Reconstructing the caisson inside the cofferdam.
The pour was the first step in sinking the steel caisson, which serves as the foundation for Pier 3, into the Mississippi River. The 67-foot by 109-foot cutting edge of the caisson was transported in sections to the middle of the river where it was assembled and reinforcing steel was added before it began its journey 50 feet below the riverbed. Four pours were needed to completely sink the caisson.
Suppliers Delta Concrete, Inc. and McDonald Co., Inc. hauled the concrete from their respective plants in Cape Girardeau to the Illinois side of the river. The concrete was transported from the Illinois side because of safety and to avoid interfering with barges in the navigation channel. A temporary bridge was constructed so the concrete trucks could transport the concrete to barges. The barges then carried the concrete to the cofferdam, where it was placed inside the caisson by cranes.
The caisson resembles a rectangular honeycomb larger than the size of a river barge. The walls were filled with the concrete and the sand areas of the riverbed located between the different chambers of the caisson's grate were removed with heavy excavating equipment. The removal of the sand is what actually caused the weight of the caisson to sink the cutting edge below the surface. The caisson will cut through the sand to the rock in the riverbed located beneath what is one of the structure's two main support towers.
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Emerson Memorial Bridge Projects