I am hollowing out a space underneath my cabin to create another room that will end up being a box within a box on its own foundation. the cabins orginal foundation is 6" wide, a couple of feet tall with a 22' length. Below ground level the foundation is roughly a foot wide (uneven) and extends below ground level about 2 feet. I am removing most of the dirt along the inside face but not undercuttting the foundation. Starting about 6" below the deepest part of the foundation I will run a 6x6 trench parallel with the original wall for my footing. My question is: have I compromised the original foundation? It seems to me the weight is downward on the foundation and not lateral so I don't think the original could fail (by buckling maybe)?