Construction of the Main Tower Pier Caissons for the Greenville Bridge in Mississippi-PDF

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The Highway 82 Bridge near Greenville, Mississippi, features a 1,378-foot cable-stayed main span supported by two deep dredged caissons. Measuring 80 by 122 feet, the caissons were sunk through about 70 feet of water and then excavated to foundations 200 and 170 feet below the river surface. Construction took place in currents reaching 11 feet per second, with substantial changes in river level and challenging soil conditions.<br /><br />Because sand-island construction was unsuitable, the contractor built each caisson as a floating structure and lowered it to the riverbed before sinking it further by excavation. Major innovations helped control the risks: large V-shaped breakwaters created sheltered work areas; articulated concrete mattresses provided rapid riverbed scour protection; specially designed half-cylinder air domes supplied buoyancy during floating and placement; and a guide-pile system controlled caisson position during touchdown.<br /><br />A comprehensive sinking plan coordinated construction sequence, weight, buoyancy, air pressure, river levels, excavation, and soil resistance. This planning enabled crews to anticipate conditions and respond to problems while maintaining control of the operation. The breakwaters, scour protection, air domes, guide system, and sinking plan collectively allowed the caissons to be positioned and constructed successfully despite the demanding river environment. The project’s solutions offered useful approaches for future caisson work on the lower Mississippi River.

Keywords

Highway 82 Bridge

Greenville Mississippi

cable-stayed bridge

caisson foundation

dredged caissons

river construction

scour protection

breakwaters

guide-pile system

Mississippi River engineering