Accelerated Bridge Construction in Challenging Geology: The Geotechnical Aspects of the Veranda Street Bridge Replacement

This case history details the unique geotechnical solutions utilized to accommodate the foundation challenges associated with the accelerated replacement of the I-295 bridge over Veranda Street in Portland, Maine. The existing three-span structure was replaced with a new shorter single-span bridge over the course of a continuous weekend outage utilizing accelerated bridge construction (ABC) techniques. This strategy required significant substructure and embankment construction beneath the active existing bridge prior to replacement to minimize activities scheduled for the weekend outage. The existing bridge was supported on battered H-pile foundations driven through up to 60 ft (18 m) of soft Presumpscot Formation marine clay. Settlement using normal-weight embankment material was estimated to exceed 6 in. (152 mm) but needed to be mitigated to avoid inducing bending in existing battered piles, which could otherwise result in deflection or damage to the piles supporting the active bridge above. Low-clearance operations and a deep and sloping bedrock bearing layer further complicated construction. A combination of deep foundation and lightweight embankment options was selected to address the project challenges and prepare the site for the ABC weekend closure. The construction phase quality assurance testing program identified the potential for variability in expanded polystyrene backfill (a.k.a. EPS geofoam) and fortified the need for a rigorous construction-phased testing program on all EPS projects beyond vendor quality control testing and third-party verification. This case history shares considerations and measures taken to successfully construct embankments and substructure beneath active bridge spans. Additionally, the case history examines the EPS testing program implemented during construction to address variability in the properties of delivered EPS fill.