Relationship of the discontinuities and the rock blasting results

Abstract

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.

Influence of natural discontinuities and mechanical properties on the fragmentation of marble by blasting in Central Africa

“…The decrease in the dip leads to an increase in the compressive strength of the blast pattern and the hardness of the slope, resulting in an increase in the explosive charge and the powder factor of the face to be shot, thus reducing the average block size and consequently increasing productivity (Table 4 to 6). These results are in line with the work of Singh et al (2015) and Adebola et al (2016), concerning the reduction in block size with the reduction in the drilling mesh, and with the work of Belland (1968), Worsey et al (1981) and Yahyaoui et al (2018), according to which the dip of the main joint planes has a considerable influence on fragmentation. Table 4 to 6 and Fig.…”

“…7 to 9 clearly show that the direction of the blast planes does not influence rock fragmentation, but rather the dip of the blast planes influences fragmentation after blasting. This result is cited in the work of Belland (1968) and Yahyaoui et al (2018). On the other hand, the direction of the firing planes has an impact on stability, the correct alignment of the front and the difficulties of felling.…”

“…The size of the fragments obtained should also not exceed the opening of the crushing plant for efficient operation (Jug et al, 2017;Shaib et al, 2020). The presence of large blocks requires secondary fragmentation to further reduce the material pulled to acceptable sizes, thereby increasing production costs (Rustan, 1990;De Lile, 2012;Mohammad et al, 2018;Yahyaoui et al, 2018;Agyei et al, 2019). In general, when blasting, there is not always a match between the size of the blocks shot and the size of the crusher mesh.…”

“…Discontinuity planes considered as firing planes allow the choice of the orientation of the felling front which favours the best fragmentation of the rock, ensures the stability of the front and minimises felling difficulties (Ash, 1973;Abu Bakar et al, 2013;Yahyaoui et al, 2018).…”

“…The choice of a free felling front that favours rock fragmentation is influenced by the dip of the plane of discontinuity, while the family class of direction to which the plane of discontinuity of firing belongs influences the stability, good alignment and security of the front (Belland, 1968;Yahyaoui et al, 2018). The experiments of Worsey et al (1981) show that the shooting results depend on the angle between the designed perimeter line and the discontinuity.…”