I have tree roots that are growing at the same level of the soil. I want to build a patio there. I know I am supposed to dig down into the ground to put rock and sand under the stone. If I do this I will kill the tree, I would like to keep it for the shade on the patio. Can I build the patio over the roots? Can I build a square with railroad ties and fill it with the rock and sand I am supposed to burry? I thought I could hold them in place with concrete. Spikes sticking out of the concrete and through the ties would keep them in place. Will this work? Thanks