EMBANKMENT, EARTIIIVORK. Embankments, in engineering, are masses of earth, rock, or other materials artificially formed, and rising above the natural surface of the ground. They are chiefly formed either (1) to carry railways, common roads, canals, etc., over depressions of the country; or (2) for hydraulic purposes, such as the forma tion of reservoirs for storing water; or as defenses against the overflowing of rivers, the encroachments of the sea, of lakes, ete.
In the formation of canals, railways, and other roads, embankment and excavation go hand in hand, and, under the name of EARTIIWORK, form-:-especially in modern times, and since the development of the railway system—a vast branch of industry, giving employment to many thousands of laborers, known in England as " navvies." The earthworks executed within the last quarter of a century in Great Britain alone have cost many millions of pounds.
In planning works of the kind alluded to, engineers follow, as much as possible, the principle of making the cuttings or excavations and the embankments balance; i.e., of making the earth, etc., taken from the cuttings be sufficient for the formation of the embankments. See RAILWAYS (ENGINEERING). In proceeding to the actual construc tion of a railway embankment. e.g., a beginning is made at the points where the level of the formation meets the surface of the ground; and on each side of these points the cutting is taken out, and the embankment formed by men using pick, shovel, and bar row, so that a roadway is formed for a distance of from 50 to 100 yards. When the " lead," or the distance between the face of the cutting and the " tip-head," or end of the embankment, is greater than this, it is no longer economical to use the barrow. To continue the cutting and embankment, several methods may be employed; the most common are dobbin carts; small wagons run upon light rails at a narrow gauge, and drawn by men or horses; ordinary earth-wagons drawn by horses, and occasionally by a locomotive; and, lastly, ballast-wagons or trucks drawn by a locomotive. The cost
of earthwork naturally varies greatly with the nature of the strata in which the cutting has to be made, the length of the " lead," and other circumstances. When rocks have to be cut through, blasting (q.v.) is had recourse to. One of the points on which con siderable doubt existed was as to the inclination of the side-slopes of embankments; but it has been found that nearly all kinds of earthwork will stand at an inclination of 1-i horizontal to 1 vertical. When, however, it is necessary to use very wet substances, such as peat-moss or wet clays, or when the embankment is of great height, a flatter slope may be necessary. In many eases, it is.adViAable'to substitute a viaduct (q.v.) for an embankment. All embankments put in as above mentioned subside more or less, the subsidence being much more distinctly perceptible in clay than in gravel. When clay is thrown by the wagon over a considerable tip, the lower half of the embankment will be seen to consist of round bullets of clay of sufficient hardness to resist being squeezed into one mass by the weight of the embankment, until, in the course of time, from the effects of moisture, they become gradually disintegrated, and a settlement or sinking of the embankment takes place, sometimes to the extent of a or even a tenth of the height. The greatest sinking usually occurs during the first wet weather after the formation of the embankment; but it sometimes goes on, though more and more slowly, for years. In the case of railway embankments, this subsidence is seldom of very material importance. If the permanent rails are laid, the labor and expense of restoring them to the level is not great, and the embankment should always be formed sufficiently wide at the top to allow of filling it up to its proper level without adding to the slopes. It is, however, practicable, though rather hazardous, to widen it at the top afterwards by cutting trenches in the slopes.