Joint spacing distribution of granites in Hong Kong

The structural stability of rock masses is dictated by the inherent geological structures present, most notably joints. Joint spacings are one of crucial parameters to control the block volume, permeability, deformability as well as strength of rock masses. While extensive rock engineering projects have been carried out in Hong Kong in the last century, the distribution models of joint spacings in Hong Kong rocks have still rarely been studied systematically and published. This research examines true joint spacings of granites in fourteen different slope outcrops at various localities of Hong Kong. A total number of 1323 joint spacing measurements, belonging to 44 joint sets spanning from 0.005 m to 4.5 m, are obtained. The mean joint spacings among 44 joint sets studied are computed in a range of 0.11 m to 1.33 m. Lognormal Distribution is found to be the dominant joint spacing distribution of granites in Hong Kong. A further in-depth understanding of joint spacing distributions of Hong Kong granitic rocks, which covers about 35% of the total land area, is of profound practical value to the assessment of rock mass excavatability and numerical modelling of rock fracture network development.