the length of line required to ease the gradient is obtained
by running backward and forward in a zigzag course, instead of
going straight up the mountain. As a full stop has to be made at
the end of every piece of line, there is no danger of the train
running away from its brakes. This device was first used among the
hills of Pennsylvania over forty years ago, to lower coal cars
down into the Nesquehoning Valley. It was afterwards used on the
Callao, Lima, and Oroya Railroad in Peru, by American engineers,
with extraordinary daring and skill. It was employed to carry the
temporary tracks of the Cascade Division of the Northern Pacific
Railroad over the "Stampede" Pass, with grades of 297 feet per
mile, while a tunnel 9,850 feet long was being driven through the
mountains.
[Illustration: A Switchback.]
With the improvement of brakes and more reliable means of stopping
trains upon steep grades, came a farther development of the above
device, which was first applied on the Denver and Rio Grande
Railroad in Colorado, and has since been applied on a grand scale
on the Saint Gothard road, the Black Forest railways of Germany,
and the Semmering line in the Tyrol. This device is to connect the
two lines of the zigzag by a curve at the point where they come
together, so that the train, instead of going alternately backward
and forward, now runs continuously on. It becomes possible for the
line to return above itself in spiral form, sometimes crossing over
the lower level by a tunnel, and sometimes by a bridge. A notable
instance of this kind of location is seen on the Tehachapi Pass
of the Southern Pacific, where the line ascends 2,674 feet in 25
miles, with eleven tunnels, and a spiral 3,800 feet long.
[Illustration: Plan of Big Loop.]
The "Big Loop," as it is called, on the Georgetown branch of the
Union Pacific, in Colorado, between Georgetown and a mining camp
called Silver Plume, has been chosen to illustrate this point. The
direct distance up the valley is 1¼ miles and the elevation 600
feet, requiring a gradient of 480 feet per mile. But by curving
the line around in a spiral, the length of the line is increased
to 4 miles and the gradient reduced to 150 feet per mile. Zigzags
were used first for foot-paths, then for common roads, lastly for
railways. Their natural sequence, spirals, was a railway device
entirely, and confirms the saying of one of our engineers: "Where
a mule can go, I can make a locomotive go." This may be called the
poetry of engineering, as it requires both imagination to conceive
and skill to execute.
* * * * *
[Illustration: Profile of the Same.]
There is one thing more which distinguishes the American railway
from its English parent, and that is the almost uniform practice
of getting the road open for traffic in the cheapest manner and in
the least possible time, and then completing it and enlarging its
capacity out of its surplus earnings, and from the credit which
these earnings give it.
[Illustration: Big Loop, Georgetown Branch of the Union Pacific,
Colorado.]
The Pennsylvania Railroad between Philadelphia and Harrisburg
is a notable example of this. Within the past few years it has
been rebuilt on a grand scale, and in many places relocated, and
miles of sharp curves and heavy gradients, originally put in to
save expense, have been taken out. This system has been followed
everywhere, except on a few branch lines, and upon one monumental
example of failure--the West Shore Railroad, of New York. The
projectors of that line attempted in three years to build a
double-track railroad up to the standard of the Pennsylvania road,
which had been forty years in reaching its present excellence.
Their money gave out, and they came to grief.
II.
We have thus briefly reviewed the development of our railways to
show what they are, and how they came to be what they are, before
describing the processes of building, in order that the reasons may
be clearly understood why we do certain things, and why we fail to
do other things which we ought to do.
In the building of a railway the first thing is to make the surveys
and locate the position of the intended road upon the ground, and
to make maps and sections of it, so that the land may be bought and
the estimates of cost be ascertained. The engineer's first duty
is to make a survey by eye without the aid of instruments. This
is called the "reconnoissance." By this he lays down the general
position of the line, and where he wants it to go if possible.
Great skill, the result of long experience, or equally great
ignorance may be shown here. After the general position of the
line, or some part of it, has been laid down upon the pocket map,
the engineer sends his party into the field to make the preliminary
survey with instruments.
In an old-settled country the party may live in farm-houses
and taverns, and be carried to their daily work by teams. But
a surveying party will make better progress, be healthier and
happier, if they live in their own home, even if that home be a
travelling camp of a few tents. With a competent commissary the
camp can be well supplied with provisions, and be pitched near
enough to the probable end of the day's work to save the tired
men a long walk. When they get to camp and, after a wash in
the nearest creek, find a smoking-hot supper ready--even though
it consist of fried pork and potatoes, corn-bread and black
coffee--their troubles are all forgotten, and they feel a true
satisfaction which the flesh-pots of Delmonico's cannot give. One
greater pleasure remains--to fill the old pipe, and recline by the
camp-fire for a jolly smoke.
[Illustration: Engineers in Camp.]
A full surveying party consists of the front flag-man, with his
corps of axe-men to cut away trees and bushes; the transit-man,
who records the distances and angles of the line, assisted by his
chain-men and flag-men; and lastly the leveller, who takes and
records the levels, with his rod-men and axe-men. The chief of the
party exercises a general supervision over all, and is sometimes
assisted by a topographer, who sketches in his book the contours of
the hills and direction and size of the watercourses.
One tent contains the cook, the commissary, and the provisions;
another tent or two the working party, and another the superior
engineers, with their drawing instruments and boards. In a properly
regulated party the map and profile of the day's work should be
plotted before going to bed, so as to see if all is right. If it
turns out that the line can be improved and easier grades got, or
other changes made, now is the time to do it.
After the preliminary lines have been run, the engineer-in-chief
takes up the different maps and lays down a new line, sometimes
coinciding with that surveyed, and sometimes quite different. The
parties then go back into the field and stake out this new line,
called the "approximate location," upon which the curves are all
run in. In difficult country the line may be run over even a third
or fourth time; or in an easy country, the "preliminary" surveys
may be all that is wanted.
The life of an engineer, while making surveys, is not an easy one.
His duties require the physical strength of a drayman and the
mental accuracy of a professor, both exerted at the same time, and
during heat and cold, rain and shine.
An engineer, once on a time, standing behind his instrument, was
surrounded by a crowd of natives, anxious to know all about it. He
explained his processes, using many learned words, and flattered
himself that he had made a deep impression upon his hearers. At
last, one old woman spoke up, with an expression of great contempt
on her face, "Wall! If I knowed as much as you do, I'd quit
ingineerin' and keep a grocery!"
A large part of the financial difficulties of our railways results
from not taking time enough to properly locate the line. It must
be remembered that a cheaply constructed line can be rebuilt, but
with a badly located line nothing can be done except to abandon it
entirely.
[Illustration: Royal Gorge Hanging Bridge, Denver and Rio Grande,
Colorado.]
It is well therefore to consider carefully what is the true problem
of location. It is so to place and build a line of railway that
it shall get the greatest amount of business out of the country
through which it passes, and at the same time be able to do that
business at the least cost, including both expenses of operating
and the fixed charges on the capital invested. The mere statement
of this problem shows that it is not an easy one. Its solution
is different in a new and unsettled country from that in an
old-settled region. In the new country, the shortest, cheapest, and
straightest line possible, consistent with the easiest gradients
that the topography of the land will allow, is the best. The towns
will spring up after the road is built, and will be built on its
line, and generally at the places where stations have been fixed.
[Illustration: Veta Pass, Colorado.]
In a mountainous country, like Colorado, the problem is how to
reach the important mining camps, regardless of the crookedness
and increased length given to the line. The Denver and Rio Grande
has been compared to an octopus. This is really a compliment to
its engineers. It sucks nutriment from every place where nutriment
is to be found. To do this it has been forced to climb mountains,
where it was thought locomotives could never climb. In one place,
called the Royal Gorge, the difficulties of blasting a road-bed
into the side of the mountain were so great that it was thought
expedient to carry the track upon a bridge, and this bridge was
hung from two rafters, braced against the sides of the gorge. In
surveying some parts of the lines the engineers were suspended by
ropes from the top of the mountains and made their measurements
swinging in mid-air.
The problem of location is different in an old-settled country,
where the position of the towns as trade-centres has been fixed
by natural laws that cannot be overruled. In this case the best
thing the engineer can do is to get the easiest gradient possible
consistent with the topography of the country, and let the curves
take care of themselves; always to strike the important towns, even
if the line is made more crooked and longer thereby; to so place
the line in these towns as to accommodate the public, and still
be able to buy plenty of land; also to locate for under or over,
rather than grade crossings.
[Illustration: Sections of Snow-sheds.]
[Illustration]
[Illustration]
In all countries, old and new, mountainous and level, the rule
should be to keep the level of track well above the surface of
the ground, in order to insure good drainage and freedom from
snow-drifts.
The question of avoidance of obstruction by snow is a very
serious one upon the Rocky Mountain lines, and they could not
be worked without the device of snow-sheds--another purely
American invention. There are said to be six miles of stanchly
built snow-sheds on the Canadian Pacific and sixty miles on
the Central Pacific Railway. The quantity of snow falling is
enormous, sometimes amounting to 250,000 cubic yards, weighing
over 100,000 tons, in one slide. It is stated by the engineers of
the Canadian Pacific, that the force of the air set in motion by
these avalanches has mown down large trees, not struck by the snow
itself. Their trunks, from one to two feet in diameter, remain,
split as if struck by lightning.
* * * * *
[Illustration: Snow-sheds, Selkirk Mountains, Canadian Pacific. The
winter track under cover; the outer track for summer use.]
After the railway line has been finally located, the next duty of
the engineers is to prepare the work for letting. Land-plans are
made, from which the right of way is secured. From the sections,
the quantities are taken out. Plans of bridges and culverts are
made; and a careful specification of all the works on the line is
drawn up.
[Illustration: Making an Embankment.]
The works are then let, either to one large contractor or to
several smaller ones, and the labor of construction begins.
The duties of the engineers are to stake out the work for the
contractors, make monthly returns of its progress, and see that
it is well done and according to the specifications and contract.
The line is divided into sections, and an engineer, with his
assistants, is placed in charge of each. Where the works are heavy,
the contractors build shanties for their men and teams near the
heavy cuttings or embankments. It is the custom to take out heavy
cuttings by means of the machine called a steam shovel, which will
dig as many yards in a day as 500 men.
[Illustration: Steam Excavator.]
On the prairies of the West the road-bed is thrown up from
ditches on each side, either by men with wheelbarrows and carts,
or by means of a ditching-machine, which can move 3,000 yards
of earth daily. In this case the track follows immediately
after the embankment, and the men live in cars fitted up as
boarding-shanties, and moved forward as fast as required. If the
country contains suitable stone, the culverts and bridge abutments
are built by gangs of masons and stone-cutters, who move from
point to point. But the general practice is to put in temporary
trestle-work of timber resting upon piles, which trestle-work is
renewed in the shape of stone culverts covered by embankments, or
iron bridges resting on stone abutments and built after the road is
running.
[Illustration: Building a Culvert.]
[Illustration]
The pile-driver plays a very important part therefore in the
construction of our railroads, and has been brought to great
perfection. It is worked by a small boiler and engine, and gives
its blows with great rapidity. It drags the piles up to leaders
and lifts them into place by steam-power, so that it is worked
by a small gang of men. Finally, it is as portable as a pedler's
cart, and as soon as it has finished one job it is taken to pieces,
packed upon wagons, and moved on to the next job.
[Illustration: (Rock Drill.)]
Tunnels are neither so long nor so frequent upon American railways
as upon those of Europe. The longest are from two to two and a half
miles long, except one, the Hoosac, about four miles. Sometimes
they are unavoidable. The ridge called Bergen Hill, west of
Hoboken, N. J., is a case in point. This is pierced by the tunnels
of the West Shore, of the Delaware, Lackawanna, and Western, and of
the Erie, the last two of which, as shown on page 25, are placed at
different levels to enable one road to pass over the other.
[Illustration: Rock Drill.]
It is by our system of using sharp curves that we avoid tunnels. It
may be said, in general terms, that American engineers have shown
more skill in avoiding the necessity of tunnels than could possibly
be shown in constructing them. When we are obliged to use tunnels,
or to make deep cuttings in rocks, our labors are greatly assisted
by the use of power-drills worked by compressed air and by the use
of high explosives, such as dynamite, giant powder, rend-rock,
etc. Rocks can now be removed in less than half the time formerly
required, when ordinary blasting-powder was used in hand-drilled
holes.[3]
[Illustration: A Construction and Boarding Train.]
III.
From data furnished by Mr. D. J. Whittemore, chief engineer of the
Chicago, Milwaukee, and St. Paul system (which had a total length
of 5,688 miles on January 1, 1888), the length of open bridges on
these lines was 115-91/100 miles, and of culverts covered over with
embankment, 39-2/10 miles. "Everything," says Mr. Whittemore, "not
covered with earth, except cattle guards, be the span 10 or 400
feet, is called a bridge. Everything covered with earth is called
a culvert. Wherever we are far removed from suitable quarries, we
build a wooden culvert in preference to a pile bridge, if we can
get six inches of filling over it. These culverts are built of
roughly squared logs, and are large enough to draw an iron pipe
through them of sufficient diameter to take care of the water.
We do this because we believe that we lessen the liability to
accident, and that the culvert can be maintained after decay has
begun, much longer than a piled bridge with stringers to carry the
track. Had we good quarries along our line, stone would be cheaper.
Many thousands of dollars have been spent by this company in
building masonry that after twenty to twenty-five years shows such
signs of disintegration that we confine masonry work now only to
stone that we can procure from certain quarries known to be good."
[Illustration: Bergen Tunnels, Hoboken, N. J.]
Mr. Whittemore is an engineer of great experience, skill, and
judgment, and there is food for much reflection in these words of
his: First--that it is better to use temporary wooden structures,
to be afterward renewed in good stone, rather than to build of the
stone of the locality, unless first-class. Second--that a structure
covered with earth is much safer than an open bridge; which, if
short and apparently insignificant, may be, through neglect, a most
serious point of danger, as was shown in the dreadful accident of
1887 on the Toledo, Peoria, and Western road in Illinois, where
one hundred and fifty persons were killed and wounded, and by the
equally avoidable accident on the Florida and Savannah line, in
March, 1888. Had these little trestles been changed to culverts
covered with earth, many valuable lives would not have been lost.
[Illustration: Beginning a Tunnel.]
It was safely estimated that there were, in 1888, 208,749 bridges
of all kinds, amounting in length to 3,213 miles, in the United
States.[4]
The wooden bridge and the wooden trestle are purely American
products, although they were invented by Leonardo da Vinci in the
sixteenth century. From the above statistics it will be seen how
much our American railways owe to them, for without them over
150,000 miles could never have been built.
The art of building wooden truss-bridges was developed by Burr &
Wernwag, two Pennsylvania carpenters, some of whose works are still
in use after eighty years of faithful duty (p. 28). A bridge built
by Wernwag across the Delaware in 1803 was used as a highway bridge
for forty-five years, was then strengthened and used as a railway
bridge for twenty-seven years more, and was finally superseded by
the present iron bridge in 1875.
These old bridge-builders were very particular about the quality of
their timber, and never put any into a bridge less than two years
old. But when we began to build railways, everything was done in a
hurry, and nobody could wait for seasoned timber. This led to the
invention of the Howe truss, by the engineer of that name, which
had the advantage of being adjustable with screws and nuts, so that
the shrinkage could be taken up, and which had its parts connected
in such a way that they were able to bear the heavy concentrated
weight of locomotives without crushing. This bridge was used on
all railways, new and old, from 1840 to about 1870. Had it been
free from liability to decay and burn up, we should probably not be
building iron and steel bridges now, except for long spans of over
200 feet; and as the table opposite shows, the largest number of
our spans are less than 100 feet long.
The Howe truss forms an excellent bridge, and is still used in the
West on new roads, with the intention of substituting iron trusses
after the roads are opened.
After 1870, the weights both of locomotives and other rolling
stock began to be increased very rapidly. This, together with
the development of the manufacture of iron, and especially the
invention of rolled beams and of eye-bars, gave a great impetus to
the construction of iron bridges. At first cast-iron was used for
the compression members, but the development of the rolling-mill
soon enabled us to make all parts of rolled iron sections at no
greater cost, and rolled iron, being a less uncertain material,
has replaced cast-iron entirely. Iron bridges came in direct
competition with the less costly Howe truss, and during the first
decade of their construction every attempt was made to build them
with as few pounds of iron as would meet the strains.
[Illustration: Old Burr Wooden Bridge.]
S. Whipple, C.E., published a book in 1847 which was the first
attempt ever made to solve the mathematical questions upon which
the due proportioning of iron truss-bridges depends. This work
bore fruit, and a race of bridge designers sprang up. The first
iron bridges were modelled after their wooden predecessors, with
high trusses and short panels. Riveted connections were avoided,
and every part was so designed that it might be quickly and easily
erected upon staging or false works, placed in the river. This was
very necessary, for our rivers are subject to sudden freshets,
and if we had adopted the English system of riveting together all
the connections, the long time required before the bridge became
self-sustaining would have been a serious element of danger.
Following the practice of wooden bridge building, iron bridges
were contracted for by the foot, and not by the pound as is now
the custom. To this accidental circumstance is greatly due the
development of the American iron bridge. The engineer representing
the railway company fixed the lengths of spans, and other general
dimensions, and also the loads to be carried and the maximum
strains to be allowed. The contracting engineer was left perfectly
free to design his bridge, and he strained every nerve to find the
form of truss and the arrangement of its parts that should give the
required strength with the least number of pounds weight per foot,
so that he could beat his competitors. When the different plans
were handed in, an expert examined them and rejected those whose
parts were too small to meet the strains. Of those found to be
correctly proportioned, the lowest bid took the work.
By the rule of the survival of the fittest all badly designed forms
of trusses disappeared and only two remained: one the original
truss designed by Mr. Whipple, and the other, the well-known
triangular, or "Warren" girder, so called after its English
inventor.
It speaks well for the skill and honesty of American bridge
engineers that many of their old bridges are still in use, designed
for loads of 2,500 pounds per lineal foot, and now daily carrying
loads of 4,000 pounds and over per foot. Sometimes the floor has
been replaced by a stronger one, but the trusses still remain and
do good service. The writer may be permitted to point to the bridge
over the Mississippi River at Quincy, Ill., built in 1869, as an
example. Most bridge-accidents can be traced to derailed trains
striking the trusses and knocking them down. Engineers (both those
specially connected with bridge works, and those in charge of
railways) know much better now what is wanted, and the managers of
railways are willing to pay for the best article. The introduction
of mild steel is a great step in advance. This material has an
ultimate strength, in the finished piece, of 63,000 to 65,000
pounds per square inch, or forty per cent. more than iron, and it
is tough enough to be tied in a knot, or punched into the shape of
a bowl, while cold. With this material it is as easy to construct
spans of 500 feet as it was spans of 250 feet in iron.
Bridges are now designed to carry much heavier loads than formerly.
The best practice adopts riveted connections except at the junction
of the chord-bars and the main diagonals, where pins and eyes
are still very properly used. Plate girders below the track are
preferred up to 60 or 70 feet long, then riveted lattice up
to 125 feet. The wind strains also are now provided for with a
considerable excess of material, amounting in very long spans to
nearly as much as the strains due to gravity. Observing the rule
that no bridge can be stronger than its weakest part, a vast deal
of care and skill has been applied in perfecting the connections
of the parts of a truss, and many valuable experiments have been
made which have greatly enlarged our knowledge of this difficult
subject. The introduction of riveting by the power of steam or
compressed air is another very great improvement.[5]
[Illustration: Kinzua Viaduct; Erie Railway.]