Let us bury retaining walls

Retaining walls should not break only by virtue of one side being higher than the wall as long as there is sufficient material on the other side. If they are completely burried there is equal pressure from both sides, and as such they should hold. This would allow us to close off mines after materials have been mined without all the retaining walls breaking in the process.

Wouldn't that kind of be a waste of resources? If you're closing a mine, why waste a ton of concrete and construction parts by just burying them?