The Thiers pit, sunk in the ordinary way through similar ground, cost £75 per foot. As the entire cost of the plant was charged to this single sinking, its employment in subsequent work will relieve the cost to the extent of nearly £13 per foot. The items directly chargeable to the freezing plant were as follows: This sum, equal to £8.06 per foot, represents the money available for pumping, temporary lining, and the other numerous expenses incidental to sinking through heavily watered strata. The total expenses of sinking may be summarised as follows: Bibliography.-The following is a list of the more important memoirs dealing with the subject matter of this chapter: : INST. C.E. Deep Winning of Coal in South Wales, T. Forster-Brown and G. F. Adams, lxiv., 23; The Sinking of two Shafts at Marsden, for the Whitburn Coal Company, John Daglish, lxxi., 178; Sinking of Two Pits near Dortmund, H. Tomson, xc., 330. AMER. INST. M.E.: A New Method of Sinking Shafts, E. B. Coxe, i., 261; Shaft Sinking at Goderich, Ontario, J. H. Harden, v., 506. FED. INST.: Notes on the Sinking at Lens Collieries by the Poetsch System, N. R. Griffith, ii., 441; Use of Cement in Shaft Sinking, B. H. Brough, iv., 343: A Combined Centre Line Apparatus, W. Foulstone, v., 364; Sinking with Rock Drills, F. Coulson, viii., 17; The Gobert Freezing Process of Shaft Sinking, A. Gobert, xi., 297. MAN. GEO. Soc. Boring Shafts in Westphalia, A. Demmler, xiv., 374; Sinking with a Tail Rope, G. Wild, xviii., 380. BRIT. SOC. MIN. STUD.: Details of Sinking Upwards, H. Jepson, i., 134; Sinking at Aldwarke Main Colliery, A. Mirfin, i., 186 and 222; Sinking through Quicksands, Marls, and Gravel Beds, R. Clough, xiv., 106; Sinking of Two Shafts at Claravale Colliery, F. R. Simpson, xix., 137; An Account of the Maypole Colliery Sinking, Wigan, A. H. Leech, xxi., 57; Description of Tubbing Shafts against Water, R. Clive, xxi., 154; A Self-filling and Discharging Water Barrel for use in Sinking Pits, Geo. E. J. McMurtrie, xxi., 160. So. WALES INST.: On the Tubbing of Shafts, E. Hedley, iv., 104; Personal Experiences in Tubbing Shafts, Geo. Wilkinson, x., 191; Excavating below Water Level by means of Compressed Air, Wm, Galloway, X., 252; An Account of the Sinking and Tubbing of a Pumping Shaft at Radstock Collieries, J. McMurtrie, xi., 66; Poetsch's Freezing System of Sinking through Quicksands, R. de Soldenhof, xv., 143 and 349; Sinking Appli ances at Llanbradach, Wm. Galloway, xvi., 107 and 268. MIN. INST. SCOT.: Notes on the Sinking of Shafts and the way they are fitted up for Winding and Pumping, Robt. Beith, viii., 234. : N. E. I. On Murton Winning, Ed. Potter, v., 43; On Sinking through the Magnesian Limestone at Seaton and Seaham Winning, N. Wood, v., 117; On the Strength of Tubbing in Shafts and the Pressure it has to resist, J. J. Atkinson, ix., 175; On the Proper Precautions to be adopted in order to prevent the Displacement of Tubbing in Shafts, J. J. Atkinson, and Wm. Coulson, Sen., xi., 9; On the Sinking of Shafts by Boring under Water as practised by Messrs. Kind & Chaudron, Warington W. Smyth, xx., 187; On the Coffering of Shafts to keep back Water, N. R. Griffith, xxvi. 3; Sinking Set fitted with a New Windbore Protector and Suction Regulator, H. Richardson, xxx., 49; Points of Interest at the Skelton Park and Lumpsey Mines, A. L. Steavenson, xxxi., 105; A Chronological Review of a number of Shaft Borings (in For. Abs.), xxxii., 76. Soc. IND. MIN.: Notice sur un nouveau mode d'approfondisement des puits d'extraction, M. Delcommune (2o Série), vii., 819; Procédé Poetsch pour les travaux à faire dans les terrains aquifères par la congélation, A. Lévy, (2o Série), xiii., 583; Emploi de cercles en fer et de plateaux en chêne pour rivètement du puits Nord-Ouest de la Cie des Mines de Montieux à St. Etienne, M. Male (2° Série), xiv., 555; Fonçage des puits de Vicq par le procédé Poetsch, MM. Saclier and Waymel (3° Série), ix., 27; L'emploi de la congelation pour l'exécution de travaux dans les terrains aquifères, F. Schmidt (3 Série), ix., 273; Note sur le fonçage des puits à grande profondeur par le procédé Poetsch, M. Saclier (3o Série), xi., 647. MID. INST.: On Iron and Stone Tubbing, T. W. Embleton, vii., 165; Artificial Foundations and Method of Sinking through Quicksand, W. E. Garforth, xi., 407. CHES. INST. Sinking at Clifton Colliery, J. Brown, viii., 345. N. STAFF. INST.: Sinking through Quicksand at Podmore Hall Colliery, W. R. Wilson, vii., 113. REV. UNIV.: Notice sur quelques faits relatifs aux fonçages de puits à niveau plein (Système Lippmann), Ed. Bautier et H. Mativa (2o Série), v., 96; Note sur la réparation du cuvelage du puits No. 3, Ste Barbe, A. Sohier (2° Série), vii., 528; Note sur la réparation de deux cuvelages en bois et sur l'installation d'un châssis à molettes en fer au charbonnages du Viernoy, A. Ledent (2o Série), xii., 352; Creusement et muraillement simultanès des nouveau siège Fanny des Charbonnages de Patience et Beaujone à Glain lez Liége, L. Thiriart (3 Série), xxii., 113; Note sur un creusement de puits à l'aide de plongeurs, G. Nordenström (3o Série), xxv., 1; Remplacement d'un rivètement en bois par un rivètement en maçonnerie sans interrompre ni l'epuisement ni l'extraction, J. Linet (3o Série), xxvii., 153. ANN. DES. MINES: Memoire sur la methode de congélation de M. Poetsch pour le fonçage des puits de mines et terrains aquifères, F. Lebreton (8o Série), viii., III; Note sur des expériences de congélation des terrains, M. Alby (8° Série), xi., 56. The Freezing Process as applied at Iron Mountain, Michigan, in Sinking a Shaft through Quicksand, D. E. Morgan, School of Mines Quarterly, New York, vol. xi., 237. 151 CHAPTER V. PRELIMINARY OPERATIONS. Underground Roads.-Having reached the seam from which mineral is to be extracted, the first operation consists in driving a series of passages called levels or roads." Their direction is governed by the relative position of the shafts and the area to be won, by the system of working adopted, and by the inclination of the seam. Their size is governed by the dimensions of the tubs employed and by the proposed system of haulage, as, if a double line of rails has to be used the dimensions of the roads will necessarily be larger than where only a single line is in operation. The direction is also influenced by the question of haulage, for if mechanical means are not employed, the gradients of the roads will have to be such that a horse can readily draw material along them, and as the dip of the mine and the position of the shafts are fixed points, the roads in this case will have to be driven in such direction that the necessary gradient is given. Another point is the question of dealing with water. Wherever possible, the gradients should be such that all water gravitates towards the shaft. Perhaps, in all seams of moderate and regular inclinations, the best plan is to drive the main road practically along the strike of the seam, only deviating from that line to such an extent as will give a slight fall towards the shaft. Where seams have undulating gradients, roads carried along the strike necessarily vary in direction with each change in the dip. For any system of mechanical haulage, the best results are obtained where the roads are driven straight, so that when the dip varies we usually find that the straightness of roads is more looked to than any actual question as to whether they are following the strike of the seam or not, as it only requires a little more engine power to haul along the material. Means of Keeping Direction.-Having decided upon the position of the roads, they are kept in the proper direction by very simple means. At the commencement two or three points are determined, and marked on the roof, with the aid of a compass or theodolite, and plumb-bobs are suspended from them in such a position that the straight line made by these three shall be in the direction in which the level is to be driven. Three points are much to be preferred to two, as in case any movement takes place in any of them, it is usually found out, such not being the case where only two are adopted; as an additional precaution, it is better that these lines should not be attached to timber frames or settings, or the pressure of the ground is liable to move them out of position. To determine whether the road is proceeding in the proper direction, an observer stations himself behind the plumbbob farthest from the face, and lights are held against the other two lines. Another workman is stationed at the face with a light, which is moved about until its position coincides with the line given by the three fixed suspended plumb-bobs. In some instances the points are fixed in the axis or centre line of the excavation, while in others they are placed nearer to one side of the road, of course preserving the same line of direction. In the latter case, the point obtained on the working face will not be the Mamb bob plumb bob middle of the road, but somewhere about a foot from the side. This latter arrangement is preferable, because if the road does get slightly out of line when the determining points are fixed in the middle, the straight line given by these points will pass down the road (Fig. 139), but if such points are only 1 foot from the side it would be impossible to get the line through (Fig. 140). *---*-line of direction Figs. 139 and 140. Means of Keeping Gradient. For haulage planes uniform gradients are preferable, as the cost of cutting through small irregularities of the floor or roof, and indeed, dislocations caused by faults, is soon repaid by the ease and smoothness with which the plane is afterwards worked. In the case of large faults, modifications of the gradients have to be introduced, but even in such cases it is usual to make the inclination approach as near to the regular one as possible. The instruments employed for keeping the gradient uniform are also of a simple character. Often an ordinary T-bob (a wooden frame shaped like an inverted T) and plumb-line are used, the vertical piece being placed on such an inclination that it corresponds with that to be given to the floor. This is rather a clumsy instrument. A more convenient form is that of a straight edge (a, Fig. 141) about 6 feet long, in the upper side of which a level, b, is bedded in a small secondary triangular block of wood, c, the angle that this latter piece makes with the former being such that, when the bottom side of the straight edge is parallel with the line of inclination of the road, the level is truly horizontal. Fig. 141. Operation of Driving.-Having determined the direction and gradient, the work is, as a rule, carried out in the following manner :The first operation consists in holing or undercutting the seam; that is to say, either the lower part of the coal is cut away with a pick, or, if a soft layer exists beneath the seam, undercutting is performed in it with the object of reducing waste, because holing the coal makes nothing but "small," which is comparatively worthless. The width of the undercutting is equal to the width of the road, but its depth. depends entirely on the nature of the seam. Strong coals require deeper holing than tender ones. In performing undercutting, the miner lies on his side, and naturally removes more height at the face than at the back, because at the former place his arms and the helve of the pick have to be inserted, while at the immediate back only a space equal to the width of the tool is necessary. If the undercutting is deep, part of the man's body is also introduced, and consequently more of the coal has to be cut away. For this reason, except where the nature of the coal absolutely requires it, holing should not proceed any further under than a man can conveniently reach without inserting his body. The coal undergone is got down by cutting a vertical groove along one side, and then breaking down the remainder either by blasting or by wedging. In some collieries gas exists in the coal under such pressures that it assists the workman in hewing the coal, and roads can best be driven by attacking the whole height of the seam at one time. If holing were resorted to, it would drain the gas, and render the operation of getting down the coal above, a more difficult and expensive one. Ventilation.-Except under exceptional circumstances, one road is never driven alone, two parallel ones (a and b, Fig. 142) being carried forward at the same time, these being connected at intervals by other roads, called "thurlings," or cross-cuts (c c'), the object of which is to provide a way for air to pass to the face and ventilate it. When the second thurling is driven, the first one is blocked up by building a wall in it. Such obstruction is called a "stopping," its object being to force the air further inbye, and prevent it going back to the shaft until it has ventilated the workings. It is obvious, however, that the current of air will naturally pass through the last thurling, and when the road goes on further, the face will remain unventilated, unless some means are adopted for carrying air to it. This is done by one of two methods; either by carrying bratticing or by iron, canvas or wooden pipes called air troughs or "trows." stopping Fig. 142. a Bratticing is generally fixed by putting props along the line of roading, but instead of using ordinary short lids to such props, a long strip of wood about 3 inches broad is employed, and firmly secured against the roof by driving the prop beneath it. The brattice cloth is attached to these laths by nails, and temporarily divides the roadway into two, as shown by dotted lines in Fig. 142. The pure air passes up one side and down the other, as indicated by the arrows. This system is largely employed, and is unsurpassed where the roof is regular, as the laths rest evenly against it, and form an airtight joint. With irre.ular roofs bratticing is impracticable, and air troughs have to be used. These consist of sheet-iron pipes, from 10 to 15 inches diameter and 6 feet long, with a socket and spigot end. A temporary stopping is built across the road, immediately before the last thurling, and one of these pipes put through it. As the heading proceeds, other pipes are added. The air passes through them, and back again along the road. In seams with a tender roof, or in deep mines subject to heavy weights, it is advisable that as few cross-cuts as possible should be made between the winning headways. As the -ordinary ventilating pressure is insufficient to force an adequate amount of air through long lengths of pipes, small subsidiary fans driven by electric motors are often employed The air current must then be conveyed to the working places through pipes, because brattice cloth is not rigid enough to resist the increased pressure. |