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which the various parts are put together and added to; but unfortunately, it often breaks, which occasions months of delay, and increases the cost of sinking. This is the only advantage possessed by wooden drums; instances are to be found where such have been pushed into an oval form, and yet have not collapsed.

When the sinking has reached the stone-head, no matter what system has been used, the procedure afterwards is always of a similar character. The ground is carefully prepared for the seating of a curb upon which the permanent lining is brought up to the surface by one of the methods to be described further on, all temporary timbering being removed as the work comes upwards. As a matter of fact, the lining is usually carried a short distance above the surface of the surrounding ground to secure some "tip" for the débris which is excavated from the sinking.

METHOD OF PROCEEDING AFTERWARDS.-On reaching the solid ground, excavation proceeds with the tools described in the previous chapter, those employed depending entirely on the nature of the strata which have to be passed through. Several difficulties are encountered where machine drills are employed. Owing to the uneven nature of the bottom, the ordinary tripod stand is used with difficulty, taking from five to ten minutes to fix, and then the legs move during drilling if the ground is soft. As no roof exists, the vertical stretcher bar has to be replaced by a horizontal one. This is not easy to fix, and takes so much time to adjust, that often, instead of moving the bar and drilling holes in the most favourable position for blowing, they are put down in such places as suit the drill, and consequently are not so effective. Considerable time is also lost in raising drills and bars out of the way when blasting takes place.

To obviate these disadvantages a boring frame is employed consisting of four main stretcher bars, a a (Fig. 104), hinged to a central support, b, and suspended by a chain, c, and capstan rope. Each of these bars is provided with a lengthening screw and claw, so that the whole structure can be readily clamped in position, and as it shuts up when not fixed against the side of the shaft, it is equally easily withdrawn. To keep the structure from lifting by the impact of the drills when boring, four secondary arms, dd, are arranged near the top of the frame, these being strutted against the sides at a slight inclination upwards, and, in addition, heavy cast-iron blocks, similar to those used on the tripod stand of an ordinary percussion drill, can be fixed on the central support b to counteract the upward thrust. As each of the arms a may be moved radially around the centre, if the drills are mounted on swinging arms (see Fig. 71), they can be placed at any angle and clamped in any position, and the holes put in anywhere.

Where drills are adopted, the general procedure is to first bore all the holes required, hoist up the frame and drills by an engine, fire the holes simultaneously, and then load up the débris until the bottom is clear, when the drills are again lowered and fixed, and drilling recommenced. In hard ground, probably only one set of holes will be bored and blasted and the rock removed in twenty-four hours.

Another practice gaining ground, is to lower the walling stage to about 8 or 10 feet from the bottom, wedge it there and form an artificial roof, and then use ordinary vertical stretcher bars.

Another method proposed, and, indeed, tried in two instances, is to start at the surface and bore a series of holes 200 or 300 feet deep with the aid of the diamond drill, and fill them up with sand. Blasting then commences by removing 4 or 5 feet of sand from the holes, and firing them in groups, this process being repeated until the bottom of the holes is reached, when the drills are again introduced, and a further distance bored. The Pottsville shaft, U.S.A., was sunk in this manner,* 25 holes being bored 1 inch in diameter about 3 feet 3 inches apart in one direction, and 4 feet in the other. The central group of holes was always fired first, and the outside rows afterwards. The process was expeditious, but the financial result does not appear to be satisfactory. At Harris Navigation Colliery, the same method was tried for about 70 yards but abandoned.

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With the object of providing support for the curb carrying the upper length of lining, when sinking recommences, the excavation is carried down for about 3 to 5 feet, lineable with the inside of the curb (a, Fig. 105), then shorn back until the diameter is large enough to take in the permanent lining, and afterwards carried downwards this size, until the strata require more support than temporary timbering affords. A seating will then be made for a curb, b, leaving a space, c, in the bottom of the shaft for the collection of water, &c., and the walling built on it up to the curb above, the ground a being removed for this purpose, not all at once, but in sections.

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Fig. 106.

Keeping the Shaft Vertical. This is done by the aid of a centre line which is either a cord of special manufacture about 3 inch in diameter, or preferably a copper wire, long enough to reach from the surface to the bottom of the shaft when completed. One end of this line is coiled on a small drum situated near the top of the pit, and the other end is led by pulleys to the exact centre of the shaft. rule, the central point is a hole bored through a baulk of timber placed across the shaft, but a better plan is to provide a hinged arm (a, Fig. "A New Method of Sinking Shafts." E. B. Coxe, Amer. Inst. M. E., i.,

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106) built firmly into the masonry. When in use this is kept in its proper position by the stop b, but if not, it is folded upwards into the position shown by dotted lines at c. After the line has been passed through the centre hole, a link is attached, from which a weight can be hung, this dipping into a bucket of water at the bottom, so that the line is steadied. As soon as the proof has been made the weight is removed, and the cord wound up again on the drum.

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In order to minimise the time lost in steadying the plumb-bob, Mr. W. Foulstone has designed an arrangement consisting of a wroughtiron girder fitted with a pulley at the end hanging over the shaft, and with a rack on its upper surface. This rack is geared into wheels supported on two fixed girders projecting a short distance over the shaft, which also carry a small winch on which the testing line is wound. By means of the gearing and rack, the wrought-iron arm

Fig. 107.

Fig. 108.

carrying the centre line can be run out, so that the latter hangs exactly in the centre of the shaft. The centre line and weight, when not in use, are left hanging in the shaft, near to the side, some 30 yards above the bottom out of the way of shots, and can be run out by the rack to the exact centre, and the weight lowered by the drum, in a few moments.

For determining whether sufficient ground is removed, the master-sinker is provided with a "centre" staff, which is a wooden rod about 1 inch square, and equal in length to the outside radius of brickwork. This is moved round the central point as excavation continues.

For setting out the curbs exactly beneath each other a series of cords (d, Fig. 105) are hung all around the circumference of the shaft at intervals of about 3 feet. These are attached to the inside of the upper curb, and serve, not only to set the curb below, but also as a guide for the amount of excavation. Every third curb will be checked by the main centre line, the intermediate ones being set out by the side lines.

Winding Débris.-The material excavated is brought to the surface in wrought-iron barrels called kibbles, hoppits, or bowks, the general shape being shown in Fig. 107. At the top is a bow of wrought-iron swung to the body by two eye-pieces riveted to the sides of the kibble. Attachment is made to the winding rope through a spring hook (Fig. 108). With such construction time is lost at the surface, as the full bowk has to be taken from the rope and replaced by an empty one. For this reason the tipping kibble is preferred. Its body is similar to the one already figured, but the wrought-iron bow is not attached at the top but at a point below the centre of gravity, so that when full, the tendency is for the kibble to turn over and empty itself. To prevent this happening during hoisting, two short vertical pins (Fig. 109) are riveted to the inside of the bucket, * Fed. Inst., v., 364.

and an ordinary chain link, sliding on the arms of the bow, passed over them. On reaching the surface the safety links are lifted off the pins, when the hoppit immediately turns over and empties itself. With such a system the kibble is only removed from the rope at the bottom of the shaft, one disconnection being saved. The seams of these kibbles must be caulked, as when there is any water in the bottom of the shaft, a certain quantity is loaded up each time with the débris.

Covering over Pit Top.-This was originally done by means of a travelling platform, which could be wheeled over the shaft when the kibble reached the surface, and removed again when descent had to be made. The labour here is considerable, and time is lost. To get over these drawbacks, two hinged doors with their weight counter-balanced are adopted. These, when open, form a fence protecting the pit top on two sides; the other two are guarded with a permanent fence. When these are down they entirely close the opening, and two rails on the upper side of each door form a continuation of the tramway going to the dirt heap.

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Even, however, with these a little time is lost, as each door has to be lifted separately; so, to remove this complaint, Mr. Wm. Galloway has designed an arrangement of levers and counterbalances (Fig. 110)

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by means of which both are opened at the same time. a a, are bolted to each door, and keyed on cross shafts, bb, to which, by means of a handle, c, and connecting links, a movement of rotation can be given, and as the hinges are fixed to the cross shafts the doors lift when the latter turn. The weight of the doors is counterbalanced by four blocks of metal, d, so that they will stand at any position in which they are placed.

Guides. The introduction of guides in sinking pits is desirable to prevent the oscillation of the kibble, which gets especially large in deep undertakings, considerable time being lost in steadying it before winding commences. Two methods are adopted; in the first, a single guide rope is passed down the centre of the shaft, while, in the other, two ropes are used. In each system these guides, which are of flexible wire, are coiled on a drum worked by a capstan engine at the surface,

and can be lengthened as the sinking proceeds; they also form the means by which the walling stage is raised during bricking operations. In the former, however (see description, p. 139), the walling stage is removed during sinking, and the kibble is guided to the bottom of the shaft; while, in the latter, one end of each guide is always attached to the walling stage which remains in the shaft during sinking, and the kibble is only guided to the point where the walling stage is suspended. Each system has its advantages, as with one central rope the kibble is guided all the way, and if a heavy weight be hung at its lower end, the centre line of shaft is obtained without any further trouble, while, in the two-rope system, walling can proceed while sinking is going on below, thus saving considerable time, an advantage not possessed by the other method.

The system of employing two guides was patented by Mr. Wm. Galloway in 1875. In it, two wire ropes (a a, Fig. 111) are connected at their lower end to the walling stage, and pass over two pulleys on

the headgear to drums worked by a steam crab, each drum being able to be moved independently, to provide for any casual irregularity in the length of guides. An iron frame, consisting of two legs joined

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together by a cross-bar, called the "rider," clasps the two guides loosely at four points, bb, thus preventing any chance of cross-binding. The winding rope passes through a hole in the centre of the rider. The capping connecting the winding rope and chain going to the kibble is provided with a buffer, c, consisting of alternate layers of india-rubber and sheet iron, which are of larger diameter than the hole in the rider cross-bar, and therefore cannot pass through it. When the kibble arrives at the surface the balanced doors are closed, a tipping waggon (one form of which is shown in Fig. 112, the sketch explaining itself) run beneath, and the kibble emptied into it. The waggon is then removed, the doors opened, and the bucket and rider lowered away until the walling stage is reached, when the arms of the rider are caught by two buffers on the bridle chains. The kibble and winding rope continue their descent, passing through the square opening in the stage, until the bottom of the shaft is reached. In ascending, the winding rope slides through the central opening in the rider cross-bar, until the buffer on the capping comes in contact with The rider is then lifted to the surface.

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In sinking the Harris Navigation shafts, the time occupied in

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