The article in the body of the work is perhaps one of the most useful essays that has hitherto appeared on this important subject. We shall therefore limit ourselves in this place to an account of some improvements as to the winning and working of coal, with which we have been favoured by an eminent Miner.
1. What is generally called the winning of a coalery, is the draining of a field of coal, so as to render the several seams accessible, by pits to be sunk from the surface.
In order to determine the most eligible situation for a winning, it is requisite that the field of coal to be obtained by it, should have been previously explored by the methods described in the body of the work.
Supposing the field of coal (see profile A, B, Plate LIX. fig. 1.) to have been explored by the borings a, b, c, d, and the crop of the seams e, and that it is determined to win the tract of coal in the seams C, D, extending from the ravine at a, to the crop of the seams at e.
In this case an adit or day-level drift or mine r, f, is set in from the ravine near to a, and is carried forward in a direct line until it cuts the seam C at f. This day-level drift also cuts the bore-hole b at f, by which the stratification from b to f is drained, and a coal-pit is then sunk upon the bore-hole b, f, from the surface to the seam C, with great facility.
In prosecuting the working of the coal from the pit f, towards the bore-hole C, a down-throw slip-dike g, is met with, which depresses the seam C to E. The extent of this depression is ascertained by driving an horizontal stone-drift from where the seam C terminates at the dike g, g to h, and by putting down the bore-hole i.
The day-level drift is then continued from f till it cuts the seam at E, and by carrying it forward to the bore-hole C, another coal-pit, c, j, is obtained in the same manner, as at b.
From j the working of the seam is carried on progressively until the upthrow slip-dike k, k is met with. An horizontal drift is then extended from l to m, from which one boring is made upwards to the seam C, and another downwards to the seam D, by which the position of both seams is proved. The day-level drift may then be extended from the pit c, j through the dike k, k into the seam D to n, to open out the bore-hole d, on which another coal-pit may be sunk through the seam C to the seam D, which may also be wrought by the pit d, n, as well as the seam C.
The workings in both seams may now be carried on from the pit d, n till they encounter the whin dike o, o, which must be set through by carrying a drift through it on the same line of ascent as the seam leading to it, as dikes of this description seldom alter the level of the strata which they intersect. From the whin dike the working of both seams may be carried on without further difficulty to the crop of the coal at e.
This tract of coal, or coalery, may now be supposed to be wrought to the utmost extent that is available, by the day-level winning, and that it is determined to win the coal lying below this level by a steam-engine.
An engine pit F, G, is, therefore, sunk upon the day-level drift f, and through the seam C to D, below which the pump-well or lodge H is dug. After the sinking of the engine-pit is completed, a drift is carried forward towards the rise of the seam to L, where it will cut the bore-hole b, f, and allow the coal-pit to be sunk from f to L, and the dike g, g having been already explored, the water course, or engine-level drift, is carried forward from the lodge at H, till it cuts the lower seam D at K, and thence forward in the seam D till it cuts also the bore-hole c, j, and the upthrow dike k, k successively; by which the whole extent of the seam D from G, by K to k, is drained and wrought by the pits b and c which have been sunk by the bore-holes discharging the water from them into the engine-level.
It will be readily seen by referring to the profile, that the engine lifts the water no higher than the day-level drift f, by which it is discharged from the pump at r into the day-level drift, and thence into the ravine at a. The dip part of the upper seam C may also be won as far as S, by extending the engine level drift from the lodge H to S, as shown by the dotted lines.
This mode of winning coaleries can however only be pursued where the localities of the situation render it eligible; but as it frequently happens that coaleries are to be won where the surface of the ground is so nearly horizontal as not to admit of any benefit being derived from a day-level drift, it is necessary in such cases to draw the water to the surface by one or more steam-engines, as the case may require.
It frequently happens in situations of this kind, as in the neighbourhood of Newcastle-upon-Tyne, that great difficulties are encountered in the sinking through quicksands and very large feeders of water, some of which have been ascertained to communicate with the river Tyne.
The quicksands lie at various depths from the surface, as low as 30 fathoms and upwards; but the largest feeders of water are seldom met with at a greater depth than 50 fathoms. The quicksands vary much in thickness, as the feeders of water do in quantity; but a feeder which discharged nearly 4000 gallons per minute has been met with in one shaft. As it would be impracticable to draw such a quantity of water from the bottom of those deep mines but at an expense which could not be afforded, they are always stopped back by what is called tubing and wedging, which is done by fixing watertight cylinders of wood or cast iron within the circumference of the shaft, so as completely to dam back the water, and prevent its falling to the bottom of the pit. In some cases, water has been dammed back in this manner to the height of 70 fathoms, and at an expense of L120 per fathom, or upwards. Quicksands are also passed through and dammed back by tubs or cylinders of wood or cast-iron, which are generally lowered down by ropes from the top of the pit, until they pass through the sand, and rest on the solid strata below.
As the sinking of pits under the above circumstances is attended with great expense and difficulty, no more are sunk than what may be barely necessary to work the destined part of coal below, and in some cases a whole coalyery is wrought by one pit.
In situations of this kind, where the whole of the operations of the mine, as the drawing of coals and water, as well as the ventilation of the workings, are to be carried on by one pit, it follows that such pits must be made of large diameter, and divided into separate shafts.
They have therefore been sunk from 9 to 16 feet diameter, and divided into two, three, and four separate shafts by brattice, or partitions of deal boards, according to the circumstances and extent of the mine.
Plate LIX. fig. 2. represents a pit of 9 feet diameter, which is divided by the brattice or partition a, b, into a coal shaft A, and an engine shaft B.
Fig. 3. represents a pit of 12 feet diameter, divided by the partitions a, b, c, into two coal shafts AA, and an engine shaft B.
Fig. 4. represents a pit of 16 feet diameter, divided into three coal shafts AAA, and an engine shaft B, by the partitions a, b, c, d.
In practice it has been found that the mode of dividing the shaft, as shown by fig. 2., is the most eligible.
Coaleries have been wrought to a great extent by pits of this description; the workings have been sometimes carried to the distance of two miles from the bottom, and the height of the air course has exceeded thirty miles. Several of the pits constructed in this manner in the Newcastle district exceed 100 fathoms in depth, and some are nearly 150 fathoms deep.
Most of these large double pits have powerful steam-engines upon them, for pumping water; they are generally of Mr Watt's construction—double power—and usually exceed 100 horses' power, besides one or two more of the same construction for drawing coals, of from 20 to 30 horses' power.
As the principal feeders of water lie near the surface, the pumping engine is generally erected when the sinking commences. The pumps, which are now invariably made of cast iron, are suspended by ropes, and lowered down by capstans, as the sinking proceeds.
Rods of fir timber 6 or 7 inches square, called ground spars, are placed (according to the size of the pumps they have to bear), one on each side of the column (set) of cast-iron pipes, to which they are firmly tied at every 9 feet by cords, called lashings. A five-fold block is fixed to the top of each ground-spear, the tail-ropes or falls of which pass round capstans placed near the top of the pit, by which the column of cast-iron pipes in the pit can be raised or lowered at pleasure. A column of pipes, generally called a "set of pumps," suspended in this way, is as steady as if it was firmly fixed in a frame of timber. Pumps of 16 to 18 inches diameter may be carried to the depth of 50 fathoms in this way, if necessary; but in this case it is expedient to add a third pair of blocks.
It is, however, only in cases of necessity that columns of pipes of this length are suspended on ground-spears, and ropes, as, if circumstances will permit, the column of pipes ought to be firmly fixed in a cistern at the depth of 25 or 30 fathoms; but in many cases no dry situation can be met with in which to place the cistern, till the pit is sunk below the level of the large top-feeders, and consequently below the tubbing, in which it has not yet been found practicable to fix a cistern.
While the pipes are suspended in the manner above described, they are called sinking sets; after they are fixed on cisterns they are called standing sets. Fig. 5. represents the method of suspending cast-iron pipes for sinking. aa, The iron blocks and ground ropes, with their falls bb, leading to the cisterns placed in any convenient situation near the top of the pit.
dd, The iron UU's which connect the blocks with the tops of the ground-spears ee.
c, The hoggar-pump, generally made of fir-staves, and fixed by an iron flange and bolts to the uppermost cast-iron pipe. Always when the increased depth of the pit requires an additional pipe, the hoggar pump is taken off, and put on the top of the new pipe again.
f, The hoggar or leathern case, which delivers the water into the laundry box.
g, The flexibility of the hoggar enables it to accommodate itself to the gradual lowering of the pipes as the depth of the pit increases.
hh, The bottom rods which connect the ground-spears with the wind-bore of the pumps. The wings ii are cast upon the wind-bore, for the purpose of attaching the bottom rods to it by slots or bolts.
kkk, The lashings by which the pipes are fixed to the ground-spears.
m, The pump rod, wrought by the engine.
n, The snore-holes of the pump, which are plugged up, or kept open, as may be required by the sinkers.
Fig. 6. shows the method of fixing a standing set of pumps.
a, The bunton, made of the root end of a large oak, ten feet long and three feet square; but the larger the better. The inner end, which is the thickest, is placed in a recess cut in the stone, and the outer end is supported by an abutment of solid stone b, left in the pit.
The inner end of the bunton is firmly held down by wooden props cc.
f, The cistern in which the pumps are placed, and into which the water from another set, either of sinking or standing pumps, may be delivered. The cistern is firmly fixed upon the bunton, and a recess is made in the side of the pit to receive it, and props d may be placed to fasten it down. The larger the cistern the better; there is no rule for regulating its size; but it ought, if possible, to be large enough to contain as much water as will supply its own pump, until the pump below delivers into it, when the engine begins to work.
g, The set of standing pumps placed in the cistern.
hhhh, The buntons with their cross collarings, iii.
The buntings have one end fixed in the shaft wall, and the other is fastened to a cleat k, which is nailed to the shaft brattice ll.
Fig. 7. shows a plan of the manner of fixing a bunton and cistern for supporting a stand-set of pumps.
aaaa Shows the recess cut in the side of the pit, with the bunton laid in its place. The inner end of the recess is cut dove-tailed, and the bunton wedged into it, so that it is prevented from moving forward by the shock of the pumps, when the engine is at work. The dotted lines show the situation of the cistern when placed on the bunton.
b, The pumps in the cistern.
cc, The situation in which the succeeding sets of pumps may be placed.
d, The main or shaft brattice.
e, The bunton to which the cross collarings ff are nailed, for securing the pumps in their proper position.
As all the operations of the engineers should be performed in the engine shaft, without interrupting the drawing of coals in the other shafts of a double pit, as much room as possible should be preserved in the engine-shaft, by occupying as small a space in collaring the pumps as circumstances will permit.
For this purpose, iron stirrups have, for some time, been introduced in the place of cross collarings of wood, with great advantage.
If the cross collaring g, fig. 7. was extended to the brattice, as shown by the dotted lines, and fixed to it by a cleat, in the same manner as the bunton e; by putting an iron stirrup round the pump with its ends passed through the collaring g, and fastened behind by the screw nuts n, the bunton e, and cross collarings ff, may be dispensed with, which will give much more room in the engine-shaft.
2. Thus far we have described the most improved methods of winning a coalery of considerable extent and depth. There are two distinct methods of working the coal, the narrow, and the long or broad way. Working the narrow way is commenced by cutting passages through the coal, both lengthways and across, leaving rectangular pillars between the passages. By the first operation one-third of the coal is generally taken out; but where the strength of the coals and the firmness of the roof will permit, a greater or less proportion of the pillars which remain are afterwards removed, commencing with the most distant, and ending with those nearest the pit. By the broad way, the coal is wrought out at once, frequently for a length of 150 yards in one face, without leaving any pillars of coal to support the roof. The former method is adapted to beds of coal which occur at a considerable depth beneath the surface, from 50 to 150 fathoms; the latter to beds which lie nearer the surface, especially if they have a tolerably strong roof.
The mode of working by the narrow way, as generally practised both in the Scotch and English coaleries, and the general principle of ventilating works so wrought, are so fully described in the body of the work, that we find little to add in this place. But as an improved system has, within the last eight years, been brought to a state of high perfection, by the ingenious Mr Buddle of Wall's End, we are happy to be permitted to avail ourselves of the description of it, as given, under his correction, by Mr Griffith, in his excellent Report on the Leinster Coal District. By means of Mr Buddle's plan, from seven-eights to nine-tenths of the coal is at present raised; whilst, eight years ago, but one-half, and frequently less, was all that could be obtained; and, therefore, through his exertions, the coal owners of the north of England may be said to have increased their property at least one-third; as more coal than is equal to that proportion, is now raised out of the same area, than could be effected according to the old system.
Mr Buddle's ingenuity has not been confined to the improvement of the method of working coal; he has also introduced a more perfect system of ventilation; and has put in practice many simple but excellent contrivances, not only to prevent the accumulation of inflammable air in any part, but also by using hanging doors, which yield to the blast of inflammable air, and are not carried away, to prevent a general explosion throughout the mine when any cavity containing inflammable air is broken into accidentally, as the works extend; by this means, when the first blast is over, the lives of the colliers and horses in the distant parts are preserved. We shall, at present, confine ourselves to the different methods of working and supplying fresh air to the most distant parts of an extensive coaly, by one or more pits.
Plate LX. fig. 1. represents the plan of the improved system of working and ventilating coaleries in Newcastle-upon-Tyne.
The circle below the letter A is intended to represent a pit or shaft, divided from top to bottom by a boarded partition nicely joined, so as to prevent the communication of air from one side of the pit to the other. Through the right-hand division of this pit, which is called the downcast, the air descends. Having passed through all the excavations that have been made through the mine, which are represented by the white or uncoloured divisions, it passes up the left hand division of the pit. To aid the draught of air, a great fire is made in the furnace at B, which rarefies the air, and causes it to ascend more quickly through the upcast pit or division. The arrows point out the direction of the course of the air throughout the mine, and the red marks are walls or stoppings, built to force the passage of the air in particular directions. The dark coloured parts in the plate represent the unwrought part of the coal.
The principal advantage of the new mode of working is, that it divides the mine into any convenient number of districts, each of which is to be wrought out in its turn, and the roof suffered to close in. But to prevent the crush created by the falling in of the roof in one part, from communicating with and injuring the coal in another, a great protecting pillar or wall of coal is left between each division. By examining the figure, the several divisions or districts may be easily traced, by observing the line of large pillars.
The first operation of working the coal is represented clearly in the district E. From the bottom of the pit two parallel passages are cut, three yards broad and twelve yards asunder, at convenient distances; cross cut passages, or headings are driven to connect the parallel passages, and thereby create a complete circulation or current of air.
The parallel passages are then continued until air again becomes deficient; a second heading is then cut, and the first is carefully closed up, so as to force the air round a lengthened circuit. This process is continued uninterruptedly round the district, as represented in fig. 1. The district being thus surrounded, broad passages, called boards or rooms, are then commenced at the lower end of the district, and are cut at regular distances upward, towards the parallel passages first described. The breadth of the boards, and that of the pillars of coal left between them, is continually varied, according to the nature of the strata which form the roof and floor of the mine. In the district F, the boards are represented in progress; this is also the case in the district K; when the boards and headings have been made throughout a whole district, this is represented by those of G and H. The next operation is to remove all the pillars; those at the farthest extremity of the district are first cut out; this operation is performed, either by commencing at one end, and proceeding regularly to the other, or by cutting the pillar in the middle, and setting a number of men to work at it. But this must depend on the strength of the roof. A few of the pillars of the district BG are represented as being removed, and the whole of the coal that could be carried away is represented as being wrought out of district I, nothing except the trifling quantity represented by the black lines being left behind. When the pillars of the district G have been wrought out nearly to the boundary pillar, between the districts I and G, the boundaries should be divided by boards and headways, and a considerable portion of them may thus be removed.
Owing to the frequent mistakes of sinking pits in improper situations, the pit A is placed in a position with respect to the coaly, that is frequently seen in practice, namely, a great part of the coal field lying to the dip, or under the natural water level of the pit. By observing the direction of the dip and rise, as represented on the plan by the great arrow, it is evident that, without some contrivance, no coal could be level or water-free below a line drawn across the pit A, at right angles to the arrow, and consequently, half the coal of the districts F and G, and the whole of the district K, must have been left behind. To overcome this evil, the pit A is supposed to be sunk below the coal to a depth more than equal to the level of the coal at M, and a drift or passage is supposed to be horizontally cut through the strata beneath the bed of coal, till it meets the coal at M; by this means the district K may be freed from water. Had the pit been originally sunk nearer to M, all the expense and trouble of driving the stone drift would have been avoided.
It frequently happens, that the stoppages or walls built to direct the ventilation, interrupt the communication from the various parts where the coal is
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* There are, however, many reasons which may render it expedient, in particular cases, to avoid fixing the engine-pit on the lowest level of the coal-field, as when a slip or dike divides a small portion of the lower part of the field from the rest, &c. In this case, the coal wrought to the dip of the pit may easily be brought up to the drawing-pit by a high-pressure engine, fixed in some convenient station, at the head of an inclined plane. working to the pit bottom. When this happens, a door is placed at a convenient distance on either side of the wall, which may then be removed, and the leader of the coal waggons, as he passes along, opens the first door, and, having led his waggons past, shuts it, and then opens the second door, by which means the regular ventilation of the mine is constantly preserved.
According to the plan just described, very extensive coalyries are worked from one pit; and passages or boards, amounting in the aggregate to 30 miles in length, are perfectly ventilated by a single pit.
The mode of passing the air through the different passages or boards, varies according to circumstances. When a very quick current is required, the air is passed up one board and down the next; or as represented in the plate; or up two boards and down two, or up three boards and down three. But in small coalyries, or where no inflammable air is met with, the passages of air round the boundaries of a district, as that of F, leaving all the ends of the passages or boards open for the air to circulate, is found sufficient. At the great coalyries at Newcastle, the ventilation consists of a current of air of thirty-six square feet, moving with a velocity of three feet in a second.
The different modes of removing the pillars, according to circumstances, are represented in fig. 2. Plate LX.: aa, cc, d and e, are the different modes of working pillars where it is necessary to preserve the air courses. The pillars are wrought in the manner represented at bb, where the outer parts are much damaged and cracked by the pressure of the roof and floor. And ff, when the roof is not sufficiently strong to remain up, while the whole pillar is removing. In this case the centre part is left, and both ends are carried away.
The consequence of working the boards too wide is represented in the elevation, fig. 3. The pillars on either side of the board, g, are represented as much broken both at top and bottom by the pressure of the roof and floor, and the coal is rendered useless. Besides, the passage through the board is nearly closed by the approach of the roof and floor towards each other. The board h' represents the appearance in elevation, of one that is driven of a proper width. In this case, the coal on both sides is solid, and the roof and floor remain in their original positions. In working all coalyries, it is better to drive the boards too narrow than too broad; in the first case, when the pillars are to be removed, the roof and the coal are both sound, and the whole of it may with safety be removed; but, in the latter, the centre of the pillars only, as represented by bb in the plate, can be removed. As there is no account in the original article of the broad method of working; we shall, therefore, lay before our readers Mr Griffith's account of this method. A good account may also be found in Mr Farey's Survey of Derbyshire.
Many of the shallow and thin beds of coal in Yorkshire are worked in the broad way, but the breadth of the banks vary in almost every coalyry, from certain local circumstances. We shall describe one, the principles of which may be applied to any shallow coalyry, and the proper breadth of the banks, which depend on the nature of the roof, will be determined better by practice than precept.
Fig. 4. represents a very simple and excellent method of working in the broad way. A shaft is divided into two parts, in the manner already described; bbb are double drifts, with proper headings for air; cc and d are banks, each thirty yards broad; the dotted marks represent three rows of wooden pillars which support the roof. The light shade represents the parts already worked out where the roof has fallen.
The first operation in the work is to drive the several double drifts. Those on each side of the pit must be completed to the full extent, before any other workings can go on. The three double drifts at right angles to the first may then be commenced; and, having advanced 20 or 30 yards, the great working or bank may be commenced, by breaking down the coal along the lines ee upwards. The coals are drawn from the face of the banks on both sides, through the openings or headings by which the air is introduced, as represented by the arrows. I and f are double doors to prevent the air from the left bank returning directly to the pit; by this means, it is forced along the face of the workings in the right bank. The first banks being proceeded on to a certain distance, a third and fourth may be commenced to the right and left, and others may be wrought to the rise, by connecting the rise drifts by cross ones at right angles to them, and working upwards from the cross drifts in the manner that has been described.
According to this plan, a very extensive coalyry may be worked from one pit; but horses should be used to draw the coal under ground; and, if the coal be thin, part of either the floor or roof must be removed, to give sufficient headway. The most approved method of conveying the coals from the face of the work to the pit bottom is the following: First, a light cast iron railway must be laid from the pit bottom, through all the main passages of the coalyry, and, branching from these, small moveable railways should be laid, from the nearest point of the main passage, or mother gate, as it is usually called, to the face of the workings. When the collier has broken down the coals, another man, known by the names of putter, hurrier, &c. is employed to fill the coal into a wicker basket, or wooden box, placed on a wooden carriage with iron wheels; this is pushed to the mother gate, along the railway, and the putter returns with an empty box, which has been placed in the mother gate; a waggon-boy arrives from the pit, leading a horse which draws six carriages chained together, each having an empty box on it. These boxes are lifted off; and, by means of a small crane, the full boxes are successively raised, and placed on the carriages, which, when thus laden, are drawn by the horse along the railway to the pit bottom, from whence the boxes are drawn up to the surface, and the empty ones returned.
The reader will find much useful information on the ventilation of mines in Mr Buddle's valuable tract, entitled, The first Report of the Sunderland Society for preventing Accidents in Coal Mines.