Active Soil Nail Wall Underpinning Solution for the Bruce Museum Project-PPT Presentation

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The Bruce Museum in Greenwich, Connecticut, undertook a $60 million expansion that included a three-story, 43,000-square-foot addition. Because excavation near the existing building required support cuts of up to 16 feet, the original plan for traditional underpinning presented safety concerns, especially given nearby foundations and sloping bedrock.<br /><br />Geosciences Testing & Research proposed an active soil nail wall as a safer alternative. The design accounted for building and soil surcharge loads, seismic conditions, and variable rock elevations. Soil nails were pre-stressed and fitted with corrosion-protection components. The final system used nails on a four-foot grid, 22–27 feet long, with #10 Grade 75 threadbars and a six-inch reinforced shotcrete facing. A rock shelf was formed where the wall reached competent bedrock.<br /><br />Construction measures included limiting excavation lifts to four feet, adjusting nail installation sequences in vulnerable areas, and installing the facing reinforcement and shotcrete on the same day as excavation. Nails were verification-tested before construction, and proof tests were conducted on 5% of production nails, with at least one test per row. Shotcrete panels were tested for compressive strength, and the wall was continuously inspected.<br /><br />Two automated monitoring systems measured movement of the existing building every two hours, with results available to the project team in real time. The wall accommodated changing rock and excavation conditions, including cuts reaching as much as 20 feet in one area.<br /><br />The project demonstrated that active soil nailing can provide permanent support, resist substantial surcharge loads, and limit deflection while reducing worker risk. Clear communication, ongoing monitoring, and engineering judgment helped adapt the design and construction to site conditions.

Keywords

Bruce Museum

Greenwich Connecticut

expansion project

soil nail wall

excavation support

underpinning alternative

shotcrete facing

geotechnical engineering

structural monitoring

corrosion protection