You literally just said a set amount of hard sand. Where does the soft sand then come from?
Not that it matters anyways.. Gaara's gourd sand is his toughest because he flows chakra through it. He can flow chakra through any other sand construct just as quickly as seen when he did so with the aerial bulwark he used to defend his village against Deidara's village busting bomb.
- 60 feet as in the underground place in that Boruto image? If yes, please figure out what a cavern is.
Again, Shukaku isn't needed. Gaara low... scratch that.. He neg diffs this character with fanfic abilities.