Deflection-Based Design for the Capitol Crossing Support of Excavation-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the support-of-excavation (SOE) design for the Capitol Crossing project, where deep excavations were built near existing structures, including the HRC and Bell Tower. The work involved more than 130,000 square feet of SOE, over 1,300 tiebacks, excavation depths up to 72 feet, and several support and underpinning systems.<br /><br />The design objective was to predict SOE and ground movements reliably enough to limit damage to nearby buildings. The team used a deflection-based approach, considering wall stiffness and movement patterns as well as earth and surcharge pressures. To reduce movement, three tieback tiers were installed within the first 17 feet of excavation, the first tier was placed close to the top of the piles, and tiebacks were locked off at full design load.<br /><br />Monitoring included three-direction survey measurements of building walls, inclinometers attached to piles, and tilt sensors on HRC columns. Measured movements were compared with estimates. Results generally showed reasonable agreement, though movements near the west end of the HRC were lower than predicted, likely because of corner effects. Monitoring also identified unexpected eastward movement of buildings as blocks.<br /><br />The SOE performed well: damage remained within the intended “very slight” to “negligible” range. The presentation emphasizes that SOE stiffness and acceptable building damage must be considered in design, and that further investigation of observed block movements and additional monitored case studies are needed.

Keywords

support-of-excavation

SOE design

Capitol Crossing

deep excavation

tiebacks

ground movement

building monitoring

underpinning

excavation support

wall stiffness