Disturbances of the Strata.

The last question to be considered relates to the disturbances which may have affected the strata; for whatever may be the absorbent power of the strata, the yield of water will be more or less diminished whenever the channels of communication have suffered break or fracture.

If the strata remained continuous and unbroken, we should merely have to ascertain the dimensions and lithological character of the strata in order to determine their water value. But if the strata is broken, the interference with the subterranean transmission of water will be proportionate to the extent of the disturbance.

Although the Tertiary formations around London have probably suffered less from the action of disturbing forces than the strata of any other district of the same extent in England, yet they nevertheless now exhibit considerable alterations from their original position.

The principal change has been that which, by elevation of the sides or depression of the centre of the district, gave the Tertiary deposits their present trough-shaped form, assuming it not to be the result of original deposition. If no further change had taken place we might have expected to find an uninterrupted communication in the Lower Tertiary strata from their northern outcrop at Hertford to their southern outcrop at Croydon, as well as from Newbury on the west to the sea on the east; and the entire length of 260 miles of outcrop would have contributed to the general supply of water at the centre.

But this is far from being the case; several disturbing causes have deranged the regularity of original structure. The principal one has caused a low axis of elevation, or rather a line of flexure running east and west, following nearly the course of the Thames from the Nore to Deptford, and apparently continued thence beyond Windsor. It brings up the chalk at Cliff, Purfleet, Woolwich, and Loampit Hill to varied but moderate elevations above the river level. Between Lewisham and Deptford the chalk disappears below the Tertiary series, and does not come to the surface till we reach the neighbourhood of Windsor and Maidenhead.

There is also, probably, another line of disturbance running between some points north and south and intersecting the first line at Deptford. It passes apparently near Beckenham and Lewisham, and then, crossing the Thames near Deptford, continues up a part, if not along the whole length of the valley of the Lea towards Hoddesdon. This disturbance appears in some places to have resulted in a fracture or a fault in the strata, placing the beds on the east of it on a higher level than those on the west; and at other places merely to have produced a curvature in the strata. Prestwich states that he was unable to give its exact course, but its effect, at all events upon the water supply of London, is important, as, in conjunction with the first or Thames valley disturbance, it cuts off the supplies from the whole of Kent, and interferes most materially with the supply from Essex; for in its course up the valley of the Lea it either brings up the Lower Tertiary strata to the surface, as at Stratford and Bow, or else, as farther up the valley, it raises them to within 40 or 60 feet of the surface.

The Tertiary district thus appears, on a general view, to be divided naturally into four portions by lines running nearly north and south, the former line passing immediately south, and the latter east of London, which stands at the south-east corner of the north-western division, and consequently it must not be viewed as the centre of one large and unbroken area, so far as the Tertiary strata are concerned.

[CHAPTER II.]
THE NEW RED SANDSTONE.

This formation has been already alluded to at pp. [5] and [8]; it is, next to the chalk and lower greensand, the most extensive source of water supply from wells we have in England, and although the two formations mentioned occupy a larger area, yet, owing to geographical position, the new red sandstone receives a more considerable quantity of rainfall, and, owing to the comparative scarceness of carbonate of lime, yields softer water.

The new red sandstone is called on the Continent “the Trias,” as in Germany and parts of France it presents a distinct threefold division. Although the names of each of the divisions are commonly used, they are in themselves local and unessential, as the same exact relations between them do not occur in other remote parts of Europe or in England, and are not to be looked for in distant continents. The names of the divisions and their English equivalents are:

1. Keuper, or red marls.

2. Muschelkalk, or shell limestones (not found in this country).

3. Bunter sandstone, or variegated sandstone.

The strata consist in general of red, mottled, purple, or yellowish sandstones and marls, with beds of rock-salt, gypsum pebbles, and conglomerate.

The region over which triassic rocks outcrop in England stretches across the island from a point in the south-western part of the English Channel about Exmouth, Devon, north-north-eastward, and also from the centre of this band along a north-westward course to Liverpool, thence dividing and running north-east to the Tees, and north-west to Solway Firth.

In central Europe the trias is found largely developed, and in North America it covers an area whose aggregate length is some 700 or 800 miles.

The beds, in England, may be divided as follows;

Average Thickness.
Keuper—Red marls, with rock-salt and gypsum1000 ft.
Lower Keuper sandstones, with trias
sandstones and marls (waterstones)		 250 ft.
Dolomitic conglomerate
Bunter—Upper red and mottled sandstone 300 ft.
Pebble beds, or uncompacted conglomerate 300 ft.
Lower red and mottled sandstone 250 ft.

The Keuper series is introduced by a conglomerate often calcareous, passing up into brown, yellow, or white freestone, and then into thinly laminated sandstones and marls. The other subdivisions are remarkably uniform in character, except in the case of the pebble beds, which in the north-west form a light red pebbly building stone, but in the central counties becomes generally an unconsolidated conglomerate of quartzose pebbles.

The following tabulated form, due to Edward Hull, Esq., M.A., shows the comparative thickness and range of the Triassic series along a south-easterly direction from the estuary of the Mersey, and also shows the thinning away of all the Triassic strata from the north-west towards the south-east of England, which Hull was amongst the first to demonstrate.

Thickness and Range of the Trias in a S.E. direction
from the Mersey.
Names of Strata.Lancashire
and
West Cheshire		Staffordshire.Leicestershire
and
Warwickshire.
Keuper Series—
Red marl3,000 800 700
Lower Keuper sandstone 450 200 150
Bunter Series—
Upper mottled sandstone 500 50 to 200absent
Pebble beds500 to 750100 to 3000 to 100
Lower mottled sandstone200 to 500 0 to 100 absent

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. In the neighbourhood of Liverpool the rock, or at least the pebble bed, is less porous than in the neighbourhood of Whitmore, Nottingham, and other parts of the midland counties, where it becomes either an unconsolidated conglomerate or a soft crumbly sandstone. Yet wells sunk even in the hard building stone of the pebble beds, either in Cheshire or Lancashire, always yield water at a certain variable depth. Beyond a certain depth the water tends to decrease, as was the case in the St. Helen’s public well, situated on Eccleston Hill. At this well an attempt was made, in 1868, to increase the supply by boring deeper into the sandstone, but without any good result. When water percolates downwards in the rock we may suppose there are two forces of an antagonistic character brought into play; there is the force of friction, increasing with the depth, and tending to hinder the downward progress of the water, while there is the hydrostatic pressure tending to force the water downwards; and we may suppose that when equilibrium has been established between these two forces, the further percolation will cease.

The proportion of rain which finds it way into the rock in some parts of the country must be very large. 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 new red sandstone, as remarked, may be regarded, in respect to water supply, as a nearly homogeneous mass, equally available throughout; and it is owing to this structure, and the almost entire absence of beds of impervious clay or marl, that the formation is capable of affording such large supplies of water; for the rain which falls on its surface and penetrates into the rock is free to pass in any direction towards a well when sunk in a central position. 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 percolation is, doubtless, much facilitated by joints, fissures, and faults, and in cases where one side of a fault is composed of impervious strata, such as the Keuper marls, or coal measures, the quantity of water pent up against the face of the fault may be very large, and the position often favourable for a well. An instance of the effect of faults in the rock itself, in increasing the supply, is afforded in the case of the well at Flaybrick Hill, near Birkenhead. From the bottom of this well a heading was driven at a depth of about 160 feet from the surface, to cut a fault about 150 feet distant, and upon this having been effected the water flowed in with such impetuosity that the supply, which had been 400,000 gallons a day, was at once doubled.

The water from the new red sandstone is clear, wholesome, and pleasant to drink; it is also well adapted for the purposes of bleaching, dyeing, and brewing; at the same time it must be admitted that its qualities as regards hardness, in other words, the proportions of carbonates of limes and magnesia it contains, are subject to considerable variation, depending on the locality and composition of the rock. As a general rule, the water from the new red sandstone may be considered as occupying a position intermediate between the hard water of the chalk, and the soft water supplied to some of our large towns from the drainage of mountainous tracts of the primary formations, of which the water supplied from Loch Katrine to Glasgow is perhaps the purest example, containing only 2·35 grains of solid matter to the gallon. Having besides but a small proportion of saline ingredients, which, while they tend to harden the water, are probably not without benefit in the animal economy, the water supply from the new red sandstone possesses incalculable advantages over that from rivers and surface drainage. Many of our large towns are now partially or entirely supplied with water pumped from deep wells in this sandstone; and several from copious springs gushing forth from the rock at its junction with some underlying impervious stratum belonging to the primary series.

[CHAPTER III.]
WELL SINKING.

Previous to sinking it will be necessary to have in readiness a stock of buckets, shovels, picks, rope, a pulley-block or a windlass, and barrows or other means of conveying the material extracted away from the mouth of the sinking. After all the preliminary arrangements have been made, the sinking is commenced by marking off a circle upon the ground 12 or 18 inches greater in circumference than the intended internal diameter of the well. The centre of the well as commenced from must be the centre of every part of the sinking; its position must be carefully preserved, and everything that is done must be true to this centre, the plumb-line being frequently used to test the vertical position of the sides.

Figs. 17, 18.

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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. On this, to line the first division of the well, a cylinder of brickwork, technically called steining, is built in mortar or cement. In the centre of the floor is dug a small pit, at the bottom of which is laid a small platform of boards; then, by cutting notches in the side of the pit, raking props are inserted, their lower ends abutting against a foot block, and their upper ends against the lowest setting, so as to give temporary support to the curb with its load of brickwork. The pit is enlarged to the diameter of the shaft above; on the bottom of the excavation is laid a new curb, on which is built a new division of the brickwork, giving permanent support to the upper curb; the raking props and their foot-blocks are removed; a new pit is dug, and so on as before. Care should be taken that the earth is firmly packed behind the steining.

A common modification of this method consists in excavating to such a depth as the strata will admit without falling in. A wooden curb is laid at the bottom of the excavation, the brick steining laid upon it and carried to the surface. The earth is then excavated flush with the interior sides of the well, so that the earth underneath the curb supports the brickwork above. When the excavation has been carried on as far as convenient, recesses are made in the earth under the previous steining, and in these recesses the steining is carried up to the previous work. When thus supported the intermediate portions of earth between the sections of brickwork carried up are cut away and the steining completed.

In sinking with a drum curb, the curb, which may be either of wood or iron, consists of a flat ring for supporting the steining, and of a vertical hollow cylinder or drum of the same outside diameter as the steining, supporting the ring within it and bevelled to a sharp edge below. The rings, or ribs, of a wooden curb are formed of two thicknesses of elm plank, 11⁄2 inch thick by 9 inches wide, giving a total thickness of 3 inches.

Figs. 19, 20.

[Fig. 17] is a plan of a wooden drum curb, and [Fig. 18] a section showing the mode of construction. The outside cylinder or drum is termed the lagging, and is commonly made from 11⁄2-inch yellow pine planks. The drum may be strengthened if necessary by additional rings, and its connections with the rings made more secure by brackets. In large curbs the rings are placed about 3 feet 6 inches apart. [Fig. 19] is a plan, and [Fig. 20] an enlarged segment of an iron curb. When the well has been sunk as far as the earth will stand vertical, the drum curb is lowered into it and the building of the brick cylinder commenced, care being taken to complete each course of bricks before laying another, in order that the curb may be loaded equally all round. The earth is dug away from the interior of the drum, and this, together with the gradually increasing load, causes the sharp lower edge of the drum to sink into the earth; and thus the digging of the well at the bottom, the sinking of the drum curb and the brick lining which it carries, and the building of the steining at the top, go on together. Care must be taken in this, as in every other method, to regulate the digging so that the well shall sink vertically. Should the friction of the earth against the outside of the well at length become so great as to stop its descent before the requisite depth is attained, a smaller well may be sunk in the interior of the first well. A well so stopped is said to be earth-fast. This plan cannot be applied to deep wells, but is very successful in sandy soils where the well is of moderate depth.

The curbs are often supported by iron rods, fitted with screws and nuts, from cross timbers over the mouth of the well, and as the excavation is carried on below, brickwork is piled on above, and the weight of the steining will carry it down as the excavation proceeds, until the friction of the sides overpowers the gravitating force or weight of the steining, when it becomes earth-bound; then a set-off must be made in the well, and the same operation repeated as often as the steining becomes earth-bound, or the work must be completed by the first method of underpinning.

When the rock to be sunk through is unstratified, or if stratified, when of great thickness, recourse must be had to the action of explosive agents. The explosives most frequently used for this purpose are guncotton, dynamite, lithofracteur, and gunpowder. Lithofracteur is now often employed, and always with considerable success, as its power is similar to that of dynamite, but, what is particularly important in vertical bore-holes, its action is intensely local; it is, moreover, safe, does not generate fumes more harmful than ordinary gunpowder, requires smaller holes, and but little tamping. The dangerous character of guncotton has hitherto prevented its adoption for ordinary operations, while the comparatively safe character and convenient form of gunpowder have commended it to the confidence of workmen, and hence for sinking operations this explosive is generally employed. We shall therefore, in treating of blasting for well sinking, consider these operations as carried out by the aid of gunpowder alone.

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 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. Indeed, such is the ignorance of this subject displayed by quarrymen generally, that when the proportioning and placing the charges are left to their judgment, a large expenditure of labour and material will produce very inadequate results. In all cases it is far more economical to entrust these duties to one who thoroughly understands the subject. The following principles should govern all operations of this nature.

The explosion of gunpowder, by the expansion of the gases suddenly evolved, develops an enormous force, and this force, due to the pressure of a fluid, is exerted equally in all directions. Consequently, the surrounding mass subjected to this force will yield, if it yield at all, in its weakest part, that is, in the part which offers least resistance. The line along which the mass yields, or line of rupture, is called the line of least resistance, and is the distance traversed by the gases before reaching the surface. When the surrounding mass is uniformly resisting, the line of least resistance will be a straight line, and will be the shortest distance from the centre of the charge to the surface. Such, however, is rarely the case, and the line of rupture will therefore in most instances be an irregular line, and often much longer than that from the centre direct to the surface. Hence in all blasting operations there will be two things to determine, the line of least resistance and the quantity of powder requisite to overcome the resistance along that line. For it is obvious that all excess of powder is waste; and, moreover, as the force developed by this excess must be expended upon something, it will probably be employed in doing mischief. Charges of powder of uniform strength produce effects varying with their weight, that is, a double charge will move a double mass. And as homogeneous masses vary as the cube of any similar line within them, the general rule is established that charges of powder to produce similar results are to each other as the cubes of the lines of least resistance. Hence when the charge requisite to produce a given effect in a particular substance has been determined by experiment, that necessary to produce a like effect in a given mass of the same substance may be readily determined. As the substances to be acted upon are various and differ in tenacity in different localities, and as, moreover, the quality of powder varies greatly, it will be necessary, in undertaking sinking operations, to make experiments in order to determine the constant which should be employed in calculating the charges of powder. In practice, the line of least resistance is taken as the shortest distance from the centre of the charge to the surface of the rock, unless the existence of natural divisions shows it to lie in some other direction; and, generally, the charge requisite to overcome the resistance will vary from 1⁄15 to 1⁄35 of the cube of the line, the latter being taken in feet and the former in pounds. Thus, suppose the material to be blasted is chalk, and the line of least resistance 4 feet, the cube of 4 is 64, and taking the proportion for chalk as 1⁄30, we have 64⁄30 = 22⁄15 lb. as the charge necessary to produce disruption.

Fig. 21.

When the blasting is in stratified rock, the position of the charge will frequently be determined by the natural divisions and fissures; for if these are not duly taken into consideration, the sinker will have the mortification of finding, after his shot has been fired, that the elastic gases have found an easier vent through one of these flaws, and that consequently no useful effect has been produced. The line of least resistance, in this case, will generally be perpendicular to the beds of the strata, so that the hole for the charge may be driven parallel to the strata and in such a position as not to touch the planes which separate them. This hole should never be driven in the direction of the line of least resistance, and when practicable should be at right-angles to it.

The instruments employed in boring the holes for the shot are iron rods having a wedge-shaped piece of steel welded to their lower ends and brought to an edge so as to cut into the rock. These are worked either by striking them on the head with a hammer, or by jumping them up and down and allowing them to penetrate by their own weight. When used in the former manner they are called borers or drills; in the latter case they are of the form [Fig. 21], and are termed jumpers. Recently power jumpers worked by compressed air, and drills actuated in the same manner have been very successfully employed. Holes may be made by these instruments in almost any direction; but when hand labour only is available, the vertical can be most advantageously worked. Hand-jumpers are usually about 4 feet 8 inches in length, and are used by holding in the direction of the required hole, and producing a series of sharp blows through lifting the tool about a foot high and dropping it with an impulsive movement. The bead divides a jumper into two unequal lengths, of which the shorter is used for commencing a bore-hole, and the longer for finishing it. Often the bit on the long length is made a trifle smaller than the other to remove any chance of its not following into the hole which has been commenced.

Drills and jumpers should be made of the best iron, preferably Swedish, for if the material be of an inferior quality it will split and turn over under the repeated blows of the mall, and thus endanger the hands of the workman who turns it, or give off splinters that may cause serious injury to those engaged in the shaft. Frequently they are made entirely of steel, and this material has much to recommend it for this purpose; the length of drills varies from 18 inches to 4 feet, the different lengths being put in successively as the sinking of the hole progresses. The cutting edge of the drills should be well steeled, and for the first, or 18-inch drill, have generally a breadth of 2 inches; the second, or 28-inch drill, may be 13⁄4 inch on the edge; the third, or 3-foot drill, 11⁄2 inch, and the fourth, or 4-foot drill, 11⁄4 inch.

Fig. 22.

The mode of using the drill in the latter case is as follows; The place for the hole having been marked off with the pick, one man sits down holding the drill in both hands between his legs. Another man then strikes the drill with a mall, the former turning the drill partially round between each blow to prevent the cutting edge from falling twice in the same place.

The speed with which holes may be sunk varies of course with the hardness of the rock and the diameter of the hole. At Holyhead the average work done by three men in hard quartz rock with 11⁄2-inch drills was 14 inches an hour; one man holding the drill, and two striking. In granite of good quality, it has been ascertained by experience that three men are able to sink with a 3-inch jumper 4 feet in a day; with a 21⁄2-inch jumper, 5 feet; with a 21⁄4-inch, 6 feet; with a 2-inch, 8 feet; and with a 13⁄4-inch, 12 feet. A strong man with a 1-inch jumper will bore 8 feet in a day. 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; for it must be borne in mind in determining the diameter of the boring that the charge should not occupy a great length in it. Various expedients have been resorted to for the purpose of enlarging the hole at the bottom so as to form a chamber for the powder. If this could be easily effected, such a mode of placing the charge would be highly advantageous, as a very small bore-hole would be sufficient, and the difficulties of tamping much lessened. One of these expedients is to place a small charge at the bottom of the bore and to fire it after being properly tamped. The charge being insufficient to cause fracture, the parts in immediate contact with it are compressed and crushed to dust, and the cavity is thereby enlarged. The proper charge may then be inserted in the chamber thus formed by boring through the tamping. Another method, applicable chiefly to calcareous rock, has been tried with satisfactory results at Marseilles. When the bore-hole has been sunk to the required depth, a copper pipe, [Fig. 22], of a diameter to fit the bore loosely, is introduced, the end A reaching to the bottom of the hole, which is closed up tight at B with clay so that no air may escape. The pipe is provided with a bent neck C. A small leaden pipe e, about half an inch in diameter, with a funnel f at the top, is introduced into the copper pipe at D and passed down to within about an inch of the bottom. The annular space between the leaden and copper pipes at g is filled with a packing of hemp. Dilute nitric acid is then poured through the funnel and leaden pipe. The acid dissolves the calcareous rock at the bottom, causing an effervescence, and a substance containing the dissolved lime is forced out of the orifice C. This process is continued until from the quantity of acid consumed it is judged that the chamber is sufficiently enlarged. Other acids, such as muriatic or sulphuric, will produce the same effects, but the result of the chemical solution will of course depend upon the nature of the stone.

After the shot-hole has been bored, it is cleaned out and dried with a wisp of hay, and the powder poured down; or, when the hole is not vertical, pushed in with a wooden rammer. The quantity of powder should always be determined by weight. One pound, when loosely poured out, will occupy about 30 cubic inches, and 1 cubic foot weighs 57 pounds. A hole 1 inch in diameter will therefore contain ·414 ounce for every inch of depth. Hence to find the weight of powder to an inch of depth in any given hole, we have only to multiply ·414 ounce by the square of the diameter of the hole in inches, and we are enabled to determine either the length of hole for a given charge, or the charge in a given space. It is important to use strong powder in blasting operations, because, as a smaller quantity will be sufficient, it will occupy less space, and thereby save labour in boring.

Figs. 23-25.

When the hole is in wet stone, means must be provided for keeping the powder dry. For this purpose, tin cartridges are sometimes used. These are tin cylinders of suitable dimensions, fitted with a small tin stem through which the powder is ignited. The effect of the powder is, however, much lessened by the use of these tin cases. Generally a paper cartridge, well greased to prevent the water from penetrating, will give far more satisfactory results. When the paper shot is used, the hole should, previous to the insertion of the charge, be partially filled with stiff clay, and a round iron bar, called a clay-iron or bull, [Figs. 24, 25], driven down to force the clay into the interstices of the rock through which the water enters. By this means the hole will be kept comparatively dry. The bull is withdrawn by placing a bar through the eye near the top of the former, provided for that purpose, and lifting it straight out. The cartridge is placed upon the point of a pricker and pushed down the hole. The pricker, shown in [Fig. 23], is a taper piece of metal, usually of copper to prevent accidents, pointed at one end and having a ring at the other. When the cartridge has been placed in its position by this means, a little oakum is laid over it, and a Bickford fuse inserted. This fuse is inexpensive, very certain in its effects, not easily injured by tamping, and is unaffected by moisture. The No. 8 fuse is preferred for wet ground; and when it is required to fire the charge from the bottom in deep holes, No. 18 is the most suitable.

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, 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. Various opinions are held concerning the relative value of these materials as tamping. Sand offers very great resistance from the friction of the particles amongst themselves and against the sides of the bore-hole; it may be easily applied by pouring it in, and is always readily obtainable. Clay, if thoroughly baked, offers a somewhat greater resistance than sand, and, where readily procurable, may be advantageously employed. Broken stone is much inferior to either of these substances in resisting power. The favour in which it is held by sinkers and quarrymen, and the frequent use they make of it as tamping, must be attributed to the fact of its being always ready to hand, rather than to any excellent results obtained from its use. The tamping is forced down with a stemmer or tamping bar similar to [Figs. 26, 27], too frequently made of iron, but which should be either of copper or bronze. The tamping end of the bar is grooved on one side, to admit of its clearing the pricker, or the fuse, lying along the side of the hole. The other end is left plain for the hand or for being struck with a hammer.

Figs. 26, 27.

All tamping should be selected for its freedom from particles likely to strike fire, but it must not be overlooked that the cause of such a casualty may lie in the sides of the hole itself. Under these circumstances is seen the advisability of using bronze or copper tamping tools, and of not hammering violently on the tamping until a little of it has been first gently pressed down to cover over the charge, because the earlier blows on the tamping are the most dangerous in the event of a spark occurring. A little wadding, tow, paper, or a wooden plug is sometimes put to lie against the charge before any tamping is placed in the hole.

Fig. 28.

To lessen the danger of the tamping being blown out, plugs or cones of metal of different shapes are sometimes inserted in the hole. The best forms of plug are shown in Figs. 28 and 29; [Fig. 28] is a metal cone wedged in on the tamping with arrows, and [Fig. 29] is a barrel-shaped plug.

When all is ready, the sinkers, with the exception of one man whose duty it is to fire the charge, are either drawn out of the shaft, or are removed to some place of safety. This man then, having ascertained by calling and receiving a reply that all are under shelter, applies a light to the fuse, shouts “Bend away,” or some equivalent expression, and is rapidly drawn up the shaft.

To avoid shattering the walls of a shaft, no shot should be placed nearer the side than 12 inches. The portion of stone next the wall sides of the shaft left after blasting is removed by steel-tipped iron wedges 7 or 8 inches in length. These wedges are applied by making a small hole with the point of the pick and driving them in with a mall. The sides may be then dressed as required with the pick.

Fig. 29.

After some 30 or 40 feet have been sunk the air at the bottom of the well may be very foul, especially in a well where blasting operations are being carried on, or where there is any great escape of noxious gases through fissures. Means must then be provided for applying at the surface a small exhaust fan to which is attached lengths of tubing extending down the well. Another good plan is to pass a 4 or 6 inch pipe down the well, bring it up with a long bend at surface, and insert a steam jet; a brick chimney is frequently built over the upper end of the pipe to increase the draught, and the lower end continued down with flexible tubing. With either fan or steam jet, the foul air being continuously withdrawn, fresh air will rush down in its place. This is far better than dashing lime-water down the well, using a long wooden pipe with a revolving caphead, or pouring down a vertical pipe water which escaped at right-angles, the old expedients for freshening the air in a well.

A means of increasing the yield of wells, which is frequently very successful, is to drive small tunnels or headings from the bottom of the well into the surrounding water-bearing stratum.

Fig. 30.

As an example, let [Fig. 30] represent a sectional plan of a portion of the water-bearing stratum at the bottom of the shaft. This stratum is underlaid by an impervious stratum, and, consequently, the water will flow continuously through the former in the direction of the dip, as shown by the arrow and the dotted lines. That portion of the stratum to the rise of the shaft, S, which is included within vertical lines tangent to the circle at the points m and n, will be drained by the shaft. The breadth of this portion will, however, be extended beyond these lines by the relief to the lateral pressure afforded by the shaft, which relief will cause the fillets of water to diverge from their original course towards the shaft, as shown in the figure. Hence the breadth of drainage ground will be a b, and it is evident that the shaft, S, can receive only that water which descends towards it through this space. But if tunnels be driven from the shaft along the strike of the stratum, as at m c, n d, these tunnels will obviously intercept the water which flows past the shaft. By this means the drainage ground is extended from a b to a´ b´, and the yield of the well proportionately increased.

Figs. 31-33.

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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 size of the headings is usually limited by the least dimensions of the space in which miners can work efficiently, that is about 41⁄2 feet high and 3 feet wide. The horse-shoe form is generally adopted for the sides and top, the floor being level, for the drawing off of the water by the pumps is quite sufficient to cause a flow, unless of course the dip of the stratum in which the tunnels are driven is such as to warrant an inclination. Where there is any water it is not possible to drive them with a fall, for the men would be drowned out.

The cost of some headings in the new red sandstone which the writer recently inspected, varied from 30s. a yard in ordinary stone, to 4l. 10s. a yard in very hard stone.

The foregoing remarks do not apply to headings driven in the chalk, where it is the usual practice to select the largest feeder issuing from a fissure and follow that fissure up, unless the heading is merely to serve as a reservoir, when the direction is immaterial.

The sides of wells usually require lining or steining, as it is termed, with some material that will prevent the loose strata of the sides of the excavation falling into the well and choking it. The materials that have been successfully used in this work are brick, stone, timber, and iron. Each description of material is suitable under certain conditions, while in other positions it is objectionable. Brickwork, which is universally used in steining wells in England, not unfrequently fails in certain positions; through admitting impure water when such water is under great pressure, or from the work becoming disjointed from settlement due to the draining of a running sand-bed, or the collapse of the well. Stone of fair quality, capable of withstanding compressive strains, is good in its way; but, inasmuch as it requires a great deal of labour to fit it for its place, it cannot successfully compete with brickwork in the formation of wells, more especially as it has no merits superior to those of brick when used in such work; however, if in any locality, by reason of its cheapness, it can be used, care should be taken to select only such as contains a large amount of silica; indeed, in all cases it is a point of great importance in studying the nature of the materials used in the construction of wells, to select those which are likely to be the most durable, and at the same time preserve the purity of the water contained in the well; and this is best secured by silicious materials.

Figs. 34-36.

Figs. 37-39.

Timber is objectionable as a material to be used in the lining of wells, on account of its liability to decay, when it not only endangers the construction of the well, but also to some extent fouls the water. It is very largely used under some circumstances, especially in the preliminary operations in sinking most wells. It is also successfully used in lining the shafts of the salt wells of Cheshire, and will continue entire in such a position for a great number of years, as the brine seems to have a tendency to preserve the timber and prevent its decay. Iron is of modern application, and is a material extensively employed in steining wells; and, as it possesses many advantages over materials ordinarily used, its use is likely to be much extended. It is capable of bearing great compressive strains, and of effectually excluding the influx of all such waters as it may be desirable to keep out, and is not liable to decay under ordinary circumstances. Baldwin Latham mentions instances in his practice where recourse has been had to the use of iron cylinders, when it was found that four or five rings of brickwork, set in the best cement, failed to keep out brackish waters; and, if the original design had provided for the introduction of these cylinders, it would have reduced the cost of the well very materially.

Fig. 40.

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.

The valve in the old form of mizer is subject to various accidents which interfere with the action of the tool; for instance, pieces of hard soil or rock often lodge between the valve and its seat, allowing the contents to run out whilst it is being raised through water. To remedy this defect the eminent well-sinker, Thomas Docwra, designed and introduced the improved mizer, shown of the usual dimensions in Figs. 31 to 36; [Fig. 31] being a plan at top, [Fig. 32] an elevation, [Fig. 33] a plan at bottom, [Fig. 35] a section, [Fig. 34] a plan of the stop a, and [Fig. 36] a plan of the valve. It consists of an iron cylinder, conical shaped at bottom, furnished with holes for the escape of water, and attached to a central shank by means of stays. The shank extends some 7 inches beyond the bottom, and ends in a point, while the upper part of the shank has an open slot, to form a box-joint, [Figs. 37 to 39], with the rods. The conical bottom of the mizer has a triangular-shaped opening; on the outside of this is fitted a strong iron cutter, and on the inside a properly-shaped valve, seen in section and plan in [Figs. 35 and 36]. When the mizer is attached to and turned by means of the boring rods, the débris, sand, or other soil to be removed, being turned up by the lip of the cutter, enters the cylinder, the valve, whilst the mizer is filling, resting against a stop. After the mizer is charged, which can be ascertained by placing a mark upon the last rod at surface and noting its progress downwards, the rods are reversed and turned once or twice in a backward direction; this forces the valve over the opening and retains the soil safely in the tool.

Figs. 41-43.

[Fig. 40] is a pot mizer occasionally used in such soils as clay mixed with pebbles; there is no valve, as the soil is forced upwards by the worm on the outside, and falls over the edge into the cone.

Figs. 44, 45.

Mizers are fastened to the rods by means of the box-joint, shown in [Figs. 37 to 39], as a screw-joint would come apart on reversing.

As many as five or six different sized mizers, ranging from 1 foot 6 inches to 9 feet in diameter, can be used successively, the smallest commencing the excavation, and the larger ones enlarging it until it is of the requisite size.

As an accessory, a picker, shown by the three views, [Figs. 41 to 43], [Fig. 42] indicating its correct position when in operation, is employed where the strata is too irregular or compact to be effectually cleared away by the cutter of the mizer. The picker is fixed upon the same rods above the mizer, and is used simultaneously, being raised and lowered with that tool.

Figs. 46-48.
Sectional Plans.

The cutting end of the picker is frequently replaced by a scratcher, [Figs. 44, 45]. This useful tool rakes or scratches up the débris thrown by the mizer beyond its own working range, and causes it to accumulate in the centre of the sinking, where it is again subjected to the action of the mizer.

Brick steining is executed either in bricks laid dry or in cement, in ordinary clay 9-inch work being used for large wells, and half-brick, or 41⁄2-inch work, for small wells.

[Figs. 46 and 47] show the method of laying for 9-inch work, and [Fig. 48] for 41⁄2 inches. The bricks are laid flat, breaking joint; and to keep out moderate land-springs clay, puddle, or concrete is often introduced at the back of the steining; for most purposes concrete is the best, as, in addition to its impervious character, it adds greatly to the strength of the steining. A ring or two of brickwork in cement is often introduced at intervals, varying from 5 feet to 12 feet apart, to strengthen the shaft, and facilitate the construction of the well.

Too much care cannot be bestowed upon the steining; if properly executed it will effectually exclude all objectionable infiltration, but badly made, it may prove a permanent source of trouble and annoyance. Half the wells condemned on account of sewage contamination really fail because of bad steining.

[CHAPTER IV.]
WELL BORING.

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; and by its continued blows the rock is pounded and broken. The chisel is withdrawn occasionally, and a bucket or shell-pump is lowered, having a hinged valve at the bottom opening upwards, so that a quantity of the débris becomes enclosed in the bucket, and is then drawn up by it to the surface; the lowering of the bucket is repeated until the hole is cleared, and the chisel is then put to work again.

[Fig. 49] is of an apparatus, on the Chinese system, which may be used either for hemp-rope or wire-rope, and which was originally made for hoop-iron. At A, [Fig. 49], is represented a log of oak wood, which is set perpendicularly so deep in the ground as to penetrate the loose gravel and pass a little into the rock, and stand firm in its place; it is well rammed with gravel and the ground levelled, so that the butt of the log is flush with the surface of the ground, or a few feet below. Through this log, which may be, according to the depth of loose ground, from 5 feet to 30 feet long, a vertical hole is bored by an auger of a diameter equal to that of the intended boring in the rock. On the top of the ground, on one side of the hole, is a windlass whose drum is 5 feet in diameter, and the cogwheel which drives it 6 feet; the pinion on the crank axle is 6 inches. This windlass serves for hoisting the spindle or drill, and is of a large diameter, in order to prevent short bends in the iron, which would soon make it brittle.

Fig. 49.

In all cases where iron, either hoop-iron or wire-rope, is used, the diameter of the drum of the windlass used must be sufficiently large to prevent a permanent bend in the iron. 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. Below the treadle, T, is a spring-pole, S, fastened under the platform on which the men stand, the end of this spring-pole is connected by a link to the working end of the lever, or to the rope directly, and pulls the treadle down. When the bore-spindle is raised by means of the treadle, the spring-pole imparts to it a sudden return, and increases by these means the velocity of the bit, and consequently that of the stroke downwards.

This method has been generally disused, iron or wood rods substituted in the place of the rope, and a variety of augers and chisels instead of the simple chisel, with appliances for clearing the bore-hole of débris. [Figs. 50 to 56] show examples of an ordinary set of well boring tools. [Fig. 52] is a flat chisel; [Fig. 53] a V-chisel; and [Fig. 54] a T-chisel. These chisels are made from wrought-iron, and when small are usually 18 inches long, 21⁄2 inches extreme breadth, and weigh some 41⁄2 lb.; the cutting edge being faced with the best steel. They are used for hard rocks, and whilst in operation need carefully watching that they may be removed and fresh tools substituted when their sides are sufficiently worn to diminish their breadth. If this circumstance is not attended to the size of the hole decreases, so that when a new chisel of the proper size is introduced it will not pass down to the bottom of the hole, and much unnecessary delay is occasioned in enlarging it. In working with the chisel, the borer keeps the tiller, or handles, in both hands, one hand being placed upon each handle, and moves slowly round the bore, in order to prevent the chisel from falling twice, successively, in the same place, and thus preserve the bore circular. Every time a fresh chisel is lowered to the bottom it should be worked round in the hole, to test whether it is its proper size and shape; if this is not the case the chisel must be raised at once and worked gradually and carefully until the hole is as it should be. The description of strata being cut by the chisel can be ascertained with considerable accuracy by a skilful workman from the character of the shock transmitted to the rods.

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.

Figs. 50-56.

Ground augers, [Figs. 50, 51, and 56], are similar in action to those used for boring wood, but differ in shape and construction. The common earth auger, [Fig. 50], is 3 feet in length, having the lower two-thirds cylindrical. The bottom is partially closed by the lips, and there is an opening a little up one side for the admission of soft or bruised material. Augers are only used for penetrating soft rock, clay, and sand; and their shape is varied to suit the nature of the strata traversed, being open and cylindrical for clays having a certain degree of cohesion, conical, and sometimes closed, in quicksands. Augers are sometimes made as long as 10 feet, and are then very effective if the strata is soft enough to permit of their use. The shell is made from 3 feet to 31⁄2 feet in length, of nearly the same shape as the common auger, sometimes closed to the bottom, [Fig. 56], or with an auger nose, [Fig. 51]; in either case there is a clack or valve placed inside for the purpose of retaining borings of a soft nature or preventing them from being washed out in a wet hole. [Fig. 59] shows a wad-hook for withdrawing stones, and [Fig. 58] a worm-auger.

Figs. 57-59.

Fig. 60.

The Crow’s Foot, [Fig. 55], is used when the boring rods have broken in the bore-hole, for the purpose of extracting that portion remaining in the hole; it is the same length, and at the foot the same breadth as the chisels. When the rods have broken, the part above the fracture is drawn out of the bore-hole and the crow’s foot screwed on in place of the broken piece; when this is lowered down upon the broken rod, by careful twisting the toe is caused to grip the broken piece with sufficient force to allow the portion below the fracture to be drawn out of the bore-hole. A rough expedient is to fasten a metal ring to a rope and lower it over the broken rod, when the rod cants the ring, and thus gives it a considerable grip; this is often very successful. [Fig. 57] is a worm used for the same purpose. A bell-box, [Fig. 60], is frequently employed for drawing broken rods; it has two palls fixed at the top of the box, which rise and permit the end of the rod to pass when the box is lowered, but upon raising it the palls fall and grip the rod firmly. A spiral angular worm, similar to [Fig. 57], is also applied for withdrawing tubes.

Figs. 61, 62.

Of these withdrawing tools the crow is the safest and best, as it may be used without that intelligent supervision and care absolutely necessary with the worms and wad-hooks, or the bell-box.

Fig. 63.

Figs. 64, 65.

The boring rods, [Figs. 61, 62], are in 3, 6, 10, 15, or 20 feet lengths, of wrought-iron, preferably Swedish, and are made of different degrees of strength according to the depth of the hole for which they are required; they are generally 1 inch square in section: at one end is a male and at the other end a female screw for the purpose of connecting them together. The screw should not have fewer than six threads. One of the sides of the female screw frequently splits and allows the male screw to be drawn out, thus leaving the rods in the hole. By constant wear, also, the screw may have its thread so worn as to become liable to slip. Common rods being most liable to accident should be carefully examined every time they are drawn out of the bore-hole, as an unobserved failure may occasion much inconvenience, and even the loss of the bore-hole. In addition to the ordinary rods there are short pieces, varying from 6 inches to 2 feet in length, which are fixed at the top, as required, for adjusting the rods at a convenient height.

Fig. 66.

[Fig. 63] is a hand-dog; [Figs. 64 and 65], a lifting dog; [Fig. 66], the tillers or handles by which the workmen impart a rotary motion to the tools. The tillers are clamped to the topmost boring rod at a convenient height for working. [Fig. 61], a top rod with shackle. [Fig. 67], a spring-hook. When in use this should be frequently examined and kept in repair.

Fig. 67.

Lining tubes are employed to prevent the bore-hole falling in through the lateral swelling of clay strata, or when passing through running sand. The tubes are usually of iron, of good quality, soft, easily bent, and capable of sustaining an indent without fracture. Inferior tubes occasion grave and costly accidents which are frequently irreparable, as a single bad tube may endanger the success of an entire boring.

Wrought-iron tubes with screwed flush joints, [Fig. 68], are to be recommended, but they are supplied brazed, [Fig. 69], or riveted, [Fig. 70], and can be fitted with steel driving collars and shoes. Cast-iron tubes are constantly applied; they should have turned ends with wrought-iron collars and countersunk screws.

Cold-drawn wrought-iron tubes have been used, and are very effective as well as easily applied, but their relatively high cost occasions their application to be limited.

Figs. 68-71.

[Fig. 71] shows a stud-block, which is used for suspending tubing either for putting it down or for drawing it up. It consists of a block made to fit inside the end of the tube, and attached to the rods in the usual way. In the side of the block is fixed an iron stud for slipping into a slot, similar to a bayonet-joint, cut in the end of the tube, so that it may be thus suspended. [Figs. 72 to 74] show various forms of spring-darts, and [Fig. 75] a pipe-dog, for the same purpose. Sometimes a conical plug, with a screw cut around the outside for tightening itself in the upper end of the tube, is used for raising and lowering tubing. [Figs. 76 and 77] are of tube clamps, and [Fig. 78] tongs for screwing up the tubes. [Fig. 79] is of an ordinary form of sinker’s bucket.

Figs. 72-79.

[Fig. 80] is a pipe-dolly, used for driving the lining tubes; the figure shows it in position ready for driving.

When a projection in the bore-hole obstructs the downward course of the lining tubes, the hole can be enlarged below the pipes by means of a rimer, [Fig. 81]. It consists of an iron shank, to which is bolted two thin strips, bowed out in to the form of a drawing pen. The rimer is screwed on to the boring rods, and forced down through the pipes; when below the last length of pipe the rimer expands, and can then be turned round, which has the effect of scraping the sides and enlarging that portion of the hole subject to its operation. [Fig. 82] is of an improved form of rimer, termed a riming spring. It will be seen that this instrument is much stronger than the ordinary rimer, in consequence of the shank being extended through its entire length, thus rendering the scraping action of the bows very effective, whilst the slot at the foot of the bows permits of its introduction into, and withdrawal from, the tubing.

Figs. 80, 81.

Fig. 82.

In England, for small works, the entire boring apparatus is frequently arranged as in [Fig. 83], the tool being fixed at the end of the wrought-iron rods instead of at the end of a rope, as in the Chinese method. Referring to [Fig. 83], A is the boring tool; B the rod to which the tool is attached; D D the levers by which the men E E give a circular or rotating motion to the tool; F, chain for attaching the boring apparatus to the pole G, which is fixed at H, and by its means the man at I transmits a vertical motion to the boring tool.

Fig. 83.

The sheer-legs, made of sound Norway spars not less than 8 inches diameter at the bottom, are placed over the bore-hole for the purpose of supporting the tackle K K for drawing the rods out of or lowering them into the hole, when it is advisable to clean out the hole or renew the chisel. It is obvious that the more frequently it is necessary to break the joints in drawing and lowering the rods, the more time will be occupied in changing the chisels, or in each cleaning of the hole, and as the depth of the hole increases the more tedious will the operation be. It therefore becomes of much importance that the rods should be drawn and lowered as quickly as possible, and to attain this end as long lengths as practicable should be drawn at each lift. The length of the lift or off-take, as it is termed, depending altogether upon the height of the lifting tackle above the top of the bore-hole, the length of the sheer-legs for a hole of any considerable depth should not be less than 30 to 40 feet; and they usually stand over a small pit or surface-well, which may be sunk, where the clay or gravel is dry, to a depth of 20 or 30 feet. From the bottom of this pit the bore-hole may be commenced, and here will be stationed the man who has charge of the bore-hole while working the rods.

Fig. 84.

The arrangement, [Fig. 84], is intended for either deep or difficult boring. A regular scaffolding is erected upon which a platform is built. The boring chisel A is, as in the last instance, coupled by means of screw-couplings to the boring rods B. At each stroke two men stationed at E E turn the rod slightly by means of the tiller D D. A rope F, which is attached to the boring tool, is passed a few times round the drum of a windlass G, the end of the rope being held by a man at I. When the handles are turned by the men at L L the man at I pulls at the rope end, the friction between the rope and the drum of the windlass is then sufficient to raise the rods and boring tool, but as soon as the tool has been raised to its intended height the man at I slackens his hold upon the rope, and as there is insufficient friction on the drum to sustain the weight of the boring tools, they fall. By a repetition of this operation the well is bored, and after it has been continued a sufficient length of time the tiller is unscrewed, and a lifting dog, attached to the rope from the windlass, is passed over the top of the rods, and then a short top rod with a shackle is screwed on. The two men at the windlass draw up the rods as far as the height of the scaffolding or sheer-legs will allow, when a man at E, [Fig. 84], by passing a hand-dog or a key upon the top of the rod under the lowest joint drawn above the top of the hole, takes the weight of the rods at this joint, the men at L having lowered the rods for this purpose; with another key the rods are unscrewed at this joint, the rope is lowered again, the lifting dog put over the rod, another top rod screwed on, the rods lifted, and the process continued until the chisel is drawn from the hole and replaced by another, or, if necessary, replaced by some other tool.

When a deep boring is undertaken, direct from the surface, the operation had best be conducted with the aid of a boring sheer-frame such as is shown in the [frontispiece]. This consists of a framework of timber balks, upon which are erected four standards, 27 feet in height, and 9 inches × 1 foot thick, 3 feet 8 inches apart at bottom, and 1 foot 2 inches at top, as seen in the front and rear elevations. The standards are tied by means of cross pieces, upon which shoulders are cut which fit into mortise holes, and are fastened by means of wooden keys, the standards being surmounted by two head pieces 5 feet long, mortised and fitted. Upon the head pieces two independent cast-iron guide pulleys are arranged in bearings; over these pulleys are led the ends of two ropes coiling in opposite directions upon the barrel of a windlass moved by spur gearing, and having a ratchet stop attached to a pair of diagonal timbers, connected with the left-hand legs or standards of the sheers, near the ground. These ropes are used for raising or lowering the lengths of the boring rod.

Eight feet below the bearings of the top pulleys, a pair of horizontal traverses is fixed across the frame, supporting smaller pulleys mounted on a cast-iron frame, which is capable of motion between horizontal wooden slides. Over these pulleys is led a rope from a plain windlass fixed to the right-hand legs of the frame, to be used for raising or lowering the shell to extract the débris or rubbish from the hole.

The lever, 15 feet long, and 9 inches × 6 inches in section, is supported by an independent timber frame. It has a cast-iron cap, fastened by means of two iron straps, cast with lugs through which bolts are passed, these being tightened with nuts in the ordinary manner. The bearing-pins at a are 11⁄2 inch in diameter, and also form part of the lower strap. Upon the cap is an iron hook, to this a chain is attached carrying the spring-hook which bears the top shackle of the rods. The top of the bore-hole is surrounded by a wooden tube 1 foot in diameter, and surrounded by a hinged valve, whose action is similar to that of a clack-valve; this has a hole in the centre for the rods to pass up and down freely. The valve permits of the introduction and withdrawal of the tools, and at the same time prevents anything from above falling into the bore-hole.

Fig. 85.

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The lever is applied by pressure upon its outer end, and as the relation of the long to the short arm is as 4 to 1, a depression of 2 feet in the one case produces an elevation of 6 inches in the other, the minimum range of action, the maximum being 26 inches.

With the sheer-frame the boring tools are worked in the same manner as in the preceding arrangements, Figs. [83], [84]; but its portability, compactness, and adaptation of means to the required end, render its use desirable wherever it is possible to obtain it.

Fig. 86.

When in the progress of the work it is found that the auger does not go down to the depth from which it was withdrawn, after trial, tubing will generally be necessary. The hole should be enlarged from the surface, or, if not very deep, commenced afresh from the surface with a larger auger, and run down to nearly the same depth; the first length of tube is then driven into the hole, and when this is effected another tube, having similar dimensions to the first, is screwed into its upper end, and the driving repeated, and so on until a sufficient number of pipes have been used to reach to the bottom of the hole. If the ordinary auger is now introduced through these tubes it will have free access to the clay or sand, and after a few feet deeper have been bored another pipe may be screwed on, and the whole driven farther down. In this way from 10 to 20 feet of soft stratum may be bored through. If the thickness of the surface clay or sand is considerable the method here mentioned will not be effective, as the friction of the pipes caused by the pressure of the strata will be so great that perhaps not more than 80 or 100 feet can be driven without the pipes being injured. It will then be necessary to put down the first part of the bore-hole with a large auger, and drive in pipes of larger diameter; the hole is continued of smaller diameter, and lined with smaller tubes projecting beyond the large tubes, as in [Fig. 85], until the necessity for their use ceases. It will be evident that to ensure success the tubing, whatever it is made of, should be as truly cylindrical as possible, straight, and flush surface, both outside and in. It will also be evident that in thus joining pieces of tubing together, the thickness ought to have a due proportion to the work required, and the force likely to be used in screwing or driving them down. Wrought-iron tubes, when driven, must be worked carefully, by means of a ring made of wrought-iron, from 11⁄2 to 2 inches in height and 3⁄4 inch thick, and of the form shown in [Fig. 86]; or driven with a pipe-dolly such as that in [Fig. 80]. The ring, or the dolly, is screwed into the lowermost boring rod and worked at the same rate and in a similar manner to the chisel, due regard being had to the depth at which the driving is being done, as the weight of the boring rods will materially affect the strength of the blow delivered. Cast-iron tubing may be driven hard with a monkey. To withdraw broken or defective tubing quickly, two hooks attached to ropes are lowered down from opposite sides of the bore-hole, caught on the rim of the lowermost tube, and power applied to haul the tubing up bodily.

[Figs. 87 to 91] show good methods of forming tube or pipe joints both in cast and wrought-iron, when not screwed.

Figs. 87-91.

P. S. Reed, an English mining engineer, gives the following instance of replacing defective tubing in a boring which had been pursued to the depth of 5821⁄2 feet, but which, owing to circumstances which were difficult to determine, had become very expensive, and made slow progress.

The 5821⁄2 feet had been bored entirely by manual labour; but Reid recommended the erection of a horse-gin, in which the power was applied to a 40-inch drum placed upon a vertical axle, the arms of which admitted of applying two horses, and men at pleasure, the power gained being in the proportion of one to ten at the starting-point for the horses.

Upon the upright drum a double-ended chain was attached, which worked over sheer-legs erected immediately over the hole, so as to attain an off-take for the rods of 60 feet, and so as that, in the act of raising or lowering, there might always be one end of the chain in the bottom, ready to be attached, and expedite the work as much as possible.

These arrangements being made, it was soon found that there was a defect in the tubing which was inserted to the depth of 109 feet, and the defect was so serious, in permitting the sand to descend and be again brought up with the boring tools, as to render it very difficult to tell in what strata they really were; this increased to such a degree as to cause the silting up of the hole in a single night to the extent of 180 feet, and it occupied nearly a fortnight in clearing the hole out again.

On carefully examining into this defect, it appeared that the water rose in the hole to the depth of 74 feet from the surface; and that at this point it was about level with the high-water mark on the Tees, about two miles distant, with which it was no doubt connected by means of permeable beds, extending from the arenaceous strata at a depth of 100 feet.

On commencing to bore, the motion of the rods in the hole caused the vibration of the water between a range of 40 feet at the bottom of the tubing, and so disturbed the quiescent sand as to cause it to run down through the faults in the lower end of the tubing.

This tubing was made of galvanized iron plates, riveted together and soldered; at the top of the hole it was in three concentric circles, which had been screwed and forced down successively until an obstacle was met with at three different places. So soon as the outer circle reached the first depth, all hope appears to have vanished, from those who bored the earlier part of the work, of getting the tube farther; a second tube was, therefore, inserted, which seems to have advanced as far as the second obstacle, where it, in its turn, was abandoned; and a third one advanced until it rested in the strata at the lower part of the lias freestone of a blue nature, as found on the rocks at Seaton Carew, and in the bed of the Leven, near Hutton Rudby. The diameter of the first tubing was 37⁄8 inches external and 31⁄2 inches internal; the second tube was 31⁄4 inches external, and 3 inches internal diameter; and the third tube was 23⁄4 inches external and 21⁄2 inches internal diameter.

Such being the account gathered from the workmen who superintended the earlier part of the boring, it became necessary to decide upon the best cause to remedy the evil. At first sight it would have appeared easy enough to have caught the lower end of the tubes by means of a fish-head properly contrived, and thus to have lifted them out of the hole, and replaced them with a perfect tube, such as a gas-tube, with faucet screw-joints; but, on attempting this, it soon became evident that however good the tubing which might have been adopted, it would be a work of the greatest difficulty to extract when once it was regularly fixed and jammed into its place by the tenacious clayey strata surrounding it; and the difficulty of extracting it, in the present case, was even enhanced by the inferior quality and make of the tubing; in short, that, unless by crumpling it up in such a manner as to destroy the hole, it was impossible to extract this tubing by main force.

There was, therefore, no other choice left but to attempt cutting it out, inch by inch; though before doing so, force was applied to the bottom of the tubing, to the extent of upwards of 30 tons, the only result being the loss of several pieces of steel down the hole, which had to be brought up with a powerful magnet.

After much mature consideration and contrivance, it was determined to order such tubing as would at the same time present as little obstacle as possible to the clay to be passed through on the outside, as well as surround the largest of the three tubes then in the hole, and present no obstacle to their being withdrawn through its interior.

These tubes were made 12 feet in length, flush outside and in, the lower portion being steeled for 6 inches from the bottom end, so as to cut its way and follow down the space, and cover that exposed by the old tubes when cut and drawn, as shown in [Fig. 92].

In order to commence operations, and avoid too much clay going down to the bottom of the hole, a straw-plug was firmly fixed in the lias portion of the hole. The lower portion of the new tubes was then screwed around the old ones by means of powerful clamps, attached to the exterior in such a manner as to avoid injuring the surface; and when they could be screwed no farther, the knife or cutter, [Figs. 92 to 94], was introduced inside the old tubing. Some force was needed to get this knife down into the tubing, but the spring a giving so as to accommodate itself to the hole, permitted its descent to the distance required; this being effected, it was turned round so that the steel cutter, shown at b, being forced against the sides of the tube, cut it through in the course of ten minutes or a quarter of an hour’s turning. See section at b, c, [Fig. 93].

Figs. 92-94.

[Larger image] (125 kB)

The old tubes being three-ply, three of these knives or cutters were required to cut out the three tubes, the inner one being detached first, and then the two exterior ones; and so soon as these latter were cut out as far as they had been forced into the clay, the work became simplified into following down the interior tubing by the new tubes, as shown by the dotted lines. From d at the lower end, it was found that the old inner tube had been so damaged or torn, either by the putting in or hammering it down, as to leave a vent or fissure for the sand to descend, and thus spoil the whole of the work for all future success in the boring, to say nothing of the very great cost of lifting the sand out, and subsequent most arduous labour to put the hole right.

Boring was recommenced after about a month’s labour in taking out the old tubings, leaving the new ones firmly bedded into the lias formation, 112 feet from the surface, and the hole was subsequently bored to a depth of 710 feet in the new red sandstone formation, proceeding at the rate of about 3 feet in the twelve hours, and leaving the hole so as, if requisite, it might be widened out to 4 inches diameter. [Fig. 92] shows the action of the knife and spring-cutter when forced down into the tubing, ready to commence cutting. It also shows the lower end of the new tubing, enclosing the others at the commencement of the work. The joints of the new tubes were made by means of a half-lap screw. [Fig. 94] is a back view of the knife or cutter b. [Fig. 93] shows the action of the spring and cutter when the requisite length is cut through and ready for lifting; the position of the tube being maintained perpendicular, or nearly so, by the ball or thickening on the rods at K, and the lower end of the tube being supported by the projecting steel cutter at b, the dotted lines from d showing the position of the new steel-ended tube when screwed down ready for another operation. In boring deeper after the tubes were removed, three wooden blocks were used round the rods in the new tube to keep them plumb.

In some cases it is necessary to widen out holes below the sharp edge of tubing, so as to permit its descent. This is effected with a rimer, Figs. [81] and [82], and is an operation requiring great care and attention.

To reduce the stoppages for the withdrawal of débris the system of Fauvelle was introduced, but it is now very little practised on the Continent, and not at all in Great Britain. The principles upon which it was founded were: first, that the motion given to the tool in rotation was simply derived from the resistance that a rope would oppose to an effort of torsion; and therefore that the limits of application of the system were only such as would provide that the tool should be safely acted upon; and, secondly, that the injection of a current of water, descending through a central tube, should wash out the débris created by the cutting tool at the bottom. The difficulties attending the removal of the débris were great; and though the system of Fauvelle answered tolerably well when applied to shallow borings, it was found to be attended with such disadvantages when applied on a large scale, that it has been generally abandoned. The quantity of water required to keep the boring tool clear is a great objection to the introduction of this system, especially as in the majority of cases Artesian wells are sunk in such places as are deprived of the advantage of a large supply.

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. It follows from this, that where the excavation is very deep, there is considerable difficulty in transmitting the blow of the tool, in consequence of the vibration produced in the long rod, or in consequence of the torsion; and, for the same reason, there is a danger of the blows not being equally delivered at the bottom. It has been attempted to obviate this difficulty, but without much success, by the use of hollow rods, presenting greater sectional area than was absolutely necessary for the particular case, in order to increase their lateral resistance to the blows tending to produce vibration.

Boring is usually executed by contract. The approximate average cost in England may be taken at 1s. 3d. a foot for the first 30 feet; 2s. 6d. a foot for the second 30 feet; and continue in arithmetical progression, advancing 1s. 3d. a foot for every additional 30 feet in depth. This does not include the cost of tubing, conveyance of plant and tools, professional superintendence, or working in rock of unusual hardness, such as hard limestone and whinstone. A clause is usually inserted in the contract, to the effect that, if any unforeseen difficulty is met with in the course of the work, it is then paid for by the day, at a rate previously determined upon, until the difficulty has been overcome.

[CHAPTER V.]
AMERICAN TUBE WELL.

This well consists of a hollow wrought-iron tube about 13⁄4 inch diameter, composed of any number of lengths from 3 to 11 feet, according to the depth required. The water is admitted into the tube through a series of holes, which extend up the lowest length to a height of 21⁄2 feet from the bottom.

The position for a well having been selected, a vertical hole is made in the ground with a crowbar to a convenient depth; the well tube a, having the clamp d, monkey c, and pulleys b, [Fig. 95], previously fixed on it, is inserted into this hole.

The clamp is then screwed firmly on to the tube from 18 inches to 2 feet from the ground, as the soil is either difficult or easy; each bolt being tightened equally, so as not to indent the tube.

The pulleys are next clamped on to the tube at a height of about 6 or 7 feet from the ground, the ropes from the monkey having been previously rove through them.

Fig. 95.

The monkey is raised by two men pulling the ropes at the same angle. They should stand exactly opposite each other, and work together steadily, so as to keep the tube perfectly vertical, and prevent it from swaying about while being driven. If the tube shows an inclination to slope towards one side, a rope should be fastened to its top and kept taut on the opposite side, so as gradually to bring the tube back to the vertical. When the men have raised the monkey to within a few inches of the pulleys, they lift their hands suddenly, thus slackening the ropes and allowing the monkey to descend with its full weight on to the clamp. The monkey is steadied by a third man, who also assists to force it down at each descent. This man, likewise, from time to time, with a pair of gas-tongs, turns the tube round in the ground, which assists the process of driving, particularly when the point comes in contact with stones.

Particular attention must be paid to the clamp, to see that it does not move on the tube; the bolts must be tightened up at the first appearance of any slipping.

When the clamp has been driven down to the ground, the monkey is raised off it, the screws of the clamp are slackened, and the clamp is again screwed to the tube, about 18 inches or 2 feet from the ground. After this, the monkey is lowered on to it, and the pulleys are then raised until they are again 6 or 7 feet from the ground.

The driving is continued until but 5 or 6 inches of the well tube remain above the ground, when the clamp, monkey, and pulleys are removed, and an additional length of tube screwed on to that in the ground. This is done by first screwing a collar on to the tube in the ground, and then screwing the next length of tube into the collar, till it buts against the lower tube; a little white-lead must be placed on the threads of the collar before the ends of the tubes are screwed into it.

The driving can thus be continued until the well has obtained the desired depth. Soon after another length has been added, the upper length should be turned round a little with the gas-tongs, to tighten the joints, which have a tendency to become loose from the jarring of the monkey. Care must be taken, after getting into a water-bearing stratum, not to drive through it, owing to anxiety to get a large supply. From time to time, and always before screwing on an additional length of tube, the well should be sounded, by means of a small lead attached to a line, to ascertain the depth of water, if any, and character of the earth which has penetrated through the holes perforated in the lower part of the well tube. As soon as it appears that the well has been driven deep enough, the pump is screwed on to the top and the water drawn up. It usually happens that the water is at first thick, and comes in but small quantities; but after pumping for some little time, as the chamber round the bottom of the well becomes enlarged, the quantity increases and the water becomes clearer.

When sinking in gravel or clay, the bottom of the well tube is liable to become filled up by the material penetrating through the holes; and before a supply of water can be obtained, this accumulation must be removed by means of the cleaning pipes.

The cleaning pipes are of small diameter, 1⁄2-inch externally, and the several lengths are connected together in the same way as the well tubes, by collars screwing on over the adjoining end of two pipes.

To clear the well, one cleaning pipe after another is lowered into the well, until the lower end touches the accumulation; the pipes must be held carefully, for if one were to drop into the well it would be impossible to get it out without drawing the well. A pump is then attached to the upper cleaning pipe by means of a reducing socket; the lower end of the cleaning pipe is then raised and held about an inch above the accumulation by means of the gas-tongs: water is next poured down the well outside the cleaning pipe, and, being pumped up through the cleaning pipe, brings up with it the upper portion of the accumulation; the cleaning pipe is gradually lowered, and the pumping continued until the whole of the stuff inside the well tube is removed. The pump is then removed from the cleaning pipe, and the cleaning pipes are withdrawn piece by piece; and finally the pump is screwed on to the upper end of the tube well, [Fig. 96], which is then in working order.

Fig. 96.

The tube being very small, is in itself capable of containing only a limited supply of water, which would be exhausted by a few strokes of the pump; the condition, therefore, upon which alone these tube wells can be effective, is that there shall be a free flow of water from the outside through the apertures into the lower end of the tube. When the stratum in which the water is found is very porous, as in the case of gravel and some sorts of chalk, the water flows freely; and a yield has been obtained in such situations as great and rapid as the pump has been able to lift, that is 600 gallons an hour. 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. When the stratum reached by driving is a quicksand, the quantity of sand drawn up from the water will be so great, that a considerable amount will have to be pumped before the water will come up clear; and even in some positions, when the quicksand is of great extent, the effect of the pumping may be to injure the foundations of adjoining buildings on the surface of the ground.

The tube well cannot itself be driven through rock, although it might be used for drawing water from a subjacent stratum through a hole bored in the rock to receive it.

Subject to these conditions, these tube wells afford a ready and economical means for drawing water to the surface from a depth not exceeding 27 or 28 feet.

[CHAPTER VI.]
WELL BORING AT GREAT DEPTHS.

The first well that was executed of great depth, and which gave rise to the adoption of tools which directed public attention to the art of well boring, was that for the city of Paris by Mulot, at the Abattoir of Grenelle. This was commenced in the year 1832; and after more than eight years’ incessant labour, water rose, on the 26th of February, 1842, from the total depth of 1798 feet. Subsequent to this, many wells have been sunk on the Continent, with the hope of attaining the brine springs so often met with in the Rhine provinces, or the springs destined for the supply of towns, and which are even deeper than the well of Grenelle, reaching in some cases to the extraordinary depth of 2800 feet; but all of them, like the Grenelle well, of small diameter. In their construction, however, the German engineers introduced some important modifications of the tools employed; and, amongst other inventions, Euyenhausen imparted a sliding movement to the striking part of the tool used for comminuting the rock, so as to fall always through a certain distance; and thus, while he produced a uniform action upon the rock at the bottom, he avoided the jar of the tools. Kind also began to apply his system to the working of the large excavations for the purpose of winning coal. Whilst the art was in this state, and when he had already executed some very important works in Germany, Belgium, the North of France, Creuzot, and Seraing, the Municipal Council of Paris determined to entrust him with the execution of a new well they were about to sink at Passy.

In sinking the well of Passy, the weight of the trepan for comminuting the rock was about 1 ton 16 cwt., 1800 kilog.: the height through which it fell was about 60 centimètres; and its diameter was 3 feet 37⁄16 inches, 1 mètre. The rods were of oak, about 8 inches on the side, and the dimensions of the cutting tool were limited to 3 feet 37⁄16 inches because it worked the whole time in water; but generally the class of borings Kind undertook were of such a description as justified resorting to tools of great dimensions. When sinking the shafts for winning coal, his operations required to be carried on with the full diameters of 10 feet or 14 feet; and he then drove a boring of 3 feet 4 inches diameter in the first instance, and subsequently enlarged this excavation. There can be no objection to executing Artesian borings of this diameter, other than the probable exhaustion of the supply; particularly as it is now known that the yield of water by these methods is proportionate to the diameter of the column; though, strange as it may appear, the first opposition to Kind’s plan of sinking the well of Passy was founded upon the assumption that he would not meet with a larger supply of water from the subcretaceous formations than had been met with at Grenelle, where the diameter of the boring was at the bottom not more than 8 inches. It is now, however, proved that there is a direct gain in adopting the larger borings, not only as regards the quantity of water to be derived from them, but also in their execution, arising from the fact that the tools can be made more secure against the effects of torsion or of concussion against the sides of the excavation, which is the cause of the most serious accidents met with in well sinking.

The trepan of M. Kind contains some peculiar details, which are shown in [Figs. 97, 98]. The trepan is composed of two principal pieces, the frame and the arms, both of wrought-iron, with the exception of the teeth of the cutting part, which are of cast steel. The frame has at the bottom a series of holes, slightly conical, into which the teeth are inserted, and tightly wedged up, [Fig. 99]. These teeth are placed with their cutting edges on the longitudinal axis of the frame that receives them; and at the extremity of the frame there are formed two heads, forged out of the same piece with the body of the tool, which also carries two teeth, placed in the same direction as the others, but double their width, in order to render this part of the tool more powerful. By increasing the dimensions of these end teeth, the diameter of the boring can be augmented, so as to compensate for the diminution of the clear space caused by the tubing, necessarily introduced for security in traversing strata disposed to fall in, or for the purpose of allowing the water from below to escape at an intermediate level.

Figs. 97-99.

Above the lower part of the frame of the trepan is a second piece composed of two parts bolted together, and made to support the lower portion of the frame. This part of the machinery also carries two teeth at its extremities, which serve to guide the tool in its descent, and to work off the asperities left by the lower portion of the trepan. Above this, again, are the guides of the machinery, properly speaking, consisting of two pieces of wrought-iron, arranged in the form of a cross, with the ends turned up, so as to preserve the machinery perfectly vertical in its movements, by pressing against the sides of the boring already executed. These pieces are independent of the blades of the trepan, and may be moved closer to it or farther away from it, as may be desired. The stem and the arms are terminated by a single piece of wrought-iron, which is joined to the frame with a kind of saddle-joint, and is kept in its place by means of keys and wedges. The whole of the trepan is finally jointed to the great rods that communicate the motion from the surface, by means of a screw-coupling, formed below the part of the tool which bears the joint; this arrangement permits the free fall of the cutting part, and unites the top of the arms and frame, and the rod, [Fig. 100]. It has been proposed to substitute for this screw-coupling a keyed joint, in order to avoid the inconvenience frequently found to attend the rusting of the screw, which often interposes great difficulties in cases where it becomes necessary to withdraw the trepan.

Fig. 100.

The sliding joint is the part of Euyenhausen’s invention most unhesitatingly adopted by Kind, and it is one of the peculiarities of his system as contrasted with the processes formerly in use. So long as his operations were confined to the small dimensions usually adopted for Artesian borings, he contented himself with making a description of joint with a free fall; a simple movement of disengagement regulating the height fixed by the machinery itself, like the fall of the monkey in a pile-driving machine; but it was found that this system did not answer when applied to large borings, and it also presented certain dangers. Kind then, for the larger class of borings, availed himself of sliding guides, so contrived as to be equally thrown out of gear when the machinery had come to the end of the stroke, and maintained in their respective positions by being made in two pieces, of which the inner one worked upon slides, moving freely in the piece that communicated the motion to the striking part of the machinery. The two parts of the tool were connected with pins, and with a sliding joint, which, in the Passy well, was thrown out of gear by the reaction of the column of water above the tool unloosing the click that upheld the lower part of the trepan, [Figs. 101 to 103]. The changes thus made in the usual way of releasing the tool, and in guiding it in its fall were, however, matters of detail; they involved no new principle in the manner of well boring: and the modern authorities upon the subject consider that there was something deficient in Kind’s system of making the column of water act upon a disc by which the click was set in motion. This system, in fact, required the presence of a column of water not always to be commanded, especially when the borings had to be executed in the carboniferous strata.

Figs. 101-104.

The rods used for the suspension of the trepan, and for the transmission of the blows to it, were of oak; and this alone would constitute one of the most characteristic differences between the system of tools introduced by Kind and those made by the majority of well-borers, but which, like the disengagement of the tool intended to comminute the rock, depended for its success upon the boring being filled with water. The resistance that the wood offers, by its elasticity, to the effects of any sudden jar, is also to be taken into account in the comparison of the latter with iron, for the iron is liable to change its form under the influence of this cause. The resistance to an effort of torsion need not, however, be much dwelt on, for the turn given to the trepan is always made when the tool is lifted up from its bed. For the purpose of making the rods, Kind recommended that straight-grown trees, of the requisite diameter, should be selected, rather than they should be made of cut-timber, as there is less danger of the wood warping, and the character of the wood is more homogeneous. He generally used these trees in lengths of about 50 feet, and he connected them at the ends with wrought-iron joints, fitting one into the other, [Fig. 104]. The ironwork of the joints is made with a shoulder underneath the screw-coupling, to allow the rods to be suspended by the ordinary crow’s foot during the operation of raising or lowering them. In the works executed at Passy there was a kind of frame erected over the centre of the boring, of sufficient height to allow of the rods being withdrawn in two lengths at a time, thus producing a considerable economy of time and labour.

Figs. 105, 106.

Nearly all the processes yet introduced for removing the products of the excavation must be considered to be, more or less, defective, because all are established on the supposition that the comminuting tool must be withdrawn, in order that the shell, or other tool intended to remove the products of the working of the comminutor, may be inserted. This remark applies to Kind’s operations at Passy and elsewhere, as he removed the rock detached from the bottom of the excavation by a shell, [Figs. 105, 106], which was a modification of the tool he invariably employs for this purpose. It consisted of a cylinder of wrought-iron, suspended from the rods by a frame, and fastened to it, a little below the centre of gravity, so that the operation of upsetting it, when loaded, could be easily performed. This cylinder was lowered to the level of the last workings of the trepan, and the materials already detached by that instrument were forced into the tool, by the gradual movement of the latter in a vertical direction. Some other implements, employed by Kind for the purpose of removing the products of the excavation in the shafts for the coal-mines of the North of France, were ingenious, and well adapted to the large dimensions of the shafts; but they were all, in some degree, exposed to the danger of becoming fixed, if used in the small borings of Artesian wells, by the minute particles of rocks falling down between their sides and the excavation from above. Their use was therefore abandoned, and the well of Passy was cleared out with the shell, the bottom of which was made to open upwards, with a hinged flap, which admitted the finer materials detached by the trepan. There were also several tools for the purpose of withdrawing the broken parts of the machinery from the excavation, or whatever substances might fall in from above; and all were marked by a great degree of simplicity, but they did not differ enough from those generally used for the same purpose to merit further remarks. In fact, the accidents intended to be guarded against or remedied are so precisely alike in all cases, that there can be little variety in the manufacture of these instruments. But there is no doubt that Kind deprived himself of a valuable appliance in not using the ball-clack, la soupape à boulet, that other well-borers employ, [Fig. 107].

Fig. 107.

At Passy great strength was given to the head of the striking tool, and to the part of the machinery applied to turn the trepan, because the great weight of the latter superinduced the danger of its breaking off under the influence of the shock, and because the solidity of this part of the machinery necessarily regulated the whole working of the tool. The head of the boring arrangement was connected with the balance-beam of the steam-engine by a straight link-chain, with a screw-coupling, admitting of being lengthened as the trepan descended, [Figs. 108, 109]. The balance-beam, in order to increase its elastic force in the upward stroke, is in Kind’s works made of wood, in two pieces; the upper one being of fir and the lower one of beech. The whole of the machinery is put in motion by steam, which is admitted to the upper part of the cylinder, and presses it down, and thus raises the tool at the other end of the beam to that part in connection with the cylinder. The counterpoise to the weight of the tools is also placed upon the cylinder-end of the beam. The cylinder receives the steam through ports that are opened and closed by hand, like those of a steam-hammer; so that the number of the strokes of the piston may be increased or diminished, and the length of the strokes may be increased, as occasion may require.

Figs. 108, 109.

The balance-beam is continued beyond the point where the piston is connected with it, and it goes to meet the blocks placed to check the force of the blow given by the descent of the tool. The guides of the piston-head are attached to the part of the machinery that acts in this manner; but at Passy, Kind made the balance-beam work upon two free plummer-blocks, or blocks having no permanent cover, that they might be more easily moved whenever it was necessary to displace the beam, for the purpose of taking up or letting down the rods, or for changing the tools; for the balance-beam was always immediately over the centre of the tools, and it therefore had to be displaced every time that the latter were required to be changed. This was effected by allowing the beam to slide horizontally, so as to leave the mouth of the pit open. The counter-check, above mentioned, likewise prevented the piston from striking the cylinder cover with too great a force, when it was brought back by the weight of the tools to its original position. The operation of raising and lowering the rods, or of changing the tools, was performed at Passy by a separate steam-engine, and the shell was discharged into a special truck, moving upon a railway expressly laid for this purpose in the great tower erected over the excavation. All these arrangements were in fact made with the extreme attention to the details of the various parts of the work which characterizes the proceedings of foreign engineers, and conduces so much to their success.

The beating, or comminution of the rock, was usually effected at Passy at the rate of from fifteen strokes to twenty strokes a minute. The rate of descent, of course, differed in a marked manner, according to the nature of the rock operated upon; but, generally speaking, the trepan was worked for the space of about eight hours at a time, after which it was withdrawn, and the shell let down in order to remove the débris. The average number of men employed in the gang, besides the foreman, or the superintendent of the well, was about fourteen: they consisted of a smith and hammerman, whose duty it was to keep the tools in order; and two shifts of men entrusted with the excavation, namely, an engine-driver and stoker, a chief workman, or sub-foreman, and three assistants. The total time employed in sinking the shafts executed upon this system in the North of France, where it has been applied without meeting with the accidents encountered in the Passy well, was found to be susceptible of being divided in the following manner: from 25 per cent. to 56 per cent. was employed in manœuvring the trepan; from 11 per cent. to 141⁄2 per cent. in raising and lowering the tools; from 19 per cent. to 21 per cent. in removing the materials detached from the rocks, and cleaning out the bottom of the excavation; and from 8 per cent. to 101⁄2 per cent. was lost, owing to the stoppage of the engines, or to the accidents from broken tools, or to other causes always attending these operations. In the well of Passy there was, of course, a considerable difference in the proportions of the time employed in the various details of the work; and the long period occupied in obviating the effects of the slips which took place in the clays, both in the basement beds of the Paris basin and in the subcretaceous strata, would render any comparison derived from that well of little value; but it would appear that, until the great accident occurred, the various operations went on precisely as Kind had calculated upon.