Chapter VI: Well Boring at Great Depths (1)

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 3-7/16 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 3-7/16 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. 101-103.]

Fig. 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 manoeuvring the trepan; from 11 per cent. to 14-1/2 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 10-1/2 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.

KIND-CHAUDRON SYSTEM.

Fig. 110.]

In the year 1872 Emerson Bainbridge, C.E., drew attention to the Kind-Chaudron system of sinking mine shafts through water-bearing strata, without the use of pumping machinery, in a paper read before the Institute of Civil Engineers. As the operation is almost identical with that which would have to be carried through in the case of a well sunk through an upper series of water-bearing strata, of minor importance or of impure quality, past rock and into the lower water strata, as for instance through tertiaries and chalk into the lower greensand, the following extract from Bainbridge's paper may be read with interest.

In the first place, it may be desirable to describe briefly the system of sinking hitherto pursued in passing through strata yielding large quantities of water. The most important sinkings of this character have been carried out in the county of Durham, to the east of the point at which the Permian overlie the carboniferous rocks. In this district there is a thin bed of sand between the Permian rock and the coal measures. Towards this bed the feeders of water are generally found to increase, and in the sand there is usually a large reservoir of water. The mode of sinking will be understood by reference to Fig. 110. Whilst sinking in hard rock, it has ordinarily been the custom to place iron curbs, or cribs, wherever a bed of stone appeared to form a natural barrier between two distinct feeders of water. Thus it has frequently happened that important feeders have been tubbed back, rendering much less pumping power necessary than would have been required had all the feeders been allowed to accumulate in the shaft. As will be seen by Fig. 110, the number of wedging cribs employed is no less than thirteen in 250 feet. The cribs forming the foundation of each set of tubbing are generally much more massive and costly than the segments of tubbing.

Fig. 111.]

Fig. 112.]

Fig. 113.]

Fig. 114.]

Fig. 115.]

Fig. 116.]

Fig. 118.]

The process of fixing the crib is as follows;--The diameter of the shaft is made about 30 inches larger than that of the inside of the tubbing. When a bed of rock, which may be considered sufficiently hard and close to separate the feeders above and below it, is reached, the shaft is contracted to the diameter of the tubbing, and a smooth horizontal face is made on which to place the wedging crib. The wedging crib, which usually consists of segments about 4 feet long by 6 inches high by 14 inches wide, is then placed on the bed. To give the crib a firm and secure position, it is tightly wedged with wood, both behind and between the joints; the tubbing is then built upon it to the next wedging crib, which rests upon a bell-shaped section of rock. When the tubbing nearly reaches this crib, the rock is removed piece by piece, and the top ring of tubbing is placed close up against the crib. It will thus be seen that the fixing of each crib is a costly process, often causing considerable delay.

In some cases, where it has been difficult to find suitable foundations for intermediate wedging cribs, the whole of the water-bearing rocks have been sunk through without attempting to stop the feeders separately, and no tubbing has been placed in the shaft till the wedging crib could be fixed below the lowest feeder. This process is more expeditious where there are small quantities of water; but where the water is excessive greater delay is caused by contending with it than from putting in numerous sets of tubbing to stop the feeders separately. The tubbing used in England has almost invariably been of cast-iron; on the Continent, till recently, tubbing of wood has chiefly been used. Illustrations of both descriptions are shown by Figs. 111 and 112.

Figs. 113, 114, show, in elevation, the plant and the arrangements generally in use at extensive sinkings. Where the water is in large quantities it is usually pumped by an engine erected for the purpose, assisted by the engine or engines intended to be employed to raise the coal. A small capstan engine is used for passing the men and material up and down the pit during the sinking, such engine being provided also with a drum on slow motion, which is used for heavy weights. The continual pumping, the placing of cribs, and the fixing of the tubbing are proceeded with till the lowest feeder is reached, when a hard bed is sought for on which to fix the lowest wedging crib. In all cases the water has to be pumped out before the wedging crib, which forms the foundation of each set of tubbing, can be placed.

From this description it will be understood that the sinkers, who number from ten to twelve at one time, working four hours at a shift in a pit, say, 14 feet in diameter, are compelled to work in water until all the tubbing is fixed. This causes a serious obstacle to blasting, and in other ways delays the progress of the work.

The tubbing used for damming back the water is generally in segments from 1 foot to 3 feet high, and about 4 feet in length, the thickness varying from half an inch to 3-3/4 inches. It is kept in position by packing with wood behind the joints; and is made water-tight by placing between the segments pieces of wood sheeting about half an inch thick, which are wedged when all the tubbing is fixed, usually twice with wood, and sometimes once with iron wedges.

Fig. 117.]

To equalize the pressure of water and gas behind the different sets of tubbing, pass pipes, Figs. 115 and 116, are sometimes used. Another expedient to effect this is to have a valve, working upwards, placed in the wedging crib, Fig. 117. A ball is also sometimes used, Fig. 118.

The various modes of piercing beds of quicksand are;--By hanging tubbing to that already fixed, and adding fresh rings as the sand is removed. This is only practicable when the quantity of sand is inconsiderable. By heavily weighting a cylinder of iron of the same size as the shaft, and thus forcing it down through the sand. By keeping back the sand by the use of piles--a resource that can only be recommended when the bed of sand is not of great thickness. When the water is excessive, by using pneumatic agency. As these operations are apart from our immediate subject we need not further discuss them.

M. Chaudron's system, which is a modification of Kind's, is divisible into the following distinct processes, which consist of;--

The erection of the necessary machinery on the surface, and the opening of the mine.

The boring of the pits to the lowest part of the water-bearing strata.

The placing of the tubbing.

The introduction of cement behind the tubbing to complete its solidity.

The extraction of the water from the pits, and the placing of the wedging cribs, or "faux cuvelage," below the moss box.

Fig. 119.]

Fig. 120.]

Fig. 121.]

Figs. 119 to 121 show in elevations and in plan the plant usually employed on the surface. O is a small capstan engine, having a cylinder 20 inches in diameter and a stroke of 32 inches, working on the third motion. Attached to this engine, and working in the small pit C, is a counterbalance weight. This engine is used for raising and lowering boring tools, and for lifting the _débris_ resulting from the boring. As far as the platform, which is about 10 feet from the surface, the pit has a diameter of 19 feet, or 4 feet more than the diameter of the pit below. A at level of about 38 feet above this platform there is a tramway on which small trucks run, carrying the _débris_ cylinder on one side, and the boring tools on the other. At a level of 48 feet above the platform are placed supports for the wooden spears to which the boring tools are attached. The machinery for boring is worked by a cylinder, which has a diameter of 39-1/3 inches, and a full stroke of 39-1/3 inches, the usual stroke varying from 2 feet to 3 feet. A massive beam of wood transmits motion from this cylinder to the boring apparatus, the connection between the beam and the piston-rod and the beam and the boring tools being made by a chain. The engine-man sits close to the engine, and applies the steam above the piston only. The down stroke of the boring tools is caused by the sudden opening of the exhaust, and a frame then prevents the shock of the boring rods from being too severe. The engines work at speeds varying from 12 to 18 strokes a minute, according to the character of the strata passed through.

Fig. 122.]

Fig. 123.]

Fig. 124.]

Fig. 125.]

Fig. 126.]

Fig. 127.]

Fig. 128.]

Fig. 129.]

Fig. 130.]

Figs. 131-134.]

After the working platform is fixed, the first boring tool applied is the small trepan, Figs. 122 to 125. This tool is attached to the wooden beam by the same arrangement shown by Fig. 109. The boring tools can be lowered at pleasure by means of an adjusting screw. Next in order comes the handle for boring. This is worked by four men on the platform, and is turned by the aid of a swivel. Attached to the handle-piece are wooden rods, made from Riga pitch pine. These rods are 59 feet in length and 7-3/4 inches square. A swivelled ring, Figs. 126, 127, is attached to the rope when raising and lowering the boring rods. The small trepan cuts a hole 4 feet 8-3/4 inches in diameter, and has fourteen teeth, fitted in cylindrical holes and secured by pins entering through circular slots. The teeth are steeled. At a distance of 4 feet 4 inches above the main teeth of the trepan there is an arm, with a tooth at each end. This piece answers the purpose of a guide, and at the same time removes irregularities from the sides of the hole. At a distance of 13 feet 6 inches above the main teeth are the actual guides, consisting of two strong arms of iron fixed on the tool, and placed at right-angles to each other. The hole made by the small trepan is not kept at any fixed distance in advance of the full-sized pit, but the distance generally varies from 10 to 30 yards. With the small trepan, which weighs 8 tons, the progress varies from 6 to 10 feet a day.

The large trepan, Figs. 128 to 130, weighs 16-1/2 tons, is forged in one solid piece, and has twenty-eight teeth. A projection of iron forms the centre of this trepan, and fits loosely into the hole made by the small trepan, acting as a guide for the tool. At a distance of 7 feet 6 inches above the teeth, a guide is sometimes fixed on the frame, but is not furnished with teeth. At a distance of 13 feet 3 inches from the teeth are two other guides at right-angles to each other. These guides are let down the pit with the boring tool, the hinged part of the guides being raised whilst passing through the beams at the top of the pit, which are only 6 feet 7 inches apart. When the tool is ready to work, the two arms are let down against the side of the pit, and are hung in the shaft by ropes, thus acting as a guide for the trepan, which moves through them. To provide against a shock to the spears when the trepan strikes the rock on the down stroke, at the upper part of the frame a slot motion is arranged, the play of which amounts to about half an inch. The teeth of the large trepan are not horizontal, but are deeper towards the inside of the pit, the face of the inside tooth being 3-3/4 inches lower than the outside. The object of this is to cause the _débris_ to drop at once into the small hole, by the face of the rock at the bottom of the pit being somewhat inclined. The teeth used, Figs. 131 to 134, are the same both for the large and the small trepan, and weigh about 72 lb. each. As a rule, only one set of teeth is kept in use, this set working for twelve hours, the alternate twelve hours being employed in raising the _débris_. This time is divided in about the following proportions;--Boring, twelve hours; drawing the rods, one hour to five hours, according to depth; raising the _débris_, two hours; and lowering the rods one hour to five hours. The maximum speed of the larger trepan may be taken at about 3 feet a day. The ordinary distance sunk is not more than 2 feet a day, and in flint and other hard rocks the boring has proceeded as slowly as 3 inches a day.

Figs. 135, 136.]

Figs. 137, 138.]

Figs. 139, 140.]

Fig. 141, 142.]

The _débris_ in the small bore-hole contains pieces of a maximum size of about 8 cubic inches. In the large boring, pieces of rock measuring 32 cubic inches have been found. As a rule, however, the material is beaten very fine, having much the appearance of mud or sand. In both the large and the small borings the _débris_ is raised by a shell, similar to Figs. 105, 106, and in this system consisting of a wrought-iron cylinder, 3 feet 3 inches in diameter by 6 feet 9 inches long, and containing two flap-valves at the bottom, through which the excavated material enters. This apparatus is passed down the shaft by the bore-rods, and it is moved up and down through a distance varying from 6 to 8 inches, for about a quarter of an hour, and is then drawn up and emptied. In some cases where the rock is hard, three sizes of trepan are used consecutively, the sizes being 5 feet, 8 feet, and 13 feet.

The several other tools and appliances used during the boring operations are shown, Figs. 135 to 140, including the key, Figs. 139, 140, used at the surface to disconnect the rods, the hook on which each rod is hung after being raised to the high platform and there detached, the bar upon which the hooks are moved, and the fork for suspending the rods or tools from the rollers when it is desired to move the rods or tools from above the shaft.

Figs. 143-146.]

Figs. 141 to 146 are of the connections to the trepan and spears or rods.

Should broken tools fall into the shaft, several varieties of apparatus are used for their recovery. In case of broken rods of any kind having a protuberance that can be clutched, a hook or crow, Figs. 137, 138, of an epicycloidal form, enables the object to be taken hold of very readily. Where the broken part has no shoulder which can be held, but is simply a bar, the apparatus shown by Figs. 147, 148, is employed. This is composed of two parts. The rods, the bottom of which have teeth inside, are prevented from diverging by the cone and slide on the main rods. When passed over a rod or pipe, they clutch it by means of the teeth, and draw it up. Chaudron has, by this tool, raised a column of pipes 295 feet in length and 8 inches in diameter. An instrument, called a "grapin," Figs. 149, 150, is used for raising broken teeth or other small objects which may have fallen into the bottom of the shaft. This tool also has one part sliding in the other, and is lowered with the claws closed. The parts are moved by two ropes worked from the surface. By weighting the cross-bar, which is attached to the moving parts, the pressure desired can be exerted on the claws. The weight is then lifted, the claws are opened, and are made to close upon the substance to be raised. This instrument is now seldom required.

Figs. 147, 148.]

Figs. 149, 150.]

In boring shafts in the manner described, without being able to prove in the usual way the perpendicularity of the shaft, it might be feared that the system would be open to objection on this account. It appears, however, that in all cases where Chaudron has sunk shafts by this system he has succeeded in making them perfectly vertical. This is ensured by the natural effect of the treble guide, which the chisels and the two sets of arms attached to the boring tools afford, and by the fact that if the least divergence from a plumb-line is made by the boring tool, the friction of the tool upon one side of the shaft is so great as to cause the borers to be unable to turn the instrument.

Boring alternately with the large and the small instrument, the shaft is at length sunk to the point at which the lowest feeder of water is encountered. In a new district this has to be taken, to some extent, at hazard; but where pits have been sunk previously, it is not difficult to tell, by observing the strata, almost the exact point at which the bottom of the tubbing may be safely fixed. This point being ascertained, the third process is arrived at.

Fig. 151.]

As the object of placing tubbing in a shaft is effectually to shut off the feeders, which for water supply may have some bad qualities, and to secure a water-tight joint at the base, it is important that the bed on which the moss box has to rest should be quite level and smooth. This is attained by the use of a tool, termed a "scraper," attached to the bore-rods, the blades being made to move round the face of the bed intended for the moss box. The tubbing employed is cast in complete cylinders. At Maurage each ring has an internal diameter of 12 feet and is 4 feet 9 inches high. Each ring has an inside flange at the top and bottom, and also a rib in the middle, the top and bottom of the ring being turned and faced. The rings of tubbing are attached to each other by twenty-eight bolts 1·1 inch in diameter, passed through holes bored in the flanges. The tubbing is suspended in the pit by means of six rods, which are let down by capstans placed at a distance of 30 feet above the top of the pit. These machines work upon long screws. When a new ring of tubbing is added, the rods are detached at a lower level, and are hung upon chains, thus leaving an open space for passing it forward. Before each ring is put into the pit it is tested by hydraulic apparatus, Fig. 151. The tubbing is usually proved to one-half more pressure than it is expected to be subjected to. At Maurage, where a length of 550 feet of tubbing has to be put in, the chief particulars respecting it are;--

+-----------+---------+------------+--------------+--------------+
| | | | | Pressure |
| | | | Pressure | at which |
| | Length. | Thickness. | expected. | Tubbing is |
| | | | | proved. |
+-----------+---------+------------+--------------+--------------+
| | | | lbs. a | lbs. a |
| | feet. | inches. | square inch. | square inch. |
| | | | | |
| Top | 130 | 1·17 | 30 | 45 |
| | 60 | 1·31 | 60 | 90 |
| | 60 | 1·57 | 90 | 135 |
| | 60 | 1·76 | 120 | 180 |
| | 60 | 1·96 | 150 | 225 |
| | 60 | 2·16 | 180 | 270 |
| | 60 | 2·35 | 210 | 315 |
| Bottom | 60 | 2·55 | 240 | 360 |
+-----------+---------+------------+--------------+--------------+

The joints between the rings of tubbing are made with sheet lead one-eighth of an inch thick, coated with red-lead. The lead is allowed to obtrude from the joint one-third of an inch, and is wedged up by a tool which has a face one-twelfth of an inch thick. The mode of suspending the tubbing to the rods will be understood by referring to Figs. 152 to 154. The rods are attached to a ring by the bolts connecting one ring of tubbing with another. The bottom ring of tubbing and the ring carrying the moss box have their top flange turned inwards, but their bottom flange outwards. A strong web of iron, forming the base of a tube 16-1/2 inches in diameter, is attached to the tubbing. The object of this tube is to cause the water in the shaft to ease the suspension rods, by bearing part of the weight of the tubbing. Cocks to admit water are placed at intervals up the tube, by which means the weight upon the rods can be easily regulated, so that not more than one-tenth to one-twentieth of the weight of the tubbing is suspended by the rods at one time. The ring holding the moss box is hung from the bottom joint in the tubbing by sliding rods.

Figs. 152-154.]

The arrangement of the moss box which forms the base of the tubbing is one of the most important points requiring attention in this system of sinking. Ordinary peat moss is used. It is enclosed in a net, which, with the aid of springs, keeps it in its place during the descent of the tubbing. When the moss box, which hangs on short rods fixed to the tubbing, reaches the face of rock, it is dropped gently upon it, and the whole weight of the tubbing is allowed to rest upon the bed. This compresses the moss, the capacity of the chamber holding it is diminished, and the moss is forced against the sides of the shaft, thus forming a water-tight joint, past which no water can escape. This completes the third process.

It may be noted that up to this point the following important differences between this and the ordinary system of placing tubbing are to be observed;--The tubbing, on reaching its bed, bears the aggregate pressure of all the feeders of water which have been met with in the shaft. The tubbing, having been passed down the shaft in the manner described, no wedging behind, or other modes of consolidating it in the shaft, have been carried out. The connection between each ring of tubbing is so carefully made, that the repeated wedging of the joints, as in the ordinary system, is rendered unnecessary. The pit is still full of water up to the ordinary level.

Under these conditions the next process is;--The introduction of cement behind the tubbing to complete its solidity.

Figs. 155, 156.]

Before the water is removed, the annular space between the tubbing and the sides of the shaft is filled with hydraulic cement, to render the tubbing impermeable, by a process of consolidation, less liable to the effect of any pressure of water or gas which may be exerted towards the centre of the shaft. The cement is inserted behind the tubbing by close ladles, Figs. 155, 156, capable of holding 44 gallons, and consisting of two iron plates, one-eighth of an inch thick, fixed on two wooden uprights 3-1/8 inches square. This apparatus is curved to suit the mean circumference of the space to be concreted. A piston is placed at the top of the ladle, and to this piston is attached a rod, which can be moved from the surface; a door is also attached to the piston. The ladle containing the concrete is passed down behind the tubbing by means of a windlass at the surface, and when it reaches the lowest point, the piston is pushed down and the cement allowed to escape from the chamber. The weight of the cement and the ladle is sufficient with a little ballast to enable it to descend easily.

A number of experiments have been made to discover a cement which will not harden too quickly, and which, when hardened, will form a perfectly compact and solid mass. A composition having the following proportions has been found the best;--Hydraulic lime, from the lias near Metz, slaked by sprinkling, 1 part; picked sand, from the Vosges sandstone, 1 part; trass, from Andernacht on the Rhine, 1 part; cement from Ropp (Haute Saone), 1/4 part.

Six men are employed in putting in the cement;--two at the windlass for letting down the ladle, two for working the rods attached to the piston, and two on the working platform. The rods referred to have been found such an inconvenience, that lately a rope on another windlass has been used, and an appliance arranged for dropping the piston by moving the rope.

Fig. 157.]

When a sufficient time has elapsed for the cement to harden, the water within the tubbing, now effectually separated from the feeders, is drawn out by a bucket worked by the crab engine,--an operation which occupies from one to three weeks, according to circumstances. When concluded, the joint between the moss box and the rock bed can be examined. In some cases this joint is considered sufficient; but it is generally thought desirable to form a base to the tubbing by building a few feet of brickwork in cement on a ring or crib of wood, as in Fig. 157. Another wooden crib is then placed on the top of this brickwork, and above this, two cast-iron segmental wedging cribs with a broad bed also wedged perfectly tight. On the base so prepared, four or more rings of tubbing in segments are fixed, the top ring coming close against the bottom of the moss box. This being done the work is completed, and the sinking of the shaft is continued in the ordinary way.

The application of the boring trepan is not to be recommended in the sinking of the dry part of the shaft. The use of the tool would cause the sinking to extend over a longer period, since the breaking of the rock passed through into such minute particles would lead to loss of time.

DRU'S SYSTEM.

Sectional Elevation showing Surface Arrangement.

Fig. 158.]

The system applied by Dru is worthy of attention, not so much on account of the novelty of the invention, or of any new principle involved in it, as on account of the contrivances it contains for the application of the tool, "_à chute libre_," or the free-falling tool, to Artesian wells of large diameters. It has been already explained that under Kind's arrangements the trepan was thrown out of gear by the reaction of the water which was allowed to find its way into the column of the excavation; but that it is not always possible to command the supply of the quantity necessary for that purpose; and even when possible, the clutch Kind adopted was so shaped as to be subject to much and rapid wear. Dru, with a view to obviate both these inconveniences, made his first trepan similar to that shown in Fig. 101, in which it will be seen that the tool was gradually raised until it came in contact with the fixed part of the upper machinery, when it was thrown out of gear. The bearings of the clutch were parallel to the horizontal line, and were found in practice to be more evenly worn, so that this instrument could be worked sometimes from eight days to fourteen days without intermission; whereas, on Kind's system, the trepan was frequently withdrawn after two days' or three days' service.

We take the following complete account of the system from a paper read by M. Dru at the Conservatoire des Arts et Métiers, Paris, 6th June, 1867.

It will be seen from Figs. 158, 159, that the boring rod A is suspended from the outer end of the working beam B, which is made of timber hooped with iron, working upon a middle bearing, and is connected at the inner end to the vertical steam cylinder C, of 10 inches diameter and 39 inches stroke. The stroke of the boring rod is reduced to 22 inches, by the inner end of the beam being made longer than the outer end, serving as a partial counterbalance for the weight of the boring rod. The steam cylinder is shown enlarged in Fig. 160, and is single-acting, being used only to lift the boring rod at each stroke, and the rod is lowered again by releasing the steam from the top side of the piston; the stroke is limited by timber stops both below and above the end of the working beam B.

The boring tool is the part of most importance in the apparatus, and the one that has involved most difficulty in maturing its construction. The points to be aimed at in this are,--simplicity of construction and repairs; the greatest force of blow possible for each unit of striking surface; and freedom from liability to get turned aside and choked.

Fig. 159.]

Fig. 160.]

Figs. 161, 162.]

The tool used in small borings is a single chisel, as shown in Figs. 161, 162; but for the large borings it is found best to divide the tool-face into separate chisels, each of convenient size and weight for forging. All the chisels, however, are kept in a straight line, whereby the extent of striking surface is reduced; and the tool is rendered less liable to be turned aside by meeting a hard portion of flint on a single point of the striking edge, which would diminish the effect of the blow.

Figs. 163-169.]

The tool is shown in Figs. 163 to 169, and is composed of a wrought-iron body D, connected by a screwed end E to the boring rod, and carrying the chisels F F, fixed in separate sockets and secured by nuts above; two or four chisels are used, or sometimes even a greater number, according to the size of the hole to be bored. This construction allows of any broken chisel being easily replaced; and also, by changing the breadth of the two outer chisels, the diameter of the hole bored can be regulated exactly as may be desired. When four chisels are used, the two centre ones are made a little longer than the others, as shown in Fig. 167, to form a leading hole as a guide to the boring rod. A cross-bar G, of the same width as the tool, guides it in the hole in the direction at right-angles to the tool; and in the case of the larger and longer tools a second cross-bar higher up, at right-angles to the first and parallel to the striking edge of the tool, is also added.

Figs. 170-173.]

If the whole length of the boring rod were allowed to fall suddenly to the bottom of a large bore-hole at each stroke, frequent breakages would occur; it is therefore found requisite to arrange for the tool to be detached from the boring rod at a fixed point in each stroke, and this has led to the general adoption of _free-falling tools_. M. Dru's plan of self-acting free-falling tool, liberated by reaction, is shown in side and front view in Figs. 170 to 173. The hook H, attached to the head of the boring tool D, slides vertically in the box K, which is screwed to the lower extremity of the boring rod; and the hook engages with the catch J, centred in the sides of the box K, whereby the tool is lifted as the boring rod rises. The tail of the catch J bears against an inclined plane L, at the top of the box K; and the two holes carrying the centre-pin I of the catch, are made oval in the vertical direction, so as to allow a slight vertical movement of the catch. When the boring rod reaches the top of the stroke, it is stopped suddenly by the tail end of the beam B, Fig. 159, striking upon the wood buffer-block E; and the shock thus occasioned causes a slight jump of the catch J in the box K; the tail of the catch is thereby thrown outwards by the incline L, as shown in Fig. 172, liberating the hook H, and the tool then falls freely to the bottom of the bore-hole, as shown in Fig. 173. When the boring rod descends again after the tool, the catch J again engages with the hook H, enabling the tool to be raised for the next blow, as in Fig. 171.

Figs. 174-178.]

Another construction of self-acting free-falling tool, liberated by a separate disengaging rod, is shown in side and front view in Figs. 174 to 178. This tool consists of four principal pieces, the hook H, the catch J, the pawl I, and the disengaging rod M. The hook H, carrying the boring tool D, slides between the two vertical sides of the box K, which is screwed to the bottom of the boring rod; and the catch J works in the same space upon a centre-pin fixed in the box, so that the tool is carried by the rod, when hooked on the catch, as shown in Fig. 175. At the same time the pawl I, at the back of the catch J, secures it from getting unhooked from the tool; but this pawl is centred in a separate sliding hoop N, forming the top of the disengaging rod M, which slides freely up and down within a fixed distance upon the box K; and in its lowest position the hoop N rests upon the upper of the two guides P P, Fig. 174, through which the disengaging rod M slides outside the box K. In lowering the boring rod, the disengaging rod M reaches the bottom of the bore-hole first, as shown in Figs. 174, 175, and being then stopped it prevents the pawl I from descending any lower; and the inclined back of the catch J sliding down past the pawl, the latter forces the catch out of the hook H, as shown in Fig. 176, thus allowing the tool D to fall freely and strike its blow. The height of fall of the tool is always the same, being determined only by the length of the disengaging rod M.

The blow having been struck, and the boring rod continuing to be lowered to the bottom of the hole, the catch J falls back into its original position, and engages again with the hook H, as shown in Fig. 177, ready for lifting the tool in the next stroke. As the boring rod rises, the tail of the catch J trips up the pawl I in passing, as shown in Fig. 176, allowing the catch to pass freely; and the pawl before it begins to be lifted returns to the original position, shown in Fig. 177, where it locks the catch J, and prevents any risk of its becoming unhooked either in raising or lowering the tool in the well.