Rigid Body Interaction with Highly Deformable Solids, a Material Point Approach in 3D *R. Bird (Durham University), W. Coombs (Durham University), C. Augarde (Durham University), Y. Sharif (University of Dundee), M. Brown (University of Dundee), G. Carter (Arup), C. Macdonald (British Geological Survery), K. Johnson (British Geological Survery)