MACHINING THE EARTH
THE ALBANIAN people have a story that the Creator recently visited
the earth and was astonished to find how it had changed. “Why, this
is not the earth I created,” He said. “Everything has changed. My
forests are cut down; My rivers have been diverted from their courses;
My hills have been blasted away, and My mountains have been robbed of
their minerals. The whole face of the earth has been altered.” But in
the course of His roamings, the Creator suddenly came upon the land
of Albania. “Ah!” He exclaimed in delight. “Here is a bit of earth
untouched by man. It is still just as I made it.”
Man’s ambition to make over the face of the earth to his own liking
dates far back of the present age of machinery. However, the work of
the ancient engineer was accomplished only at the expense of decades
and generations of hard manual labor. To-day, with powerful and
gigantic machinery to do our bidding, we do not hesitate to change the
course of rivers, to level off the hills, to carve highways through the
mountains and pierce them with tunnels, to bore into their depths for
treasure and drive deep holes into the bowels of the earth in quest of
liquid fuel. We are able to machine the earth in much the same way as
a piece of metal is machined in the machine shop. In fact, the drill,
the circular saw, the slotter, and even the milling machine have their
counterpart in the excavating machinery of to-day. Of course we cannot
expect to find the counterpart of such machines as the lathe, boring
mill, and planer, in which the work revolves against the tool, because
this planet of ours is rather too big a piece of stock to be placed
between lathe centers or to be bolted to a planer bed.
MECHANICAL MONSTERS
The twentieth century finds this planet again stocked with monsters
larger and more powerful than the gigantic saurians that dominated
the earth in the Jurassic and Cretaceous epochs, but our mighty
fire-breathing, steel-sinewed beasts are humbly subservient to the will
of man.
The spectacle of a large steam shovel at work makes one feel at once
very small and very big. Before the work of this monster the human
shoveler shrinks to the proportions of a mere insect. Seven to eight
cubic yards shoveled into a cart is considered a fair day’s work for a
laborer, but a big steam shovel can easily gobble up as much material
in two bites. However, when we contemplate that this mammoth machine is
a human creation and an absolute slave to human command, we are rather
inclined to be puffed up with the greatness of man.
Steam shovels are ideal machines for excavating railroad cuts and were
primarily developed for just such work. The general operation of the
machine is very similar to that of hand shoveling. The shovel proper
consists of a big scoop or dipper and a dipper handle which correspond
respectively to the blade and handle of a hand shovel. Like the
shovel, the dipper is supported at two points. The dipper is suspended
by a chain from the end of a boom while the handle of the dipper is
also supported in the boom. By loosening the hoisting chain the dipper
is lowered to the ground, and by moving the handle forward the toothed
cutting edge is made to bite into the ground or sand bank. The hoisting
chain then hauls up the dipper, making it scoop out the bank, after
which it is swung to one side over a car on an adjoining track. The
rear of the bucket is fitted with a door which is opened by a spring
latch and the contents are emptied out. Some of the largest steam
shovels for ordinary grading have dippers with a capacity of 5 cubic
yards. They are not confined to railroad grading, but are applicable to
any excavation where a firm footing is provided for the heavy machine.
They are even used for excavating the cellars of large city buildings.
The machine must be supported on road wheels or on skids. When used
for excavating sewer trenches, it is sometimes mounted on a platform
spanning the trench. However, the steam shovel is rather limited in
its reach. The largest ordinary steam shovels have a clear lift of but
sixteen feet and can make a cut only sixty feet wide at the top.
For more extensive excavating as well as for digging ditches and
trenches the drag-line excavator has recently come in to use. In these
machines a scraper takes the place of the dipper. This is suspended
from the end of a long crane and it is dragged along the ground by a
cable, scooping up a load of earth. In some cases the scoop or scraper
is merely attached to a cable leading from the hoisting engine to
an anchorage and back to the engine. To adapt excavating machines
for service in soft ground they are mounted on broad wheels or on
track-laying tractor surfaces. One peculiar form of walking traction
used by a drag-line excavator was described in Chapter XIII.
DITCHING AND TRENCHING MACHINES
For digging narrow ditches and trenches, particularly for sewers, water
mains, gas-pipe lines, etc., a number of very interesting machines
have been invented which are of two general types, the endless chain
and the wheel excavators. The first type consists of a traction engine
with a ladder at the rear that drops down into the trench. About this
ladder runs an endless chain which carries a series of scoops or
buckets. These are dragged up against the breast of the work and carry
the excavated earth to the top of the ladder where it is dumped upon a
transverse belt conveyor and carried to one side of the trench. With
the larger sizes of chain excavators, trenches may be dug to a depth
of twenty feet and the width of the trench may be from two to six feet
wide.
The wheel type of trenching machine is similar in principle to the
chain excavator. Instead of the chain of buckets, it has a wheel fitted
with buckets. In one prominent type the wheel has no hub or spokes, but
consists of a rim that is supported on and is turned by four friction
rollers mounted in a rigid frame. This frame is mounted on a boom which
can be raised or lowered as desired. Such machines can commonly dig to
a depth of a dozen feet or so.
A ditch differs from a trench in the fact that its side walls are
sloping instead of vertical. A trench is usually a temporary excavation
for the laying of pipes or conduits while the ditch is left open and
serves for irrigation or drainage. There are chain ditching machines
in which the chain of buckets runs laterally across the course of the
ditch, dipping into the earth to form a V-shaped channel. In connection
with the draining of the Everglades of Florida, a peculiar wheel type
of ditcher was built. The wheel is of gigantic proportions, consisting
of a series of radiating shovels or scoops shaped to conform to the
outline of the ditch. As the wheel revolves it scoops up the mud which
slides down toward the hub of the wheel and is carried to one side by a
traveling conveyor.
FLOATING EXCAVATORS
The main difficulty in drainage work is to provide a good footing for
the machine which must necessarily be very heavy. Broad caterpillar
tread surfaces are about the only means of locomotion. In very soft
swampy regions dredges have to be used. Dredges are merely floating
excavators. In them the problem of support and locomotion disappear and
there are no limitations of size and weight to be considered. Floating
excavators are therefore much more powerful than excavators that run
on land. The ordinary dipper dredge is merely a floating steam shovel
with a much longer dipper handle and much larger dipper. When work on
the slides of the Panama Canal had proceeded far enough to admit of
using dredges in place of steam shovels material progress was made. Two
enormous dipper dredges were built, each provided with a dipper that
had a capacity of fifteen cubic yards or about twenty tons at a single
lift. The dipper was big enough to hold thirty men. The dipper handle
was seventy-two feet long and it could reach down to a depth of fifty
feet. A smaller dipper of ten cubic yards capacity was also provided.
The power of these huge dredges was illustrated when one of them, while
using its ten-yard bucket, picked up an enormous bowlder weighing forty
tons. It was much bigger than the dipper that had raised it and it was
far too big to be placed on the mud scow that was receiving the spoil
brought up by the dredge. Had it been rolled off on the scow it would
have crashed right through the bottom of the boat and so the big rock
had to be drilled and broken up on the dipper before it could be dumped
into the scow.
For work on a soft bottom, grab buckets are used in place of dippers.
These may be made of two scoops as in the clam-shell bucket or of
four leaves as in the orange-peel bucket. No rigid handle is provided
for these scoops. They are spread open as they are lowered into the
water and on hauling in the hoisting cable, the scoops or leaves come
together biting into the bottom and lifting up a load of mud. Grab
buckets are largely used for picking up coal, ore, gravel, etc.
The equivalent of the chain trench-digging machine is found in the
ladder dredge. A ladder is hung over the stern of the dredge and
carries a chain of buckets which dig into the bottom and bring up the
mud or sand.
GOLD MINING WITH A DREDGE
It is a dredge of this type that is put to the peculiar task of gold
mining. The dredge eats its way into gold-bearing sands, the material
passing through a system of separators which extract the gold and then
being discharged at the rear of the dredge. The dredge floats in a pool
of water that it carries with it, for as it excavates ahead it builds
up sand banks behind. In this way it may travel far from the river from
which it first started.
[Illustration: DIGGING A TRENCH WITH A CHAIN TYPE MACHINE]
[Illustration: MULTIPLE PLOWING ON A WESTERN WHEAT FIELD--TURNING FIFTY
FURROWS AT ONCE]
SUCTION DREDGES
Suction dredges are particularly adapted for excavating sandy bottoms.
One type used for dredging channels consists of a large steam vessel
with large bins into which the dredged material is pumped. At each side
of the boat there is a long pipe which may be let down into the water.
Each pipe terminates in a drag or footpiece with grated opening which
is designed to be dragged along the bottom as the vessel slowly steams
ahead. Powerful pumps suck a stream of water up the pipes which carries
with it a quantity of sand. The sand and water flow into the bins, the
solid matter settling to the bottom while the liquid flows out over the
top. When the settlings have filled the tanks, the drags are pulled
up and the vessel steams out to sea. Here doors in the bottom of the
bins are opened and the material drops through. The idea of opening
up the bottom of a boat to empty it seems rather startling until we
consider that the bins are sealed off from the rest of the boat and do
not contribute to its buoyancy. The sand that is dumped out of them is
much heavier than the water that takes its place when the bin doors are
opened.
CANAL DIGGING UNDER WATER
The Ambrose channel in lower New York Bay was dredged by means of
suction dredges. The channel is forty feet deep at low water and the
bottom had to be excavated from ten to twenty-five feet to attain
this depth. About seventy million cubic yards of material had to be
excavated or nearly a third as much as was excavated in the Panama
Canal. The Ambrose channel is seven miles long while the Panama Canal
is forty-five miles in length. Two of the larger dredges each had a
capacity of forty-five hundred cubic yards in their bins or enough to
load a train about a mile long, composed of 175 cars. It took less than
three hours to fill the bins. The openings in the gratings of the drags
measured about eight by nine inches and any stones or solid matter
small enough to pass through them was easily sucked up into the bins.
When a pile of stones of larger diameter was encountered a deep hole
was dredged around it and then by means of a water jet the stones were
forced into the hole.
The material sucked up by a dredge is sometimes dumped into a scow
alongside. This makes the structure of the dredge less expensive, but
where work has to be conducted in bodies of water exposed to storms it
is more expedient to let the dredge collect the material within its own
hull.
LAND BUILDING WITH DREDGES
The sand drawn up by a suction dredge is valuable material for land
building. In fact, a suction dredge is often used for the double
purpose of excavating and filling in low land. Sometimes its only
purpose is to fill in tide flats to above tide level. The material is
discharged through a pipe line which may be over a mile in length.
This pipe line is supported on a string of wooden or steel pontoons.
The pipe sections are connected by means of heavy rubber sleeves so as
to make the line flexible. This permits the dredge to move about and
also allows of moving the discharge end about to distribute the sand
properly.
Unfortunately all dredging does not consist of sand and mud. Sometimes
snags and matted roots are encountered which give trouble. For handling
such material rotary cutters are used. The bow of the dredge is fitted
with a hinged ladder about sixty to seventy feet long in which the
cutter is mounted. The ladder also carries the suction pipe close to
the cutter. The ladder is lowered to the bottom and the revolving
cutter chops up the roots into pieces which are drawn up into the
suction pipe. The size of the pieces that are sometimes sucked up is
remarkable. The greater part of the area of the New Orleans Inner
Harbor Navigation Canal was filled with stumps and matted cypress
roots. The cutters tore up and cut these roots and stumps and the
pieces were transported through a pipe line about 600 feet long. Stumps
that were too large to be handled in this way were undercut and sunk
below grade.
Cutters are used also for loosening packed hard bottoms and some of
them will dig into hard pan and even soft rock. A pressure of 100 to
150 pounds per square inch is maintained in a discharge pipe twenty to
twenty-four inches in diameter, which is enough to carry along heavy
bowlders dug up by the cutter.
THE DEEPEST MINE SHAFT
So far we have dealt only with surface conditions, but man has not been
content to stay on the surface of this planet. True, we have scarcely
begun to explore the crust of the earth. The deepest mine in the world
is the Morro Velho in the province of Minas Geraes, Brazil. Here the
earth has been penetrated to a depth of 6,426 feet in quest of gold.
This is a depth of less than a mile and a quarter and it shrinks into
insignificance when we reflect that we must go more than 3,000 times
that distance to reach the center of the earth. However, we have
made material progress in shaft-sinking in recent years, and it is
quite likely that the lure of scientific research may prove even more
powerful than that of gold and that some day we shall be induced to dig
many miles into the crust of the earth just to learn something more
about this globe that whirls us through space.
We have not yet reached the point at which hand labor may be dispensed
with in tunnel work, but there are machines which will do what formerly
could only be accomplished with the manually wielded pick and shovel.
We have already (in Chapter VII) described the pneumatic tunnel shield
and explained how it is sometimes driven forward through soft silt
by means of hydraulic jacks without any excavation of material. This
method of tunneling which is analogous to driving a punch through soft
metal, has a very limited field of application. It is impossible to
force the shield in this manner through sand or through any but very
soft silt.
TUNNELING BY MACHINE
The city of Cleveland takes its drinking water from Lake Erie. In
order to obtain water that is not contaminated by the refuse of the
city, tunnels are carried out under the bottom of the lake about two
miles from the shore where they terminate in water intakes far enough
below the surface to avoid floating impurities and far enough above
the bottom to avoid impurities that have settled to the lake bed. The
material through which the tunnels pass is a stiff clay, that cuts like
cheese. So uniform is this material that a special machine was built
to bore the tunnel through it. This machine is somewhat similar to a
boring mill. It has an arm that revolves against the face of the tunnel
heading and carries a cutter that travels along the arm so that it cuts
a continuous spiral ribbon of clay. The clay ribbon passes back through
the machine and is loaded into a train of dump cars.
For boring tunnels in hard rock many different machines have been
invented, but not one of them as yet has proved an unqualified success.
One very interesting machine, which was tried on the New York subway
excavation at 42d Street and Lexington Avenue, consisted of a series
of chipping hammers which, by means of pneumatic mechanism, were made
to hammer and pulverize the face of the rock with repeated blows. The
hammers were arranged in a circle and were revolved as they hammered
so that the whole surface of the heading was attacked and a circular
tunnel was cut through the rock. A serious disadvantage under which
the machine labored was the fact that the rock had to be crushed to a
powder or into small chips before it could be removed.
In ordinary rock excavation holes are bored into the heading and the
rock is then blown out by means of dynamite or some other explosive.
Large fragments of rock are then broken up into pieces small enough to
be handled readily, but no energy is wasted in reducing the material
to a powder. The percussion drills with which the rock is bored have
already been briefly described. When boring holes for a blast in soft
material, such as bituminous coal, a drill is used which resembles in
many respects an ordinary twisted auger bit except that it is many feet
in length. It is driven by hand into the coal by the use of a common
bit brace. Percussion drills or punches are also used. These are driven
either by pneumatic or electric power.
COAL-CUTTING MACHINERY
When excavating coal the heading is first undercut, that is, a deep
slot is cut in the wall of coal along the floor line. Then blast holes
are bored into the coal above this cut so that when the charges are
fired the coal will be broken downward. To undercut the coal special
machines are used, driven by compressed air or electricity. These
have endless chains fitted with chisel or pick points that bite into
and cut the coal. After the material has been shattered and reduced
to fragments of convenient size special machinery may be employed to
shovel it away from the heading and into dump cars. One electrically
driven shoveling machine which was tried out on some of the Catskill
aqueduct excavation had a broad open shovel which could be driven into
the pile of rock fragments under the control of an operator and would
scoop up the material, delivering it upon a traveling belt conveyor
which carried it on to the train cars. Many types of mechanical
shoveling and loading machines have been built for use in mines. They
are driven either by pneumatic or electric power.
EXPLORING SUBSURFACE CONDITIONS
In all engineering work it is highly important to explore subsurface
conditions before starting any construction or even drawing up plans.
The ordinary pneumatic percussion drill will not serve for deep holes.
Instead a rotary boring motion is requisite. The tool is mounted with
black diamond cutters which cut through the hardest rock. Water is
introduced into the hole to lubricate the tool and also to wash out
the abraded material. By trapping this material the character of the
rock penetrated may be determined. The material, however, is pulverized
and does not furnish, as a general rule, a fair sample of the rock.
When it is highly important to determine the exact nature of the rock
or other material a core drill is used. In other words the drill is
a hollow tube set with cutting crystals about its periphery. As the
tool is revolved it cuts an annular slot in the rock leaving a central
core standing. This core is broken off and drawn to the surface and
furnishes a true sample of the material encountered by the drill.
There is an interesting type of core drill in which steel shot is used
in place of diamonds. The cutting end of the drill is a collar with a
notched edge. Steel balls are fed into the drill and under the cutting
head. The balls are caught in the notches and rolled around against the
rock surface. There is also a partial dragging action. The friction
is sufficient to wear away the rock. As the balls wear away they are
replaced with new ones. Very evidently such drilling costs less for
upkeep than diamond drilling, but it is not as rapid as the latter.
LOCATING ROCK UNDER HUDSON RIVER
A notable illustration of exploration drilling was furnished by the
surveys for the Hudson crossing of the Catskill Aqueduct. To bring
water from the Catskill Mountains to New York City it was necessary to
cross the Hudson River. In order to furnish a permanent conduit it was
decided to carry the water in an inverted siphon bored through solid
rock. It was necessary to obtain a profile of the rock at the point
where a crossing seemed most feasible. Borings were therefore made
from a barge anchored in the river, but it was impossible with such
an unsteady working base to carry on the boring to any considerable
depth. Tides, the wash of passing steamers, floating ice, all combined
to obstruct the work. Drills were constantly broken. Finally it was
decided to do the boring from opposite banks of the river at such an
angle that bore holes would meet or pass each other under the middle
of the river. The exploration boring from the barges indicated that
solid rock lay at a considerable depth below the river bed and that
the bore holes would have to be set at a sharp angle to keep from
breaking through rock. The river at that point is about 3,000 feet
wide and a boring from the surface at the middle of the river had been
driven to a depth of 768 feet without striking solid rock. Two shafts
were sunk to a depth of about 250 feet and from these diamond drill
borings were started at such an angle that they would cross at a depth
of 1,500 feet. Excellent rock was encountered throughout the boring.
Then a second set of borings was made which crossed at a depth of 950
feet without encountering any appreciable amount of water. It was
accordingly decided to carry the aqueduct in vertical shafts, one at
each side of the river, at a depth of 1,100 feet below water level, and
then connect these shafts with a horizontal tunnel. It was important
to have a good solid rock cover over the tunnel because the aqueduct
reaches the river with a head of 400 feet which added to the 1,100 feet
of depth of the inverted siphon gave a total head of 1,500 feet or a
hydraulic pressure of about forty-two tons per square inch.
Although the diamond drill borings just mentioned were remarkable
because of their inclination and because of the cramped quarters from
which they were driven, they do not begin to compare in depth with some
of the borings made in search of water and of oil. The deepest boring
in the world to date is near Fairmount, West Virginia, where a hole six
inches in diameter was driven to a depth of 7,579 feet or nearly a mile
and a half. At that point an earth slide stopped further borings.
BORING FOR OIL
The time-honored method of boring for oil known as the percussive
system is to hammer through the earth and rock with a heavy steel
drill. The drill really consists of a long string of parts measuring
altogether as much as sixty feet in length. (See Figure 64.) The drill
proper or bit has a cutting edge adapted for the character of the
material it is to penetrate. The bit is attached to a steel bar known
as the “auger stem” which may be from twelve to forty-five feet in
length. Then come the “jars” or a link member which allows a play of
about sixteen inches. The purpose of this is to assist in freeing the
bit from the material it is penetrating by jarring it upward on the
upstroke of the drill. Above the jars there is another bar known as the
sinker, and this is provided with a rope socket to which is attached
the cable that carries the string of drill parts. The cable passes
over a pulley to a walking beam which gives the necessary up-and-down
motion.
[Illustration: FIG. 64.--A STRING OF WELL-DRILLING TOOLS]
The loose material in the bore is removed by a sand pump. To protect
the bore from caving a casing of steel pipe must be lowered into the
well. The boring may proceed at the rate of ten to sixty feet per day,
depending upon the material penetrated and the depth of the well. All
sorts of difficulties are liable to interrupt the work. The cable may
break, the string of tools may become unscrewed, or the casing may drop
into the hole, and then follows the tedious process of fishing for the
lost parts and hauling them up out of the well.
As the drilling proceeds, the bore becomes progressively smaller and
casings of smaller diameter must be used. The well is completed by
lowering a pipe within the casing through which the oil flows to the
surface and is carried to the storage tanks and thence by pipe lines to
the refineries.
While the percussive system of drilling is very generally used
throughout the American oil fields, rotary methods of drilling are
largely employed in California.