Settling Concrete Floor Slab?

Concrete floor slab settlement is often the result of changes in moisture content or density of the supporting soils. For example, soils beneath a concrete slab can dry and shrink over time due to extended drought-like conditions, leaking HVAC systems, etc. Loosely-compacted fill soils can also consolidate beneath the weight of the slab or fill layers above. A different condition, plumbing lines under the slab can leak, in turn piping soil out and away from under the concrete slab. Each of these conditions creates a void under the concrete slab. If the concrete slab is not strong enough to span the void, the slab will crack, break, and settle into the void. 

Options for repair that are less desirable, alternative methods that don't work:

Concrete slab replacement- Very expensive, very disruptive, and does not address the probelm (slab likely to settle again)

Mudjacking- Messy, high-pressure grout spews out of other holes and cracks in the slab, does not address the problem (slab likely to settle again)

Re-leveling grout on top of slab- Adds additonal weight, potentially making the problem worse, addtional grout may dislodge if it doesn't bond well to existing slab, does not address the problem (slab likely to settle again)

Helical Slab Piers- Heavy equipment needed on site, relies on emperical formula to calculate capacity, difficult to install in areas of limited access

Author: Foundation Support Works 2014 "Slab Pier System" Brochure