The technique of soft soil improvement by rigid inclusions allows the transfer of the load applied at the mattress top towards the piles by two mechanisms: arching in the granular mattress and membrane tensioning if a geosynthetic has been included in the mattress. A parametric study has been carried out to understand the role of the thickness of the mattress on the load transfer and the differential settlements. The experimental results obtained on centrifuge models have been compared with the “Recommendations for Design and Analysis of earth Structures using Geosynthetic Reinforcements” and finite element modelling.