The embankment problem in hand is very difficult to analyze since it represents a time dependent consiolidation problem.  With the new advanced PLAXIS software it was possible to work this problem and suggest solutions.  The most suitable solution for us is the use of GEOFOAM on top of a geotextile layer.  The idea being to replace the exiting sand fill with material of less density, thus reaching the planned elevation with same or even lesser weight.  The alternative solution suggested by the client, consisting of continuous backfilling until stabilization was also modeled.   This showed that about 1200m3 of sand may be needed per meter run in order to reach a stable ground.  This alternative is not our option at this stage since it holds many loose ends, like limitation of PLAXIS for large movements, unknown lateral confinement for this new heavy fill in the clay layer.