Unusual Moult Behavior

[charcoal44]

I have 3 crabs in my new tank, all now appear to be in the moult phase.
The smallest has been under fro must be almost 2 weeks now, the large one about a week, but the middle sized one keeps making a hole and going down, then resurfacing a few hours later.

Longest he was down was almost 24 hours, so far, he's made 4 holes.
Currently he's reburied himself.

Is this "normal"?

Edit:
He's just created another tunnel, I swear he must have been a coal miner in a previous life.
Currently chilling out on the climbing tree

[Wai]

He's probably just exploring the tank; though he may be testing out the areas to find a safe place to hide. The former seems more likely.

[StellaCrab]

I agree, my crabs do this sometimes before they molt, some more than others, but they always ended up down to molt after a few times of coming back up.