Surface and Underground Work.— Sur face work includes that class of excavation occurs in open air, and underground operations include such borings as are under groupd. Surface drilling may be applied for opening up canals, for quarrying purposes, for opening up ways for railroads and similar undertakings. Such work may necessitate the use of tripod, column and shaft-bar, quarrying machines, channelers, gadders and the like. (See QUARRYING). Underground work neces sitates the use of rock drills and compressed air machinery for purposes of sinking shafts, open ing mines, etc. In shaft sinking and tunnel work, as in driving headings and enlarging, it has been found that the column is the best means of mounting rock drills. These columns are simply round, extra heavy, wrought steel tubes with a suitable claw-foot or rosette on one end and either one or two clamping or jack screws on the other. Stoning bars and tripods are also extensively used for special features.
Submarine Work.— Submarine or subaque ous rock excavation is essential for converting shallow rivers and harbors into navigable waterways. The conditions under which sub marine rock excavation must be done are diffi cult to the last degree, calling for special appa ratus of unusual strength and endurance. This character of work is nearly always carried on where tides, currents, winds and storms are present in a varying degree, and these elements are practical obstacles to rapid and economical work. Add to these troubles deep water, ir regular bottom covered over with mud, sand and other shifting material, which fills in al most as fast as removed, and the undertaking is seen to be extremely difficult In the early days the usual method was to lower explosives to the surface of the rock and attempt frac turing by surface blasting. Later a form of
drop bore was introduced. This system has been abandoned for the more progressive method of drilling a hole and inserting the charge of explosive as is done in rock excava tion on land.
The removal of submarine rock is becoming a more important feature owing to the increas ing depth of ocean and lake-going vessels de manding deeper channels for harbors and rivers. A barge, scow or float fitted with a suitable frame to support the drill guides, drill, boilers and other auxiliary apparatus, is usually em ployed in submarine excavation. The barge is towed into place and anchored by means of cables, anchor chains or spuds, or a combina tion of these methods, depending upon the rise and fall of the tide, or the currents to be en countered. The form of framework depends largely upon the system used to feed the drills down, as the hole is cut into the rock. The height of the frame and the length of feed de pend on the rise of tide and the depth of water over the rock and the depth to which the hole is to be drilled.
Various styles of mountings are employed in submarine excavation work. The drills used for such operations are generally of the heaviest type, as the work to be done is always severe and difficult See Danl..