Jacket platforms are piled into the seabed but need to be supported temporarily by mudmats during installation. They sometimes need to be located next to seabed features such as pug marks formed by previous deployments of jack-up rigs. These features may influence the bearing capacity of the mudmats. This is a 3D problem for which simplified approaches are unsatisfactory, simplified 2D plane strain simulations can lead to over-conservative results. This paper presents a project example in very soft clay for which the software package Plaxis 3D has been successfully used. The presence of a pug mark was found to degrade significantly the yield surface in the VHM load space. A comparison between 2D and 3D analyses shows that the beneficial 3D effects are substantial, especially when the pug mark is located at the corner of the mudmat. The zone of influence of the pug mark is also much more limited when the problem is modelled in 3D.