© 2015 Thomas Telford Services Ltd, All right resereved. A generalised framework is presented for predicting the consolidated undrained capacity of rectangular mat foundations on normally consolidated soft clay under combined loading in six degrees of freedom as a function of relative preload and degree of consolidation. Consolidated undrained response is investigated by coupled small-strain finite-element analysis using the modified Cam Clay plasticity constitutive model. Increases in the load-carrying capacity of a foundation under combined loading in six degrees of freedom following vertical preload with subsequent consolidation are demonstrated and quantified. The results are presented as failure envelopes in multi-directional load space and are shown to expand proportionally as a function of degree of consolidation for a given relative preload. A methodology and a set of expressions are provided to predict the shape and size of failure envelopes for rectangular mat foundations for any degree of preloading and consolidation.