Foundation Design Principles and Practices
Builders have long recognized the importance of a solid foundation, and that the integrity of a structure can be no greater than that of its foundation. If a foundation fails, the overlying structure fails with it. These truths were especially evident in Palladio’s renaissance Venice, where heavy masonry structures were being built on small islands in a lagoon underlain by very soft soils. In addition, as Palladio observed, defects in the foundation are very difficult to repair after the structure has been built. Thus, well-designed and well- constructed foundations continue to be an essential part of successful construction.
However, foundations can also be very expensive, so over-designed foundations are needlessly wasteful and inefficient. Our goal is to provide sturdy foundations that properly support the superstructure, while avoiding costly over- design. The methods of doing so form the subject of this book.
Foundations are structural elements that transfer loads from the superstructure to the underlying soil or rock. A structure may be supported on a system of individual foundations, or on a single large foundation. Engineers classify foundations into two broad categories: shallow foundations and deep foundations, as shown in Figure 1.1.
Shallow foundations transmit the structural loads to the soils immediately beneath the foundation, and are discussed in Chapters 6 to 11.
The most common type is a spread footing,which spreads the applied load over a sufficiently large area to maintain soil stresses within tolerable limits. Spread footings are easy and inexpensive to build, and are most often used to support small to medium size structures on sites with good soil conditions. Typically, each column has its own spread footing, although sometimes multiple closely- spaced columns are supported on a single footing. Thus, a building might have dozens of individual footings.
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