File:Bulletin (1910) (14595489907).jpg

Identifier: bulletin190unit (find matches)
Title: Bulletin
Year: 1910 (1910s)
Authors: United States. Bureau of Mines
Subjects: Mines and mineral resources Mines and mineral resources Mining engineering
Publisher: Washington U.S. Govt. Print. Off. (etc.)
Contributing Library: Gerstein - University of Toronto
Digitizing Sponsor: University of Toronto

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t can be gathered from experiments will be useful whenexploitation of deeper parts of the beds is undertaken. SURFACE SUBSIDENCE AND DRAINAGE. In Washington, except in rare instances, the maintenance of thesurface in an undisturbed condition is not requisite. In this respect,conditions of the coal industry of the State differ greatly from thoseof some other districts in which the desirability of leaving the surfaceundisturbed is so great that large quantities of coal are left in theground as pillars. In Washington permanent pillars are not leftunless it is necessary to protect railroads, streams, or importantbuildings. Subsidence frequently results in serious increase in ex-pense for draining the mines. In mining the first lift, called the water level, it has been the cus-tom to drive working places to the surface, and then to extract asmuch pillar coal as possible. As a result the surface subsides along 36 COAL-MIXING PROBLEMS IX THE STATE OF WASHINGTON. a>/z>/u/ AdmBudB unofy-
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WESTERN WASHINGTON. 37 the outcrop into a series of catch basins, from which water entersthe mines. This subsidence might not be serious if the water-levelgangways were kept open and the pillars below them remained un-cracked, as the water would then drain out to the surface. Fre-quently, however, these gangways have not been kept open, andsometimes it might be impracticable to do so. In some mines, more-over, the barrier pillar or chain pillar below the gangway is sobadly robbed that it no longer protects the lower workings from thesurface water. All the water that penetrates below the water-levelgangway has to be pumped out, thus increasing the cost of operation.Even when the water-level gangway is kept open trouble may arisefrom water entering as a result of subsidence. When the areabelow water level has been worked to a considerable extent and thepillars have been drawn, the roof caves and the resulting cracksreach upward for a great distance, sometimes for several hundredfeet. Th

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