Ernest Spon

“ The system of blasting employed in well sinking is that known as the small-shot system, which consists in boring holes from 1 to 3 inches diameter in the rock to be disrupted to receive the charge. The position of these holes is a matter of the highest importance from the point of view of producing the greatest [45] effects with the available means, and to determine them properly requires a complete knowledge of the nature of the forces developed by an explosive agent. This knowledge is rarely possessed by sinkers. ”

“ In some other soils, such as sandy loam, the yield in itself may not be sufficiently rapid to supply the pump; in such cases, the effect of constant pumping is to draw up with the water from the bottom a good deal of clay and sand, and so gradually to form a reservoir, as it were, around the foot of the tube, in which water accumulates when the pump is not in action, as is the case in a common well. In dense clays, however, of a close and very tenacious character, the American tube well is not applicable, as the small perforations become sealed, and water will not enter the tube. ”

“ The engineer who has to superintend the construction of a well should be ever on the watch to see whether, in the course of the work, the strata become so modified as to overthrow conclusions previously arrived at, and on account of which the well has been undertaken. ”

“ A running sand in soft clay is, however, the most serious difficulty met with in well boring. Under such circumstances the bore-hole has to be tubed from top to bottom, which greatly increases the expense of the undertaking, not only by the cost of the tubes, but also by the time and labour expended in inserting them. When a permanent water supply is the main object of the boring, the additional expense of tubing the bore-hole is not of much consequence, as the tubed hole is more durable, and the surface water is thereby excluded ”

“ Tools with nippers are sometimes used in large borings, as it is not advisable to subject the rods to a twist.
When the boring tool has detached a sufficient quantity of material, the boring rod and tool are drawn up by means of the rope O, Fig. 158, winding upon the drum Q, which is driven by straps and gearing from the steam-engine T. A shell is then lowered into the bore-hole by the wire-rope U, from the other drum V, and is afterwards drawn up again with the excavated material. A friction break is applied to the drum Q, for regulating the rate of lowering the boring rod down the well. ”

“ At the time of an accident a well kept journal is a precious resource, and at a given moment all previous observations, trivial as they may have often seemed, will form a valuable clue to explain difficulties, without this aid perfectly inexplicable. ”

“ In practice it is necessary, as with the common chisel, to turn the boring tool partly round between each stroke, so as to prevent it from falling every time in the same position at the bottom of the well; and this was effected in the well at Butte-aux-Cailles by manual power at the top of the well, by means of a long hand-lever fixed to the boring rod by a clip bolted on, which was turned round by a couple of men through part of a revolution during the time that the tool was being lifted. ”

“ In the ordinary system of well boring, innumerable breakages and delays occur when a boring is required to be carried to any depth exceeding 200 or 300 feet, owing to the buckling of the rods, the crystallization of the iron by the constant jarring at each blow, and particularly the increased weight of the rods as the hole gets deeper. ”

“ To sink a well by underpinning, an excavation is first made to such a depth as the strata will allow without falling in. At the bottom of the excavation is laid a curb, that is, a flat ring, whose internal diameter is equal to the intended clear diameter of the well, and its breadth equal to the thickness of the brickwork. It is made of oak or elm planks 3 or 4 inches thick, either in one layer fished at the joints with iron, or in two layers breaking joint, and spiked or screwed together. ”

“ If we consider the rock as a mass completely saturated with water through a certain vertical depth, the water being in a state of equilibrium, when a well is sunk, and the water pumped up, the state of equilibrium is destroyed, and the water in the rock is forced in from all sides. ”

“ The well-sinker has often, in executing his work, to contend with the presence of large volumes of water, which, under ordinary circumstances, must be got rid of by pumping; but by the introduction of iron cylinders, which can be sunk under water, the consequent expense of pumping is saved.
When sinking these cylinders through water-bearing strata, various tools are used to remove the soil from beneath them. The principal is the mizer, which consists of an iron cylinder with an opening on the side and a cutting lip, and which is attached to a set of boring rods and turned from above. ”

“ It is always desirable to sink a cast-iron well, such as that at the Horse Fort, as nearly as possible down to the level at which the water stands in the bore-hole. The sinking of such a well [150] is rendered an easy and rapid operation, with the aid of the boring machine in winding out the material from the bottom, and keeping the sinkers dry by the use of the dip-bucket, shown in Figs. 214 to 216, which will lift from 50 to 100 gallons of water a minute, for taking off the surface drainage. ”

“ The first method of well boring known in Europe is that called the Chinese, in which a chisel suspended by a rope and surrounded by a tube of a few feet in length is worked up and down by means of a spring-pole or lever at the surface. The twisting and untwisting of the rope prevents the chisel from always striking in the same place ”

“ When working in sandstone there is no adherence of the rock to the chisel when drawn to the surface, but with clays the contrary is the case. Should the stratum be very hard, the chisel may be worn and blunt before cutting three quarters of an inch, it must therefore be raised to the surface and frequently examined; however, 7 or 8 inches may be bored without examination, should the nature of the stratum allow of such progress being made. ”

“ When the line of least resistance has been decided upon, care must be taken that it remains the line of least resistance; for if the space in bore-hole is not properly filled, [51] the elastic gases may find an easier vent in that direction than in any other. The materials employed to fill this space are, when so applied, called tamping, and they consist of the chips and dust from the sinking, sand, well-dried clay, or broken brick or stones. ”

“ An Artesian well, so called from the province of Artois, in France, is a shaft sunk or bored through impermeable strata, until a water-bearing stratum is tapped, when the water is forced upwards by the hydrostatic pressure due to the superior level at which the rain-water was received. ”

“ The course of water flowing underground is not strictly analogous to that of rivers on the surface, there being, in the one case, a constant descent from a higher to a lower level from the source of the stream to the sea; whereas, in the other, the water may at one time sink far below the level of the ocean, and afterwards rise again high above it. ”

“ When the rock, as is generally the case in Lancashire, Cheshire, and Shropshire, is partly overspread by a coating of dense boulder clay, almost impervious to water, the quantity probably does not exceed one-third of the rainfall over a considerable area; but in some parts of the midland counties, where the rock is very open, and the covering of drift scanty or altogether absent, the percolation amounts to a much larger proportion, probably one-half or two-thirds, as all the rain which is not evaporated passes downwards. ”

“ The weight of the hammers used with drills is a matter deserving attention; for if too heavy they fatigue the men, and consequently fewer blows are given and the effect produced lessened; while, on the other hand, if too light, the strength of the workman is not fully employed. The usual weight is from 5 to 7 lb.
As the labour of boring a shot-hole in a given kind of rock is dependent on the diameter, it is obviously desirable to make the hole as small as possible, due regard being had to the size of the charge ”

“ Where the water is in large quantities it is usually pumped by an engine erected for the purpose, assisted by the engine or engines intended to be employed to raise the coal. A small capstan engine is used for passing the men and material up and down the pit during the sinking, such engine being provided also with a drum on slow motion, which is used for heavy weights. The continual pumping, the placing of cribs, and the fixing of the tubbing are proceeded with till the lowest feeder is reached, when a hard bed is sought for on which to fix the lowest wedging crib. ”

“ On the opposite side of the windlass is a lever of unequal leverage, about one-third at the side of the hole, and two-thirds at the opposite side, where it ends in a cross or broad end where men do the work. The workmen, with one foot on a bench or platform, rest their hands on a railing, and work with the other foot the long end of the lever. In this way the whole weight of the men is made use of. The lift of the bore-bit is from 10 to 12 inches, which causes the men to work the treadle from 20 to 24 inches high. ”

“ As the object of placing tubbing in a shaft is effectually to shut off the feeders, which for water supply may have some bad qualities, and to secure a water-tight joint at the base, it is important that the bed on which the moss box has to rest should be quite level and smooth. This is attained by the use of a tool, termed a “scraper,” attached to the bore-rods, the blades being made to move round the face of the bed intended for the moss box. The tubbing employed is cast in complete cylinders. At Maurage each ring has an internal diameter of 12 feet and is 4 feet 9 inches high. ”

“ Goldstone Bottom is a naturally formed basin in the chalk, [169] the lowest side of which, nearest the sea, is more than 60 feet higher than the middle or bottom of the basin. The water is obtained as at Lewes Road, from fissures running generally at right-angles to the coast-line, but they are of much larger size and at far greater distances from each other; whereas at the Lewes Road well it is rare that 30 feet of headings were driven without finding a fissure, and the yield of the largest was not more than 100 to 150 gallons a minute. ”

“ It should be remarked that when the strata is horizontal or depressed in the form of a basin, that is, when it partakes more of the character of a reservoir than a stream, the only use of tunnels is to facilitate the ingress of water into the shaft, and in such case they should radiate from the shaft in all directions. They are also of service in case of accident to the pumps, as the time they take to fill up allows of examination and repairs being made in that time to the pumps, which could not be got at if the engines stopped pumping and the water rose rapidly up the shaft. ”

“ The transmission of water through a porous medium being so rapid, we may easily understand why springs are thrown out on the side of a hill, where the upper set of strata consist of chalk, sand, and other permeable substances, whilst those lying beneath are composed of clay or other retentive soils. ”

“ The formation may be looked upon as almost equally permeable in all directions, and the whole mass may be regarded as a reservoir up to a certain level, from which, whenever wells are sunk, water will always be obtained more or less abundantly, This view is very fairly borne out by experience, and the occurrence of the water is certainly not solely due to the presence of the fissures or joints traversing the rock, but to its permeability, which, however, varies in different districts. ”