Well, here's the little baby I've cooked up and am requesting permission for! I kinda like the imagery of one of these guys tearing their way out of the ground in a shower of earth, stone and fire, followed by dwarven assault teams charging out of the newly made tunnel

I *think* I've put in all the relevant info and calculated it all correctly.
Brass Guardian
Large Construct
Hit Dice: 8d10+30 (75hp)
Speed: 40ft, Burrow 40ft (can go through stone as well as earth)
Initiative: +0
Armour Class: 24 (+15 natural, -1 size)
Base Attack/Grapple: +6/+10
Attack: Claw +15 (2d6+10)
Full Attack: 2 Claws +15/+10 (2d6+10)
Space/Reach: 10ft/10ft
Special Attacks: Flames of the Forge
Special Qualities: Construct traits, Damage Reduction 9/ magic, Fire Resistance 20, Spell Resistance 15, Tremorsense
Saves: Fort +2, Ref +2, Will +5
Abilities: Str 30, Dex 10, Con - , Int - , Wis 16, Cha 1
Skills: None
Feats: None
Challenge Rating: 7
Alignment: None
From the sacred forges of the dwarves come the brass guardians, hulking constructs carved with arcane sigils of warding and protection. Towering over normal men, one of these creations appears as a hunched figure of brass plates and pistons, a head bearing glimmering ruby eyes slung forwards on a heavily armoured neck. Each arm ends in a massive digging claw, but these appendages are just as suited for tearing enemies apart with the massive strength of the construct. Brass guardians are usually designed to appear as ferocious as possible by the artisans who craft them, their heads shaped into bestial, snarling visages and sagas of dwarven heroes carved as pictures into their brass hides.
A brass guardian is both a powerful defender of the dwarven lands, its belly burning with the fierce fires of their forges that it can spew forth over foes, and a useful servant construct capable of tearing entire new excavations through rock in the time it takes a normal dwarven mining team days to achieve. The magically reinforced armour of the guardian helps protect it against both falling rocks and debris, and the attacks of enemies as well.
Flames of the Forge: Breath weapon, 6d6 fire damage in a 40ft cone every 1d4 rounds (Reflex save for half damage, DC 14).
Construct Traits: No Constitution score, low-light vision, 60' darkvision, immunity to all mind-affecting effects, immunity to poison, sleep effects, paralysis, stunning, disease, death effects, and necromancy effects; no natural healing; not subject to critical hits, nonlethal damage, ability damage, ability drain, fatigue, exhaustion, or energy drain; immunity to any effect that requires a Fortitude save (unless the effect also works on objects, or is harmless); not at risk of death from massive damage; immediately destroyed at 0 hp; cannot be raised or resurrected; bonus hp based on size (30 hp large); proficient with weapons mentioned in entry, proficient with no armor; no need to eat, sleep, or breathe.
Large Size - +0.8
Construct - +0.7
Hit Dice - +2.8
Burrow - +0.5
AC - +1.5
Full Attack - +1.05
Breath Weapon - +0.6
Damage Reduction - +0.3
Fire Resistance - +0.4
Spell Resistance - +0.5
Tremorsense - +0.1
Abilities - +1.7
CR Result: 10.95
Golden Rule: 8.275
Silver Rule: 7.03375
Rounded down Silver Rule: 7