Secant Pile Wall Design and Construction for Below Grade Excavation and Construction Adjacent to Operating Rail Line-PPT Presentation

PPT Presentation

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The project involved constructing two levels of underground parking beneath a Boston air-rights development, with a 16-foot excavation only 9–10 feet from active commuter rail tracks. Because the tracks and nearby highway had to remain operational, the excavation support system needed to be stiff and watertight, with movement limits governed by potential track settlement.<br /><br />A secant pile wall was selected to provide temporary excavation support and serve as the permanent basement foundation wall. Rock-socketed drilled shafts were incorporated at every fourth pile to support building column loads. The design team assessed both wall deflection and predicted ground and track movement, and engaged the support-of-excavation designer early to review drawings and calculations and reduce schedule and project risks.<br /><br />Monitoring included inclinometers in the wall and rail targets installed at 15.5-foot intervals. An automated total-station system provided remote, near-real-time track data and alerts when threshold or limit values were reached.<br /><br />The wall performed well: measured movement was approximately 0.5 inch, closely matching the predicted movement of about 0.6 inch. The project highlighted that enabling work and other factors may cause movements that are difficult to predict and can be significant where tolerances are small. It also underscored the need to account for environmental influences on instrumentation, provide redundancy in automated monitoring, interpret alerts carefully, and establish clear communication and response procedures to avoid alert fatigue.

Keywords

underground parking

Boston air-rights development

secant pile wall

excavation support

track settlement

rock-socketed drilled shafts

wall deflection

automated monitoring

inclinometers

basement foundation