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Rock Quality Designation (RQD) values for slightly weathered granite, feldsparphyric rhyolite and volcanicrock are 55%, 47% and 56% respectively, and these values generally reduce with increasing weatheringgrade. Average RQD values of 48%, 28% and 30% respectively are found in moderately weathered granite,feldsparphyric rhyolite and volcanic rock. Fracture index values range from 5 to 15 in all rocks, and there isno significant increase in. fracture index with increasing weathering grade, or measurable variation amongthe different rock types (Woods, 1993).Joint persistence in granitic rocks observed from coastal exposures indicates that the dominant joint sets(e.g. northeast- and eastnortheast-trending joints) may range up to to 30 m. Similar persistence has beenobserved in shallowly-dipping sheeting joints, whereas minor random joints have a persistence of only afew 10s of mm. Joint persistence in volcanic rocks observed in the water tunnel from Ngong Ping to ShekPik Au averages 10 m (Woods, 1993).Minor variations in joint regularity have been recorded among different rock types. For example, smoothand planar joints are generally a feature of volcanic rocks, whereas joints in the granites and feldsparphyricrhyolites are often irregular, and for gently dipping joints, often wavy.38