MINE TIMBERS versus CONCRETE AND STEEL 



CHE modern up-to-date mine is more and more, where possible, using con- 

 crete and steel in place of timbers. If this can be generally done the 

 amount of timber which will be saved, according to statistics obtainable 

 in the anthracite regions in Pennsylvania, will be approximately that cover- 

 ing a hundred and fifty thousand acres. It is an axiom that the price of mine 

 timbers is rapidly increasing and the supply as rapidly decreasing. It has 

 been estimated that the cost of timber per ton of coal mined is eight cents. 

 The saving in mine timbers by the use of concrete and steel is readily conceded. 



The accompanying diagram (Fig. 1) shows the various factors which 

 make the timbering of a mine so costly. 

 Decay is the greatest of these; it can- 

 not be prevented; it can only be mini- 

 mized. Foresters believe it can to a cer- 

 tain extent be overcome by ''peeling," 

 by seasoning, and by treating with oils 

 and chemical salts ; but it is produced 

 by bacteria and fungi, which perhaps 

 are in the timber when cut or passed on 

 from other decaying timber in the mine, 

 and which grow through checks, cracks 

 and nail wounds. All this can, to a cer- 

 tain degree, be overcome by preventive 

 measures ; but the greatest element in 

 the decay of mine timbers is tlie condi- 

 tion which prevails in the mine it- ^^^' ^' 

 self, the lack of ventilation and, above all, the alternating states of damp- 

 ness and dryness. In the great mine disasters which we constantly read of, 

 the cause is frequently given as decaying timbers which rot and fall burying 

 miners and creating a condition in the mine itself which takes much labor 

 and money to overcome. With concrete and steel "timbering" of course no 

 element of decay enters in. 



From an inspection of the diagram it will be seen that breakage, or 

 "crush" or "squeeze" due to a sudden fall of coal and of rock, is the next 

 largest factor. Many times the mine timbers are broken only after they 

 have been weakened by decay. Sometimes new timbers are crushed. Concrete 

 and steel would the better withstand the shock of this sudden deluge. Under 

 breakage, also, wear must be considered. The cross ties in the main haulage 

 ways, the wooden rollers, the drum laggings, are worn by constant contact 

 with the ropes and cables, and concrete construction would obviate many of 

 these difficulties. 



Insects also are a factor in the waste of mine timbers. They are usually 

 brought into the mines in infested timber, and passed along indefinitely to sound 

 wood. The waste through decay or fracture of timbers though many times 

 confined to but one part of the set, often renders the whole set useless. The 

 sizes of timbers are sometimes too large, sometimes too small to support the 

 weight, sometimes badly and carelessly set. And this inefficiency affects life 

 and property. 



411 



