June 29, 1917. THE COLLIERY GUARDIAN. 1215 Foster, It. J.—To include the factor of thickness of seam, when conditions are normal, the following for- mula is suggested: — Radius of pillar = 3 VDt, in which D = depth of shaft, - t = thickness of seam. Mining Engineering (London).—For shallow shafts a minimum of 60 ft. radius should be adopted, and for deeper shafts this should be increased by one-tenth of the depth multiplied by the square root of one-third the thickness of the seam in feet. R = 60 + 5 I io 3 Boberton, E. II.—In Northumberland and Durham the practice is shown by the following formula: — R = 0 2 vzDt R = radius of the shaft pillar in feet, D = depth of shaft, t = thickness of seam. Scotch engineers, in order to protect buildings, have pillars from one-third to one-fifth larger than the floor plan of the building. This diversity of opinion among engineers is well shown by fig. 20. o § 1 >'i! X O’! V SI A0' *1 Q/ I ■Scale of Feet O______ JOO________600 Fig. 20.—Sizes of Shaft Pillars, by Different Foraiuije. The Central Coal Basin rule, presumably founded upon the experience of mining men in Illinois and surrounding States, is: “Leave 100 sq. ft. of coal for each foot that the shaft is deep. If the bottom is soft, the result given by this rule is increased by half. For 5 or 6 ft. coal beds, the Central Basin rule may be used unless it has been shown by other operating mines in the district that a larger pillar is needed. With thicker coal a larger pillar should be left.” The practice of some coal companies in the Connells- ville region of Pennsylvania is to leave pillars under buildings so that there is a margin of from 25 to 30 ft. of coal around the building. If the tract is large, from 50 to 60 per cent, of the coal is removed, the remainder being left in pillars proportioned so that they will serve in the most advantageous way to pro- tect the building. This is the practice for depths from 150 to 300 ft. In determining the size of the pillar necessary to protect objects upon the surface, as has previously been noted, the ability of the pillar to carry the load is not the only question to be considered. Among the most important of the other problems is that of draw or pull over the pillar previously noted, and the ability of the underlying bed to sustain the load concentrated upon it by the pillar. Quite frequently the underlying bed is less stable, and has less crushing strength than the pillar. It seems logical then to proceed as follows in determining the size of pillar necessary to protect an object upon the surface : — (1) Determine the lateral extent of pillar necessary in order to prevent damage by draw. (2) Determine whether the pillar thus outlined is sufficiently large to support, without crushing, the burden of the overlying beds. (3) Determine whether the load upon the pillar will cause the pillar to be forced down into the underlying beds, or cause a flow of the underlying material. Room Pillars. In his discussion of methods of protecting the sur- face, M. Fayol referred to the use of pillars between the working places. “ The meshes of the network consisting of pillars with working places between them Fig. 21.—Effect of Extent of Excavation on Amount of Movement. n /z 13 zf -■e- ——z^. X'u 1. Z_il_1**A_\__ should be made smaller as the workings are shallower. As the depth becomes greater, the size of the meshes can be enlarged and dimensions of the areas worked can be increased relatively to the sizes of the pillars that are abandoned, regard being had to the height and width of the zones of subsidence, so that the various zones may be kept distinct from each other. This general rule is susceptible of many combinations according to the thickness, the inclination, the number and depth of the seams worked. If the excavation is of small dimensions, the subsidences which take place above them are restricted in size, and become enlarged both in width and height as the excavation increases in area. If each of the pillars 1, 3, 5, and 7 (fig. 21) be taken out singly, zones of subsidence similar to Zp Z3, Z5, and Z7 would be produced; but when pillar 2 is taken out, the line of roof subsides on to the floor, and the zone of subsidence rises to Z2. The same thing happens when No. 6 pillar is taken out, and if No. 4 pillar is taken out, the space comprised between the zones Z2 and Z(1 is set in motion, and determines the formation of zones Z4.” It follows from this statement of Fayol that if the room pillars are properly proportioned and properly spaced, the disturbance of the strata may be limited to the volume within the zones. The material outside these zones throws no weight upon the material within the zones. Necessarily, then, any vertical pressure must fall upon unmined material forming the pillars, and the pillars must be large enough to withstand the pressure. In a paper before the Pennsylvania State Anthracite Mine Cave Commission, 1913, Douglas Bunting said : — “ The application of a formula for determining the safe size of coal pillars for various thicknesses of veins and depths can be considered practical for depths greater than 500 ft., but it is doubtful if the same for- mula would be of any practical value for application to veins at less depth, and certainly of diminishing practical value with reduction in depth and thickness of veins, for the reasons that the variable conditions of vein, top, bottom, etc., are of more consequence with small pillars than with large pillars.” D. Bunting made a careful study of chamber pillars in deep anthracite mines on light dips. He considered the crushing strength of coal, which for anthracite was found to average 2,5001b. per sq. in. for cubes. The ratio between the strength of prisms and cubes was taken as follows : Strength Erism = 0.70 0.30 \ strength oi cube h in which \ = width of pillar, h = thickness of vein. The weight of overlying strata was taken at 144 lb. per cu. ft. (1) Load per sq. ft. on a pillar = in 612 which y = depth below the surface, b1 — width of pillar, z = distance between chamber centres. With 1,000 lb. per sq. in. as the safe load for a cube, we obtain by substituting in equation (1) : = 144,000 ( 0 70 + 0-30 h ) or yz = 1,000 ^0-70 + 0’30 By making proper allowance for the crushing strength of the pillar material and the weight of over- burden, this formula may be used generally for flat beds. The relative widths of rooms and pillars are deter- mined largely by practice. For bituminous coal of medium hardness and good roof and floor, the follow- ing rule is sometimes used: “Make the thickness of room pillars equal to 1 per cent, of the depth of cover for each foot of thickness of the seam, according to the expression: in which W^ = pillar width, t = thickness of seam, D = depth of cover, and then make the width of room or opening equal to the depth of cover divided by the width of pillar thus found, according to the expression: Wo = in which Wo is the width of the room. ■ Wv “ Frail coal and coal that disintegrates readily when exposed to the air, and a soft bottom, may increase the width of pillar required as much as 50 per cent, of the amount found above; also, a hard roof may increase the same as much as 25 per cent.; while, on the other hand, a frail roof or a hard coal or floor may reduce the width of pillar required 25 per cent.” “ As to the thickness of pillars in the Pittsburg seam with strata 100 to 500 ft. thick, the following rule should be a safe one to follow, in which the pitch is from 1 to 5 per cent. : — Thickness of surface. Thickness of pillars, George's Creek. Thickness of pillars. Fairmont. Ft. Ft. Ft. 100 25 18 150 32 20 200 40 25 250 50 30 300 6" 35 350 70 40 400 80 45 450 i0 50 500 100 55 These figures are based on experience in this seam. where the floor or bottom is hard and not affected by water. For a fireclay bottom, somewhat thicker pillars would be necessary to withstand any extraordinary weight. Rooms should be not more than 14 ft. in width in the Georges Creek region and 20 ft. in the Fair- mont region.” The average dimensions of pillars and rooms in ordi- nary pillar-and-room mining in Illinois are shown below: — Dimensions of Pillars and Rooms in Pillar-and-Room Mining in Illinois. Average Room Pillar Average District. depth width width thickness of c^al in feet. in feet. in feet. in feet. II. ... 140 .. 26 ... 19 { Top bench, 2ft. Bottom do.,3 ft 9 in. III. ... 90 .. . 22 ... 18 4 ft. IV. ... 201 . 25 9 4 ft. 8 in. V. ... 243 .. . 26 ... 16 4 ft. 8 in. VI. ... 270 . 22 ... 18 9ft. 5in. VII. ... 227 .. 31 ... 30 7 ft. VIII. ... 174 .. 27 ... 8 { Seam No. 6—6 ft. Seam No. 7—5 ft. Average* ... 208 . .. 26 ... 19 * Average of 48 representative mines. The question of the thickness of cover is an impor- tant one in connection with the size of the room pillars, and particularly when the drawing of pillars is con- sidered. This has been emphasised by F. W. Cunning- ham as follows: “ The topography of the surface rela- tive to hills and vales should be considered when start- ing to draw pillars, and relative to this subject a ques- tion may be asked, which is an important one, viz. : How many coal properties have contour maps of the surface? Suppose, for example, the rocks at the sur- face rise abruptly on each side of a narrow valley to, say, 200 or 300 ft. Would it be proper to commence pillar drawing under this valley?” (To be continued.) MINERS’ PERMANENT RELIEF. Increased Benefits Without Extra Contributions. The special report of 'the board of management of the Lancashire and Cheshire Miners’ Permanent Relief Society on the valuation report of Mr. R. Tod- hunter, M.A., F.I.A., of London, the actuary, and the society’s benefits, was presented at a special general meeting of the society at Wigan on Saturday week. Although the society was formed some.45 years ago, the valuation of the quinquennium ending Dec. 31, 1916, is the first to show a surplus; and this satisfac- tory state of affairs is partly due to the favourable character of the various risks—disablement cases, fatal accidents, widows, and children — and partly to the society’s greatly increased earning capacity as regards the rate of interest on its investments, thus enabling the actuary to assume a 4 per cent, rate for valuation purposes, instead of 3 per cent, hitherto assumed. The result has been to yield a surplus of £2,513 on the incumbent liabilities at December 31, 1916, with an annual accruing surplus of £4,500. It was pointed out in the report that the present scale of contribu- tions and benefits was, with one or two slight excep- tions as regards benefits, adopted some 16 years ago. A great deal has happened since then, not the least important event being the great increase in the cost of living. As it is very probable that high prices will prevail for many years after the war, it appears desir- able that those connected with societies like the Per- manent Relief Society should endeavour to bring the present scale of contributions and benefits more in harmony with altered conditions of living, and especi- ally to help the widows and children. The board of management have decided on a scheme providing for a moderate increase of benefits without any increase of contribution, the principal idea underlying the scheme being that of restoring as far as possible the benefits to the rates in force prior to the coming into opera- tion of the Workmen’s Compensation Act in July 1898. Among the proposals submitted in the special report of the board were the following : —That the 80 cases of disabled members who came on the funds previous to 1898 shall have their present allowance raised from 7s. to the original rate of 10s. per week; disabled members coming on the funds since 1898 to be paid at the ordi- nary rate of 7s., and not reduced to 5s. per week; that the grant of £15 to the parents, or next of kin, on the death by accident of single members or widowers leav- ing no dependent relatives be increased to £20 ; widows receiving 4s. per week to have this sum increased to 5s. per week, and the weekly allowance of 2s. paid to children being increased to 2s. 6d. It was also recom- mended that the illegitimate children of married mem- bers be recognised under the rules of the society and paid as in the case of other children, while it was pro- posed that the board of management should be empowered to provide for disabled members’ treatment by specialists, massage, and other similar treatment, artificial and other surgical appliances, on the under- standing that as a result the injured members would be enabled to return to work; also to send disabled members to convalescent homes, etc., as well as to arrange for disabled members to attend technical and other schools to learn trades, on the understanding that the members would be enabled to return to work at some trade or business. Mr. Alfred Hewlett, J.P., the president of the society, in moving that the special report be approved and adopted, said he had frequently stated that he looked forward to the time when they would be able to pay 20s. in the £, and he was glad to find that they were in that position while he was alive. The improvement in the society’s financial position had been of steady growth during the last 10 or 15 years. Describing the character of the work of the society during the 44 years of its existence, he pointed out that the society had dealt with 3,944 deaths from acci- dent, at a cost in funeral allowances of £38,370. In the same period, 2,269 widows had been in receipt of annuities, at a cost of £258,806, and at the close of the year 1916 there were on the funds 760 widows. ■ The society had also provided annuities for 4,335 children, at a cost of £166,768, and at the close of the last year there were 762 children on the funds. The society had dealt with 379,298 temporary accident cases, and 7,408 permanent disablement cases, or altogether 386,786 cases of accident among the members. These accident cases cost the society £1,010,748. As they knew, mining was a dangerous business, and they were always trying to reduce the number of accidents. It was for the Lancashire and Cheshire Miners’ Perma- nent Relief Society, when there were accidents, to pro- vide, as they had done, for the wives and the widows and the children, and they had been able to do that great thing by using carefully their own money. There was no charity in that record of beneficent work, all the benefits having been paid for by the contributions of the members themselves. The proposition, having been seconded, was carried. The partnership between John Morgan Jones, of Ty Goytre, Nant-y-derry, near Abergavenny, Monmouth, and David Edward James, of The Larches, Ystradgynlais, Brecknock, colliery proprietors, trading as the Brynygroes Colliery Company, has been dissolved.