Using Rigid Inclusions, Helical Piles and Micropiles to Revitalize 1600 Smallman Street-PPT Presentation

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The 1600 Smallman Street project involved a five-story parking garage in Pittsburgh’s Strip District, near the Allegheny River. The site’s soils consist of variable fill over alluvial sandy clay and sand and gravel. Low overhead clearance and the need to support nearby condominium elevator shafts and stairwells shaped the foundation work.<br /><br />The garage was initially designed with 107 reinforced, 16-inch-diameter auger-cast-in-place piles extending about 65 feet. Menard proposed an alternative of 136 controlled modulus columns (CMCs), 12 and 18 inches in diameter, averaging 35 feet deep. Right-of-way constraints, a small site, other active trades, and grout delivery required close coordination. The source material notes a CMC load test but provides no results.<br /><br />Magnum Piering installed helical piles to support two elevator shafts, two stairwells, and a garage ramp. Three load tests were conducted. Strict settlement limits applied: 0.2 inches net settlement at design load and 1 inch total settlement at ultimate load. Test results showed 0.29 inches net settlement at design load, so additional piles were added to meet the criteria.<br /><br />Nicholson Construction installed micropiles beneath one stairwell where obstructions prevented helical-pile installation. Because rock elevation varied and nearby borings were limited, final pile lengths were determined in the field; the piles reached 65 feet. The design used a 40-kip load, a 5-foot bond length in siltstone, steel casing and reinforcing bar, and 4,000-psi grout. Installation required modifications to the drill mast for low clearance, and cobbles slowed drilling on some piles.<br /><br />The maintained micropile load test held 80 kips—200% of design load—for 12 hours. It met all acceptance criteria, with 0.03 inches net settlement, 0.25 inches total settlement, and no plunging failure.

Keywords

1600 Smallman Street

Pittsburgh Strip District

parking garage foundation

auger-cast-in-place piles

controlled modulus columns

helical piles

micropiles

settlement criteria

load testing

siltstone bond length