Found a couple of photos from when I worked at the dam project. We had a very wide clay core zone. It was probably 200 ' wide, or more. We placed fill for the dam all during the winter of 73-74. Worked 6 days/week with 2, 12 hour shifts. One thing the contractor was absolutely forbidden to do, was to place any new core material on top of a frozen layer. So, before starting a new lift in the core, the contractor ran a "jet drier" over the surface and melted the frost. It was then scarified and recompacted before new fill could be placed. It took about 2 days to get a new area ready for fill when it had to be thawed first. Jet drier photos: