Hi Bill;
The powerful forces of freezing ground water are the cause of many foundations here in the North. The best thing to do is to do enough digging that you can put a drainage system around the outside of the foundation as it is being fixed. Gutters help control ground water too. Stone foundations are a good way to go, but concrete repairs are probably more common.
Sometimes you can bank dirt up against a barn foundation to stop the inward movement, but where you say stones have fallen in, you should repair the foundation, not just stabilize it.
Jim
