The ETH geotechnical drum centrifuge was used to model ground improvement on soft double porosity clay. Ground improvement was carried out in-flight and the techniques tested were dynamic compaction and an array of stone columns. Foundation tests on improved soil models showed that stone columns were more effective at increasing subsoil resistance at higher load. This may be because stone columns improve drainage of the clay layer and thus allow the clay itself to become stiffer. © 2009 Taylor & Francis Group.