quarrying, open, or surface, excavation of rock used for various purposes, including construction, ornamentation, road building, and as an industrial raw material. Rock that has been quarried is commonly called stone. Quarrying methods depend chiefly on the desired size and shape of the stone and its physical characteristics. For industrial use (e.g., limestone for preparing cement), as the aggregate in concrete, or for road beds, the rock is shattered. Explosives are detonated in a series of holes drilled in the rock in a pattern designed to yield the greatest amount of fracturing. The rock fragments may be further reduced in crushing machines and sorted according to size by screening. For building stone, rocks that do not shatter are separated by blasting; for softer rocks or when explosives cannot be used (e.g., because they would disturb adjacent workings), a process known as broaching, or channeling, is used. In this process a line of holes is drilled perpendicular to the joints or cleavage planes of a formation; wedges are inserted into the holes and hammered until the stone splits off. This method was probably used in ancient times, notably by the Incas and the Egyptians. Much quarrying of ornamental stone today is done by using pneumatically operated channelers. After the vertical cuts have been made, gadding machines (working on the same principle) are used to make horizontal cuts. Wedges are then used to split off the long blocks, which are subdivided and removed. Wire saws are also used; these consist of several pulleys over which passes an endless steel wire. Holes are drilled in the rock, each hole being made large enough to accommodate a pulley and the shaft to which it is attached. The wire, extending from one pulley to another, presses down against the rock between them. As the cut is deepened by the constantly moving wire the pulleys are continuously lowered into the holes.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.
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