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August-September 2004: Pier 37 capped, Pier 39 drill shafts under construction
For reference, component parts of the two main bridge towers are shown in this diagram.
Pier 37 - Forms are in place for the pier cap, the final concrete pour on the pier shaft portion of the tower.
Rebar and frames in place prior to concrete pours for the pier cap at Pier 37. Ducts for post-tensioning are visible within the rebar. 19 strands of post-tensioned steel will eventually be threaded through each duct to reinforce the structure.
Pier 37 reaches roadway level as yellow gang forms for pedestal blocks are placed atop the completed pier cap. Roadway elevation is just above the first level of the forms.
Steel reinforcement is very dense at this level. Rebar is set on 6-inch (15cm) centers.
Workers screed and finish the top of the pedestal block at Pier 37. Steel girders for the roadway will sit atop the pedestal block. "Lockup" devices, which act like shock absorbers. will be installed at this level. These devices provide seismic damping and allow for expansion and contraction when temperatures change.
Construction begins on the north leg of the tower at Pier 37.
At Pier 39, on the Mississippi side of the river, workers prepare a cylindrical rebar cage for placement inside one of the 15 drill shafts. Pier 38 is visible behind them.
Pier 39: A crane begins to lift the 16-ton steel rebar cage.
Pier 39: In the first phase of drill shaft construction, 48-foot tall drill shaft casings or "cans" are driven into the ground with a vibratory hammer.
Like a chuck on a drill, the yellow crane attachment turns a 6-1/2 foot (2m) diameter coring bucket, which removes soil and other material from inside the drill shaft casings.
The coring bucket.
The actual drill shaft is 125 feet (38m) deep. During excavation, the shaft is filled with a slurry containing Bentonnite clay. The Bentonnite bonds to the walls of the shaft and holds them in place.
A gauge is lowered into the drill shaft to sample the slurry. Samples are taken at intervals along the shaft from top to bottom.
Slurry can contain no more than four percent sand by volume. An excess of sand could contaminate concrete that is poured into the shaft.
The steel rebar cage is lowered into the drill shaft. The Bentonnite slurry filling the shaft is visible. The slurry is eventually displaced from the drill shaft by the weight of the rebar and concrete.
The steel rebar cage is installed in two sections. An 80-foot (24m) tall section is lowered into the drill shaft first, and a 45-foot (13m) section is spliced onto it. The 120-foot (37m) rebar cage is too heavy for the crane to lift all at once.
A steel rebar cage is lowered into a drill shaft.
Concrete is placed into the drill shaft through a hopper standing over the shaft. The tremie pipe that guides the concrete into the shaft is visible below.
A concrete bucket places concrete into the tremie hopper.
The Pier 39 site in September 2004. Cranes are placed on barges, where they continue working as the waters of the Mississippi River rise.
More than 30 people representing Mississippi DOT, the contractor (Massman-Traylor Joint Venture), the engineer (HNTB Corporation) and several dozen subcontractors and suppliers visited the site during an annual partnering session in August 2004. Partnering is a positive commitment to honesty and integrity and helps keep project on schedule and on budget.