Gowanus Pumping Station: Design and Construction Challenges related to excavation support, seepage mitigation and structure foundation using jet grout bottom seal and deep jet grout support columns.-Paper

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The rehabilitation of Brooklyn’s Gowanus Flushing Tunnel and pumping station required a deep excavation in a congested urban area, with nearby buildings, roads, utilities, and potentially contaminated groundwater. The planned reuse of an old concrete slab supported by timber piles proved unreliable, creating urgent concerns about groundwater inflow, excavation stability, and settlement of the new combined sewer overflow (CSO) chamber extension.<br /><br />Designers adopted a jet-grouted system to provide both temporary seepage control and permanent foundation support. A roughly 15-foot-thick jet-grout bottom plug was combined with a perimeter seal tied into the existing cement-bentonite excavation wall. At least 10 deeper, six-foot-diameter jet-grout columns extended to dense sand to support the completed structure. In total, 84 columns were installed.<br /><br />Construction was complicated by variable fill, buried obstructions, timber piles that could disrupt column continuity, an electrical duct bank, and contaminated ground. The team carefully planned column spacing and wet-in-wet sequencing to ensure overlap and limit gaps, used angled drilling around the duct bank, and incorporated the existing slab and wall into the grout mass. Casings, spoil containment, and off-site disposal helped prevent contamination from spreading and controlled construction waste.<br /><br />Quality assurance included monitoring drilling and grouting parameters, testing grout and spoil, and coring completed columns. Test pits confirmed minimal groundwater inflow before full excavation. The system successfully kept the excavation dry and provided foundation support, demonstrating that thorough planning and quality control can address complex ground and access constraints in dense urban projects.

Keywords

Gowanus Flushing Tunnel

jet-grouted system

deep excavation

groundwater control

CSO chamber

urban construction

foundation support

seepage control

cement-bentonite wall

quality assurance