This is a tough situation. Forget pouring concrete it does not bond and expand at the same rate as stone .In a couple of cases we made a sediment pool and dumped 80%clay material cleaned of rock and dug down. We then mixed the sediment pit wiyh a 4"pump and then pumped over the rock formation in layers.This process took over a week to seal up rock in stages. The slurry was like a milk shake and done in four layers,then capped off with 2 foot of soil. Maybe this is helpfull or gives you an idea.
Scott
