The effect of foundation embedment ratio and soil–skirt interface roughness on the consolidated undrained capacity of skirted circular foundations under planar loading in normally consolidated clay has been investigated through coupled three-dimensional finite element analyses. Results are presented as failure envelopes, and changes in shape and size of the normalized vertical–horizontal–moment (VHM) failure envelopes are described as a function of relative magnitude and duration of applied preload. Results show that embedment ratio and interface roughness affect the load distribution within the soil mass, but that consolidated undrained capacity under planar loading scales proportionately with the (unconsolidated) undrained capacity of the foundation. This latter feature enables the results to be neatly synthesized into a relatively straightforward method for use in engineering practice for prediction of gain in undrained VHM capacity due to preload and consolidation.