Centrifuge modelling of railway embankments under static and cyclic loading

With past embankment failures on the heavy haul coal export railway line between Ermelo and Richards Bay in South Africa, a study was conducted focusing on the modelling of embankments in a geotechnical centrifuge. This was done in order to investigate the influence of static and cyclic loading on settlement, and to evaluate the potential failure of the embankment under the loading conditions. The effect that moisture has on the slope stability was also investigated. A suitable loading system was developed that could be used to apply static and cyclic loading to a model embankment in the centrifuge. Embankment models representing a standard slope and using one material type with varying moisture content were built and tested in the centrifuge. Clayey sand material was sampled from one of the sites where a failure occurred on the coal line and was used for the tests. The loading system simulated the loading created by a heavy haul coal train with a 26 t per axle load along the length of an embankment. The results from the tests conducted in the geotechnical centrifuge indicated that settlement resulting from the cyclic loading was on average 67% higher than that of the static loading when considering loaded time. It was observed that the tests with increased moisture content exhibited significantly reduced stability. A completely developed slip surface failure was not observed. However, cracks formed at the crest of the embankment along its length, which indicated a downward shift of material. The research therefore concluded that cyclic loading on railway embankments increases permanent vertical settlement of the embankment compared to static loading. As the moisture content was increased for the different tests, there was a clear increase in crack development at the crest of the embankment along its length.