Abstract:
This paper discusses design experiences with deep foundations relevant to projects performed since 1990 in the Philadelphia metropolitan area. The geology in the Philadelphia metropolitan area is varied, but mostly the area is underlain by Wissahickon Formation schist.Foundation types were considered by reviewing various options such as spread footing and deep foundations. Spread footings were selected where competent rock and/or soil overburden were shallow. Also, ground improvement of the overburden soils using an earth surcharge load and wick drains to induce consolidation settlement enabled the use of spread footings placed on the deep deposits of clay, sand, and gravel. The types of deep foundations used are end bearing steel piles (frequently HP 12x74), drilled shafts with H-Piles seated into bedrock or driven into decomposed rock, and friction piles, such as concrete-filled pipe piles with conical points. Alternative foundation systems were studied and compared with the finally selected and constructed foundations. For all cases, in addition to spread footings, other types of deep foundations, such as monotube piles were considered.Designs considered issues such as ultimate and allowable values, settlement, negative skin friction, downdrag, uplift capacity, lateral movement, pile buckling, etc.
In addition to geotechnical issues, space limitations and work time restrictions had to be addressed/complied during onsite design and construction activities in Philadelphia's congested city environment, which is heavily trafficked by both vehicles and pedestrians. The foundation designs have to address the construction of the foundation in a metropolitan environment, such as placement of pile foundations for an active elevated railroad, or in busy highways. This paper will discuss the projects that were completed in the City of Philadelphia, the Philadelphia International Airport access and departure routes, South Street bridge replacement, and the Commodore Area Bridge Ramp extension.