Civil Engineering Reference
In-Depth Information
determined by the thickness of the block and the layer formation. The depth of the
hole is also important. A 'rimmer' is knocked into the hole. This makes ruts in the
wall of the hole along which the block will crack. The hole is then filled with gun-
powder, rather than dynamite. Gunpowder has a lower rate of burning and gives a
more muted explosion. Dynamite causes microscopic hairline cracks in the blocks
which decrease their strength, although for crushed stone this is of no consequence.
Soft stone such as marble, limestone and soapstone can in many cases be
removed with a wire saw. This consists of a long line of diamonds which cut
20-40 cm an hour. For rock rich in quartz, e.g. granite, a jet flame can be used. The
equipment for the jet flame is a nozzle mounted on a pipe in which there is paraf-
fin or diesel under pressure. The temperature of the flame is about 2400°C, and
the speed is very high. A jet flame smelts out about 1-1.5 m
3
stone block per hour.
Dividing and cutting blocks
Stone is seldom used as an unfinished rough block. It is usually divided up into
smaller units. This can be done in several ways.
Wedging
Wedging is shown in Figure 7.2. The alignment of the wedges happens in three
stages. It requires skill, good knowledge of the nature of the stone and the direc-
tion of its layering, and much work.
Figure 7.2: Dividing a block with wedges: (a) the seam for the wedge is made; (b) the wedges are
knocked in; (c) the block splits.
