Hi - a dozer is usually plenty to compact clay at the right moisture content. The right moisture content is when you can get the clay to make a firm ball in your hand that resembles the consistence of play-dough. Too dry and it becomes blocky and won�t �mold� together, too wet and it be (and you get the dozer stuck!).
As far as the layered lifts, the measurement is the thickness of the UNCOMPACTED layer of soil; however, 24� seems thick to me. The specs we use call for 9� uncompacted layered lifts and then traverse that uncompacted layer with the dozer. In the end, that 9� lifts turns into 5� or so compacted. Personally, I wouldn�t go as high as 24� layers.
As Bocomo stated, if there are layers of sandy or gravelly material under the dam, then a core trench is usually needed. We have �squeaked by� without a core, but that is only when there is heavy clay from ground level down to the depth of the pond.
Good luck!👍
