Anyone do mud-jacking??

[JasonRR]

Need a void under my new patio filled back in...had a sprinkler head that wasn't disabled before the new patio was poured, so a good deal of the dirt irrigated out and I want to make sure to put enough dirt back up in there to support the slab. It's already showing some signs of cracking and pulling away slightly from the house.

Anyone have any experience with this??