I have a driveway which is on a pretty steep grade, so the builder installed a drain trench running perpendicular to the slope to make sure the water didn't collect at the bottom of the hill and freeze in the winter. Well, that trench apparently wasn't hooked up to the storm drain correctly and it had been leaking for over a year. All of a sudden last week I noticed a relatively small hole in the asphalt above that bad connection. Looking closer, I saw that the hole underneath was huge.

So I fixed the leak and filled the hole with gravel (50 gallons worth!). Then i poured concrete over the gravel, and added asphalt on top. I thought that would do it, but after another heavy rain today, I noticed that whole area had sunk a little, and on a closer look, saw that another huge hole underneath was there, at least as big as before. I can barely see any of the gravel I put in there last week.

Did I do something wrong? Where is all this gravel and dirt going? How can I fix the problem?

Thanks-

G