DISCONTINUITY OF GRANITES AND ITS EFFECTS ON ROCK MASS CLASSIFICATION

For hard rocks as granite, rock mass class is mostly associated with discontinuities. This paper presents three case histories of granitic engineering projects in China. Focuses are on distributive features of discontinuities by means of field investigation, stereographic projection, statistic methods of structure and geo-stress. The discontinuity includes faults, joints, veins, contact zone and fissures with distinctive scales and formation. Most commonly occurred are of joints reflecting geo-stress orientation. The most widely used rock mass classification indices RMR, Q, BQ and T systems are compared. By means of interaction matrix, it was found that the interaction coefficient of RMR and BQ is the largest, next is the T values, the last one is the Q value. The results indicate that discontinuity density, orientations and hard rock are of dominant parameters in classification index for site selection and design of tunnelling projects.