This is called PAHS, passive annual heat storage and has been tried in some alternative energy housing.

You put pvc pipes into a hill of dirt that is covered by a plastic sheet or other waterproof membrane; during hot summer months you use a small fan to put heat into the pile; during winter the heat moves from the dirt to the house.

This is definitely not what the OP is talking about.

He is talking about electrically heating very large amounts of dirt to temperatures of 600C or more. Your PVC tubing approach is talking about 50 times smaller swings.