High-Capacity Auger Pressure-Grouted Piles to Support a Multi-Family Tower in Downtown Philadelphia-PPT Presentation

PPT Presentation

Pdf Summary

The 500 Walnut Street project used high-capacity auger pressure-grouted (APG) piles to support a 26-story multifamily tower near Independence Hall in Philadelphia. The site overlies historic Dock Creek, which was filled in the late 18th century. Subsurface conditions include fill to about 23 feet, alluvial soils to 78 feet, and decomposed or weathered mica schist from roughly 78 to 90 feet. Groundwater was encountered at 23 feet.<br /><br />Drilled shafts were initially selected for their high capacity and ability to resist compression, uplift, and lateral loads. Value engineering led to APG piles, which offered installation advantages and had demonstrated high capacities in similar local geology. Piles were designed to extend into weathered rock. The design used 5,000-psi grout to achieve the required 200-ton compressive capacity. Two pile types shared the same dimensions and grout strength but differed in reinforcement, depending on whether tension resistance was required.<br /><br />The load-test program included compression testing to 500 tons—2.5 times the design load—and tension testing to 200 tons, twice the design load. Results showed generally linear load-displacement behavior for piles socketed in weathered rock and bearing on intact rock. Lateral testing informed the soil model and subsequent analysis of pile groups, with group effects considered where spacing was less than eight pile diameters.<br /><br />Production averaged 10–15 piles per day. In total, 263 piles were installed: 249 for the building and 14 for the tower crane. Challenges included out-of-tolerance locations, broken tooling, and refusal depths beyond the tooling’s reach. The project demonstrated that APG installation can penetrate difficult geomaterials and provide a cost-efficient, high-capacity foundation solution, supported by load testing and growing case-history evidence.

Keywords

500 Walnut Street

APG piles

auger pressure-grouted piles

Philadelphia

Independence Hall

deep foundations

load testing

weathered mica schist

foundation engineering

multifamily tower