When the Netherlands' major rivers-the Ijssel, the Rhine, and the Meuse-overtop their banks, the flood-waters sometimes block roadways, causing access problems for local residents. Similar problems result when one of the country's many bridges is closed for repair. In search of an innovative solution, the Directorate-General for Public Works and Water Management recently held a design competition to solicit ideas for a floating road.

The winning team developed a system of aluminum modules, each 5.5 m wide, 3.5 m long, and 1.5 m high, that can be linked together to form a floating road for either temporary or permanent use. The team recently built and tested a prototype on a tributary of the Mouse in the Netherlands near Hedel.

While various types of floating bridges that can be rapidly assembled have been designed for military applications, driving on these structures is typically "so uncomfortable that they are useless" for civilians, says Jan Brouwer. The goal of the Dutch project, in contrast, was to create a floating road on which motorists could drive as safely and comfortably as on a normal road, at speeds of up to 80 km/h.

The modules are stiff, lightweight aluminum boxes that are partially filled with polystyrene to keep them afloat. The bottom of the structure is porous, allowing water to enter the modules and fill the spaces beneath and between the polystyrene blocks. This design imparts stability to the structure, says Frans Soetens, a structural engineer for TNO Building and Construction Research. The road is further stabilized by aluminum breakwaters on each side.

The modules are designed to be transported easily by truck. Once at the site, they are placed in the water and linked by stainless steel clamps. Some of the modules, which are spaced at regular intervals, are equipped with rings that project from the sides. Steel piles are driven through these rings to anchor the structure to the riverbed. The distance between the piles and the depth to which they are driven depend on local conditions. Constructing a road some 50 m long in this manner would typically take as little as two days, says Martin Cornelissen, the project designer for the DHV Group.

The 70 m long prototype, installed earlier this year, includes more than a dozen floating modules and two transitional structures, each 10m long, which form ramps on each bank of the river. It was tested for both a 2,000 kg private car and an emergency vehicle weighing 7,500 kg. Waves were also generated in the water to test the roads stability. The tests were successful, and the structure has now been approved for public use.



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