Influence of blast-hole shape on efficiency of explosion of the charges

Abstract

UDCIt is well-known that after explosion of charges in contouring blast holes in the rock beyond the contour, a series of cracks is formed and propagated some way from the surface of the working.Cracks in the walls of workings reduce the subsequent resistance of the rocks to loads, and hence reduce the overall stability of the workings.Furthermore, inexact drilling of the mouths of the blast holes and deviations of the holes during drilling from the plane of the contour of the working usually cause overcutting and roughness of the walls and roofs of the workings.It is usually assumed that the size of the zone of crack formation depends on a number of factors, primarily on the charge weight and type and the mechanical properties of the surrounding rocks. For spherical charges the dimensions of the zone are usually considered to depend on the radius of the charge, i.e., the radius of the cavity occupied by explosives of a certain weight. Therefore it is natural to ask how fracture and crack formation will occur when the charges are of elliptical cross section.Yanovskaya et al.[1] investigated the velocity field arising in an infinite medium on explosion of an elliptical charge using a simplified model of the action of the explosion according to the theory of O. E. Vlasov. According to this theory the action of the explosion is instantaneous, and at the moment at which the energy of the explosion gases is transferred to the medium, the latter is regarded as an ideal incompressible liquid. During the explosion, the velocity field of the particles of the medium has a potential which, at all points within the region, satisfies the well-known equation of Laplace.

Directed fracture of rocks by blasting

“…Other possibilities for prior weakening of the contour zone of the borehole are given in [3,4] (see Table i, Ib, ic).…”