GeoCentrifuge

When building dikes, roads, pipelines, tunnels, construction pits or harbours, it is very important to know beforehand what the impact will be on the surrounding soil. And to know how the dikes themselves, which are generally made of soil as well, will respond. Soil behaviour can only be partly captured in computer models and, with complex structures, model experiments are often needed as well. Because civil engineering structures are large by definition, scale models are often needed. The problem with scale models of soil is that soil consists of grains and so the models cannot replicate reality accurately unless gravity is enhanced artificially. This is the job of the GeoCentrifuge.

Projects

Piping research
Rijkswaterstaat's SBW (Strength of and Loads on Flood Defence Assets) research programme looking at Water Defences includes a component dealing with piping, the phenomenon in which water seeps under a dike, gradually undermining the structure as a whole. The research started with small model experiments. A piping event was then modelled on the 1:100 scale in the GeoCentrifuge. In late 2009, there was a field experiment at the Smart Dike.

Anchor chain tests
The idea behind the anchor chain tests is to measure the penetration and forces exerted by anchor chains cutting into cover layers protecting pipelines. Usually, pipelines are protected by berms built of broken rock against buckling and by damage caused by anchoring vessels. The required thickness of the rock layer is mainly the result of years of working experience, with a considerable safety margin. The design of the thickness of the cover is not based on a fundamental understanding of how the chains cut through the broken rocks.

Collision tests on a bridge pier
Large ships that swing out of line in ports are a serious hazard for bridge piers. Deltares conducted experiments in the GeoCentrifuge for a bridge in Hong Kong and one near Incheon (Korea) to check whether the forces exerted on bridge piers are acceptable if a heavy container ship bores into the slope around a pier. The model of the container ship was made by MARIN in Wageningen; Fokker Space helped with the design and construction of the other equipment for these experiments.

Short sheet pile wall
When dikes get too weak, inner berms are sometimes needed on the side facing the polder. However, there is not always enough space, for example when houses are in the way. In these circumstances, an option is to install a long sheet pile wall with anchors. A cheaper alternative is a short sheet pile wall, which is usually driven down into the pleistocene sand layer. However, it doesn't reach ground level and its short length means no anchoring is required. To demonstrate how sheet piling of this kind works, experiments took place in the GeoCentrifuge.