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Centrifuge Tests on the Failure of Dikes Caused by Uplift Pressure, Page 1 of 2

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A series of centrifuge tests has been carried out to investigate the behaviour of dikes under uplift conditions. Particular attention has been paid to clay dikes that are founded on a permeable layer of sand. A rising water level in the river causes an overburden pore water pressure underneath the clay layer, resulting in a reduction of friction between the sand and the clay layer, which can lead to failure of the dike. Although the principle of the mechanism is known, very little was known at what conditions failure occurs. A test set-up has been developed to model a complete system including riverbed and hydraulic gradient in the sand layen The groundwater flow has been manipulated by adapting sand layers consisting of different types of sand. Points of research are the determination of length and location of the uplift zone and the influence of material and geometrical parameters. The effects of berms and ditches and the combination of them have been studied as well. In order to study in particular the behaviour of the uplift zone the horizontal driving force of the embankment is simulated by a mechanical loading system (bulldozer tests). A comparison is made between the centrifuge tests and analytical and numerical calculations using a finite element program. The centrifuge tests are compared qualitatively with the results of a field test. The tests have led to a better understanding of the failure mechanism of dikes founded on sand layers.