MACHINING THE EARTH
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,[252]
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.
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[253] 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.[254] 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.
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[255] 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.
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.
[257]
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.
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.
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.
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[262] 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.
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.
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.
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[267] 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.
by A. Russell Bond
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[253] 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.[254] 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[255] 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[256] 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.
DIGGING A TRENCH WITH A CHAIN TYPE MACHINE
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[258] 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[259] 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[260] 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[261] 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[262] 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[263] 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[264] 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[265] 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[266] walking beam which gives the necessary up-and-down motion.
FIG. 64.—A STRING OF WELL-DRILLING TOOLS
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.
by A. Russell Bond
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