GROUND IMPROVEMENT IS RARELY A ONE-SIZED FITS ALL SOLUTION: A Case Study on Ground Improvement at a Pennsylvania Distribution Center Site-PPT Presentation

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A proposed 1-million-square-foot warehouse in Olyphant, Pennsylvania, was planned on former strip-mining land with major grade changes, up to 50 feet of moisture-sensitive mine spoil, soft soils, localized trapped water, and historic underground mines. Heavy rainfall before construction further saturated the ground. The project required ground capable of supporting 4,000-psf allowable bearing pressure and 500-psf floor loads.<br /><br />The initial plan called for dynamic compaction across most of the site, settlement monitoring beneath thick fills, and grouting to address potential mine subsidence. Field conditions prompted adjustments: exceptionally soft, saturated soils and deep craters in two areas required aggregate piers instead of dynamic compaction. The completed program combined dynamic compaction, aggregate piers, mass earthwork, settlement monitoring, and targeted deep-mine grouting.<br /><br />Dynamic compaction treated about 900,000 square feet using a 15-ton weight dropped from 60 feet. Average post-treatment blow counts increased 47% across the upper 25 feet of mine spoil. Aggregate piers were designed either to limit building settlement or to reinforce and improve drainage beneath a deep embankment. Settlement monitoring in areas with 25–40 feet of fill recorded about 1.5–2 inches of settlement, leveling off after roughly 90 days—below the anticipated maximum of three inches. Investigation found mostly collapsed mine roofs, so only about 30 cubic yards of grout were needed.<br /><br />The project highlights that ground improvement must respond to actual subsurface conditions rather than rely on a single treatment method. Thorough geotechnical assessment, collaboration among the project team, settlement compatibility, and a stable working platform were essential. Managing water was also a major construction challenge.

Keywords

warehouse construction

ground improvement

dynamic compaction

aggregate piers

mine spoil

geotechnical engineering

settlement monitoring

mine subsidence

strip-mining land

moisture-sensitive soils