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

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The redevelopment of 1600 Smallman Street in Pittsburgh’s Strip District combined historic-building renovation with construction of a new five-story retail and parking structure. Ground conditions were uncertain because site borings were limited, and the former industrial site contained variable fill, buried foundations, cobbles, and boulders.<br /><br />Continuous Menard-modulus columns (CMCs), or rigid inclusions, were selected to support the new structure. Design and construction required coordination to address existing building foundations, eccentric loads, and limits imposed by an adjacent city alley and utilities. A compression test on an 18-inch-diameter CMC reached 388 kips, exceeding the 155-kip test target; measured settlement was about 0.3 inches at maximum load.<br /><br />Helical piles were initially chosen for stairwells, elevator shafts, and a garage ramp inside the existing building, where low overhead restricted equipment access. Cobbles and variable bearing conditions complicated installation. Load tests showed net settlement of 0.29 inches at the 30-kip design load, above the project’s 0.2-inch limit. The design load was therefore reduced to 24 kips per pile, and additional piles were added. About 62 helical piles were installed.<br /><br />At Stairwell D, cobble removal threatened the existing slab, so the team substituted micropiles, which could penetrate the obstructions and transfer loads to bedrock. Twenty micropiles were installed under similarly restricted working conditions. Their test reached 80 kips—twice the design load—with less than 0.25 inches of total deflection and 0.03 inches of net settlement.<br /><br />The project demonstrates how collaboration among the owner, engineers, general contractor, and specialty contractors enabled changes in foundation methods to address unforeseen conditions while meeting performance requirements.

Keywords

1600 Smallman Street

Pittsburgh Strip District

foundation redevelopment

continuous Menard-modulus columns

rigid inclusions

helical piles

micropiles

historic building renovation

poor ground conditions

load testing