quantify the mineralogical and textural characteristics of various rocks using an optical microscope (e.g., Mendes et al., 1966; Onodera and Asoka Kumara, 1980), scanning electron microscope (SEM) (e.g., Clelland & Fens 1991), or other tools. Among the typical petrographic characteristics that affect the mechanical properties of rocks, grain size has long been recognized to be closely related that in general the strength of rocks is greater for finer grained rock. Hugman and Friedman (1979) suggested that the peak uniaxial compressive strength decreases linearly with the mean grain size in carbonate rocks. However, it has been more frequently found that the peak strength decrease inversely with the square root of the grain size by Olsson (1974) for marble, Brace (1961) for quartzite, Brace (1964) for dolomite and limestone, and Fredrich et al. (1990) for calcite marbleand limestone. For Yuen Long marbles in Hong Kong, Wong et al. (1996) also found experimentally similar conclusion for fine-grain and coarse-grain Yuen Long marbles.

The purpose of this study is to apply correlation analysis to investigation the relationships between grain size and engineering properties of local marbles. A variety of marble rock samples from Ma On Shan area in Hong Kong were subjected to microscopic investigation. The rocks can be categorized into white, light grey and dark grey type, depending on the amount of impurities in the original limestone before metamorphism takes place. The white marble is typically coarse-grain, and the light grey and dark grey marbles have relatively smaller grain size. The same samples were then tested to determine the specific gravity, Schmidt hardness, point load strength index, uniaxial compressive strength, modulus of elasticity and the Poisson's ratio. The relationships between these properties and average grain size are described by simple regression analysis.

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