Why haven't we researched 'peaceful' nuclear explosions?

It is proven that nuclear weapons are far cheaper and safer to use for underground mining then conventional explosives are or drilling, so why are we not exploring this option? It can release large pockets of trapped oil, minerals and natural gas thousands of feet underground. It can also be very effective for digging large canals and harbors with little effort, all the radiation would be trapped in the liquefied bedrock so there is no worry. The other option is to use them to start small earthquakes artificially to defuse the possibility of a larger one being a threat to urban areas.