I had a situation just like this, was pushing brush forward and then hit a soft spot. Tried to back up, but I sunk just enough that a rock caught the rear of the dozer, so backing up was not an option. Had another time, rental CAT D6 with ripper on back and got stuck because I couldn't get the ripper high enough so it kept me from backing up, had to go forward.

On the first one, gave up after breaking chains and straps and called a wrecker - the biggest heavy duty truck they had. We bent a 1 1/8" pin in pulling the machine out, wrecker guy said it was over 80 tons pulling force.

Another stuck story, not me, tractor was plowing, duals front and back, sunk to the belly in a soft spot. They had to wait for the area to dry out and it took 2 large track hoes to dig a path to get to the tractor and then a bunch of digging out the tires and then they finally got it out a day or so later...