Engineering properties of fresh and decomposed igneous rocks from Hong Kong

The influence of degree of decomposition on the strength and elasticity of fresh to highly decomposed igneous rocks in Hong Kong is described and summarized. Assessments of degree of decomposition by rock grade, rock quality designation, apparent porosity, ultra-sonic velocity, and point load index are discussed from the point of view of estimating rock behaviour. For engineering purposes a sufficiently precise measure of decomposition could be based on the point load index, and a sufficiently reliable estimate of elastic modulus could be calculated from the ultra-sonic velocity.