Cooperative Effort Overcomes Problems with Pier and Cofferdam Construction Caused by Rock Slope-PDF

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The replacement of Rochester’s Stutson Street Bridge was complicated by unexpectedly steep, weak shale beneath Pier 1. The rock slope across the pier site was 42 degrees rather than the anticipated 12 degrees, creating a 13-meter elevation difference across the cofferdam and making the original stepped rock foundation impractical.<br /><br />The initial response was to redesign the cofferdam for deep excavation. This required stronger master-pile walls, rock anchors, extensive underwater bracing, and difficult drilling into the shale. The owner then redesigned the pier foundation: instead of a footing stepped into the rock, the pier would rest on 24 drilled shafts socketed into the rock beneath a large tremie-concrete seal.<br /><br />Construction shifted from a largely land-based operation to a complex water-based one. Crews installed the drilled shafts, built the cofferdam around them, excavated contaminated river sediments, and placed the tremie concrete. Work had to fit within a narrow site bordered by an operating railroad and a navigable river. Equipment also had to clear the channel for commercial freighters, while environmental restrictions limited when river work could occur. Divers often worked in deep, murky water, making installation, cleaning, and cutting operations especially challenging.<br /><br />The redesign and construction required extensive coordination among engineers, contractors, subcontractors, and transportation agencies, with careful attention to safety, constructability, equipment, and material availability. The unforeseen conditions delayed the project by 18 months. Cofferdam-related design, construction, and delay costs rose by nearly $3 million, and the overall contract increase exceeded $10 million. Despite the added time and expense, the collaborative effort produced a safe, reliable foundation and an unusual cofferdam system that enabled the bridge project to proceed.

Keywords

Stutson Street Bridge

Rochester

cofferdam redesign

shale foundation

drilled shafts

tremie concrete

bridge replacement

underwater construction

project delay

transportation engineering