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The Geological discontinuities such as joint are the most common discontinuities present in the rock mass. A model scale study was carried out to evaluate the effect of the joints on rock blasting. Single hole tests at three selected burdens (optimum, less than optimum and more than optimum) were done on six different joint orientations. The joint orientation angles were 0°, 30°, 60°, 90°, 120° and 150° rotating in anticlockwise direction from the floor of the bench in a plane perpendicular to the free face. Bench models of dimensions 515x335x215 mm with a bench height of 50 mm were prepared by binding sandstone slabs of 25 mm thickness with an adhesive. The models were blasted by n°6 electric detonators. The dynamic and static properties of sandstone are given. The bench crater formed and the fragmentation produced were predominantly influenced by the position of charge with respect to the joint orientation. Severe toes were noticed in models with vertical joints and with joints dipping away from the face. Over breaks were observed in horizontally bedded models and in models with joints dipping towards the free face. Over breaks were observed in horizontally bedded models and in models with joints dipping towards the free face. The size of the broken fragments at 20 mm burden was found to be finer than the fragments obtained at 30 mm and 40 mm burdens for all joint orientations except vertical.

Relationship of the discontinuities and the rock blasting results