Here is a Mighty Protectors Tunneling Ability that is a home-brewed rule, based upon Living Legends "Burrowing" power.
This is a Voluntary attack ability with no range that can also be used against inanimate matter at a cost of movement only. Each inch of movement tunnels through 1 cubic game inch (5 feet x 5 feet x 5 feet) of SR 1 material; multiply the movement cost by the SR of the material being tunneled through, then divide it by the maximum SR capability of the character's Tunneling ability. There is a PR cost of 1 per Round.
For example, if Tunnel Rat's Tunneling ability works against a maximum SR of 4, and he uses it against the ground at SR 1, then he can tunnel through 4/1=4 cubic game inches of earth per inch of movement he spends.