Wave action and the effects of the environment on sandbag dike performance

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Offman, Raymond
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Winnipeg, Manitoba experiences annual flooding and has a history of major floods that have exceeded its permanent flood protection infrastructure. During these major flood events, sandbag dikes have been used to temporarily protect the community, with little knowledge of how they work. These dikes, like all flood fighting techniques have an inherent risk associated with their use. This thesis provides an understanding of the engineering behaviour of these structures that aims at reducing the risk of their use. Specifically this thesis examines the effects of wave action on dike stability and the effects of building dikes on foundations affected by Manitoba’s environment. The testing program included both full-scale and large-scale testing. The full-scale testing consisted of wave testing of 5 ft (1.524 m) sandbag dikes, built according to the City of Winnipeg standard dike cross section, to examine the effects of wave height on dike stability. The full-scale dikes were built and loaded with waves in a 100 foot (30 m) long hydraulic wave flume. The large-scale testing comprised of large-scale direct shear tests carried out in an environmental chamber to establish the effect of the environmental factors such as moisture, temperature and snow, on the dike-foundation interface strength. The wave results showed that as significant wave heights were increased to the range of 0.41 m to 0.45 m, that the dikes built according to the City of Winnipeg cross section became unstable. The thesis recommends modifications to the dike construction and material for dikes that are to be built in areas prone to waves of similar height. The direct shear tests provided Mohr-Coulomb shear strength parameters for the dike-foundation interface when exposed to environmental conditions typical to Manitoba. The results show that snow in the interface provided the lowest capacity to resist lateral movements. Recommendations are provided for the use of these parameters and include the removal of snow from the sandbag dike corridors prior to their construction. Overall, the thesis provides an understanding of the behaviour of sandbag dikes exposed to wave action and environmental effects. This knowledge can be used to create policies for reducing the risk of using sandbag dikes during flood events.
sandbag, dike