With the Foehammer archetype, when using an adamantine weapon would he automatically succeed when using the Ground Breaker ability.
Ground Breaker (Ex)
At 13th level, as a full-round action, a foehammer may strike the ground with his hammer. If the attack deals more damage than the floor's hardness, the space he occupies and all adjacent squares become difficult terrain. Creatures in those squares, except for the foehammer, are knocked prone (DC 15 Reflex negates).
Adamantine Weapons
Weapons fashioned from adamantine have a natural ability to bypass hardness when sundering weapons or attacking objects, ignoring hardness less than 20.
Also does anyone know additional ways of getting more attacks in a full attack other than Haste? I want to get full usage of the Rhythmic Blows ability, already have Hammer the Gap and /might/ get a Furyborn weapon.