PCI has precast post tensioned shearwall info....shearwalls in seismic areas need the toughness of A706 reinforcing in their chords...i wouldn't think p/t strands have nearly enough ductility.
look into atlas piers....they have a system for fixing what you are talking about. they use a screwed in soil anchor as a foundation/support to jack up the settling foundation and permanently support it. also, their guys whom i have dealt with can tell if there is some other problem.
have fun
tony