Concrete foundation repair
Concrete will deteriorate over time depending on the mineral content of the soil that is in contact with the concrete. Removal of the entire pour is not required or recommended. This would be costly and time consuming. The areas that sound hollow will have to be removed. These areas act like a cancerous pocket and will harbor the moisture that is partly causing the deterioration.Steps to consider:


Remove all hollow sounding areas with a pneumatic chisel hammer. (small one would be better).
Retrofit some rebar into the areas removed into the good concrete and set with epoxy.
Reinforce your basement with new shotcrete concrete.


Note: you will be tying into your existing concrete with new rebar and epoxy. Then set some screte boards to the depth of the new shotcrete wall thickness. Then you will be ready to hire a contractor who will apply the shotcrete with a pumper. You might want to contact a structural engineer to confirm this course of action... Good luck.