Modeling two blocks on top of each other in abaqus?

If you have solved the problem with Abacus, I suggest to compare your results with the experimental investigation recently carried out on a stack of two dry-jointed tuff blocks subjected to different loading conditions.
The article is:
C. Casapulla, F. Portioli, Experimental and analytical investigation on the frictional contact behavior of 3D masonry block assemblages.
The goal of this research was to investigate the interactions
among shear, torsion and bending moments on the contact surface.

If sliding is possible in the real problem, and if there are no other contact surfaces (e. g. on the left/right handside of the upper brick), your contact definition should be appropriate.