Gravis' first stop was to understand the Soft Complex materials. He needed to get his defense in order and complete the Complex Laws. Right now, he had enough time to entirely focus on them. He had nothing to do but comprehend Laws, and this would be the perfect time to comprehend Laws that required a lot of time.
Since Gravis had already comprehended the water part of the Soft Complex Laws, the next thing he wanted to check would be the liquid metals and fire. Sadly, Gravis couldn't find the liquid metals very quickly.
So, he decided to mine.
He dug a hole in the ground and used his Composition Law of the Earth to stabilize it as much as possible so that it didn't simply collapse.