In this paper, the use of vacuum consolidation to improve soft ground and increase its undrained shear strength (Su) is discussed. Since peat and organic clay have very low Su values, the construction of embankments and structures on these soils often cause ground failure. For the trial embankment conducted in this research project, soft ground composed of peat, organic clay and clay was improved by using vacuum consolidation, resulting in a significant increase in Su values, and an embankment 10.7 m high could be constructed on the improved ground without causing ground failure. It was demonstrated that the increased Su was the result of synergy of the relatively high normalised strength (Su/σ′v, where σ′v is the effective overburden stress) of peat and organic clay, and the unique loading mechanism of vacuum consolidation. It was also demonstrated that in the case of a relatively narrow embankment (e.g. road embankment and river levee), the effect of isotropic consolidation also contributes to increase the stability of the vacuum consolidated peaty ground. It was also found that if the (Su/σ′v)NC of the original ground and the overconsolidation ratio are known, the (Su/σ′v)OC of the given ground overconsolidated by vacuum consolidation can be predicted.