The use of polyurethane to raise concrete and stabilize soil has many advantages compared traditional mudjacking which uses cement and sand.  Below are just a few benefits:

Longevity – Polyurethane will not shrink or breakdown over time

Looks – smaller and less injections holes are needed.

Performance –Extremely light compared to sand/cement and very effective at filling open voids

Here are some of the most common reasons concrete slabs sink:

Gravel base was never compacted properly during construction

Concrete was built over soil that was once back-filled (such as around a foundation or pipe trench) and soil has now settled

Water is draining or pooling around edge of slab which can cause the base to wash away over time

Cracks and gaps in the concrete allow water to seep below the slab and cause seasonal frost heaving which can create voids.

The most important thing you can do is to fill all the cracks and gaps in your concrete where the settling occurred.  A polyurethane crack sealer sold in caulk tubes is the best way to do this. Make sure downspouts are directing water away from your concrete.  Also equally important is to fill the area along the edges of your concrete with soil in order to prevent water from washing away the base.