In my inexperienced mind...coring a dam does a couple basic things...

1.) It allows for exploring the unknown of what type of earth is beneath the dam's location. If it's all good solid clay then there was less of a need to go there, but you'd never know otherwise. If you find sand/gravel veins or less desirable water holding materials...see #2.

2.) Coring allow the excavation of less desirable materials that can be replaced with good clay. Once layered and packed in, this ties the water holding clay "bowl" to the dam.

Some folks that live on the clay pans out here near the Midwest can often get away with scrapping off the topsoil, digging a hole and piling/packing good clay to form the dam. As Clint would say..."do you feel lucky...?".


Fish on!,
Noel