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Mines and Mining

feet, galleries, military, shaft, enemy and explosives

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MINES AND MINING, Military. In all periods of the history of warfare, particularly in siege operations and the somewhat similar operations in trench warfare, recourse has been had to the use and construction of subterranean passages, either as a means of penetrating the lines of the enemy, or to avoid a dangerous advance under fire at the surface, or for the destruction of a hostile position by the use of explosives, or to prevent on the part of the enemy undertakings such as those already de scribed. These operations constitute military mining, and the charge of explosives set off under a position of the enemy is known as a mine. While any of the devices and methods employed in commercial mining may be used in appropriate military situations, military min• ing is dominated by the consideration of sim plicity— for complicated tools cannot be brought up to the battle-line — speed and incon spicuousness. In addition, by far the greater part of the work is done in soil which is suffi ciently soft to present relatively little difficulty to excavation, but which manifests a constant tendency to cave in. This tendency is accentu ated by the continual disturbance of the soil by artillery fire and the countermines of the enemy. Accordingly the reinforcement of the walls of his excavation is generally among the chief problems of the military miner. The methods used are much the same, whether the excavation is a vertical shaft or an approxi mately horizontal gallery. They fall into two general classes. In one casings are inserted as the work progresses. These consist of four lengths of stout planking surrounding the exca vation. Two opposite lengths are provided with mortises and the other two with tenons. In the other type of mining, longitudinal planks known as sheathing are held in place by frames of strong timber.

Galleries are divided into great or grand galleries (6 feet high by 3% feet); half gal leries (41/2 feet by 3 feet) ; branches (3% feet 'by 2% feet); and small branches (2% feet by 2 feet). The smaller galleries are often excavated by earth augers; the larger ones by ordinary excavating tools reduced in size so as to be adapted to use in a confined space. An

especial digging tool known as the push-pick is also employed. The direction of galleries is determined by the ordinary surveying instru ments used on the surface, due allowance being made for the unreliability of the compass un der ground. The targets are of course slits through which an artificial light shines. The azimuth is transferred from the top to the bot tom of a shaft by means of a pair of plumb lines, which are oriented by compass and map above ground. Ventilation is essential, and is secured by various mechanical means, or in a system of galleries with two or more outlets, by a fire near the upper end of a shaft. In difficult places, air may be pumped in by a hose. Respirators may be worn in case of emergency. Drainage is secured by sloping the floors of the galleries and supplying them with gutters. If it is not possible to make all the galleries slope toward the entrance, a sump is dug from which the water is pumped or carried in buckets. The lighting of galleries is often a difficult problem. on account of the nearness of explosives and the difficulties of ventilation. Electric lights arc often used. Where it is possible, daylight is reflected into the gallery by mirrors or white surfaces, and the walls are whitewashed. The disposal of the excavated earth is often a diffi cult problem. It is usually taken away in sacks or relays of wheelbarrows. Sometimes small narrow gauge railways have been used.

The mine chamber is nearly cubical or of the shape of a cylinder with an altitude twice its radius. It is often simply the end of a gallery or shaft. The charge is usually some high ex plosive such as dynamite or trinitrotoluol. It is set off by a detonator and primer, usually fired by electricity, though a powder fuse may be used. The charge is tamped by obliterating from 6 to 10 feet of the passage leading up to the chamber.

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