Sand compaction piles are used in practice for ground improvement of soft subsoil in order to accelerate consolidation, reduce compressibility, and increase strength. The current design procedure of sand compaction piles is based on simple empirical calculations, which does not take full account of the sand pile behaviour. This research project investigates the behaviour of a base reinforced embankment constructed on a soft clay layer, which is improved with sand compaction piles. In order to gain a better understanding of interactions within the structure, physical investigations are being conducted by means of centrifuge modelling. Tests were performed under plane strain conditions in a strong box, using a newly developed sand compaction pile installation tool for in-flight pile construction. Initial analysis of test data shows the change in stress state due to sand compaction pile installation and the influence on clay behaviour. © 2006 Taylor & Francis Group, London.