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 The chisel is withdrawn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either for hemp-rope or wire-rope, and which was originally made for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.
[Illustration: Chinese System.
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, 2-1/2 inches extreme breadth, and weigh some
4-1/2 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.
[Illustration: Well-boring Tools.
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 3-1/2 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.
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.
[Illustration: Withdrawing Tools.
Figs. 57-59.]
[Illustration: Bell-box.
Fig. 60.]
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.
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.
[Illustration: Boring Rods.
Fig. 61, 62.]
[Illustration: Hand-dog.
Fig. 63.]
[Illustration: Lifting Dog.
Fig. 64, 65.]
[Illustration: Tillers.
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.
[Illustration: Spring-hook.
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.
[Illustration: Tubes with Screwed Joints.
Fig. 68.]
[Illustration: Tubes with Brazed or Riveted Joints.
Figs. 69, 70.]
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.
[Illustration: Stud Block.
Fig. 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.
[Illustration: Spring-dart.
Fig. 72.]
[Illustration: Spring-Dart.
Fig. 73.]
[Illustration: Spring-dart.
Fig. 74.]
[Illustration: Pipe-dog.
Fig. 75.]
[Illustration: Tube Clamp.
Fig. 76.]
[Illustration: Tube Clamp.
Fig. 77.]
[Illustration: Tongs.
Fig. 78.]
[Illustration: Sinker's Bucket.
Fig. 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.
[Illustration: Pipe-dolly.
Fig. 80.]
[Illustration: Rimer.
Fig. 81.]
[Illustration: Riming Spring.
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.
[Illustration: Boring Apparatus.
English, for Small Works.
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.
[Illustration: Boring Platform.
For Deep or Difficult Wells.
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 1-1/2 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.
[Illustration: Diminishing Tube Diameter Arrangement.
Fig. 85.]
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.
[Illustration: Driving Ring for wrought-iron Tubes.
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 1-1/2 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.
[Illustration: Fig. 87.]
[Illustration: Fig. 88.]
[Illustration: Fig. 89.]
[Illustration: Fig. 90.]
[Illustration: Fig. 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 582-1/2 feet, but which, owing to circumstances which were
difficult to determine, had become very expensive, and made slow
progress.
The 582-1/2 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 3-7/8 inches external and 3-1/2 inches internal;
the second tube was 3-1/4 inches external, and 3 inches internal
diameter; and the third tube was 2-3/4 inches external and 2-1/2 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.
[Illustration: The Action of the Knife or Spring-cutter.
Prepared for Cutting.
Fig. 92.]
[Illustration: The Action of the Knife or Cutter.
Ready for Removal after Cutting.
Fig. 93.]
[Illustration: Back View of Knife or Cutter.
Fig. 94.]
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 1_s._ 3_d._ a foot for the first 30 feet; 2_s._
6_d._ a foot for the second 30 feet; and continue in arithmetical
progression, advancing 1_s._ 3_d._ 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.