A gopher dug a burrow under the corner of my concrete slab patio. The underlying soil is a sandy/clay mix, and the hole is approximately 6-8 inches in diameter. I need to know the best way to fill it. Should I back fill with the excavated dirt, or should I fill with gravel first and then the dirt?
Use the old soil, put it loosely in the hole and ram compact it with the end of a 2×4. This allows the soil to be compacted through the hole with an inexpensive tool. The end of the 2×4 can really pack the soil. If you have difficulty ramming the 2×4, use a sledge hammer to hit the end of the 2×4 board.
After you are finished compacting the soil, then soak water into the hole to wet the new dirt. Using gravel in the hole will create a sump and collect water in the gravel cavity below the patio. Dirt is the better answer.