[Westwater Mining] > [Library] > [Mining by Longwall -- 1862]

On Mining by Longwall


Mr. William Alexander, M.E.

A paper read on April 2, 1862 at a meeting of the Institution of Engineers in Scotland, and published in 1862 within Volume 5 of their Transactions.

In the centre of this large and important county, remarkable for its mines and iron manufactories, it will be unnecessary for me to take up your time in explaining either the term colliery or mine; and for our present purpose, it may be sufficient to remark, that a colliery is a place where minerals are worked, and this operation has received the name of mining.

Owing to the endless variety of conditions under which seams of coal and other minerals are found, various modes of mining have been aimed at and carried out; and these, while they may often differ only a little in detail, have still a very important bearing upon the broad question of safety and economy; whilst in some cases, apparently a trifling modification in the system of working a seam of coal has been the turning point of success in a mining enterprise.

It is not my intention in this paper to describe the various schemes which have been practised, or the different modes of mining which have from time to time been introduced; indeed, such an attempt would either be too prosy or too general. I have therefore arranged a few plans illustrative of one system of mining, generally known as "longwall," and which has been successfully practised for many years throughout this and other mining districts in Great Britain. I have not been able to trace the origin of this system, nor yet to arrive at any satisfactory conclusion regarding why the name "longwall" has been applied to it. However, it is a mode of mining which cannot be practised without forming walls along the roadways for the purpose of supporting the roof and maintaining a means of communication with the shaft and the works; and it may remain a question whether that circumstance or the fact that the working places are by this system of much greater length than by any other, first gave rise to the term.

Though the economising of mineral-fields will naturally lead to a more general adoption of this system, I am inclined to think that the originator was not actuated by such a consideration; and several attempts must have been made at modified systems, simply to meet local difficulties, partaking of "longwall" and "pillar work," long before the bold and comprehensive plan of working out the seam altogether, and allowing the overlying mass to partially subside and rest upon the loose buildings and refuse of the mine, was first thought of or systematically practised. [p.3/4]

The figures 1, 2, 3, 4 and 5, Plate I., have been selected for illustration, and with the view of conveying an idea of the probable steps by which some of these modified arrangements were first introduced and afterwards arranged upon a system; always premising, however, that the original mode of working collieries was by forming pillars of coal of sufficient strength to support the roof, and by which, roadways and other communications were maintained from the working parts to the bottom of the shaft.

Referring to fig. 1, this system is sometimes practised under a light cover, near to the surface, and a brittle roof. The narrow openings, A, A, form the means of communication with the shaft, and in some cases do not exceed four feet in width. The pillars ranged alongside of the roadways average nine feet wide, and seldom extend beyond ten feet in length. The main openings, B, B, which I shall here term the walls, range from ten to fourteen feet wide. The pillars serve for the protection of the roads and the maintenance of the ventilation. The main openings, B, B, are worked at a width in which the workmen can secure themselves either with wood or otherwise, the roof being allowed to close behind within a short distance of the face, but so as not to interfere with the "ends," C, C, which, till other openings are made, form the course of ventilation, and a means of communication with the roadways, A, A. Narrow roadways are about 1.2 metres wide, and the pillars are about 2.7 by 3.0 metres. The wider rooms, or walls, are 3.0 to 4.3 metres wide.
Packwalls 'A' are carried along one side of the advancing faces 'D.' Fig. 2 is a more systematic mode of working, and is frequently practised where a seam is associated with a heavy "falling." The walls, A, A, formed with the "falling," are carried irregularly along one side of the main openings, and while they assist in supporting the roof, and in securing the roadways, also admit of a greater width of "face," D D, being opened.
Fig. 3, when carefully compared with figs. 1 and 2, will be found to be only a slight alteration; but by it the main "wall," D D, which is considerably enlarged, instead of being worked with the advancing mines, E, E, is at a given distance returned upon, and the coal is worked back, leaving the roof to fall as the excavation is made. Pairs of narrow headings 'E' are driven, followed by wider retreating faces 'D.'
Packwalls are built along the sides of the advancing faces 'F. Pairs of narrow headings are kept slightly in advance. In fig.4 we have the first attempt at forming or packing walls, principally for the security of the roadways; but it must also have had the effect of giving greater security to the workmen engaged at the wall faces, F, F, consequently a greater width of face could be excavated with safety at a time; but, with this exception, it is in every other respect worked in the manner sketched in fig. 1. 
This trifling alteration, however, was the grand step, and led imperceptibly to a further modification and improvement illustrated by fig.5, where narrow mines were abandoned, and blocks of coal were excavated in widths varying from twenty to thirty yards, pack walls being formed to maintain the roadways on the one side, and solid coal on the other. At a suitable distance the solid blocks of coal, H, H, were returned upon and worked back, the same roadways forming a means of communication, and also enabling a system of ventilation to be carried on throughout the working parts. [p.4/5] Here the narrow headings have been dispensed with altogether. Walls 18 to 27 metres wide are worked on the advance.

Although it might be very interesting to pursue this subject with the view of investigating step by step, and adducing illustrations to show how the various systems of pillar working had only been so many modified arrangements leading imperceptibly to the system of working at present under consideration, I do not think such an attempt is at all necessary, as, indeed, no particular advantage could be obtained from such an inquiry, and in general the "longwall" of the present day may be explained as slight variation of the figure last described, where, instead of forming pillars of coal for support, or otherwise, to be afterwards worked away, the coal is taken out as the operations advance.

The defects of these arrangements, as compared with taking out the whole seam, would consist chiefly in forming pillars, in consequence of which an increased quantity of "cutting" or "shearing" would be required, whilst a greater amount of small coal would be produced; and the irregularity in the weight of the overlying  strata, occasioned by the partial support of the coal and walls, must have prevented a constant and effective pressure from acting on the solid coal at the point of excavation, where alone it could be of any practical advantage.

The "longwall" system of working, then, when properly carried out, is simply the excavation of a large block or pillar of coal, the "winning" out walls being the only parts where "shearings" or "cuttings" require to be made. The roadways, and the openings along the face of the coal, where the workmen are employed, are maintained by buildings of stone obtained from the roof or pavement of the mine.

To realise the full advantage of this system, there are several points which require to be clearly understood. The nature of the coal must be carefully considered, with the view of taking advantage of the natural rents, "backs," and "cracks," which are known to exist in the majority of coal seams. The line of "back" is comparatively regular in its bearing, and generally the distance between the "backs" ranges from ten inches to three and a half feet. The distances between the cracks and the angles at which they lie are very irregular. Before laying out a pit to be worked upon this plan, it is of importance, then, to examine carefully the situation of these natural rents, a neglect of which has in some cases led to a difference of as much as one-sixth in the cost of mining in one district of a mine compared with another.

Fig. 6, Plate I., will show nearly enough for all practical purposes the position of a working in a pit, where this difference in the cost of production came to the writer’s knowledge; and the extension upon the same figure will illustrate the alterations afterwards introduced, which enabled the works to be carried out at a uniform rate.

Coal is easily worked off the 'backs' on the left side 'A B' and the far right side 'G H' of the mine.

It will be observed that the division of working, A B, happened to be laid out so as to work off the "backs" of coal, by driving the roads nearly at right angles to them, and the division, C D, simply followed the same [p.5/6] form that is, the roads were branched off the heading in a level course direction without reference to these natural rents. The consequence was that the coal worked easily from A to B, but it was with difficulty that workmen could be induced to work in the division, C D, at an advanced rate of nearly fourpence a ton. The alteration shown by the extension on the same figure at G H seems very simple, but by it a uniform rate was introduced, the coal was obtained in a better state, and the objections previously urged by the workmen were at once abandoned. I have purposely introduced this practical illustration with the view of attracting the attention of young engineers to a subject which has sometimes escaped the observation of really practical men.

In fig. 7, Plate II., the line of "back" lies nearly parallel to the line of level, and under such circumstances, when the inclination of the strata is moderate, say, one in eight or thereby, such an arrangement is found to work very satisfactorily; the roadways leading to the various faces being cut off at suitable distances by more permanent " slope" roads, which afterwards form the trunk or mainways of the mine.

Stepped walls work gently updip, across the 'backs' of the coal. Coal is gathered along the sloping cross-roads.

I do not anticipate that any mode or arrangement of working can be introduced directly applicable to every mineral-field ; but, as a general rule, it may be safe to adopt the following in laying out "longwall" works — that the roads be driven at right angles, or nearly so, to the line of "back" of the coal; that the distance in advance between each wall do not exceed the width of a "back," and that no following-up wall should be driven in advance of the one which should give it "cut."

In Fig. 8 (left) a face gets too far ahead of its neighbours. In Fig. 9 (right) the packwalls provide good support to the faces. The disadvantages attending a following-up wall getting in advance of the one designed to give it "cut," as shown at A, fig. 8, are, the increased difficulty of working occasioned by "shearing," and a diminished pressure upon the seam; and this defect of pressure increases so rapidly, that when a wall has advanced a few yards in the "fast" or solid, as represented at A, fig. 8, the effect of the overlying weight ceases altogether to act upon the working of the seam at that point, or, in miners' phrase, the "weight's off." 

Where the distance back from one wall to another, as at B C, fig. 8, is more than a few feet, an opening or "cundie" requires to be formed and maintained for the purpose of allowing the ventilation to pass, but where the roof is tender, this description of opening is difficult to maintain, and the consequence is, the roof is apt to break and fall along the "rib side" of the coal, and destroy the air course. Under any circumstance, a "cundie" along a "rib side" is objectionable; but where the roof is tender, these openings should be altogether prohibited, and this can only be done by arranging the walls to follow in regular order.

These provisions, while they will be found to apply to the working of coal generally, may, under certain conditions, be slightly changed to advantage; as, for example, when the pressure is active at the face, and where the "backs" are thin, it may sometimes be judicious to drive the walls on [p.6/7] "end," and by such an arrangement there will be an increased per centage  of round coal. The line of "back" in the coal does not generally extend through the strata immediately overlying, but where it does, it may under such circumstances be beneficial to arrange the roadways so that the buildings along the face shall not be placed parallel to them, but interrupt the continued line of "back," as sketched in fig. 9. This mode of crossing the line of rent with the buildings tends materially to preserve the roof along the face, and gives greater security to the workmen employed therein. Where the seams lie steep, the question of haulage must become important, and will probably receive greater consideration than the precise mode of excavation; but this, like many other details, under judicious management will, after a few trials, resolve itself into a question of pounds, shillings, and pence.

There is a great deal of ingenuity displayed by able workmen in the manner they arrange their work, and those accustomed to "longwall" generally contrive to undermine the coal along their wall face during the after part of the day, leaving it to be acted upon by the overlying weight during their absence, which, being only partially supported upon the loose buildings, gently forces off the undermined portion of the coal before they return.

The subsidence or collapse of the roof depends to a certain extent upon the nature of the buildings and the quantity of material stowed into the waste; but, taking an average, and under ordinary circumstances, the subsidence of the roof will generally be at rest from fifty to eighty yards back from the working face, and the extent of that subsidence will range from a half to two-thirds of the thickness of the excavation. Owing to the constant movement of the bending roof if the works are not kept advancing regularly, serious inconvenience is sure to follow. The roof under ordinary circumstances will bend gently from the face of the coal back upon the buildings; but if the operations are neglected or abandoned for a few days, or prosecuted irregularly, it will break right along the face of the solid coal, in some cases completely closing up the face of the work; and when such interruptions take place, it is generally found more economical to open out the face of work again from an open "end" than to "red" and  clear away the mass of fallen roof.

There is a diversity of opinion as to the effect which seams of coal have  upon each other, when worked at different levels under this system. I am aware that considerable stress is laid upon the effect which gas existing under pressure has in aiding the miner to extract the coal, and I have no doubt that in pillar working such an effect takes place to a certain extent, and that in some instances the drainage of these gases, occasioned by the operations in an upper working, has affected the economical working of the seam immediately underlying; but I am quite satisfied that the good effects produced under "longwall" are wholly due to the action of the over- [p.7/8] lying weight, and not the pressure of the pent up gases lodged in the crevices and pores of the surrounding strata. Indeed, we know this well, that it can be calculated with a degree of certainty, very nearly the time after a "longwall" working has commenced, when the effect of the weight upon the seam will be produced. If it were gas, we would experience the good effect immediately at the pit bottom on commencing to open out the mine; whereas, w find it is not till the works have been extended to a sufficient distance to enable the roof to bend and subside that the effect of the pressure referred to in "longwall" work is produced at all; and if at any time a wall is driven in advance of the range of work, say, eight yards, it gets beyond the line of depression upon the roof, fails to be affected by it, and, comparatively speaking, ceases to be worked to advantage. It is therefore well known to those who practise this mode of working, that the movement induced upon the roof by its gradual subsidence, and slowly acting upon the face of the seam, is all the advantage which can be obtained from "longwall" working, as compared with any other system, in undermining and taking down the coal.

When we consider that generally throughout the coal measures the seams of coal lie ranged in groups near to each other, an important question suggests itself as to how this advantage of pressure, this important power, is to be maintained and made serviceable under all conditions. Unfortunately there are few collieries where this mode of working has been generally practised throughout all the seams, or, indeed, where the seams are sufficiently numerous and equally well adapted for this description of work; and, before making the following remarks, allow me to add that I do not think we have yet obtained sufficient data to enable us to lay down general rules for future guidance upon this very important  subject; neither have the cases in practice which might be adduced in support of any theory been sufficiently numerous, nor have they been conducted with that degree of accuracy, to enable any one to give a very definite opinion as to what are the exact conditions under which seams overlying each other at various distances ought to be worked in relation to each other, so as to yield the most advantageous results.

We are perfectly acquainted with the effect which the working of a seam by longwall has upon the overlying strata; to a certain extent, we also know the effect of such a working upon a seam immediately underlying; and so far as we require to consider the question of mining, without regard to the nature of the strata, inclination, gas, or water, the entire subject may be considered under these two heads.

The direct effect which the working of a seam of coal or other mineral has upon the overlying mass is to lower it from a half to two-thirds the thickness of the exhaustion. This depression may not in all cases extend uniformly to the surface; but I am of opinion that, as a rule, subsidence will not be quite so much at the surface as in the [p.8/9] vicinity of the mine. When the excavations are extended in regular order, the subsidence will be nearly complete at eighty yards back from the face of the workings; or, in other words, the overlying roof will have settled permanently at that point. If the workings are hurried forward, perhaps it would be more correct to reduce it to time, and say that the depression will be complete in twelve months after the exhaustion has been made. Where seams are situated so that the workings produce an excess of "stowing" or "packing," the extent of depression will be slightly reduced. Varied results will also be obtained in a working where the roof is strong and principally composed of rock, or where the pavement is so soft as to induce a "creep;" and, under these circumstances, the waste will not be perfectly settled till the soft pavement has penetrated and closed up the various openings throughout the waste, the same as in pillar working, where it is well known that a "creep" will seldom come to rest till the roof and pavement in the several openings are brought together. In a shaft where seams of coal are situated at, say, twelve, sixteen, and eighteen fathoms separate, the effect of working the second seam upon the one immediately underlying would be, that for a given time, at least twelve months, the continuous action of the overlying weight would be lessened upon it; and if during that time the third seam was worked, the result of this want of pressure would be felt by its being more difficult to work; the undermining, if in shale, would become tough and hard, and the coal, from the diminished weight acting upon it, would be much more difficult to force down. But in the event of the third seam being tender and easily broken, such an arrangement might have a very beneficial effect upon it in a commercial point of view, and prevent that pulverizing action to which there is a tendency in all "longwall" work. The upper or first seam, under the conditions thus described, and until the strata have permanently settled, would be affected in a different way; the action of the overlying weight would not be so continuous and decided; but the seam, if of a splinty nature, would generally be found to have "parted" with the pavement, and in some cases to such an extent as to aid the miner directly at the face of the work in holing and taking down the coal. The formation and upkeep of roadways form a very important item of cost; and under no condition can two seams at different levels be worked at the same time without materially affecting the permanency and safety of these openings. If the upper seam is worked in advance, the roadways in that working will be deranged by the subsequent movement in the under seam; and if the under seam is worked in advance, the roads there will to a certain extent be affected by a second subsidence induced by the upper working. Where of necessity two seams of coal require to be worked together as described, I believe the roadways in these seams wou1d be most economically maintained by keeping the operations in the under one least eighty or a hundred yards in advance. [p.9/10]

If fire-damp exists generally throughout a coal-field, the "longwall" method of working, which has the effect of breaking and opening the overlying strata, will induce the drainage of the gas to the surface or to higher levels. With water the effect will just be reversed, and I am afraid that no arrangement of tubbing back water can be of great or permanent advantage where the seams lie nearer to the surface or to one another than forty fathoms; indeed, it is very questionable if tubbing can be advantageous under any circumstance where this system of working is practised. However it is most likely to be effective where the strata are principally composed of layers of shale and fire-clay, and under these conditions the filtration to the lower levels may in some cases be altogether prevented.

Seams of coal are sometimes so situated with reference to their distance from one another, and also with reference to the strata with which they are associated, as to baffle all order in working them out. I had occasion some time ago to examine three seams rather awkwardly situated, lying at two and one and a half feet separate, being worked under the "longwall" system, and in the following order: —

Fig. 10, Plate II., and fig. 11, Plate III., will illustrate their relative positions, and the order of excavation.

The lower seam, A, fig. 11, separated from the one overlying it by two feet of fakes, is worked first to a given limit, commencing at the main road, D E, fig. 10, and extending to the line, G H, a distance of, say, one hundred yards. When this excavation is completed, the seam, B, separated from the one overlying it by eighteen inches of shale, is next worked, commencing again at the main road, D E; and new roadways are formed as the workings progress, in the same order as shown in working the seam, A; the bold lines, K, represent their position.  Gateroads in the two lowest coal seams are staggered. The third, uppermost, workings reuse the roads from the underlying coal.

When the seam, B, is extended to the boundary, G H, the upper seam, C, is next operated upon, not from the main road, D E, as in the former cases, but from the limit, G H, and back to the main road, D E; the drawing roads which had been used while working the seam, B, remaining available, and into which the coals are lowered and filled into hutches, as sketched in section, fig. 11.

The bottom coal is worked first, then the middle coal is worked slightly leading the top coal.

This arrangement for working out these seams, though for some time practised, is not yet thoroughly matured; but I have no doubt that experience will suggest some details tending to simplify, and further reduce it to a system, more particularly with regard to the roadways and ventilation. Such trials, though only successful in part, are valuable; and in this case the broad fact has been established, that the whole of the coal can be obtained in a good marketable state; and it is fair to assume that seams of coal may sometimes be worked advantageously under what may be considered unfavourable conditions for mining, and at any distance from each other, without deterioration. [p.10/11]

Perhaps it is unnecessary to remark that where two seams of coal lie near to each other, say at two, three, or five feet separate, that the lower seam should be worked away first, particularly if the intermediate stratum composed of shale or other brittle material.

The most serious objection to "longwall" work is the cost of forming the "pack walls," or buildings to secure the faces and maintain the necessary height of roadways. In some cases where the cost of "brushing" is expensive, the length of wall or face is increased; but where there is no "falling" with the coal, and where the brushing is the only material fit for building purposes, it then becomes necessary to reverse the above arrangement, and increase the brushing, either in height or by forming additional roadways.

Timber supports are used to keep a passageway open along the advancing face, so that coal can be taken to roadways 'A.' Fig. 12, Plate III., is an example of this description of "long-face," where, to avoid the formation of roads, a partial opening is maintained along the wall face by means of "brittices" or wooden supports, wide enough to admit of rails being loosely laid, and along which the coal is drawn to the permanent roadways A, A. 

Where the arrangements are less complete, a rail is sometimes laid along the face of the stowing, and the hutch is drawn upon this and the pavement of the mine; or where the seams are thin, and hutches cannot be introduced, "slipes" (shallow boxes), shod with malleable iron, are drawn along the face for the purpose of transporting the coals from the extremity of the walls to the hutches or tubs at the permanent roadways.

There is no particular limit to the length of face by this mode of working; it may extend from twenty to one hundred yards or more, and the only considerations are safety and economy. If the roof is strong, and does not break readily, then a considerable length of face may be opened out; but if the roof is tender and apt to fall, it will be necessary to diminish the length of face, and advance the works more rapidly.

It is no part of my design at this time to enter upon the subject of mine ventilation; but in laying before you some of the advantages to be obtained by working "longwall," I feel bound to make the following digression, and would remark that, in all extensive explosions of fire-damp in collieries, the chief loss of life is occasioned by the after-damp, induced by the suspension of the ventilation, and the explosion and consumption of the life-sustaining gases.

With deference I hold the opinion that no system of pillar-working, where stoppings require to be made, can, under the severe test of an extensive explosion, prevent altogether this lamentable state of things; and a few years ago I proposed a scheme, arranged upon the "longwall" system, intended to alleviate the destructive effects of the after-damp —  which in some extensive explosions has been estimated to carry off at least 75 per cent. of the unfortunate sufferers.

Fig. 13, Plate III., will illustrate the proposed arrangement; referring to it, the coal is worked on the "longwall" system, and divided into [p.11/12] suitable districts, 1, 2, 3, 4. The ventilation is maintained by two pits, A, B, downcast and upcast pits. The course of the air is indicated by the arrows; it is split at the bottom of the downcast, A, and taken into the several districts as may be required.

Workings in a large mine are divided into several districts, and the ventilation split between them.

The advantages anticipated from this system of working, in the event of an extensive explosion, are — the air-courses will be preserved, the districts will remain perfectly isolated, and, from the peculiar situation of the upcast, the ventilating currents must of necessity make the circuit of the mine before they can get into it. If you are satisfied with the practicability of the scheme, it will strengthen my arguments for the extension of this mode of working, which, if under all circumstances it is not the most economical, is under all conditions the most safe. Sectional view of an air-crossing, where one roadway is driven in rock above another one.

I am not an alarmist regarding the duration of our coal-fields, but I do think that sufficient attention has not been directed to the economizing of them. By some of the present modes of working, a large amount of our most valuable and easily obtained seams are being rapidly exhausted; not by working them out, but by leaving from a fourth and upwards buried in the mine. It is in vain to urge that this is a question for colliery owners alone; with them it is simply a matter of business; they lease their fields, and in many cases are compelled to work upon this extravagant system; their profits are not large, compared to the uncertain nature of the investment; and probably no capitalist has less security for the money he invests than he who embarks in a mining speculation.

The question, then, of economizing mineral-fields, if it involves a more expensive mode of working, is not so much a matter for the lessees of mines to consider, as it is for manufacturers and the general public. I hold, therefore, that the principle of economy upon which from a half to a fourth of many of our valuable and easily obtained seams are at present cast away is false and ruinous to posterity; and sooner or later it will have the tendency to impoverish the nation in that article which has aided more than any other to raise this country to its present eminent position, and which is indispensable to its future greatness and continued prosperity.

In the discussion which followed:—

Mr. Alexander, in answer to a question by the President, said that he could not state exactly the proportion of coal mining conducted on the longwall system as compared with that on the stoop-and-room plan; but he believed that at least three-fifths of it was by pillar working. In Lanarkshire, and throughout the west of Scotland, seams of ironstone were all worked on the longwall system, and this was principally owing to the thinness of the seams. It would be very difficult to take out a seam six inches thick in any other way. [p.12/13]

The President said that it had been found difficult and expensive to work the blackband ironstone where it was only six to eight inches thick; but where the seam was from eighteen inches to two feet six inches thick, drawing roads were more easily preserved, and the same inconveniences were not experienced. The great difficulty in coal mining was the tender roof, which prevented the lessee in many cases from working by longwall, as it increased the danger of the strata overlying the coal sinking. He thought Mr. Alexander’s remarks on the desirability of economizing fuel and getting all the coal out of the coal-fields, were well worthy the attention of coalmasters and proprietors of coal-fields generally.

Mr. Alexander thought that the economizing of mineral-fields was not so much a question for the coalmaster to consider, as it was for the community generally. His aim was to work out his coal as cheaply as possible; and if in future the fittings should become more expensive, or the seams more difficult to work the difference of cost must of necessity fall upon the consumer.

Mr. A. Simpson asked whether, in the plan proposed for dividing a longwall working into sections for safety in cases of explosion, a good stowage between the roads would not serve the purpose as well as a barrier of coal?

Mr. Alexander thought that, under all circumstances, such a stowage or building would be less perfect than the "rib" of coal in question; and as the object of leaving the coal was to secure a perfect separation of the districts, he did not think the trifling difference of cost should be taken into consideration.

Mr. A. Simpson did not think there would be any difficulty as regarded leaving an opening, and sketched a diagram showing how the stowage would meet the case. The coal barriers] would, he thought, add to the expense of winning out the coal to the rise of them, the expense of shearing, and the probability of the coal in the barriers being lost.

Mr. Forrester believed some one had said that the reason why coal was not more generally worked by longwall, was owing to the tender nature of some of the roofs; but he did not think that was a correct view of the matter, as he thought that the more tender the roof was the more necessity was there for working it by longwall. If the roof was tender, and the coal worked by stoop-and-room, then the stoops would be apt to go through the roof, and the roads become closed; whereas if the coal were taken out by longwall, the subsidence would be more general, owing to the buildings yielding to it.

Mr. M'Call said that at first sight it might appear that longwall mining was the best for the lessee, because the whole of the coal was got out — but that was very much a matter of opinion. He thought it depended on the thickness of the coal whether it was cheaper or dearer for a lessee to get out his coal by longwall or stoop-and-room working. If the seam was from [p.13/14] four feet to six feet thick, it was found that the stoop-and-room system was the cheapest; but if the seam was thin or the roof bad, it was better to get out the coal by longwall. He knew of a colliery where there would be a loss if it were worked by longwall, whilst it was remunerative the other way, even although a fourth of the coal was left in.

Mr. W. M. Neilson asked if it was not possible to take out all the pillars by working back upon them?

Mr. M'Call said that could not always be done.

Mr. Lawrie remarked that the father of the present Mr. William Dixon, the coalmaster, was the first, he believed, who worked mines on the longwall system, in Scotland at all events, and he in some instances adopted the plan also of going back and taking out all the stoops the roof might be supported with. But both systems were attended with very injurious effects on the surface of the ground. The falling in occurred so unevenly as to produce lochs or ponds of water.

The President corroborated what Mr. Lawrie had said regarding the late Mr. Dixon. He remembered that in 1823 or 1825 Mr. Dixon introduced the longwall system at Faskine and Greenend and he was the first to work the longwall system, at any rate, in this neighbourhood. The usual mode of taking out the pillars left by working on the stoop-and-room system was to begin at the far end, allowing the roof to fall after the pillars had been taken out.

Mr. Alexander remarked that the longwall system could not be practised without affecting the surface. Mr. M’Call spoke of a colliery near Glasgow where on the longwall system the coal could only be worked at a loss; it was a fact, however, that at Mr. Dixon’s pits the whole of the seams were worked by this system.

Mr. Lawrie said that the uneven depression of the surface arose from an inequality in the hardness of the strata, or crust.

Mr. M'Call remarked that in the field he had referred to, they worked on the longwall system only where the roof was bad, and adopted stoop- and-room at other places.

Mr. Alexander said that, without an exception, Mr. Dixon at Govan worked every seam by longwall, and of course the same seams as those referred to by Mr. M’Call.

Mr. M'Call said it was a matter of expense.

Mr. Alexander remarked that that was exactly the case; and he might add that Mr. Dixon was also proprietor of the coal, which gave him a double interest in working it all out.

Mr. W. M. Neilson thought this was a most important question which had been started, as it had reference to the saving of a large amount of coal. If they were losing about twenty-five per cent, of the coal-fields by the stoop-and-room system, he thought it was an extraordinary thing that there was no law or means of protecting this important property of the [p.14/15] country from being wasted thereby. Of course, the proprietor must let his fields to the best advantage, and the lessee must likewise be able to work them with remuneration, so that there was difficulty in the way of getting out all the coal if the longwall system could not be profitably adopted; but it was very desirable that the difficulties in the way of adopting the longwall system should be removed, in order that coalmasters might be induced to adopt it instead of the stoop-and-room system. It was a wonder that Government did not step in and interfere in this matter. They knew that in various places on the Continent — in France, for instance, where trees were much used as firewood — there was a law that made it imperative on parties to plant as many as they cut down, in order that the supply of firewood might not be stopped. He thought, perhaps, that the British Government would yet have to step in and say, "You shall no longer mine on the stoop-and-room system where longwall working is possible."

Mr. Alexander said a very good illustration of the evil of the system would have forced itself upon the ironmasters of Lanarkshire at the present time if the same ruinous system of working the coal seams had been practised in the famous seam of blackband ironstone; that is to say, if from a third to a fourth of it had been left in pillars.

Mr. D. More asked whether mining by longwall or stoop-and-room was the safer system for the miner?

Mr. Alexander said they were perhaps equally safe. He knew nothing objectionable in the longwall system to prevent its introduction into every seam, but the question of cost. He believed that where the seam exceeded two feet nine inches or three feet in thickness, the longwall was the dearer system; but if the seam was only two feet thick, it was decidedly more applicable and economical than pillar work.

Mr. James Russell said there was another recommendation for the longwall system. In East-Lothian it was almost the universal practice to work on the stoop-and-room system, and the lessees were generally bound to allow the pillars to remain for the benefit of the landholder; but in some cases where the stoops were subsequently taken out, those coals never brought the same price as the other coals of the pit; in fact, they would only sell when coals were scarce, as they were of an inferior character. Now, when coal could be worked profitably by longwall, it was all taken out at first, before the quality was deteriorated by exposure to the air and water.

Mr. Forrester said he might mention that, in the district where he was located, there was a seam of coal five feet six inches thick, which was now being worked by longwall, instead of by the stoop-and-room system, and it was now got more cheaply than before. When they tried to take out some of the pillars, they found the coal of them did not turn out nearly so well. The advantages of the longwall system were that a much larger quantity of round coal was turned out, and consequently a half less dross than under the pillar system of working. A man could put out [p.15/16] more coals than formerly, and there was saved the extra expense that had to be paid for narrow work.

Mr. Alexander said that was an exceptional case, and did not admit of a fair comparison, because there were fourteen inches of stone in the seam, which the miner had to turn over, under either system; but fortunately under the longwall system it could be turned over to advantage and be partly used in building.

The President asked if that stone was used in the pit for building supports to the roof along the wall face? — and was answered in the affirmative. He proceeded to say that as there were a number of mining engineers connected with the Institution absent, perhaps it would be as well to postpone the closing of the discussion until next meeting.

Mr. W. M. Neilson asked Mr. Alexander if he knew the quantities and positions of the various backs or cracks in the different strata of coal. He thought these might have reference to the crystalline character of the coal.

Mr. Alexander said they varied, and some seams were found without them. However, from observation, he was of opinion that these rents were better defined in the gas coal seams than in any others.

Mr. W. M. Neilson said it seemed to him that the position of the face would have a very great influence as regarded the facility of working. The longwall system was a very beautiful one, and he understood Mr. Alexander to say that it was easier for the miner. He thought it was an excellent idea to undermine the coal, and then give it time to be squeezed out by the weight of the strata above. He could not sit down without expressing his great pleasure and thankfulness to Mr. Alexander for bringing the subject before the Institution. There was no question of more importance than that of mining in this quarter, and it was most desirable that discussions should take place among mining engineers collectively, so as to bring out and collect the experience that existed in Glasgow upon this subject. He believed that very important practical results would be attained if they combined skill and science, for such combinations always elicited something good. He would ask the President to desire Mr. Alexander to follow up this paper by others on kindred topics — such as the ventilation of mines, on draining, and on winding — all very important subjects.

The President coincided with the suggestion, and then moved that the discussion be adjourned until the next meeting, which was agreed to.

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This document is presented as a conscientious and fair copy of the original 1862 text, including spellings and typography as found. Some of the mining methods described, and conclusions as to their application, are not in accordance with present-day understandings of good coal-mining practice. This document is provided for historical and educational purposes only, and it should not be construed as a substitute for advice by a qualified mining engineer.
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