I'm using Cavern_1.12.2-v1.10.3.jar

I added sand to the mineassistant quick allowed items.
And I added iron shovel to the allowed tools.

My quickMiningLimit is 30.

I used quick on a beach near my house and it just broke all sand blocks.
I ended with something like 40 full 64 piles of sand blocks.

Btw, as far as I saw, the limit is not being respected in any case, with any tool