Two Miles of Anchored Bulkhead Supports Howard Frankland Bridge Megaproject-Paper

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The Howard Frankland Bridge project required two bulkheads totaling more than 11,000 ft (3,350 m) to create land for a new 3.2-mile (5.1-km) I-275 bridge across Tampa Bay. A total of 1,287 permanent, double-corrosion-protected grouted soil anchors supported the sheet-pile and combi-wall structures, which in places retained 20-ft (6.1-m) embankments. Anchors ranged from three to eight strands and reached lengths of 200 ft (60.1 m).<br /><br />Design and construction were complicated by highly variable karstic limestone, including changes of nearly 100 ft (30.5 m) in its elevation. Larger anchors had to bond into the limestone, while the uncertain geology made anchor lengths and loads difficult to predict. A three-dimensional model of the limestone surface helped tailor each anchor’s length and orientation, avoid existing and planned structures, and reduce overdesign. Settlement from embankment construction was also considered because it could increase anchor loads.<br /><br />Most drilling took place from barges, with some work completed from land where access was restricted. Tidal fluctuations and wave action limited when crews could weld the waterside walers and connections, and weather also affected anchor testing. Tight spatial constraints required many anchors to be skewed or inclined to avoid conflicts while maintaining adequate clearance between bond zones.<br /><br />All anchors were tested to the required design criteria and locked off at 80% of service load. More than 99.5% passed proof, performance, or creep testing without issues—an exceptional result in the area’s karstic geology. The project demonstrates the value of detailed three-dimensional modeling and close coordination between designers and field crews on large marine anchoring projects.

Keywords

Howard Frankland Bridge

bulkheads

I-275 bridge

Tampa Bay

soil anchors

sheet-pile

combi-wall

karstic limestone

three-dimensional modeling

marine anchoring