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C684
Touching the Earth Lightly: The U.S. 20 Iowa River Bridge

Jeffrey Syken

On July 4th 1776, King George III of England wrote in his diary: “Nothing of any significance happened today.” Little did he realize that, on that very day, very much did happen that would dramatically affect the Empire he ruled. When motorists travel U.S. 20 between Dubuque and Fort Dodge, Iowa, and pass over the Iowa River Bridge, little do they realize the effort involved in spanning the environmentally sensitive Iowa River Greenbelt below. At first sight, it appears to be an ordinary deck-girder highway bridge with long-spans between piers. In fact, most motorists probably don’t even realize they’re crossing a bridge at all since the structure is below, out of view. If they knew of the twenty-five year effort to design a bridge that would “Touch the Earth Lightly” and the innovative methods used to construct the span, they might appreciate the experience of crossing the bridge even more. Special precautions were taken so as not to disturb the native wildlife (i.e. bald eagles) or pollute the river valley and/or Iowa River itself. This included selective tree removal, a temporary crane mat (in the river), a fluid containment system, drill-shaft pier foundation/s (with sheet-pile enclosures to prevent artesian water from entering the river), silt-basin channels (lined with cable concrete) and a sealed drainage system. The structure itself used, for the first time in the U.S. for a steel girder highway bridge, the Incremental Launch Method so as to cause minimal disturbance in the valley. To reduce maintenance activities, weathering steel was used. The bridge – opened in 2003, has become a model for enlightened, environmentally conscious civil construction projects.

This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.


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