When a patio or walkway has settled over time due to erosion, there are very few options for repairing it. One is to completely replace the patio with a new patio, which is time-consuming and expensive. The alternative is to raise the existing slab using a process called mudjacking or slabjacking. Slabjacking is the process of injecting a clay material under the sunken slab to raise it back to its original level.
Hire a clay truck to come to your job site. They are similar to cement trucks, but they hold a mixture of sand and clay that will not erode much over time.
On the side of the slab that you want to lift, use a concrete bore saw to drill a hole through the concrete, approximately 1 3/4 inch in diameter. A bore saw makes a hole just like a drill, but leaves the cylinder of material in tact so you can put it back in when you're done. If the slab is long, you may want to bore two holes, one on either side of it. The process of boring the hole will create concrete cylinders that fit back into the hole. Set aside the concrete cylinders.
Lower the clay truck valve into the hole and begin injecting the clay slowly, being sure not to lift the concrete above the level you want. When in doubt, inject less clay because you can always raise it a bit more, but you will not be able to get it lower once you’ve injected too much.
Replace the cylinders into the concrete, and spread some wet concrete or concrete-patching product over it to close the seams.