How close to edge, of unreinforced trench fill foundation, can wall be before concrete cracks?
In layman terms, it will be no stronger than its weekest point. The fact you have unreinforced concrete suggests the designer was relying on the sub-surface to be the structural support. As u have mentioned it is not good, chances are u will need to make modifications to something in order to do what you want. Good luck. And it is a good idea to ask your local building inspectors this question.
