Charles George Warnford Lock.

Economic mining: a practical handbook for the miner, the metallurgist and ... online

. (page 7 of 76)
Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 7 of 76)
Font size
QR-code for this ebook


narrow strip of thin gutta-percha sheet, which is
pressed by means of the moistened fingers around the
twisted wires until they are quite insulated. As re-
gards rubber wires, the insulating material should be
removed for about 1 in. from the end, and a short piece
of rubber tube slipped over one of the cores ; the con-
ducting wires are then cleaned and twisted together,
and the rubber tube is slipped over them and tied at
eadi end tightly over the insulation of each core. In
ntuations where it might be troublesome to cover the
temporary joints in gutta-percha wires in the way de-
Bcrihed above, the method with rubber tube can be
employed.

WaXer Cartridges, — Experiments have demonstrated
that the risks of blasting in coal mines can be greatly
reduced by enclosing the explosive in a waterproof
euTclope, which renders impossible the escape of name
or sparks. Such implements have come to be known
M " water-oartridges," but a more accurate term would
1« ** water-jacketed cartridges.*'

The form, introduced by Miles Settle, of the Madely
Coal and Iron Ck>mpany, consists of a simple arrange-
ment of discs or supports, whereby a most essential
advantage is obtained, namely, the fixing of the ex-
plonve charge in such a manner that it retains a
central position, and is therefore entirely and equally .
^rrounded by water, whatever the angle of the bore- jacketed
hole. Without this precaution security from escape of CARTBrooi.
flame cannot be assured.

The water-cartridge bag is usually made 18 in. long and 2 in.
diam., and of specially prepared waterproof material. Gelatine
dynamite or gelignite are the explosives used in it. When it is
necessary to use more than one cartridge they should be joined by
wooden skewers and pressed closely together, to prevent water getting
l«tween and causing a missfire. A complete doubly-charged cart-



Digitized by



Google



so



ECONOMIC MINING,



ridge is shown in Fig. 9 : a, watertight envelope ; 6, fuse ; c, wire leading
to battery or exploder ; d, tin discs for keeping cartridges central ;
c, cartridges ; /, wooden skewer joining cartridges.

Wedges. — Fig. 10 illustrates a mnltiple wedge, for bringing down
rock and coal without the use of explosives. The cost is, No. 1, 1 j in.
diam., 2 ft. 6 in. long, 2L 10«. ; No. 2, 2 in. diam., 3 ft. long, 31. lOt.
But there is scarcely any wedge able to hold its own as a means of
breaking down coal. The cause is much the same as that which has
been the means of limiting the use of the lime-cartridge. The want
of success is due almost entirely to the fact that it is difficult to get
combined, a face of coal which will break down easily, a roof which



Wedi«



tMtion «r Wadgt




CxpAoded.



with third W«df«



Fig. 10. — Multiple Wkdge.



will separate freely, and a coal which will break off well, conditions
which are generally required, whether the wedge or the lime-cartridge
is used, both being slow means of applying force to break dowD
coal. A wedge usS with great success in Belgium and the North of
France consists of two long steel wedge-pieces, which are placed in
the shot-hole, the thick end inwards, and a third long wedge is
driven between the two. The objection to it is that, with the lime-
cartridge or any other means of breaking down coal, simple ordinary
explosive/orce is applied ; with the wedse, a considerable quantity of
** elbow-grease " is required, and a man has to take 5-10 minutes in
striking the centre wedge in order to get the coal broken down.



Digitized by



Google







SHAFT AND WELL SINKING.

Thi dimensions and arrangements of shafts must always depend
upon the circnmstances enoountered, provision having to be made for
the miners to enter and leave, for raising the ore, for pumping ont
the water, and for ventilation.

In ordinarily dry gronnd no particular difficulty presents itself,
bfit where wet ground has to be sunk through, various problems arise,
uid some useful hints may be gathered from the following examples
of shaft-sinking operations carried out under adverse conditions.

(1) In 1881, Fo»ter Brown pointed out the great difficulty and
expense attending the sinking of shafts through water-bearing strata,
and suggested that a boring might be put down in advance of the
siDking, into which a pump might be placed to facilitate the opera-
tion of sinking. The water being pumped down in the borinj? below
the bottom of the shaft, the sinking would be done in dry ground,
and would go on without intermisMion. The suggestion appeared to
be very -valuable. In sinking shafts and wells through water-bearing
strata on time-honoured methods there is not only the great cost, but,
what is often more serious, the great length of time taken in doing
the work. A single well for town water supply often takes 2 or 3
years or more to execute.

The problem is simply that of keeping down the water in water-
bearing strata in advance of the sinking operations, so that the exca-
vation of the shaft or well shall be done in dry ground.

The ordinary method of shaft or well sinking is to sling a pump
or pumps in the shaft, and to lower the pumps from time to time, as
the sinking continues. Obviously the excavation has to be performed
in water ; and if the quantity of water to be dealt with is very great,
a large portion of the work has to be done by the men working in a
depth of 2-3 ft. of water. To facilitate the work, and to reduce
the water in which the men have to work, a sump is made under
the suction pipe of the pump, shown in Fig. 11, and it is the
keeping this sump excavated in advance of the other work which is
most difficult and tedious. Then there is the delay occasioned by the
lowering of the pumps and providing the appliances necessary to the
operation.

In the plan proposed by Henry Davey, the pump illustrated in
Fig. 12 would be placed in a borehole made before the commencement
of the idnking of the shaft. The only novelty in the pump is that of
adapting it to the purpose. It is necessary that d&m» shall not go
down the borehole in quantity sufficient to choke it up. That is pro-
vided against by means of a heavy taper shield of cast steel surround-
ing the pump, and resting on the edge of the borehole. This shield

E 2

Digitized by VjOOQIC



52 ECONOMIC MINING.

is perforated with holes inclined upwards towards the pump, to allow
water to get into the borehole, but to exclude debris. The shield is
made very heavy, and by its own weight follows the excavation
around the pump, and also protects it from injury through the blast-



FiGs. 11, 12, 18.— Sinking Shafts in Wet Ground.

ing of the rock. The pump is made without a foot-valve, the rod oi
the bucket working through the seating of a valve which rests on the
top of the working barrel. By this arrangement, the drawing of the
bucket also draws the valve ; and should the bottom of the borehole

Digitized by VjOOQIC



SHAFT AND WELL SINKING. 53

be filled up with sand, it can be removed by lowering a scoop 8uob as
is nsed in making boreholes. The borehole should be made to a
greater depth than that required for the pump, to provide a space for
sand and a^nri$.

The application of this pump to the sinking of shafts can be
varied to suit the local circumstances and the geological formation of
the strata to be passed through.

It is quite evident that in some situations the shaft might be
drained by means of boreholes outside.

It is the usual and necessary practice to provide duplicate pump-
ing engines; and where two engines are made to pump from the
same well, the well must be very htrge that it may accommodate two
sets of pumps, as in Fig. 13. Such wells are usually 12-14 ft. diam.
To sink such a well in an ordinary way is a very long and costly
undertaking, especially if quicksand is met with. On the completion
of the well it may be necessary to drive adits to increase the water
supply. A simple borehole is made very cheaply and very ezpe-
didoosly — ^four 30-in. boreholes can be put down in a very small
fraction of the time required to sink a 12-ft. well in the ordinary
way.

Instead of making a large well, Davey would put down 4 bore-
holee, as in Fig. 13, to accommodate the pumps to each engine. The
boreholes being completed, the pumps are lowered into them, and
coupled up to the permanent engines. Immediately that is done,
the water found in the boreholes can be pxunped and supplied for use.
Should it be insufficient then, a small well would be sunk in the dry
to the bottom of the borehole pumps. The boreholes at the level of
the pumps would be connectea to the centre well, and adits driven to
collect more water. Should the boreholes yield sufficient water then
there would be no necessity to sink the well.

Fig. 11 is the section of a completed well from which adits have
been driven to collect additional water to that yielded by the bore-
holes. When such a well is made, the changing of the working -parts
of the pumps may be done underground, thus obviating the necessity
of drawing the pump rods from the top.

This system of making wells and shafts certainly promises ad-
vantages under ordinary conditions, but the advisability of its
adoption in anv particular case must be a matter of judgment with
the engineer planning the work.

^2) A diamond dnil bore was put down 760 ft. from the bottom
of toe North Magdala Company's shaft, Victoria, which was 920 ft.
deep, making the total depth from surface 1680 ft. The drill was
fixed on the snrface, and placed over the shaft and in such a position
that the bore went down in the north-west comer.

A hole 4 in. diam. was first bored by hand to a depth of 10 in. in
the bottom of the shaft, and plumb beneath where the 3-in. tubes
were intended to come down. The tubes extended to the surface, and
were lowered into this hole to within 1 in. of the bottom. Oakum
was not procurable locally, so a substitute of chopped hemp and coal
tiT was used. This was caulked into the space between the 3-iD.
tubes and the 4-inch hole until it was well filled ; a piece of 1-in.



Digitized by



Google



54 ECONOMIC MINING,

tarred hemp rope was then wound round the tube on top of the hole,
80 as to make the rope stand up above the hole about 1 in. Over the
rope a washer 6 in. diam., of ^in. rubber, was placed, and over this
washer was also plaoed an iron washer 6 in. diam. and f in. thick
(both of these being placed on the tubes before thej were lowered). A
pair of clamps were then bolted on the tubes, pressing down on the
iron washer. The tubes were lowered to rest their whole weight of
5 tons on the iron washer, which pressed on the rubber washer and
hemp rope, forcing it down the space between the 3-in. tubes and
4-in. hola The tubes were then secured to the wood framing of the
shaft with stays and clamps every 12 ft. These stays were necessary
to prevent vibration, and keep the tubes perfectly rigid. When the
tubes were full of water, the pressure at the joint was 407 - 56 lb. per
sq. in., pressing against the rubber and iron washers ; but the tuoes
being 5 tons in weight, it was considered there was sufficient margin
over the power of the water in the column of tubes to keep the joint
perfectly tight It was found, however, upon trial, that the pressure,
though not sufficient to lift the tubes, buckled them to such an extent
as allowed the water to force out the hemp packing at the joint.

The following method was then adopted with complete success : —
Over the bottom 3-in. tube a 4-iii. covering tube, 7 ft. 5J in. long,
was placed, the top end of which pressed against an iron washer fixed
under a wooden frame in the shan; the bottom end rested on an iron
flange, which had 4 bolts screwed into it ; these screws pressed down
on another iron washer, which likewise pressed on a rubber washer
covering the hole. By this plan, the tubes rested on the rock at the
bottom of the hole, and, as the tightening of the joint threw the strain
only on the covering tube, the 3-in. tubes had no tendency to buckle.
The caulking was the same as in the first method tried.

There were many advantages obtained by the plan adopted over
that of putting a drill down at the bottom of the shaft It was more
expeditious and economical, as when the joint was made tight the
water oould be allowed to rise, which saved the expense of keeping
the water out. A larger drill was also used than would be possible
down a shaft, and consequently a deeper bore could be sunk. No air-
compressing plant was required, and in this alone a ^reat saving was
effected. The diamond drill used in connection with this bore is
known as the " Victorian Giant Drill." Among other improvements
in the construction of this drill were larger hydraulic cylinders and
the substitution of friction rollers in place of friction rings, which
had hitherto been used on all drills. The rollers,' about 20 in number,
are of hardened steel, of a shape known as truncated cones, and work
between two troughs whose internal faces are made to suit the oonee
or rollers. The difficulty with the rings was that in work it was im-
possible to keep them efficiently lubricated ; conbequently they were
continually heating, and had to be relieved of a part of the weight
by a oounterpoise when the bore had attained a depth of 600 ft. But
with the cone friction gear the lubrication is complete ; the troughs
being filled with oil, the roller was thoroughly oiled as it revolved io
the trough. The beneficial effect of the substitution of roller f rictioD
gear in place of rings was demonstrated at the North Magdala to be



Digitized by



Google



SHAFT AND WELL SINKING. 55

Buinifold. Not only did they lessen the friction of working, but
enabled the drill to bore to a depth of 1700 ft. without the aid of a
connterpoiae or back balance. This is by far the greatest depth
attained without the aid of a counterpoise, and is solely due to the
adoption of friction rollers in place of friction rings. With such ease
and freedom from heating did the rollers do their work at 1700 ft.
that it is believed that a depth of 2700 ft. could be bored without any
aid from a counterpoise being necessary ; and those who have been
compelled to use a counterpoise will readily appreciate the economy
and saving of time thereby effected. Another improvement intro-
duced is the friction break on the drum. This allows the drum to be
thrown out of gear when lowering rods, as this can be done by the
break, thus saving time and the great wear and tear of the machinery
that is caused by lowering rods with the engines.

(3) An extensive swamp covers a large part of the town site of
Norwav, Michigan, and adjacent land. Through this swamp run two
panllel oil formations. On the edge of the swamp, about 1000 ft.
from the Aragon mine, a diamond drill, in the fall of 1889, located
an or^bearing formation, to explore which, the Penn Iron Mining
Company proposed, in the spring of 1890, to sink a shaft.

The depth of the eladal drift being more than 60 ft., and a large
flow of water having been struck at a depth of 20 ft. by a test pit, it
WHS decided to sink a caisson or dropnahaft. Two 40 h.p. boilers, a
Lidgerwood engine, with 4-ft. drum and a good derrick, were set up,
and two No. 10 Knowles pumps, rated at 400 gal. a minute, were
brought on the ground.

llie dimensions adopted for the top of the shaft were 6 ft. by
13 ft. inside. To give sufficient space for pumps and working, and to
aid the shaft to settle, it was made 4 ft. larger each way at the bottom,
llie shaft was divided, to within 12 ft of iJie bottom, into three com-
partments, the middle one uniformly 4 ft. wide. This compartment
was used for hoisting, a ladder-way and pipes. The pumps were
placed one in each end compartment. Above the pumps the end
compartments were planked up to be filled with sand to increase the
weight. A ventilation-box was put in one comer. The bottom of
the shaft was left unobstructed for working purposes, and sufficiently
hi^ to allow two additional pumps to be put in under the first.

The bottom-pieces, made of oak and constituting what is called
the shoe a. Fig. 14, were 15 in. square, but the bottom inside was
bevelled off to 6 in. Above the shoe, white pine timbers 6, 12 in.
spiare, framed in set^ were laid close and bolted together and to the
shoe with eight 5 ft. bolts. The successive sets were reduced 1 in. in
length and width, until at 48 ft. above the bottom their dimensions
corresponded with the top. Comer-posts 12 in. square, of unequal
lengths so as to break joints, were bolted to every other side-piece
and end-piece. The bolts, being put in from the inside and having
the nuts countersunk, were easily unscrewed and recovered when the
comer posts were removed. Like the comer posts, side posts were
put in, one at each comer of the middle compartment ; 12-in. dividers
were used every 5 ft.

After the levelling of the ground the timbers were built up and



Digitized by



Google



S6



ECONOMIC MINING.



bolted as far as the derrick and backet would permit, nearly 30 ft
The seams were then carefully caulked outside, and 3-in. planks in
unequal lengths were spiked on, to protect the caulking and timbers
and to strengthen the shaft.

Ground inside the shaft was broken in the morning, and by next
morning the shaft had gone down 6 ft. On the fifth day, at 15 ft,
the pumps had to be started. The first week's work resulted in 18 ft
sunk. During the first three days of the second week 9 ft. more were




Fio. 14. — Sinking Shaft thbough Glacial Dbht.

sunk. At this time it was evident that both pumps had to run fast
to keep the water out, and if one should break down or the water
should increase, the men would be drowned out. Therefore, before
sinking the pumps below the water-level, it was necessary to get
more power.

Two portable boilers, of 35 h.p. and 100 h.p. respectively, were
connected, and two No. 10 Cameron pumps were placed, without air-



Digitized by



Google



SHAFT AND WELL SINKING. 57

chambers, 4 ft. under the Knowles pumps. Darmg the stop the shaft
was bnilt up again as high as possible.

Everything went well. The pumps were kept busy; three
nmning constantly, and the Knowles pumps often making 160
strokes a minute. The quantity of water was estimated at 1500 gal.
a minute. The sand-boxes were now filled to keep the shaft down to
the bottom of the excavation. The sand and gravel would come in
under the shoe, and the surface about the shaft settled into a large
pit which continually grew larger.

At this time the shaft was down 50 ft., and it became necessary
to again build it higher. This took three days. A drill in the
bottom gave some encouragement, as at 10 ft. it struck something
hard. During the next three days hard pan was found in a comer
of the shaft At this point the shaft did not settle well, even when
the ground was out 1 ft. or more from under the shoe. To increase
still further the weight of the shaft, 30 tons of rails were laid loosely
OQ the top. While going through the hard pan, the settling of the
shaft was irregular, accompanied by inrushes of sand and water which
kept the pumps busy. Props hcid to be placed against the shaft at
diferent times to keep it straight. It took 18 days to go through the
14 ft of hard pan ; but parts of two days were spent in weighting
the shaft and one day with an accident which bade fair to stop pro-
oeedingB summarily.

The time spent in sinking may be summarised as follows : — 4 days
sinking 15 ft above water-level ; 17 days sinking 42 ft through wet
gravel and quicksand; 16 days sinking 14 ft through hard pan;
4 days sinking 2 ft. in slates ; making a total of 41 days sinking
73 feet To this must be added 6 days required to build up the shaft
and 2 days weighting shaft with rails, or a total of 49 days, or one
day over 8 weeks actual working time.

The shaft was now down firmly in the ledge; but the most
delicate part of the operation was still to come, namely, stopping the
flow of water. Before that could be done, however, many things were
necessary.

The rails had to be removed from the top and the sand from the
boxes, the pipes changed, and the shaft built up to the surface.
There was now a sink- hole about the shaft 75 ft. diam. and 20 ft
deep, and the top of the shaft was about 6 ft below the original surface
leveL The shaft was but little out of plumb, the top set having to
be raised 2 in. at one end to level it. The comer posts were taken
out, the bolt-holes were plugged, and the shaft was caulked on the
inside. This work took 8 days. The next 14 days were spent in
sinking 11 ft farther into the ledges, which work proceeded slowly.

The work of sealing up the bottom of the drop-shaft was now
nndertaken. A set, 6 ft by 13 ft inside, of 12 in. square timber,
was carefully placed in line with the top set of the shaft, about 6J^ ft
below the shoe. This was thoroughly blocked against the rock all
around with wedges. Six sets c of the same size were placed on top
of the first and each bolted to the next Behind the sets as they were
built up was put a thin layer of clay over the wedges and then con-
crete of equal parts of sand and cement The midSe of the top set d



Digitized by



Google



58 ECONOMIC MINING.

was about opposite the bottom of the shoe. Through this set twentj
2-iii. holes had been bored. Behind the holes a layer 4 in. deep of
gravel and broken stone was laid, leaving a free passage for the water.
Upon this perforated set were put three other sets t of inoreasing
inside dimensions, so that the top set was against and bolted to the
drop-shaft. The space behind these sets was filled with concrete as
before. This timbering and cementing in such a flood of water was
a tedious process, and took 18 days. The holes were plugged with
some difficulty, but this finally accomplished, the water at once fell
to about 200 gaL a minute. After the pumps and side-posts had been
removed, and the interior had been thoroughly caulked, the water
was deoiNdased to about 90 gal. After the shan had been sunk farther,
and bearers put in, a small station was cut at one end and the water
was gathered to a No. 8 Cameron pump. Below this the shaft was
sunk with a No. 4 Cameron, which now works about 1^ hour a day.

The time taken for sealing up the bottom may be summaribed as
follows : — 8 days to alter sha^ after it rested ; 14 days to sink 11 ft.
in slates ; 18 dfays to timber and cement ; 16 days to remove pumps,
caulk and arrange shaft for regular sinking, giving a total of
56 days.

References : — a, oak bottom-pieces ; 5, white pine sets ; e, series of
6 sets bolted together; (2, top set opposite bottom of shoe; e, seriee
of 3 sets of increasing inside dimensions ; /, hard pan ; ^, sand and
gravel ; &, slate ; t, ooncrete ; i, broken stone ; {» day ; m, wedges.



Digitized by



Google



59



VENTILATION.

Natural yentilation is obtained by a onrrent of air passing through
the workings, indnoed by the difference in level between the two
opeoings of liie mine at the snr&oe. In summer the current is
ordinarily from the higher towards the lower, while the reverse
direction prevails in winter. The greater the difference in tempera-
tore between the exterior and interior, the greater draft tilie current
will have.

Local conditions vdll often determine the direction of this current
without reference to the aforesaid principle which primarily controls
this question. Likewise the draft increases with an increase in the
diiorenoe of elevation between the two openings of the mine. Where
there is naturally a strong current, no difficulty is experienced in
Tentilating the portions or block of ground within the circuit of the
cmrent. The air can be directed by means of properly disposed
do(»8 into any desired portion of the workings within the limits
above specified. It may be also carried into the face of drifts
beyond this circuit by wooden boxes or other means subdividing the
coirent.

ScMuetimes, to increase the draft, a fire is made near the mouth of
the upcast shaft, or a suction £&h is used for the same purpose. The
•action &n of tiie Idaho mine is 12 ft diam. with 4-ft. face ; 8 h.p. is
recjoired for its operation. But in many mines there are certain
pomts situated vnthout this course of the current, to which, from
Uck of strength, it cannot be carried in sufficient quantities to renew
the air fouled by gases generated by blasting quickly enough to enable
the uuinterrupted prot»ecution of work. In such cases recourse must
be had to some system of artificial ventilation. Where pneumatic



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 7 of 76)