スムースブラスティングにおける破壊機構の一考察

Abstract

In the first part of this study, the effect of decoupling has been studied. One of the main results obtained is as follows: the maximum tangential tensille stress produced at the inner surface of the charge hole by the detonation of the charge of which diameter is one half of the hole diameter (decoupling=2.0) is about 1/16 of that for the fully coupled charge, therefore, the extent of the radial crack caused by an explosion is decreased with increase of the degree of decoupling.Next, the effect of the guide hole which is drilled close to the charge hole on the the crack propagation has been studied. And it was clarified both theoretically and experimentally that even in the case where the cracks produced around the charge hole due to an explosion could not reach to the guide hole, other cracks could be produced independently from the guide hole along the direction to the charge hole. In the practical smooth blasting operation, a charge hole could be regarded as the guide hole for the stress wave produced by the explosion of the adjacent charge hole. Accordingly, the cracks would be produced previously from the inner surface of the hole ahead of the detonation of the charge in it. Then, the detonation of one hole after another leads to produce cracks from hole to hole and finally the explosion gas pressure will act for these cracks to develop as open ones, resulting in producing a smooth wall along these cracks.Lastly, a method to produce the crack only in the predetermined direction from the charge hole has been proposed to improve the effect of the present technique of the smooth blasting.