As is well known, the occurrence of local failure in uniform brittle materials, in particular in hard rocks, is caused by a factor such as stress concentration in areas of ensuing failure. A classification was given in [1] of directional breaking of rocks by blasting which revealed two principal variants for creating stress concentration leading to directional crack formation. The first is connected with mechanical weakening of the peripheral zone of the blast-hole or borehole in the directions of planned crack formation, accomplished either previously or at the instant of blasting. The second does not require the presence of stress concentrators in the peripheral zone of the blast-hole or borehole, and it is accomplished using special devices and attachments placed within the charge cavity. Superposition of these variants describe all of those directional crack formation mechanisms currently known with blasting of single blast-hole or borehole charges in a uniformly brittle material. Also described in [i] was one of the most effective and easily effected methods in practice for directional breaking using strong shells in blast-holes and boreholes having longitudinal cut slits orientated in the plane of planned failure. In this way the start of failure (radial crack initiation) was dependent on achieving a pulse of tangential tensile stresses in the blast-hole periphery of a certain critical value J, [i] which was calculated on the basis of considering the piston action of detonation products in the blast-hole cavity. However, strict argumentation of the conclusion about the contribution of the piston action of detonation products to the mechanism of directional crack initiation and unimportant wave and gasdynamic factors due to the limited size of the article was not given.