A Treatise On The Principles And Practice Of Dock Engineering

PRACTICAL POINTS. jgj of stability has proved useless. The stability of a wall depends to as large an extent upon the immobility of its foundation as upon its own inherent resistance to overturning. The importance of adéquate drainage, in this connection, has already been alluded to. Where springs or other sources of continuous flow are met with during the building of the wall, they should be conducted to some suitable vent where they may escape freely. Any attempt at repressing them will only result in an outburst elsewhere. Infiltrations of water into the foundation should be dealt with by a temporary drain at the base of the wall leading to a pumping well. With the same object in view, the filling behind a wall for a thickness of 2 feet or so will advisedly be composed of packed rubble stone and broken brick, the interstices of which will act as conduits for subsoil water leading to weep-holes, or outlets, running through the wall at stated intervals. These weep-holes may be formed by drain pipes of from 4 to 9 inches diameter, and they will generally be placed at distances of from 50 to 100 feet, according to the nature of the backing. Fig. 106.—Old Lock Wall at Leith (1806). Fig. 107.—Quay Wall at Sheerness. In order to derive as much benefit as possible from the cohésion of the particles, the earth backing should be carefully punned in 12-inch layers, and well watered to ensure thorough consolidation. Offsets in the back of the wall, for the purpose of reducing its thickness, should be narrow and shallow, in preference to being broad and deep, par- ticularly in cases where the foundation is at all unsatisfactory, as the former arrangement is conducive to greater uniformity of pressure. The batter usually assigned to a wall, when the face is not plumb, varies between 1 in fe and 1 in 24. A battering face to a wall naturally increases its stability, but, at the same time, it detracts from its efiiciency. Modern ships have vertical sides with an upper “tumble home,” or inward inclina- tion, so that the advisability of, and even the necessity for, walls with plumb