When the side-slope of the ground on which an embankment is to be formed is very steep, the whole work has a tendency to slip laterally; and to prevent this, trenches or steps are cut in the ground before putting in the embankment. When the material is' very wet, it sometimes is impossible to prevent the slopes from bulging out, in which case it is generally sufficient to put in additional stuff until the work stands. Peat-moss is seldom used to form an embankment, but frequently an embankment has to be formed where thp ground below is moss to a considerable extent. In this case, many plans have been adopted to form a substantial, unyielding work, which, where the moss is deep, and contains much water, is often very troublesome and expensive. Among these, per Imps, in most cases, the best is to continue throwing in earth until no further subsidence takes place. In some cases, piling has been adopted, and in others, a layer of tree-tops and brushwood has been placed on the moss under the embankment. When this is done, it frequently happens that the ground on each side of the embankment opens in great rents, rises to a considerable height, and moves laterally from the embankment. A good example of this may be seen on the Scottish Central railway, a short distance to the s. of the Bridge of Allan station.
Embankments, when finished, have their side-slopes usually covered with soil and sown with grass-seed; this not only improves their appearance, but adds considerably to their stability, preventing rain and wind from doing the damage that might otherwise take place.
In regard to embankments to restrain or prevent the encroachment of water, it is necessary, in addition to forming them of sufficient height and strength, to cover the surface of the slopes in such a way that the action of the water will not affect it. Of course the method adopted must depend entirely on the nature of the case; where, for example, the water only occasionally touches the embankment, as in the case of river floods, and does not run with great violence along it, good turf pinned to the slopes has been found effectual. Where, however, the slopes are subject to the action of waves or rapid water, more effectual and expensive measures must be adopted, such as stone pitching, piling, etc. Embankments of this nature are used on a great scale in Holland.
See DYKE.
Embankments for damming up water so as to form ponds or reservoirs, require, in addition to the. other conditions, to be perfectly water-tight; and for this purpose a " puddle-wall" of clay is carried from top to bottom in the heart of the structure. The great difficulty lies in preventing the water from finding its way between the bottom of the puddle-wall and the foundation on which it rests, or even through the substances of which that foundation consists; and the wall must often be carried to a great depth below the surface of the ground until an impermeable stratum be found. A knowledge of the geology of the place is here essential to the engineer.