What I'm describing is not just covering the rhizomes. The rhizomes basically are on top of the existing soil rather than in it and the prox 4' of sand is where the rhizomes exist. I'm not really all that careful, so some rhizomes probably get in the top 1/2" of soil sometimes and other times there is probably sand between the rhizome and the soil. Basically, though, the rhizomes are resting in the sand layer rather than in the soil layer. My growing conditions are so vastly different from yours I don't know if it might work or not. Seems like sand wouldn't heave as much due to the good drainage it has.
Texas Zone 7b, USA