Thousands of homes in Connecticut, mainly the northeastern part, are in danger of becoming “worthless’ as foundations crumble, as a result of a quarry and concrete operation from the 1980s that resulted in material with too much iron sulfide. Kristin Hussey and Lisa W. Foderaro have a story on p. A16 of the New York Times here. The symptoms are that homes will have very loud pops and shakes in a succession suddenly.
However I recall that in Texas in the 1980s, people would wet their foundations in the summer to prevent cracking, and it is possible to repair foundations by pumping more material in.
ABC 20-20 one time reported some large new homes in the Kansas City area collapsing.
Homeowner's insurance normally does not cover faulty construction or foundation failure.
The land would still be of value in many cases; but houses could have to be raised and rebuilt. There have been scams,but some foundations can be repaired for about $200000. Since the houses are thirty years old, many mortgages should have matured.
The state has a political problem in how it can help the homeowners with special bonds.