Stanesby, “Railways”, part 4
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Ballasting and Laying the Rails, &c.—In order to obtain a firm dry foundation for the blocks or sleepers to
which the rails are fastened, a layer or stratum of broken stone, technically called ballast, is spread over the
road for a thickness of a foot or more, varying according to circumstances. After the rails are laid down, similar
materials are used to fill in the spaces between the blocks and sleepers. The broken stone should be so small that any
piece would pass through a ring two inches and a half in diameter. Other substances are occasionally used, especially
for the upper part of the ballast, as gravel, river-sand, and burnt clay. In some situations, with good ballast, no
surface-drains are necessary; but drains consisting of a brick channel along the middle of the line, with small cross
drains at intervals towards each side alternately, are often required.
There is great variety of opinions as to the best form and manner of fixing the rails. The most important question
involved in these differences is that of the intermediate or
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continuous support of the rails. The most common method of fixing them is to fit them into iron chairs, which are spiked
down to blocks of stone imbedded in the ballasting. This plan, although it appears by experiment to afford the firmest
foundation, has several disadvantages. The points of support, being isolated from one another, are liable to be deranged
by any subsidence in the ground, as well as by the constant vibration consequent upon the rapid passage of heavy trains,
and the small but irresistibly powerful action of temperature in causing the expansion and contraction of the rails.
The former of these inconveniences is in some degree obviated by substituting cross sleepers of wood (like those
described as being used in the early railways) for the stone blocks upon such parts of the line as are likely to sink.
The two rails, being, in this case, attached to the same sleeper, are not liable to be thrown out of gauge, or, in other
words, to lose their parallelism, although the unequal sinking of the sleeper may cause one rail to become lower than
the other. This application of wooden supports has been in most cases considered a temporary one, it being intended to
lay stone blocks in their stead so soon as the ground became sufficiently firm; but it appears from experience, both in
this country and in North America, that the motion of carriages on those parts of a line supported by wood is smoother
and quieter than on others.
In both of these modes of supporting the rail it is sustained only at intervals of three or four feet, the intervening
portion acting as a bridge, which, though very rigid, yields in a slight degree when the heavy locomotive engines pass
over it. The surface of the rail is thus converted into a series of minute undulations, the effect of which is to
increase the resistance. It has been thought that these undulations were of little consequence, the gain in descending
being a counterbalance to the retardation of the ascent; but Professor Barlow, in reporting on experiments made by him
in 1835, for the London and Birmingham Railway Company, expresses an opinion that “the advantage of the descent
is, owing to the velocity and the shortness of the inclined plane, scarcely appreciable, and that the result of the
deflection will be equivalent to the carriage being carried up a plane of half the whole length, the other half being
horizontal.”
These and some other considerations have led to the adoption of a continuous support to the rail, which has been
effected in several different ways, and with various success. Intermediate supports, being the most extensively
employed, will be first noticed; and stone blocks, according to general opinion, claim the precedence among them.
The blocks used upon recently-constructed railways are about two feet square and one thick, though much smaller ones
were considered sufficient before the use of locomotive engines became general. They are roughly squared, but have so
much of the surface, as is to receive the chair, accurately flattened. The chairs are usually fastened down by two or
three iron spikes, to receive which holes are made in the stone, and filled with wooden plugs. The plugs should always
be bored to receive the spike, and driven tight into the stone, though they are sometimes put in loose and split by
driving the spike. Spikes or pins of well-dried oak have been used instead of iron spikes for securing the chairs, and
have been found very durable; but are not generally approved for lines worked at great speed. The introduction of a
piece of felt between the chair and the block is useful in deadening concussion. As it is highly important that stone
blocks should be well bedded, it is usual to cause them to form a solid foundation for themselves by repeatedly falling
from a small elevation upon the spot where they are to rest; sand or very fine gravel being thrown under them between
the times of falling. For this purpose a portable machine with an elastic wooden lever about twenty feet long is used,
the block, to which the chair has been previously attached, being suspended from the short end, and a man stationed at
the opposite end to raise and drop it. When the stone has made a firm bed, and has dropped in the right position, which
is determined by levels and sights, it is detached from the lever and stir-rounded by ballasting.
Fig. 13 is
a ground-plan illustrating the use of stone blocks and wooden sleepers. a a represent blocks laid square
with the road, and b b the same laid diagonally, a position now generally preferred, being convenient in
repairing the road when a block sinks, because workmen can get at every side for the purpose of ramming ballast under
it. Blocks of Scotch asphalte have been tried in lieu of stone, but with what success the writer is not aware. Other
similar substances have been suggested in order to diminish expense. It has also been proposed to use cast-iron
bed-plates instead of blocks, by which several important advantages were anticipated, but no such plan appears to have
been brought extensively into use. In the Dublin and Kingstown Railway an attempt was made to ensure increased solidity
by introducing throughgoing stone blocks, which were formed of granite, six feet long, two wide, and one thick,
and stretched across the track. These were placed fifteen feet apart; ordinary single blocks being used between them, at
intervals of three feet. Owing, perhaps, to the difficulty of bedding such large blocks, the plan did not answer, the
motion over them being harsh and unpleasant, and the vibration such as to break many of the long blocks. In some cases,
particularly on sharp curves, iron tie-rods have been used to connect two opposite chairs, and counteract any tendency
to separate which might arise in such situations from the isolation of the blocks.
The use of cross-sleepers, which are represented by c c, Fig. 13, needs little remark. They are
mostly from seven to nine feet long, and consist sometimes of whole trunks of small size, and in other cases of
half-trunks laid with the flat or sawn side downwards.
These and other timbers connected with a railway are now almost always
Kyanized.
Several lines of railway have recently been laid entirely upon these sleepers.
The distance between the points of support varies from three to five feet. Bearings of greater length have been used,
but on railways for locomotive engines have been found unsuitable, from their greater liability to get out of repair.
Experience has not fully decided the comparative advantages of long bearings with heavy rails and blocks, and short ones
with comparatively light supports; but a greater length than three feet nine inches, or four feet, has seldom proved
successful. Owing to the deflection of the rails, Professor Barlow enforces the importance of placing the supports
exactly opposite to each other, that both sides of a carriage may be equally affected.
Rails and Chairs.—The experiments of Barlow and others leave it questionable whether any additional
strength is obtained from a given weight of iron by the fish-bellied shape, and therefore parallel rails are now almost
universally adopted. Among other advantages which they possess, the length of bearing on the different sides of a curved
track may be so varied as to keep the chairs opposite to one another, which cannot be done with fish-bellied rails.
Fig. 14 represents some of the principal varieties of form and contrivances for fixing the rails which have
been introduced on English railways: a is a section of the fish-bellied rail originally used on the Liverpool and
Manchester Railway, the shaded part being that which enters the chair, and the outline indicating the increased depth in
the centre: b is the same rail, as fixed in
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the chair, the black part representing the end of an iron wedge or key, which is driven in to secure it.—c
and d are a section and side view of a plan invented by Mr. Losh, and used on the Newcastle and Carlisle Railway.
The rails are made with a curved projection on the under side, to fit into a suitable concavity in the chair, as
indicated by the dotted lines in d. Two iron keys are used, driven in opposite directions. Any contraction of the
rail tends to draw it laterally out of the chair, but in doing so the curved base rises in its seat and tightens the
keys, which press downwards as well as sideways.—e and f are similar views of a method contrived by
Robert Stephenson, and used on part of the London and Birmingham Railway. In this the seat of the rail is flat, but
bears upon a segmental piece of iron laid loose in a concavity in the chair, so that an irregularity which may cause the
chair to tilt in the direction of the tail may not affect its position. The rails are secured by cylindrical pins, the
points of which enter depressions in the side of the rail. Each pin has a slit through it, which, when in its proper
position, tallies with holes through the cheeks of the chair. Iron keys driven into these holes prevent the pin from
moving, and, acting as wedges against the end of the slit, force the pin tight against the rail. The chair represented
is a joint chair, and g shows the form of the joint, which is called a half-lap. The narrow part of the rail is
not divided, but turned aside at the joint, as shown by the dotted lines. Intermediate chairs are similar, but have a
pin on one side only. This mode of fixing allows the rail to slide a little in the chair, on account of expansion and
contraction, and the keys are not so liable to work loose as when in contact with the rail. These are all for
fish-bellied, and the following for parallel rails.—h is a rail and chair invented by Mr. Daglish, and
rewarded by the London and Birmingham Railway Company, as presenting the best sectional form of rail. The chair is
proposed to be fixed to the block or sleeper by bolts passed through from the under side, and keyed above the chair. The
rail is fastened by two semicircular iron keys driven in opposite directions. This arrangement, though ingenious, has
the disadvantage that the rail could not be taken up without removing the chair.—i is a contrivance in
which an iron ball, dropped into a socket in the chair, is forced against the rail by a key driven through a hole in one
cheek of the chair. It is simple, and affords sufficient lateral movement for the effect of temperature on the rail.
This form of rail is known as the T rail.—k and o are a section and ground-plan of a chair in which
the rail is held by a wooden key. The keys are well seasoned, and when in use become by expansion almost immoveable;
because, as shown in o, they are most compressed in the centre. So great, indeed, is the expansive force of the
wood, that it occasionally breaks the chairs. This mode of construction is extensively used on the Grand Junction,
Birmingham, South-Western, and other railways.—m and n show another application of a wooden
fastening, adopted by Mr. Storey on the Great North of England Railway. A block of wood is so placed in the chair as to
be prevented from moving endways, and is held to the rail by an iron wedge driven through the cheek of the
chair.—l is a rail contrived for the purpose of fitting the wheel more accurately than those of the
ordinary shape, but it is not much used. The rails here represented vary much in strength: a and b were
made about thirty-five pounds to the yard, but have been found too light, and replaced by parallel rails of sixty
pounds: e and f are fifty-pound rails, for three-feet bearings. Rails similar to k are made from
sixty to seventy-five pounds per yard or more, for bearings of three to five feet, and they are now seldom used of less
weight than seventy pounds to the yard. The most common joints are square, as n and o, but half-lapped and
scarfed or diagonal joints are also used. The concussion produced by a very slight irregularity at these points is so
injurious, that probably increased care and expense in making them perfect would be well bestowed. Chairs are almost
invariably made of cast-iron, as their complex form renders it difficult to manufacture them otherwise with sufficient
economy; but as they are liable to breakage from their brittleness, it has been proposed to make them of malleable iron,
and machinery for the purpose has been patented, but apparently not yet brought into operation.
Railways on Continuous Bearings.—The introduction of this kind of railway is perhaps mainly to be
attributed to the extensive use of timber in such works in North America. It has not only been used in lieu of stone,
but also in a great measure in the place of iron. In many of the American and some of the Continental railroads, beams
of timber laid continuously, and firmly connected together by cross-pieces, are made to supply the strength usually
given to iron rails; and the application of iron is limited to a flat bar or plate two inches and a half wide, and from
half an inch to an inch thick, nailed to the beams on their inner edges, for the wheels to roll upon. Though differing
in details, this construction of railway is very like the old wooden tramway. Frequently these beams or wooden rails are
supported upon cross-sleepers; but, whether they are so or not, their breadth of surface causes them to receive
considerable support from the ballast or road materials along their whole length. Mr. I. K. Brunel, engineer of the
Great Western Railway, was one of the first British engineers who proposed a similar construction, which he did with the
hope of obtaining a smoother and more elastic road, which should at once be more agreeable to ride upon, cheaper to
maintain, and safer for travelling at high velocities, than a railway constructed in the ordinary manner.
Although some of the supposed advantages are at present questionable, the superior smoothness of motion on such a road,
when in good order, is pretty generally admitted; and an opinion seems to be gaining ground, that though longitudinal
timber bearings do not produce so firm and unyielding a railway as stone blocks, and may therefore require rather more
power in working, this disadvantage is more than counterbalanced by the diminished wear and tear, of which the
comparative absence of noise is a tolerably accurate criterion. The Great Western Railway can hardly be compared with
any other on account of its increased width, but the London and Croydon, which is entirely, and the Manchester and
Bolton, Hull and Selby, and several other lines, which are partially laid in this manner, and which in other respects
resemble those of the more common construction, may be fairly brought into comparison with them. The Greenwich Railway
is a remarkable instance of the superior comfort of timber bearings to those of stone, the rigidity of the latter being
aggravated by the circumstance of being on a viaduct. On this line, as in that from Dublin to Kingstown, it has been
deemed advisable to remove the blocks, and substitute a more elastic structure of wood. The longitudinal timbers on the
Croydon Railway vary from nine to fourteen inches wide, and four and a half to seven inches deep; and cross-sleepers are
bolted under them at intervals of three feet. The rails are of the form shown at
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p, fig. 15, and are screwed down at intervals of eighteen inches on each side, a layer of felt being
interposed between them and the timbers.
These rails weigh about forty-seven pounds to the yard.—q,
fig. 15, is the rail of the Great Western Railway, which is fixed in a similar manner, but the screws on the
inner side of the rail are round-headed and countersunk, while the others are ordinary square-headed bolts. The
longitudinal timbers are of larger dimensions, and the cross-pieces or transoms are placed fifteen feet apart, and
framed with them, their office being more to keep the track in gauge than to bear any considerable part of the
weight.—r and s are forms of rail sometimes used on continuous bearings, r being fastened by
clamps or pins driven in obliquely. Rails similar to p have been fixed in the same manner, but the use of screws,
though expensive, is decidedly preferable.
Continuous bearings of stone have been tried, but found too harsh and rigid.