ground-breaking, open up farmland
墾 centers on breaking new ground for cultivation: the act of clearing and opening up land to create farmland.
墾 combines 貇 (a phonetic component likely related to clearing or opening) with 土 (earth), suggesting the idea of working the soil to open new farmland.
The top 貇 looks like a wild beast being tamed, and the bottom 土 is soil. Imagine breaking wild ground with a beast-drawn plow to open up new farmland.
For コン, picture a con-man breaking ground on a fake farmland scheme: con -> コン, and he's opening up the earth with a shovel.