Slab Jacking, Slab raising, Floor raising, or Mud jacking
Slab jacking is the raising of sunken or settled concrete floors by drilling holes and Injecting grout underneath.
Determining what caused the settlement is important to determine the best method for a long term fix. Small test holes are drilled to find out the size of the voids and stability of soil underneath so that an accurate estimate can made. The same holes can also be used as vent holes when grouting. Custom packers are inserted and low density, lightweight cellular grout is injected to fill the voids and stabilize the ground, then lift the slab back to an acceptable elevation. Most slabs can be raised by only 1 psi.
Cellular grout is most often used because it is flowable, half the weight of the existing ground, and also works well in cold regions as a good insulating fill but with structural strength.
With unstable soil underneath, compaction grouting is the best method to densify poor underlying soils to stabilize, and then raise the ground and slab.