A chainsaw is not the tool to use because the dirt will dull it in a few minutes and it will not cut. As suggested a reciprocating saw the way to go. It will cut through anything including steel but not rock. You may not think that you will ever use it again but I still use mine which I bought to the 70's and when I need it there is no substitute for it. Spend the money now and you'll be glad you did. You can get one for as little as $22 dollars at places like Harbor Freight and Walmart.