Foundations


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Foundations

Structures or other constructed works are supported on the earth by foundations. The word “foundation” may mean the earth itself, something placed in or on the earth to provide support, or a combination of the earth and the elements placed on it. The foundation for a multistory office building could be a combination of concrete footings and the soil or rock on which the footings are supported. The foundation for an earth-fill dam would be the natural soil or rock on which the dam is placed. Concrete footings or piles and pile caps are often referred to as foundations without including the soil or rock on which or in which they are placed. The installed elements and the natural soil or rock of the earth form a foundation system; the soil and rock provide the ultimate support of the system. Foundations that are installed may be either soil-bearing or rock-bearing. The reactions of the soil or rock to the imposed loads generally determine how well the foundation system functions. In designing the installed portions, the designer must determine the safe pressure which can be used on the soil or rock and the amount of total settlement and differential settlement which the structure can withstand.

The installed parts of the foundation system may be footings, mat foundations, slab foundations, and caissons or piles, all of which are used to transfer load from a superstructure into the earth. These parts, which transmit load from the superstructure to the earth, are called the substructure (see illustration).

Examples of foundation systemsenlarge picture
Examples of foundation systems

Footings or spread foundations are used to spread the loads from columns or walls to the underlying soil or rock. Normally, footings are constructed of reinforced concrete; however, under some circumstances they may be constructed of plain concrete or masonry. When each footing supports only one column, it is square. Footings supporting two columns are called combined footings and may be either rectangular or trapezoidal. Cantilever footings are used to carry loads from two columns, with one column and one end of the footing placed against a building line or exterior wall. Footings supporting walls are continuous footings.

Mat or raft foundations are large, thick, and usually heavily reinforced concrete mats which transfer loads from a number of columns or columns and walls to the underlying soil or rock. Mats are also combined footings, but are much larger than a footing supporting two columns. They are continuous footings and are designed to transfer a relatively uniform pressure to the underlying soil or rock.

Slab foundations are used for light structures wherein the columns and walls are supported directly on the floor slab. The floor slab is thickened and more heavily reinforced at the places where the column and wall loads are imposed. See Caisson foundation, Retaining wall

References in classic literature ?
Having exterminated the leaders, and turned their partisans into his friends, the duke laid sufficiently good foundations to his power, having all the Romagna and the Duchy of Urbino; and the people now beginning to appreciate their prosperity, he gained them all over to himself.
Yet there were in the duke such boldness and ability, and he knew so well how men are to be won or lost, and so firm were the foundations which in so short a time he had laid, that if he had not had those armies on his back, or if he had been in good health, he would have overcome all difficulties.
So too, like Voltaire in his time, uninvited defenders of the law of inevitability today use that law as a weapon against religion, though the law of inevitability in history, like the law of Copernicus in astronomy, far from destroying, even strengthens the foundation on which the institutions of state and church are erected.
In fact, the reefs extend only to that distance from the shore, at which a foundation within the requisite depth from 20 to
We have seen that we are driven to believe in the subsidence of those vast areas, interspersed with low islands, of which not one rises above the height to which the wind and waves can throw up matter, and yet are constructed by animals requiring a foundation, and that foundation to lie at no great depth.
At this day it cannot but strike us as extraordinary, that it does not appear to have occurred to any one member of that assembly, which had laid down in terms so clear, so explicit, so unequivocal, the foundation of all just government, in the imprescriptible rights of man, and the transcendent sovereignty of the people, and who in those principles had set forth their only personal vindication from the charges of rebellion against their king, and of treason to their country, that their last crowning act was still to be performed upon the same principles.
It would be worth the while to build still more deliberately than I did, considering, for instance, what foundation a door, a window, a cellar, a garret, have in the nature of man, and perchance never raising any superstructure until we found a better reason for it than our temporal necessities even.
In a word, they did not appear to me to be beginning at the bottom, on a real, solid foundation, to the extent that they were at Hampton.
To this catalogue of circumstances that tend to the amelioration of popular systems of civil government, I shall venture, however novel it may appear to some, to add one more, on a principle which has been made the foundation of an objection to the new Constitution; I mean the ENLARGEMENT of the ORBIT within which such systems are to revolve, either in respect to the dimensions of a single State or to the consolidation of several smaller States into one great Confederacy.
He came over with the first settlers, and had been the intimate companion of all those excellent and famous men who laid the foundation of our country.
This father, Noel Collins, had been a successful animal trainer in England, before emigrating to America, and in America he had continued the success and laid the foundation of the big animal training school at Cedarwild, which his son had developed and built up after him.
No more I do, my dear; but then, you know, there must be some foundation.

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