Civil and Building Engineering.

The design of every foundation presents a unique challenge to the engineer.

Designs must take into account the nature and cost of the structure, geology and terrain, quality of subsurface investigation, kind of agreement with the owner, loadings over the life of the structure, effects of the proposed construction on buildings near the construction site, sensitivity of the proposed structure to total and differential settlement, requisite building codes, potential environmental effects due to the proposed construction including excessive noise, adequacy of the analytical tools available for making the design, result
of a failure in terms of monetary loss or loss of life, availability of materials for foundations, and competent contractors in the area. A considerable effort will normally be necessary to gather and analyze the large amount of relevant data.

To create foundations that perform properly, the engineer must address carefully the topics in the above list and other relevant factors. Failures will occur if the foundation is not constructed according to plan and in a timely manner, if detrimental settlement occurs at any time after construction, if adjacent buildings are damaged, or if the design is wasteful.

The topic of designing wasteful foundations is of interest. An engineer could cause more than necessary resources to be expended on a foundation in the absence of peer review. An engineer increases the size of a foundation because the extra material gives a measure of ‘‘pillow comfort.’’ An engineer in a firm was asked to describe the technique being used to design the piles for an important job and replied: ‘‘We use an approximate method and always add a few piles to the design.’’ Such failures may never be seen, but they are failures nevertheless.

Casagrande (1964) wrote of calculated risk in earthwork and foundation engineering and gave several examples of projects where risk was used in the design and construction of major projects. Risk is always involved in geotechnical engineering because of the inability to get good information about the factors listed above and because of that sometimes unusual behavior of soil that cannot be anticipated in spite of diligence. Risk is minimized by prudent engineers who use available tools and techniques and who stay
abreast of technological advances.

Peck (1967) presented a keynote address at a conference where the emphasis was on improved analytical procedures. He gave five sources of error with regard to the bearing capacity and settlement of foundations: (1) the assumed loading may be incorrect; (2) the soil conditions used in the design may differ from the actual soil conditions; (3) the theory used in the design may be wrong or may not apply; (4) the supporting structure may be more or less tolerant to differential movement; and (5) defects may occur during construction. The technical literature is replete with examples of foundations that have failed, many for reasons noted by Peck.

The following sections present brief discussions of some examples, emphasizing the care to be taken
by the engineer in planning, designing, and specifying methods of construction of foundations.

Lacy and Moskowitz (1993) made the following suggestions concerning deep foundations: understand the subsurface conditions in detail; select a qualified contractor; take care in preparing specifications for construction; provide full-time inspection by a knowledgeable person who has the necessary authority; and monitor adjacent structures as construction progresses.