Page:The American Cyclopædia (1879) Volume V.djvu/76

 72 COLLIERY to sink the shafts as usual down to the solid rock, and then by means of a number of dia- mond drills, each driven by its own machinery, to bore a series of holes about 300 ft. deep. The bit used is concave, with circular grooves and cylindrical holes for the outlet and circula- tion of water, which is forced down through the centre of the boring rods, made of gas pipe 1 in. in diameter, and the holes when drilled are If in. The water takes up the fine sand or pulverized rock, carries it away from uDder the bit, and rises outside of the rods or pipe to the surface. In the W. shaft, which is 25 ft. 8 in. long by 13 ft. 10 in. wide, 35 holes are bored in five rows of seven holes in each, the outside rows being along the sides and in the corners, making the holes 4 ft. 3 in. one way and 3 ft. 6 in. the other from centre to centre. As soon as one of the holes has been bored to the required depth the machine is moved to the next, and the operation is con- tinued until all the holes in the shaft are drilled. Two or three machines can work at the same time on the same bed plate. No cores are removed, all the rock being ground to powder and carried off by the water, and it is therefore not found necessary to take out the rods very often. Steam may be used as the power to drive the boring machines, but in the lower levels compressed air is obviously much better. When all the holes are bored to a depth of 250 or 300 ft. the machines, pumps, Ac., are taken to the other shaft to bore the holes there. During the boring in the second shaft the rock is blasted and removed in the first, which requires much more time than the drilling. On the completion of the holes they are filled to the top with sand, and the work of blasting and removing the rock is done by removing the sand by means of a sand pump from all the holes, except those along the sides and in the corners, to a depth of from 3 to 4 ft. Clay is then forced into each hole so as to made a plug 6 in. to a foot long, and on top of this a cartridge of dualline is placed and the holes are then tamped with clay. The car- tridges are connected together by wires lead- ing to a galvanic battery, and are all fired at once. The loosened rock is removed, and the remainder of the holes are then charged and fired in the same way, but only those on one side at a time. When all the holes have been fired, the miner begins again by taking out more sand, and the work goes on until the depth to which the holes have been bored is reached. The drilling machines are then brought from the other shaft, and the holes are again bored from 250 to 300 ft. deeper. No diffi- culty is found even at a depth of over 1,000 ft. in maintaining a rate of speed in sinking of from 50 to 60 ft. a month, which is 50 per cent, greater speed than has been attained in hand drilling through similar rock in shafts of equal sectional area, which in these shafts is 224 and 364 sq. ft. The greatest depth blasted in one month was 112 ft., and 125 ft. of the shaft was timbered in the same month. The cost per foot is about the same as by hand drilling, but the great advantage of this sys- tem is the saving of time, which is a considera- tion of immense importance in an operation involving the outlay of so much money. By the old system, as only a few men could work at a time in so small a space, the sinking of the shaft was very slow, the large capital in- vested was unproductive, and the profits to be derived from the mine in active operation were lost. When it is necessary to put in metal casing or tubing to dam back water, quick- sands, or decomposing fire clays, such as are met with in some of the bituminous coal fields at great depths below the surface, the usual method is employed. The casing is taken down the pit in sections and bolted together to form the tube at the bottom ; and this may be done below or above the shield. When the surface water has been properly stopped and all the heavy springs dammed back as they are met, the water will not be difficult to manage with buckets, even when great springs or under- ground watercourses are met with. But when the accumulation of many streams descends to the bottom of the shaft, any great feeder of water might overcome both buckets and pumps. The purpose of such walling, cementing, and tubing is to avoid the use of pumps either during sinking or permanently, because the water can be drained more effectively. This method of damming back the water has not been used in the anthracite mines of Pennsyl- vania, and rarely if ever in any American pits, most of which are square or oblong, and both sinking and permanent drainage are effected by pumps, at great and constant cost. The best pump for sinking is that known as the Cornish bucket pump, with the column pipe larger than the working barrel, so that both the buckets and the clack valve may be drawn to the surface through the pipes, if necessary for repairs, in case of accident. The pump rods must work inside of the pipes in this plan. This pump may be greatly improved for ordina- ry permanent lifts by reversing the above or- der and providing a working barrel of double the capacity of the pipes, and combining the plunger and bucket principle in the working barrel. Thus the down stroke forces one half the water from the barrel, and the up stroke draws the remainder. This is the cheapest, simplest, and most effective style of pump for all purposes, worked from the surface. But most of the large collieries of the world are now drained by the common Cornish plunger or force pump, the principle of which is well known. Some of these are operated by complicated ma- chinery, but the best are those in which the pump rods are connected directly with the steam piston of the engine, without additional gearing. These are used to force water 500 ft. high, but 200 to 250 ft. vertical height is far more economical and safe. Mining pumps of a new and far more effective style have been