Subsurface Savings

by S. V. Nathan, Assoc. Partner; Woodward-Clyde Consultants, Plymouth Meeting, PA,


Serial Information: Civil Engineering—ASCE, 1988, Vol. 58, Issue 1, Pg. 68-70


Document Type: Feature article

Abstract:

Less conservatism than usual in designing building foundations is being accepted or demanded by some owners to save money. The article describes four examples of cost-cutting innovations, some of which reduce factors of safety and/or increase building subsidence. An office building in the marshland of the Meadowlands across the Hudson River from New York City, was knowingly designed to eventually settle 9 in., yet it is likely the building will not suffer unacceptable damage. A 24 story hotel/condominium in Philadelphia was knowingly designed for twice the usual 6 tsf bearing pressures on the spread footing foundations; settlements are expected to be no more than 2 in., and to be acceptable. In Atlantic City a 37 story condominium tower was designed with a hybrid foundation having both a concrete mat and short piles. This is thought to be the world's first such foundation in sand. Finally, a building was designed to be founded on caissons socketed in bedrock. In the traditional design approach, load transfer is assumed to take place into the rock only through the drilled caisson's bottom. It was possible to design for bearing pressures twice as high as usual, by taking into account load transfer that also takes place through the sides of the rock socket.

Subject Headings: Building design | Foundation design | Rocks | Pile foundations | Load transfer | Load factors | Load and resistance factor design

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