Burrower

A creature with this trait can move through solid objects by burrowing through them.
The number in parentheses (X) indicates its speed when burrowing.
Such creatures can burrow through soil, rock, sand, and so on, though some (expressed in the creature entry) can even burrow through metal. When a creature burrows, it leaves behind a tunnel. Characters with a Size trait value lower than the burrower can enter these areas without impediment. At the end of each round after the burrower passes, roll 1d10; on a result of 5 or lower, the tunnel collapses behind the creature.

Dark Heresy - Core Rulebook - 134