I'm the guy that had the garage footing fall. Can I just jack up the sill plate on top of the foundation wall instead of underpinning the foundation? I've cut down the oak tree and that should stop the clay from drying out. I've also watered the foundation, this won't build the clay back up but it should stop the drying process.
Answer:
You'd have to be sure of how deep the undermining has gone and more important than that, where that soil was washed to. You may have a lot more in the way of cavity(cavities) down there than you think.
