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March 2004: Caissons completed, Piers 37 & 38
The last phases of caisson construction involve a) filling the bottom 30 feet (9.1m) of the caisson with concrete; b) covering the dredge wells with concrete covers; c) topping the upper caisson with a beveled concrete distribution cap.
A 230-foot long pipe known as a trimie, with a hopper at the top, is used to place 30 feet (9.1m) of concrete at the bottom of the caisson. By using the trimie method, water is displaced by the concrete and the overall mass of concrete is uncontaminated by water.
With the seal pours complete, dredge wells on Pier 37 are covered with round concrete covers 15 feet (4.5m) in diameter and 2-1/2 feet (76cm) thick. The covers can be seen beneath the rebar for the distribution cap at Pier 37.
A worker ties rebar into place for the 15-foot (4.5m) thick concrete distribution cap.
Workers tie rebar into place for the 15-foot (4.5m) thick concrete distribution cap.
Workers tie rebar into place for the 15-foot (4.5m) thick concrete distribution cap that will top Pier 37. Note how the rebar is angled to create a beveled edge.
The distribution cap is poured in two lifts, 6 feet (1.8m) and 10 feet (3m) deep. Here, the first lift is complete. Concrete will be introduced for the second lift through the orange hopper pipes.
The completed distribution cap at Pier 37 is seen surrounded by the "follower cofferdam" structural steel framework. The steel reinforcing bars protruding from the top of the distribution cap define the starting point for the graceful 400-foot tall (122m) tower that will support the bridge spans.
The beveled top of the distribution cap.