'PNE' = "Peaceful Nuclear Explosions". Check Operation Plowshare for the concept. I always thought the Cape Thompson idea had promise as a 'proof of concept'.
The 1962 "Sedan" plowshares shot displaced 12 million tons of earth and created a crater 320 feet deep and 1,280 feet wide.
Sedan apparently worked like a charm. Why wasn't this technology refined?
Nicaragua presents no challenge at all!