336 



MINE. 



Mines of working by means of numerous winnings, the quantity 

 Coal - j of water which is likely to be found in a new winning 



~^'C*" "* may be estimated from what is found in the other 

 >* inning a *. ,. . . *_ rip 



coal-field, works adjoining ; and it has been found from experi- 

 ence, that even in opening up colleries in new districts 

 of coal fields, the water found in sinking is generally 

 such as can be drawn by pumps of from ten to fifteen 

 inches diameter, excepting in cases where the strata are 

 connected with rivers, sand-beds full of water, or 

 marshy ground. 



In cases where feeders of water proceed from rivers 

 or sand-beds, they can be prevented from descending 

 the pit, and therefore the growth arising from these 

 sources needs not be taken into the calculation of the 

 water to be drawn ; and it is found in sinking pits, 

 that although the growth which cannot by any means 

 be prevented from descending into the mine, may be 

 very great, and even so great as to exceed the power of 

 the engine for some time, yet as the extra flow of water 

 frequently proceeds from the drainage of fissures, these 

 gradually abate to a moderate quantity. An engine 

 having eight or ten hours' work drawing water each 24 

 hours, is reckoned moderate and comfortable for a new 

 colliery. In the course of years, as the workings ad- 

 vance, many fissures are cut, and as the coal is exca- 

 vated towards the crop, and approaches the alluvial 

 cover, a constant increase of water is found, so that a 

 colliery which has been long at work frequently be- 

 comes very heavily loaded with water, and the machi- 

 nery is required to go night and day. When a colliery 

 is thus loaded with the ordinary daily growth of water, 

 its situation is rendered dangerous and uncomfortable, 

 to obviate which, the power of the engine is either in- 

 creased, or additional engines erected. In practice, 

 working barrels are seldom used of greater diameter 

 than 18 inches, and in place of having pumps so large, 

 many of the mining engineers prefer having two en- 

 gines with less powers, and moderate-sized working 

 barrels, on account of the unwieldy nature of such 

 heavy machinery, and the great extra tear and wear at- 

 tending them. 



The extent of the winning to be made, as to depth, 

 and the power of machinery to be employed, having 

 been determined upon, the mode of sinking engine pits 

 has next to be described. 



First, When the depth is moderate, and the process 

 comparatively very simple. 



Second, When the depth is great, and the process 

 laborious and intricate. 



Shape of In any winning, the figure of the engine pit is a pri- 

 mary consideration. In winnings of a moderate depth 

 many forms are used, as circular, oval, square, octago- 

 nal, oblong rectangular, and long-elliptical. 



In pits of inconsiderable depth, and where the allu- 

 vial cover is of a firm and dry consistency, any shape 

 thought the most convenient may be used ; but in all 

 deep pits, no shape but the circular ought to be used. 

 Indeed, when water requires to be stopped by tub- 

 bing or cribbing, no other shape will do, the circu- 

 lar shape being the only one which presents a uniform 

 resistance in all points to the uniform and great pres- 

 sure of water even the elliptical shape, where there 

 is but little difference between the two diameters, is 

 not suitable ; it has been tried, and has always given 

 way when exposed to pressure of any considerable 

 degree. Besides, the circular shape renders the pit 

 stronger in the shaft walls, and is likely to be less 

 injured than any other shape, in the event of the shaft 

 being shaken by a sit or crush arising from the failure 



Mine) ol 

 Coal. 



of the pillars left in working the coal. As to the size* 

 of engine pits, the smallest should be ten feet diameter, 

 to admit the pumps to be placed in the lesser segment, 

 and the coals to be drawn at the larger one, as in 

 Plate CCCXC. Fig. 9, which is termed a double pit; 

 but if much work is to be done in drawing coals, and cccxc: 

 particularly if the coals are large, it would be an eco- fig. . 

 nomy to have the pit wider than ten feet. When a pit 

 is to be divided into three divisions, one for the engine 

 pumps, and two for drawing coals, as in Fig. 10, which Fig- 10. 

 is termed a triple pit, it would require to be twelve feet 

 diameter. If it is to be divided into four divisions, and 

 made a quadrant pit, as in Fig. 11. with one division Pig' 'I- 

 for the pumps, and three divisions for ventilation and 

 coals drawing, it would require to be fifteen feet dia- 

 meter. These sizes of pits are regulated by local cir- 

 cumstances, and by the output of coals proposed to b 

 raised. 



In sinking engine pits, the first point is the mode Stoking 

 of passing through the alluvial cover. If it is of a firm " 

 and dry consistency, the process is easy, whether the j 

 depth be great or not. As all engine-pits require to be 

 particularly well executed, and every part of the work 

 done in a substantial manner, the shaft which passes 

 through the' alluvial cover ought to be secured with 

 masonry of jointed ashler, with the joints accurately 

 bevelled to the centre of the circle which forms the area 

 of the pit. The stones used are from a foot to sixteen 

 inches in thickness, about a foot in depth, and of any 

 convenient length. The pit is therefore begun, and 

 sunk of a circular form, through the alluvial cover, of 

 such an extra width as to admit the thickness of the 

 masonry or stone cradling, as it is termed. When the 

 depth is about 12 or 15 feet, the bottom is made 

 level, and a ring or crib of oak or elm, about four and 

 a half inches thick, and ten inches broad, laid in the 

 bottom. Upon this the ashlar is built upwards to the 

 mouth, and all the void betwixt the ashler and the earth 

 walls firmly beat up with clay. The next operation 

 is to sink again, keeping the sides about three inches 

 inside of the perpendicular of the ashler walls. This 

 sinking is carried down from three to nine feet, ac- 

 cording to the consistency of the cover, and when the 

 distance is fixed upon for another crib, the pit is widen- 

 ed out at the bottom, so as to admit the second crib to 

 be laid exactly in a perpendicular direction below the 

 other ; and when this crib is laid in its place, about 

 three or four feet in breadth is taken out from one of 

 the sides, and in this a pillar of ashler is built resting 

 upon the lower crib, and supporting the upper one. 

 The same thing is done on the side immediately oppo- 

 site, and then at the other quarters of the circumfer- 

 ence, after which the intermediate spaces are widened 

 and built up. In this manner the pit is sunk until the 

 rock head is found, when it is made level, and the lower 

 part of the ashler rests upon it. When stones can- 

 not be easily procured, hard bricks are substituted, ten 

 inches or a foot in length, with a bevel to suit the ra- 

 dius of the pit. When ashler is built in stages, as be- 

 fore described, the under building may be sometimes 

 done with three pillars, and then filled up around; 

 but when no cribs are used, as is sometimes the case, 

 very narrow pillars are built up, to secure the mason- 

 ry above. 



When the cover is not very firm, the stages sunk at 

 a time, and built up with masonry, will not admit of 

 being more than from two to three feet, and when the 

 cover is of such a kind as not to admit of this mode of 

 operation, a different plan must be adopted. 



