measure rock and built up simultaneously with the inner 9-inch circle. A space of 2 inches separated these two rings, and when built there were three concentric rings of brickwork, the space of 24 inches between the inner and the next one being filled in with pure Portland cement, to form an impervious barrier to water from the quicksands. The larger space of 2 feet 8 inches between the outer ring of brick

16.0

Figs. 47, 48.-SHAFT-SINKING AT ASHTON MOSS COLLIERY THROUGH THE DRIft
OVER-LYING THE COAL MEASURES.

work and the next one was filled in with soil and loose material as the building proceeded, so as to make the whole coffering compact and solid up to the surface. Fig. 47 is a section showing the shaft at the time the first 9-inch ring

O

of brickwork was finished, and the shaft continued down

to a hard impervious bed prepared to receive the walling crib, while Fig. 48 is a section and Fig. 49 is a ground view of the shaft at the time of completion of that portion between the surface and the walling crib. Both downcast and upcast shafts have a diameter of 16 feet in the clear. No tubbing was used in either, but the 9-inch lining of brickwork was brought up from the shaft bottom throughout to join the walling crib shown in Fig. 48 This coffering has proved most effectual in keeping back the water from the shafts. The advantage of cement over cast iron for lining shafts is that of durability. If able to resist the pressure after the lining is complete it remains unaffected by mineral water, which corrodes and wastes unprotected cast iron tubbing.

SECTION.

On the Continent, tubbing of cement blocks, and also of moulded concrete blocks has been used, shaped so as to form water-tight segments when in position in the shaft. The concrete blocks are rammed through vertical flutings with a cementing material, and the space behind, with concrete.

A disadvantage in the use of cement, whether used as at the Ashton Moss Colliery or in tubbing-blocks, is in the necessarily increased size of shaft and increased expense of sinking. If the pressure is great the blocks must be very thick, and to make room for their insertion in the shaft additional material must be taken out. Probably the relative thickness of cement tubbing, compared with metal, sets a limit to its use in resisting a certain head of water.

Powdered cement has been used on the Continent in sinking shafts through shifting sand in water-bearing strata. It is injected into the ground by the force of compressed air, steam, or water, so as to consolidate it.

The temperature of the strata increases in proportion to the depth. This obviously points to a practical limit beyond which it will be impossible, owing to the heat, for coal mines to be worked.

To sink a deep shaft even under favourable circumstances, requires a large outlay, and if serious difficulties occur the cost will be proportionately heavy. A fair return on this large capital cannot be expected without having extensive areas of coal, which must be worked to one centre, necessitating great lengths of haulage roads and airways, which augment the working cost.

The high temperature of the strata in deep workings heats the air circulating through the passages of the mine all the year round, except perhaps during a few days in summer, when the surface air is at a high temperature. The entering air absorbs heat from the surfaces of galleries exposed to the current. The difference of temperature between the strata at the bottom of the shaft and the entering air, which will be at a maximum in winter, causes this absorption to be greatest at the first: it becomes less and less at points of the intake airway further away. Summer and winter make no difference in the temperature of the air in mines, except for a short distance from the shaft. If it is cooler on entering in winter it has greater capacity for absorbing heat, and so the greater difference in temperature is soon overcome. The working face has more influence in raising the temperature of the air than old airways the surfaces of which have become cooled by long exposure.

Mr. Lindsay Wood ascertained from experiments made in the Hetton Collieries that there was a gradual approximation of the temperature of the air to that of the strata as the air travelled from the shaft to a distance of 3,422 yards. The volume of air flowing varied from 41,800 cubic feet to only 3,000 cubic feet per minute. The difference between the temperature of the air and the strata at the shaft was 7° F. and at the working faces, 3° F. Other observations confirm those of Mr. Wood in which it was shown that increased ventilation has but little effect on the temperature of the air at great distances from the shaft. Where the working faces are much nearer the shaft, the temperature of the air may not approximate nearly so closely to that of the coal freshly exposed.

Little reduction of temperature, therefore, can be anticipated at the working face of a colliery whose shafts are so deep as to necessitate long permanent airways. Even the use of compressed air in the workings will have but little effect in this direction.

When the temperature is as high as 80° F., and the air is moist as in the case of the Monkwearmouth Colliery workings, it begins to affect the physical powers of the colliers, who can only work for a limited number of hours per day, and so the cost of working is increased. A much higher temperature can be endured where the air is dry, but in most colliery workings air contains much watery

vapour, and is frequently saturated. In many cases, owing to the dryness of workings at great depths, means are taken to saturate the air as it travels from the shaft in order to lay the dust. If the only consideration were that of the power of the workmen to bear a high temperature, the very opposite course should be adopted, and some method be devised to deprive the entering air of moisture. If this were done, it would ensure a moderately dry atmosphere reaching the face, and by assisting free evaporation from the body would enable the workmen to endure a higher temperature than would be possible in a moist atmosphere. But the drying of the air would also cause the roadways to be filled with dangerous clouds of fine coal-dust, which can at present be prevented only by frequent watering, or by the destruction of the coal-dust.

As the temperature of a moist atmosphere rises above 80° F., the less labour will it be possible for miners to perform in it, and the higher will be the cost of working. The normal heat of the blood in the human body is 98° F. In atmosphere a little higher than this, work can only be carried on at all in short periods, the shifts of workmen being relieved by removal to a cooler region.

As questions are sometimes given at the examinations, having reference to the cubical contents obtained from sinking shafts, the following example is given and worked out in order to show candidates how to do similar calculations.

Question 1.-A pit is sunk 17 feet 6 inches in diameter, and walled with good bricks 13 inches in the bed, 6 inches deep by 12 inches long inside, but more at the back-being moulded to suit the circle of the pit-the diameter of the shaft when the walling is finished being 15 feet in the clear. The pit is 100 fathoms deep.-How many cubic feet of excavation would be taken out, and assuming 14 cubic feet of it to weigh a ton, state the total weight? Also, if walled from top to bottom, how many bricks of the above dimensions would be required, and how much would they cost at £5 per thousand? Here we have to get the area of a circle whose diameter is 17 feet 6 inches, and to multiply it by the depth of the pit in feet to get the cubical contents. 175 175 × 7854 × 600 = 144,317 cubic feet,

and 144,317
14

= 10,308.38 tons.

47 124 X 12
12.25

To find the number of bricks we must find the circumference of a circle whose diameter is 15 feet; 15 × 314159 = 47°124, and if we allow of an inch for mortar at the joints we should require =46'16, the number of bricks which we should require for one ring; allowing of an inch for the horizontal 100 × 6 × 12 joints the pit would have = 1,152 rings. Therefore 1,152 X 61

4616 53,176 32, the number of bricks required, and 53,176.32 × 100

=

=

5,317 632 shillings £265 17s. 7d. as the cost of the bricks.

1,000

CHAPTER V.

FITTING UP THE SHAFT AND SURFACE ARRANGEMENTS.

Arrangement of Pit Bottom for Small and Large Trams-Shaft Gates-Conductors--Buntons -Keeps-Pit Cages-Safety Cages-Detaching Hooks-Pit Head-gear-Pulleys-Ropes -Capping Round and Flat Ropes-Observations for Users of Ropes-Tables of different qualities of Round and Flat Ropes and of Chains-Method of Splicing Ropes-Shaft Signals-Pit Stage-Tipplers--Screens and under Railways-Winding Engines-Conical and Spiral Drums-Steam-brake to prevent over-winding-Counterbalancing the Load in Shaft-Rules for Winding Engines-Calculations of Sizes required under given Conditions -Questions and Answers on Steam and Steam-engines-Systems of Winding Coal up Shafts without using Drums.

THE shaft bottom and roadways, for some distance, leading from the pit bottom are generally arched. Where small trams are to be used the space round about the shaft bottom is usually laid with flat sheet-iron for facilitating the operations. Where large trams are used rails are laid leading to each cage from opposite directions. This allows of the empty trams being propelled from the cage on one side as the loaded ones enter it at the other.

Where flat sheets are used, they allow of light full tubs, or the lighter empties, being quickly turned in any direction without having to follow a particular course. The pit is sunk a few feet below the level of the flat sheets to form a sump, and into this the water (if any) drains; from thence it is raised direct by the pumps placed in the shaft or conveyed elsewhere to be dealt with. The pit bottom is arranged so that the loaded tubs are pushed towards the cage down a slightly falling road, and the empty tubs pass out of the cage on the opposite side of the shaft.

The top of the pit and any intermediate loading places between the top and bottom, are provided with gates for the protection of those moving about.

Shafts are fitted with CONDUCTORS OF GUIDES, which, if of wood or iron, are attached to buntons or crosspieces fixed across the pit and which have either been built into the walling or are afterwards let into it. The strength of the buntons must be proportioned to the size of shaft and the weight of the load; for a shaft 10 feet in diameter with single cages carrying one tram of 12 or 15 cwts., Memel or red pine, 9 inches by 3 inches, placed at intervals of six feet in the shaft, would be sufficient. The guides (if of wood) should also be of Memel pine, not less than 4 inches by 3 inches in section, and properly bolted to the buntons. Bolts and nuts are preferable to wood screws which are often used for this purpose. There is usually only one guide on each side of the cage, but the arrangements respecting them are various, according to the requirements of the case. Frequently, instead of wood, bridge or single headed rails are used for guides, and in some cases angle iron, they being kept in line by suitable fish-plates and bolts, and securely fastened by bolts to the buntons. In Lancashire and Yorkshire some pits have guides consisting of round bars of iron fixed at the pit bottom and screwed up to the head frame. There are two rods for each cage, the cross bar of which, having a ring at each end, runs upon the rods.

In most of the large collieries in South Wales wire-ropes are used as guides,

fixed to wooden balks at the shaft bottom and to the head frame, where they are tightened by screws; another means of keeping them tight is to suspend heavy weights from their lower extremities beneath the balks, or by weights hanging over pulleys on the surface.

Where the depth and consequently the cage-speed is great, three and sometimes four of these guides are required to prevent excessive vibration. In some instances two additional ropes are suspended between the cages to prevent one cage from catching the other in passing. Rigid guides are so fixed that the cages shall have not less than 9 inches of clearance as they pass each other, and if iron wire guides are used and the pit a deep one there should be from 12 inches to 18 inches of clearance, according to the depth of the shaft, the number of guides used, and the speed of the cages in the pit.

66

99 66 KEEPS,' FANS," or "SHUTS " are supports for the cage on its arriving at the surface or shaft bottom, and at intermediate loading places, if there be any. They are arrangements of counterbalanced levers, and those placed on the pit top offer no obstacle to the ascent of the cage, which after passing by the "keeps" is lowered by the engine-man on to the supports. With double-decked cages, when the tub on the bottom deck has been changed and a signal received that the tub in the top deck (which it must be remembered stands on the shaft bottom "keeps," when the bottom deck of the other cage is on the "keeps" at the surface) is also changed, the engine-man lifts the cage from the supports, and the attendant, by means of a lever, pulls them back clear of the cage until the bottom deck is lowered below them, when the attendant lets go his hold of the handle and they form a support to the top deck. During the change here, the tub in the bottom deck is changed at the pit bottom, and this being effected, the cage is lifted by the engine-man, the attendant pulls back the "keeps," the cage is lowered, and when it has descended clear of the "keeps" they are allowed to spring back ready for use again. The "keeps" at the shaft bottom are necessarily handled differently. As the loaded cage leaves the shaft bottom the attendant there pulls the handle of the "keeps" back and secures it there, by this means preventing the "keeps" from protruding in the pit. As the cage in its downward course approaches him, he takes the handle of the lever which works the "keeps" in his hand, and having allowed the bottom deck of the cage to pass below the level of the "keeps" they are allowed to spring out and support the top deck of the cage. The tub is changed here whilst the bottom deck of the other cage is changed at the surface. The "keep" handle will not require further attention from the attendant below until the cage has left for the surface when he secures the handle back in its place.

Stauss's patent keeps, shown in Figs. 50 to 55, have been designed to dispense with the lifting of cages before they are lowered into the pit.

Figs. 50 and 51 show the arrangement of these keeps, fixed on wooden spring cantilevers, to take the shock of the cage when lowered on to the keeps, and Figs. 52 to 55 show the details.

The wear and tear of the winding ropes and engines are reduced, because owing to there being no lifting of the cage before descending, the accompanying jerks are avoided; and jerks are the main cause of deterioration of ropes and engines. When these keeps are used, the winding rope must of course be adjusted in length, so that the cage does not fall after drawing back the keeps. The sinking of the cage should not amount to more than the slack of the rope when unloaded.

The length of the rope can easily be adjusted by means of Freudenberg's cageadjusting hangers, as shown in Figs. 56 and 57, or similar appliances. This is only necessary for the first few days with new ropes; later on very seldom.