As a young lad, I helped the neighbor dig his basement with a slip (that is a scoop that has handles and usually was pulled by horses) and very similar to what I think you have for a scoop on the 3 ph. I drove a small H John Deere to do the pulling and the repeated trips in and out of that basement hole (prolly for a 24 x 24' house) were endless. But we did get it done.
Most of the original railroad beds were done with gangs of slips and horses moving dirt.
Yes, it can be done. And the depth is only limited by the patience you have getting one scoop at a time. No other limitations that I can imagine unless you have a problem with water (seeping in or falling from the sky).