Arbutus: Damaged root of my Arbutus

I have been doing some excavating(by hand) in my backyard. The area is very rocky with a lot of pockets of air and soil. Everything has been fine until I think I accidently went through a root of my Arbutus. I am approximatly 3 feet away at the closest point to the Arbutus and the root is about 1" in dimeter. If this is indeed a root of the tree, which I suspect it is, what must I do to protect it. Also will this cause any damage to the tree?

Thanks for your time and I look forward to your reply.
JP