modified volumetric joint count to check for suitability of granite outcrops for dimension stone production

This study compares the characterization of fractures of some granite outcrops in Southwestern Nigeria. Some geometrical properties of discontinuity (orientation, persistence, aperture, infilling and spacing) were evaluated. On the granite studied, most of the mapped joints have orientations that fall within 84○/020○ and 86○/300○. These patterns are compatible with the regional fracturing, which is predominantly shaped by NW-SE, NE-SW, NNE-SSW, ENE-WSW and WNW-ESE structure of tectonic origin. The XX type joint persistence is dominant while RR type is in minority. Closed aperture was observed at Ore, Awo and Ikole granite outcrops. The infilling materials are mica and quartz; their percentages are constant for all the outcrops studied. The modified volumetric joint count (JV) ranges from 0.67 m-1 to 1.24 m-1 and the average spacing of all sets varies from 1.62 m to 2.50 m. Fracture network characterization as carried out revealed that, for an outcrop to be economically suitable for dimension stone production, the modified volumetric joint count (JV) should not be above 1.7 m-1 and must be at least ‘good’ rock according to conventional rock mass classification. Numerical modeling of block size distributions of selected granites in Southwestern Nigeria was done using AutoCADTM 3D.