Btw, I talked with my cousin about this. He does a lot of grading,
They do this all the time, and to do it, they build a "lift" or a "bridge", which just means anytime they're working, they always keep a prescribed amount of fill under the machinery and over the muck/swamp. He says you can work on top of some pretty nasty ground if you keep the fill thick enough. If the machine starts to sink, back up quickly and start with a thicker layer everywhere. Once you're done, you can backscrape the excess off, to an extent.
