In an attempt to evaluate current models for the safety assessment of dykes on soft soils, STOWA, the foundation for research on regional dykes in the Netherlands, launched and supported a full scale test on a regional historical dyke, which included observation of the pre-failure response and the design of its failure. The stress test on the dyke included progressive excavation at the toe and rapid drawdown in the ditch next to the toe of the embankment, until failure eventually occurred. The data and the observations collected on site during the test are a unique body of information on the coupled hydro-mechanical pre-failure behaviour and on the resistance of the earth construction. A selection of these data was included in the formulation of the Theme C of the 15th International Benchmark Workshop on Numerical Analysis of Dams, held in September 2019 in Milano, Italy. This contribution presents the main outcomes of the numerical benchmark, coming from the results of the different groups, which analysed the case with current geotechnical constitutive and numerical models.

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One of the most frequent causes of failure of earthen structures subjected to water seepage, such as pervious dams and embankments, is the internal erosion of particles developing into piping. Similar phenomena may also occur in permeable foundation soils under impervious dam structures. This study focuses on the design and set up of a new laboratory device for testing internal erosion and piping on the representative elemental volume and on the small scale.The possibility is given to investigate the influence of the stress state and of the flow path length and direction, with respect to the soil layers inclination, for given seepage conditions. The quantity of eroded particles and the pore pressure distribution along the flow path are measured during the process. The results of preliminary tests on glass beads samples, in unsaturated conditions and under unconfined seepage, allow for a first assessment of the device control and testing procedure.@en