ASSESSING THE EFFECTS OF JOINT ORIENTATION AND ROCK MASS QUALITY ON FRAGMENTATION AND OVERBREAK IN TUNNEL BLASTING

It is well known that rock mass properties exert considerable influenc e on the process of fragmentation. Observations in a model study and f ield study using conventional bulk blasting were compared in order to determine the effects of rock mass quality and joint orientation on fr agmentation and profile control in tunnel blasting. It was observed in the study that blast results such as average fragment size and depth and cross-sectional area of broken zone were considerably influenced b y the joint orientation. Accordingly, it is concluded that larger-capa city loading equipment and deeper blast holes are required information s with joint planes perpendicular to the tunnel axis. However, the num ber of blast holes should be greater in the case of joints parallel to the tunnel axis. Furthermore, the powder factor (kg/m3) is found to b e directly related to the rock mass quality (Q). Optimization of pull and charge per round is required for efficient blasting in weak format ions. The use of the contour blasting technique seems to be essential in poor and fair rock masses in order to minimize the overbreak, reduc e the support cost, and improve the stability of the opening.