I built a wall the other week that was next to a driveway that hasn't been pored yet. Before I built the wall a water main pipe was dug up and buried where the wall crossed in one section. The hole was filled with looked like crush gravel all the way to the pipe. I didn't excavate all the way down. I guess I assumed the gravel would have been compacted. Guess not. I will have to replace now. Bummer.