Risky Business Managed: Up-down Construction in Dense Urban Setting-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes risk management for a 62-story office and residential tower built on Boston’s filled land. The project used deep excavation and “up-down” (top-down) construction, allowing the superstructure to rise while below-ground levels were excavated. A central challenge was limiting movement and other impacts to neighboring properties.<br /><br />The design approach included a slurry-wall support system, temporary dewatering, and analysis of movements caused by permanent building loads. Wall stiffness was important: a modest increase in wall thickness could more than double its moment of inertia. The project also established movement criteria and used detailed design to anticipate excavation and groundwater effects.<br /><br />An independent geotechnical peer review was initiated to address the project’s elevated risks and neighbors’ concerns. Reviewers examined geotechnical reports and soil and rock samples, conducted independent calculations and finite-element modeling, and compared predicted strut loads with empirical estimates. The process was collaborative, involving the developer, engineers, neighbors, attorneys, city officials, and a project neutral. It led to adjustments to the slurry-wall location and a comprehensive instrumentation program.<br /><br />Monitoring included piezometers, crack gauges, tilt meters, seismographs, automated movement targets, water-level measurements, survey points, observation wells, inclinometers, and extensometers. This instrumentation tracked ground, groundwater, and adjacent-building performance during construction.<br /><br />The project’s measured performance was consistent with expectations. The presentation concludes that detailed design and instrumentation are essential for managing deep-excavation risks, while a constructive peer review can ease concerns, add value, and reduce risk.

Keywords

deep excavation

risk management

slurry wall

top-down construction

geotechnical peer review

groundwater monitoring

instrumentation

Boston filled land

movement criteria

finite element modeling