The trepanning process is performed on a round workpiece, allowing a larger diameter hole to be drilled with the same amount of power, and also retaining a re-usable metal core.
I am digging a hole to install a sonotube with a bigfoot footing for my 18x24 ft barn foundation. Depth of the hole is 4 feet, diameter is about 30 inches. Sonotube is 12 inches. I needed 6 holes like this. Ground is rock, sand and gravel... not fun to dig.