Abstract : Two approaches were used to study the behaviour of compressible soils during the widening of an embankment: the testing of small scale models in a centrifuge and numerical analyses by the finite element method. In the centrifuge, the embankments were built in flight by using a new hopper, which was designed for this test. Seven containers of reconstituted Speswhite clay were prepared and equipped with surface settlement, pore water pressure and horizontal displacement sensors. Seven tests were made. The first three tests were used to define the test procedure and the last four ones to compare two types of embankment widening. The analysis of the measurements and observations made on the models showed the importance of the soil preparation conditions and of the detailed history of the soil from its pouring into the container until the end of the test. The clay behaviour in the centrifuge depends on a combination of consolidation and creep, which in turn depends on the initial overconsolidation state of the clay and makes the interpretation of the experimental results more complicated. The numerical analyses were made by using CESAR-LCPC. They concerned the centrifuge small scale models and the behaviour of a motorway widening embankment, built 25 years after the motorway construction. For the finite element coupled elasto-plastic analyses, some of the necessary geotechnical data were not available; the comparison of numerical and experimental data was therefore not conclusive, despite their qualitative agreement. In order to get more useful results for practice better information about the mechanical properties of the soils is thus needed.