sure they work on wet clay (i live on wet clay) but any
raised bed at all will work on wet clay..
I even filled one bed with branches and clay to see how it would work out..the clay is lifted 6 to 12 " above grade..and this is it's second year..the clay is at this time planted with sugar snap peas, kale, mesclun, spinach, cabbage and a few other crops, there are some areas not yet planted..the plants seem to be growing fine on it..I did put a heavy
mulch over it last fall, and will mulch again as soon as the baby plants are up high enough to be mulched..this is an experiment I wouldn't necessarily recommend..
there are some threads on here about clay..might search for them
I have had suggested to me to try both sweet potatoes and regular potatoes in the clay raised bed..and I have one section waiting for warm enough (michigan) weather for putting out my baby sweet potatoes into the clay and I have potatoes coming, will stick "2" of them in the clay to see how they do, the rest will go where I had planned to plant my taters..will update later..or on my blog