We are often asked which is better? Polyurethane (poly) foam injection (or mud jacking) or deep compaction grouting? The answer requires some explanation of various conditions. Generally Poly injection is about 5-8 times cheaper, however it does not improve the soil below…. so it is a surface treatment. See my blog for a discussion of poly as soil improvement: http://www.foundationaz.com/blog/grouting-smoke-and-mirrors-part-I.html and http://www.foundationaz.com/blog/grouting-smoke-and-mirrors-part-ii.html
Look at the diagrams below:
The above shows a typical settlement dynamic. Note the reason for the slab settlement is rooted in the footing settlement because of the void space, illustrated below.
In other applications such as basement backfill zones, or other deeper soil problems without the benefit of the footing slab interaction, poly injection presents a less confident solution as it does not improve soil conditions but rather only raises the slab to a more desirable elevation. Even in these applications it may still make sense to select it over compaction grouting since it can be reinstalled several times for less than the cost of compaction grouting. The deciding factor is usually things like downtime, inconvenience, avoiding multiple repairs to floor finishes etc.
Both compaction grouting and poly/mud jacking injections have valid arguments for use depending on circumstances and site conditions.