MINE TIMBERING IN THE UNITED STATES.
By John Birkinbine, M. Am. Inst. M. E.
WHEREVER mining is carried on, timber is used as a support to ground which has been disturbed by excavation. The quantity, the size, the character of the wood, and the method of framing or placing the limber are influenced by the abundance or scarcity of convenient forests, the width of the mineral vein matter, lode, or lens to be removed, by the dip of the strata, by the quality of the vein and the adjoining rocks, and other considerations.
In operations prosecuted where the material excavated is such as to safely sustain the roof or walls by pillars, the quantity of mine timber employed may be insignificant, and the application of supports may be confined to single props or stulls. In others, the character of the vein matter or of the inclosing walls, and the length, width or pitch of the deposit of mineral to be won, may demand liberal quantities of mine timber, applied in various methods which add considerably to the cost of mining.
In open-pit excavation timber may be required for other purposes than supports, and in some pits supplemental drifts need to be protected; but as this paper is intended to discuss timbering applied as artificial support to unsafe ground in mining, the comparatively limited employment in the "open" may be dismissed.
In passing, notice should, however, be taken of the liberal application of wood in connection with mining operations independent of that used for support. Below ground the ventilating and drainage systems, the landing platforms, the chutes or winzes, the tramway tracks, sleepers, and the mine cars; and above ground the shaft or head houses, breakers, power houses, trestles, shops, dwellings, sorting platforms, bins, railroads, etc., all demand rough timber or sawn lumber. Ample wood for other uses than support is an essential for mining, and the absence of this may cause mines to lie idle which, under more favourable conditions, would be active.
So important is an ample supply of timber, that the general custom in wording mining leases has been to specify whether or not the lessee will be permitted to cut timber from the lands of the lessor for use in the mine or mines; and the right to thus employ the surface resources for the prosecution of underground operations, is considered a valuable feature in the rentals of many mining properties. An abundance of mine timber so closely influences the success of mining that some large companies buy outright, or purchase "the wood leave" of timber lands, and maintain extensive equipments of machinery and considerable forces of men to fell trees, and cut, frame, and handle the necessary timber.
There are mines, wrought entirely underground, which require but little, if any, timber to sustain the walls or roof, as shown by the illustration on page 22; but even in these there are usually portions of the excavation where artificial supports must be applied, and in this class of workings, shafts or slopes may necessitate heavy and costly framing for protection. On the other hand, even placer deposits which are worked
