Boston Seaport Parcel P / 400 Summer Street Project Case Study-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes the excavation support system for 400 Summer Street, a 16-story mixed-use development in Boston’s Seaport, built over an I-90 tunnel ramp. The project includes primarily laboratory space and ground-floor retail.<br /><br />The main excavation used a 30-inch slurry wall with load-bearing elements, extending to depths of up to 66 feet and 162 feet, respectively. Two levels of internal bracing included 36-inch cross struts, reinforced-concrete internal wales, and external steel wales. Construction near the existing I-90 westbound tunnel required addressing an existing soil-mix wall and tiebacks extending into the project site.<br /><br />Design analyses used both limit-equilibrium methods and finite-element modeling, including DeepEx and PLAXIS 2D, to evaluate earth pressures, global and base stability, and wall behavior. Site soils included cohesive fill and marine clay. Monitoring showed that slurry-wall deflections generally matched estimates and remained within allowable limits, with three-dimensional effects and uneven loading related to the excavation geometry.<br /><br />The elevator pit required a separate excavation up to 50 feet deep, supported by three bracing levels. Its third-level “super mega brace” was supported by a previously installed mat, which also provided diaphragm action. In the “back of house” area beneath the Summer Street Bridge, existing sheet piles were reused for excavation support after their length and thickness were verified through parallel seismic testing and ultrasonic measurements. The work also involved bracing modifications and planned openings to accommodate construction clashes.

Keywords

excavation support

slurry wall

I-90 tunnel

Boston Seaport

deep excavation

cross struts

finite element modeling

PLAXIS 2D

marine clay

elevator pit