SINKING ON THE SEASHORE AT MUSSELBURGH.

BY ROBERT MARTIN.

Introduction.--Olive Bank colliery is situated in the burgh of Musselburgh on the banks of the Firth of Forth, within 900 feet. of high-water mark and about 12 or 14 feet above the level of high tide. Fig. 1 (Plate IV.) shews a cross-section of the MidLothian coal-field, indicating the position of the "edge" seams at Niddrie and Newcraighall and across to Wallyford. The Niddrie coal-seams occur in the Carboniferous Limestone series, and the seams at Olive Bank and Newcraighall are in the Upper Coal-measures.* The Olive Bank seams, known in the district as the "fiat" seams, have been extensively worked, farther south, at Stoneyhill, Millerhill and Smeaton.

The strata at Olive Bank have been proved by boring to a depth of 912 feet. The Splint coal-seam is 5 feet thick, at 600 feet; lower down the Rough and Beefie seams; and the Jewel coalseam, 4 feet 8 inches thick, to which the pits are to be sunk, is at a depth of 912 feet. The section near the surface, so far as this paper is concerned, is as follows:---

Sinking the Cylinders.-Two shafts, 70 feet apart, and each 14 feet in internal diameter, have been sunk through the alluvial deposits into the red sandstone. The shaft-lining consists of a steel cylinder, 18 feet in diameter, lined internally with brickwork and concrete, 2 feet thick. Figs. 2, 3, 4, 5 and 6 (Plate IV.) show the cylinder in various aspects. Fig. 2 represents the whole length of the cylinder, namely, 81 feet, consisting of the cuttingedge ring, 5 feet long and 3 inch thick, and 19 rings, 4 feet long and inch thick. The cylinder was supplied by Messrs. Somervail and Company.

"The Mid-Lothian Coal-basin," by Mr. Robert Martin, Trans. Inst. M.E., 1893, vol. vi., page 388.

Both pits were sunk of square shape, 18 feet inside, through the boulder-clay, and lined with white pine, 9 inches by 4 inches. In this shaft, over 30 feet of the cylinder was constructed and partly lined inside with brickwork and concrete, before any attempt was made to lower it. The cutting-edge ring, a, is widened to 18 feet 2 inches in diameter at the foot, or bell-mouthed, so as to give clearance when lowered. The cone-shaped arrangement of plates, b, is intended to stiffen the cutting-edge ring. On the top of the cutting-edge ring (Figs. 5 and 6) is a platform, c, supported by angle-iron brackets, d, upon which the brickwork-and-concrete lining is built. In the first cylinder that was sunk, in order further to stiffen the cutting-edge ring and to assist in carrying the heavy load of brickwork and concrete, the space between the cone, b, and the platform, c, was filled with pitchpine blocks, bolted to the cylinder, and these were afterwards removed. In the second cylinder, it was found more simple and as efficient to fill this space with brickwork, each course projecting over the lower one until the full thickness was attained. Fig. 5 shows the interior of the cylinder. Above the cutting-edge ring were added the 4 feet rings, each consisting of 8 plates 7 feet long, attached together by T irons, f, 6 inches by 3 inches and inch thick. These T irons extended from one ring to another and tied them together. Each ring is strengthened with 3 horizontal angle-irons, e, 3 inches by 3 inches and inch thick (Fig. 5). The angle-irons at the ends of the rings form an internal flange, and the flanges of adjoining rings were fastened together by 56 bolts. Counter-sunk bolts and rivets were used on the outside of the cylinder, which presented a perfectly smooth surface, and reduced sliding friction to a minimum.

The internal lining of the ring consisted of 2 rings of 9 inches brickwork, the bedding of one ring breaking joint with the other so as to blind the joint. Behind the brickwork and next the cylinder, the remaining space of 6 inches was filled with cementconcrete, run into the interstices of the angle-irons, T irons, nuts and rivet-heads. The mortar used for building and concreting was ordinary lime (1 part of shell-lime to 3 parts of sand) and as much Portland cement.

When the square shaft was sunk sufficiently far down, the cylinder was built in it to a height of 8 feet above the surface, and adjusted so as to be exactly vertical. About 2 feet of silt was dug out of the bottom, and brickwork was built in the cylinder so as to

force it into the space, if it did not move. This process was repeated until the brickwork reached above the surface, and its weight proved insufficient to press down the cylinder. In both shafts, this stage was attained when the cylinder had reached at depth of about 75 feet.

The rate of sinking ranged from 3 feet to a few inches per day. The estimated weight of the cylinder and brickwork was about 5 tons per foot. In the sinking of the first shaft, about 200 tons of additional weight of pig-iron was required to force down the cylinder for the last length of 32 feet. The pig-iron was laid on scaffolds supported upon buntons built into the walling. When the first shaft reached a depth of 94 feet, the bottom was forced upward by a water-feeder varying from 300 to 400 gallons per minute. At this depth the cylinder sank, amongst the mud, about 2 feet per day, until it rested on the rock. The surface or skin-friction of the cylinder was about 2 cwts. per square foot of rubbing surface.

The sinking of the first cylinder took from August 21st, 1901, to January 14th, 1902, to reach the rock-head, or less than 5 months; and the second cylinder took from February 20th, 1902, to July 13th, 1902, to reach the rock-head, also about 5 months.

In the second shaft, a weight of 400 tons of pig-iron was required to force down the cylinder. This gives a skin-friction of 3 cwts. per square foot of rubbing surface, due to the absence of the large feeder of water, which practically undermined the first cylinder. In both pits, a small feeder of water was encountered in the gravel.

The silt was, at times, so soft as to be difficult to stand upon and tough to dig; but when dry, it was easy to dig with a shovel. In the second shaft, it was necessary, latterly in order to induce a movement of the cylinder, to dig outside the cylinder and to facilitate inrushes of mud and water. As a consequence, the cylinder and silt sank together, and a large surface-subsidence, about 20 feet in depth, was formed round the pit-mouth, by the time that the cylinder had reached the rock.

Both cylinders were sunk sufficiently deep into the red sandstone, so as to dam back the mud, and when this depth was attained, the tops of the cylinders were 26 feet below the surface. The upper portion of the shaft was then built up to the surfacelevel with 18 inches of walling.

Sinking the Shafts. When these operations were completed, the work became that of ordinary sinking, except that it was necessary, for some depth below the cylinder, to excavate the sandstone in such a way so as not to undermine and induce an inrush of silt into the shaft-bottom. This was done by carefully hewing and dressing the sides of the shaft to a slightly less diameter than the cylinder, to a depth of 6 feet. At this point, the diameter of the shaft was reduced to 14 feet, thus leaving a ledge or foundation-bed for a brick-wall. This walling was carried upward till the tapered cutting-edge was built in. Below the ledge or foundation-bed for the wall, the shafts were widened out and are being sunk to allow of a thickness of fully 9 inches of brickwork, with which the shafts are being lined. As the sides of the shafts are very irregular, owing to blasting, and as the brickwork is extended into these irregularities, the wall is practically selfsupporting.

The feeders of water are confined into and carried downward in hassons, rings, etc., in the sides of the shaft behind the brickwork. This makes a dry shaft, and there is no water on the face of the brickwork. Where necessary, the feeders are caught in rings and run into insets with lodgments, and are dealt with by special stationary pumps.

Consequently only the lowest feeders require to be raised by the sinking pumps. In each shaft, three Evans sinking pumps are placed, two with 12 inches, two with 9 inches, and two with 7 inches buckets by 2 feet stroke. These six pumps, capable of raising 2,600 gallons per minute against a head of 300 feet, are suspended on chains, with 6 inches links of 13 inches iron, tested to 30 tons, attached to beams either on the pit-mouth or in the shaft, and are raised or lowered as required by means of wireropes on hand-cranes.

Owing to the limited area of the shaft, the volume of the feeders of water, and the number of steam-pipes, water-pipes and airpipes in the shaft, it was found impracticable to sink and wall the shafts simultaneously. The method is to sink and wall a length of 9 to 12 feet, that is, all the work is done below the pumps, which In this almost fill the shaft at the point where they hang. way, no cribbing or timbering is required, unless the strata are extremely soft, and the danger of sinking with from 60 to 70 feet of shaft secured by temporary timbering is avoided

VOL. XXIV.-190 -1903,

Where a

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rock seat for the walling is not required or cannot be obtained, a few iron pins or crampets are driven in round the circumference, and when covered with boards they are sufficient to carry the walling until a secure foundation is got. As before remarked, if the wall is built into the sides with a good lime-and-cement mixture, it is self-supporting in a few days.

It may be mentioned that the pumps have sometimes been drowned to a height of 40 feet above the steam-cylinders, and that these continued working, or if stopped, were started until the water was lowered.

To discover the best type of bucket was perhaps the principal difficulty experienced with the pumping. The cost for frequent renewals was serious, not to speak of the loss of time in the sinking operations. Dermatine cups, indiarubber rings, cast-iron blocks lapped with Manila rope and gunmetal angular rings were used, the latter being preferred. In every case, the pump-barrel was lined with gunmetal. As the vibrations of long columns of steam-pipes and water-pipes carried by chains on which the pump was hanging and working was bad for the joints, bracketpipes have been introduced for each column. Between this bracket-pipe and the pump there is an expansion-pipe which allows the pump and the pipes immediately attached to the pumps to move freely up and down, but above the bracket-pipe the column is stationary.

The shafts are fitted with ordinary pitchpine slides attached to buntons for guiding the sinking-kettle. The kettle is kept in position by two pieces of wood bolted across the bow, and at each end of these beams is a recess, which fits the slides. By this device, the kettle can run at a high speed in a shaft filled with pipes, air-tubes, chains, etc. The kettle is discharged on the surface after being disengaged from the slides, which are flexible at the top and is swung out by means of a chain suspended from a beam at the pit-mouth; and the kettle is inverted, being hung at its centre of gravity, into an iron tub placed underneath a scaffold so as to receive the contents.

Mr. ARCHIBALD BLYTH (Hamilton) asked how far the cylinder varied from the vertical when down.

Mr. MARTIN replied that it was 18 inches.