Just done a large house leveling project last winter, I had the same problem with the soft ground near a lake. I had several 1/4" x 2' x 2' steel plates cut to sit under the jacks, I also had them make me some tops for the jacks (a 1/4" x 6" x 6" square plate with a piece of pipe welded to it to sit over screw on jack to keep screw from pressing into 6 x 6. Worked pretty well.