A manual of the principles and practice of road-making: comprising the location, construction, and improvement of roads, (common, macadam, paved, plank, etc.) and rail-roads. By W. M. Gillespie ...

294 RAIL-ROADS.
EMBANKMENTS.
The embankments of railroads demand the use of every
possible precaution to ensure their solidity; not only on
account of their size, but because the vibrations imparted
to them. by the passing trains, greatly increase their tendency to slip. The expense and time required to form
them in layers, as recommended on page 166, often forbid
the adoption of that method. They are usually constructed by raising them to their full height at one end,
and so carrying them onward. Temporary rails are laid
along the bank, and extended with it, and on them wagons,
containing each about 3 cubic yards, are drawn by horses,
or by locomotive engines, if the distance, or " lead," be
great.
It has been ascertained that, contrary to the usual theory and practice, the quantity of work which can be done
on an embankment so made, and, consequently, the time
which will be required for its completion, does not depend on the area of the face of the cutting which supplies
it, or on the number ot wagons which can be filled in it
together; but on their rate of speed, and on the number
of them which can be emptied in a given time over the
head of the embankment, to the top width of which this
element is proportional. The number of wagons drawn
together in a " set," should increase or decrease with the
length of the "lead;" and the breadth of the end of the
bank; and the number of "sets" should be increased at
certain exact periods in the progress of the work, which
are susceptible of mathematical determination.*
* These points are very clearly and fully examined in " Le. sa f Ex.
cavation and Embankment on Railways," London, 1840.