Does anyone know the grade like if your excavating close to a giant tree? I have 80 feet tall 3 feet round dougless fir tree's all over. Id like to cut as close as I can to the tree when I did the pond, but worried that the tree would topple over into the pond (or on me!) haha Does anyone know the rule of thumb on this? From the base of the tree. Where should I start digging and what grade? Should I use if I have heavy clay soil? I only want to dig down 8 feet..so just wondering?