Active Soil Nail Wall Underpinning Solution for the Bruce Museum Project-Technical Paper Upload

Technical Paper Upload

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The Bruce Museum expansion in Greenwich, Connecticut, required new foundations as much as 16 feet below the existing building’s shallow footings. Traditional underpinning was judged hazardous and complex because of highly variable soil and bedrock, sloping rock, heavy building surcharges, and the need for multiple excavation and support stages.<br /><br />As an alternative, Geosciences Testing and Research designed a permanent “active” soil nail wall installed slightly in front of the existing foundations. The system supported the surrounding ground and building surcharge while allowing excavation to proceed to the new foundation elevations. Soil nail lengths and positions could be adjusted as conditions were exposed. Nails were preloaded and locked off at 50% of design load to limit the wall movements typical of passive soil nail systems. The design used up to four rows of corrosion-protected nails, a reinforced shotcrete facing, and conservative assumptions about soil strength.<br /><br />Construction was carried out in shallow, short excavation sequences to limit ground loss and disturbance. Drilling methods were selected to reduce vibration and soil loss, and excavation methods protected the ground beneath existing footings. Because rock elevations and site conditions varied, the team used the observational method: engineers inspected work daily and adapted the nail layout as needed.<br /><br />Performance was checked through nail verification and proof testing, along with automated, near-real-time deformation monitoring of the wall and museum using robotic total stations. Monitoring showed minimal movement of the existing structure, and testing confirmed that soil and rock bond stresses were consistent with design assumptions.<br /><br />The project demonstrated that an actively preloaded soil nail wall can provide a safe, efficient alternative to traditional underpinning where existing structures must be protected amid complex ground conditions. Close coordination among designers, contractors, and the project team, supported by monitoring and field adjustments, was central to its success.

Keywords

Bruce Museum

Greenwich Connecticut

soil nail wall

active preloaded system

underpinning alternative

foundations excavation

shotcrete facing

ground monitoring

observational method

foundation support