Suspension Underpinning of A Waterfront Chemical Facility-Paper

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The paper describes rehabilitation of an early-20th-century chemical facility dock on the Delaware River in Philadelphia. The approximately 500-foot timber relieving platform had deteriorated, and excavation was needed to replace its decking and build new structures. The facility had to remain operational, with chemical-transfer equipment and utilities kept in service and movement limited to about 6 mm.<br /><br />Conventional underpinning was impractical because the existing timber deck had limited capacity, the underlying marine soils were soft, the site was crowded with active equipment and utilities, and construction was constrained by tides. After evaluating alternatives such as pit underpinning, micropiles, and grouting, the project team selected suspension underpinning.<br /><br />The method supported structures from above rather than from below. Steel beams, anchors, driven piles, and—in some locations—the existing seawall carried loads while foundations and soil beneath were excavated. Hydraulic jacks lifted and shimmed the structures before excavation to prevent immediate settlement. The adaptable system supported pipe-support footings, containment slabs, sump pits, strip footings, a steel tower, and other equipment. Designs were modified as excavation revealed differences from historical drawings and as construction requirements changed.<br /><br />Work took place at an active, confined facility, with tidal conditions limiting some tasks to roughly four hours per shift. Construction also required coordination with plant operations, vessel traffic, hot-work restrictions, and rehabilitation of the existing timber piles.<br /><br />The project demonstrates that suspension underpinning can provide a practical alternative where conventional methods are restricted by weak existing foundations, sensitive utilities, soft ground, or limited working space.

Keywords

rehabilitation

chemical facility

Delaware River

suspension underpinning

timber relieving platform

excavation

micropiles

marine soils

hydraulic jacks

active utilities