Sometimes a corner break is made by putting in two of the
regular V-shaped holes in the lines of the proposed break and without
the use of the corner hole. A useful application of this system is in
splitting up large masses of loose stone. For this purpose the
V-shaped grooves are sometimes cut in four positions and breaks are
made in four directions radiating from the center of the hole as shown
in Fig. 12. In this way a block is divided into four rectangular
pieces.
[Illustration: FIG. 12.]
Though the new system is especially adapted to the removal of heavy
masses of rock, yet it has been applied with success in cases where
several light beds overlie each other. In one such instance 10 sheets,
measuring in all only 6 ft., were broken by a blast, but in cases of
this kind the plug and feather process applies very well, and the new
system, when used, must be in the hands of an expert, or the loss will
be serious.
Referring again to our stone step, let us imagine a case where this
stairway runs between two walls.
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