in the image there is a retaining wall with backfill and foundation soil. To get a uniform mesh size I have done partition in foundation soil such that it's alignment is along the retaining wall. The problems like- "Contact pair (assembly_wall, assembly_backfill) has not been defined and hence, cannot be used for *model change" and " 7 nodes have dof on which velocity/displacement/acceleration/base motion etc. constraints are specified simultaneously. The nodes have been identified in node set ErrNodeBCRedundantDof" are the main problems due to boundary conditions on this highlighted area as it is being shared by both foundation soil and retaining wall also the boundary conditions are separately applied on both??

Abaqus ​​​​​​​