Cut off walls have been a standard accepted solution by most local forensic geotechnical engineers. This method involves trenching around perimeter of the house or building to a depth recommended by the geotechnical engineer and installing a very thick layer of plastic which is run up the trench and adhered to the base of the foundation. It is then backfilled with either grout or soil cement.
Often times we use this method along with using helical piers on failing foundations, depending on the situation and the location of the house. Areas around the valley which we have seen the most movement within the soils would be the phoenix metro area, including Scottsdale, Mesa, Peoria, and Chandler.
New construction basis:
With the proper design on a new construction project, the addition of a cut off wall can allow the structural engineer to reduce the thickness of the concrete and decrease the spacing of the cables on a post tension slab. It can therefore pay for itself in first costs in addition to providing for a better protection against heave or settlement.