The project is to rebuild a small brick walkway, about 15' long. The current walk has heaved quite badly due to freeze/thaw in the spring. The previous installation was not dug down very deep and only sand was used (according to the homeowner). In addition, they get a lot of water flow in the spring. The soil is clay and the house is situated on a moderate hillside. I need to rebuild and alleviate the drainage/freezing issues. Rebuilding with a good sub-base will likely eliminate most, if not all of the problems but I don't want to take any chances. Also, the homeowner has talked to "others" who have suggested putting Styrofoam insulation under the walkway, similar to what is often done under cement slabs. I've never done this before, however, but it doesn't seem like a terrible idea. At the very least, if the walk does move, it will move in 4' x 8' sections! Anyway, my plan is to excavate deep and fill/construct with the following: 1. Geofabric over existing subsoil 2. 5" of 3/4 compacted crushed stone with drainage pipe that will exit from the side of the walkway This should allow any water traveling through the ground to move freely under the walk and out the drain pipe 3. Geofabric over the stone to prevent mixing 4. 4" compacted gravel 5. 1" sand bedding layer 6. Brick So where should I put the styrofoam? Seems the most logical place would be between the gravel and the sand BUT would this prevent water from percolating through the walkway, thus keeping the sand layer saturated and prone to freezing and heaving, and second, will the foam, that close to the surface make the walkway spongy?