Replacing an Urban Foundation

by George B. Morschauser, (M.ASCE), Vice Pres.; ICF Kaiser Engineers, Part of the DKP Joint Venture Engineers, Baltimore, MD,
James E. B. Davis, Project Engr.; Nicholson Construction, Frederick, MD,

Serial Information: Civil Engineering—ASCE, 1990, Vol. 60, Issue 12, Pg. 58-60

Document Type: Feature article


Baltimore's new subway extension will pass close to a 6-story reinforced concrete building near the Inner Harbor. Its timber piling foundation was threatened by the dewatering necessary for subway construction, and plans were made for conventional underpinning. The specialty contractor instead used pin piles, which are typically 6-10 inches in diameter and up to 200 ft long. The pin piles would limit the undermining required at any one time to stabilize the building. Installation was done in four phases: 1) mass excavation with small equipment; 2) drilling the casing, placing rebar and grouting to 100 psi; 3) hand excavation below existing caps; and 4) installing new reinforced concrete caps. Pumping all concrete solved problems of limited work areas and restricted access, but several instant engineering decisions had to be made. One decision transferred the load from an overloaded existing column via a needle beam; another redesigned the new cap after a timber and stone mat was discovered under an existing cap. Extensive tests were carried out, and recorded settlements were less than a half-inch.

Subject Headings: Reinforced concrete | Urban areas | Foundations | Subways | Wood | Piles | Excavation | Existing buildings

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