Abstract:
The Riverwalk development is located on one of the last remaining development parcels along Philadelphia's Schuylkill River waterfront. When complete, the mixed-use community will feature two residential towers connected by a pedestrian bridge. Over 100,000 sf of floor space will be generated for the rapidly growing Center City district.
Keller collaborated with the project team on the deep foundation design for the mixed-use podium and 28 and 32 story high-rise structures. The anticipated 6500-kip tower column loads drove preliminary drilled shaft foundation designs to lengthy 8-foot diameter rock sockets founded in Philadelphia's Wissahickon Formation. The differential weathering of the mineral layers in the foliated schist and banded gneiss commonly cause hard layers to occur over soft layers. This complexity of the formation often leads designers to use conservative end bearing and skin friction design parameters, thus necessitating larger shaft diameters and/or longer rocksockets. To help meet Pro forma project financials, Keller's primary objective was to quantify and maximize end bearing and side resistance in this challenging geologic environment. Keller executed two full-scale drilled shaft load tests. A key element in Keller design approach was to increase the allowable end bearing capacity from the “presumptive†values historically used in this neighborhood. More specifically, Keller's design engineer modeled a potential “punch out†failure at the shaft bottom.
The successful load test program substantiated use of significantly higher end bearing and side resistance values thought never used in this formation; a knockout punch for the project team! The collaborative efforts of the Owner's geotechnical (Langan) and structural (Thornton Tomasetti) engineers together with Keller and our geotechnical-structural foundation design consultant (Foundation Test Group) were essential for the technical and commercial success of the project.Panel presentation:
- Martin McDermott, PG
- Jeffrey Goodwin, PE
- John McElroy, PE
- Frank Cocuzza , PE