Founa'ations in Soft Soil.—In the second order of foundations a soft soil demands the introduction of an artificial bearing-stratinn. In this case the first requirement is a trench of sufficient depth to permit the footing of the walls to reach below the action of rain and frost. The bottom of this trench can be covered with a bed of stones well rammed down and covered with concrete. Sand is also used, and is remarkably well fitted for the pur pose of a foundation-bed, as it distributes the pressure both vertically and horizontally. One of the most common methods of making a foundation bed in loose ground is by driving wooden piles into the soil and buildin,9, the foundation-walls upon them. Straight-grained timbers are required for this purpose, the preferred woods being fir, beech, oak, Florida yellow pine, spruce, and hemlock. A modern substitute for wooden piles, both for economy and service, is the pile made of sand. When the soil is not very loose and wet, holes can be made in the bottom of the trench about 6 feet deep and 6 or more inches in diameter, and filled with damp sand well rammed down, which transmits the vertical pressure over a larger sur face of the underlying soil than can be effected by the use of wooden piles. A bed of masonry or concrete should cover the ground above these piles, to prevent the sand being forced upward, and upon this bed the foundation walls can. be placed.
Concrete Foundations.—In many places concrete is superseding every other form of artificial foundation, because of its cheapness and conveni ence. Ramining of concrete, when thoroughly done, consolidates the mass five or six per cent., rendering- it less porous and very materially strong-er. Concrete has also proved of great utility in the erection of foundations and walls beneath water, modern ingenuity having invented a species of box in which it can be let down into the depths, where a pin drawn out by a rope reaching to the surface permits the side of the box to swing- out an,' deposit the concrete upon the very spot where it is required. Concrete is useful in filling in cavities in rock and in bringing up uneven foundations to a level for the support of masonry. In making foundations in compressi ble soil it is sometimes found possible to extend excavations through it to a firmer stratum beneath, but this often involves great expense.
beginning the foundation-walls of a building, the spreads or footing courses, already mentioned, are of essential import ance as a means of distributing, the weight over an increased surface and diminishing vertical settlement. They should be securely bonded into the body of the work, and of sufficient strength to resist any cross strains to which they may be subjected. Footings of undressed rubble should always be laid in cement plaster to form a solid mass. Bricks used for courses should be of the hardest and strongest quality, and the bottom course should invariably be double. Foundation-walls, always starting- below the
line of frost, should be made as compact as possible. The bottom courses are frequently laid dry, and the rest in cement mortar. When composed of stone, they should never be less than zo inches thick; and if of brick, not less than 12 inches thick. In wooden buildings a foundation-wall, when of brick, is generally 12 inches thick, and when of rubble, 18 inches or more.
Drainage.—As a general term, " drainage " is used to express the Mode in which the waters of a country pass off by its streams and rivers; but when used in connection with building, it is restricted to the drains and sewers by which water is removed from cities and all works erected by builders. The system as adopted for cities and towns is usually distin guished as " sewerage "—a term used also, improperly, to express the material collected and discharged by sewers and drains. For convenience in discrimination, the material collected is now generally termed " sew age." The art of freeing- land from superfluous water by artificial means has long been practised by various methods of ditching. Drains made of tiles have been used most successfully in the reclamation of wet lands, which then become more productive to tillage. A concave bottom for all kinds of drains is found to facilitate the discharge of the contents and pre vent the accumulation of impurities.
modern improvements, drain-pipes of hard vitreous substance are introduced wherever possible, as not being susceptible of any chemical action from the sewage, and as being little affected bv frost. Pipes or hollow cylinders of terra-cotta and well-burnt glazed stoneware make efficient house-drains, and are put together with great accuracy with sockets, so as to fit spigot and faucet fashion, removable tops being arranc.,Y. ed to give access to the interior when required. Modern science has been applied extensively to improvements in drainage, and minute investigation devoted to various questions of foundation, incline, securing action of flow, and every particular of ventilation and security. Estimates of rainfall over given areas have also necessarily entered into the computation of competent supplies of drainage facilities, with careful consideration of all obstacles, both natural and artificial, which present hindrances to effectual service. In using pipes for drains, the capacity should be abundantly large for any possible flow, a bore of not less than 6 inches being advised by some authorities. Among the various drain-pipes now used, the slip-glazed clay pipe is composed of fire-clay glazed with a species of clay called "slip." Other pipes are glazed by the vapor of salt thrown into the fire during the manufacture and chemically uniting with the clay, which vitrifies under the intense heat into a glassy, impenetrable coating.