The Admiral Land quote form 1942 is well known to those of us who follow the topic. The consensus is that it is not a use of the phrase as such, but just a random collocation of words. He’s literally referring to nine shipyards. Plus it’s really obscure statement, given in congressional testimony by a not-famous military man and not widely reported. It’s highly unlikely to have been the inspiration for the phrase.
And power shovels are frequently measured in cubic-yard or cubic-meter capacity. So a nine-yard shovel would hold nine cubic yards of dirt and would have been one of the biggest shovels in existence in the late 40s. (They’re much, much larger nowadays; I’ve seen a reference to an 80-yard shovel.) But I’ve never seen any evidence of the phrase being linked to mining or excavation.