Go for hakonechloa aureola ...loves heavy soil. Lovely deciduous yellow grass with hints of red and orange. Classy beautiful for front of borders. Deschampsia too thrives in heavy soil.....lovely billowing airy flowers all summer. Miscanthus varieties too for height and late flowers. Carex....not strictly grasses.....like testacea are evergreen. Bowles golden grass, millium Aureum, is stunning. Yellow stems, leaves and flowers and good in partial shade and heavy soil. Acorus Ogon is another evergreen grass like plant. I find elymus magellanicus, a very blue grass, copes with some shade if it gets sun too. Uncinia, uncinia rubra is evergreen foxy red "grass" and Imperata red baron may do well there.....it's a blood red grass looking fabulous from mid summer. ophiopogon is a black grass worth checking out. Molinias will do well there and have many varieties to chose from
For variety mix in some Japanese painted ferns like Ursulas Red.......blue grey fronds with red veins and stems. Add couple of heucheras too. Superb.