Why do potholes always return to the same spots, even after they are repaired?
Norman Dennis, professor of civil engineering, replies:
Potholes are always related to water. Potholes often return in places where we put a “bandage” on the pavement by patching the hole, but don’t fix the real source of the problem.
In cold climates, water that seeps through joints and cracks in the asphalt collects under the pavement and freezes to form what are known as ice lenses. These lenses can become quite large, measuring up to two meters in diameter.
When the ice lenses melt, either during the heat of the day or during the spring thaw, the water drains away, leaving a void near the surface. When cars drive over the place where the void exists, the pavement collapses into the void, creating a pothole.
In the South, where the temperatures rarely stay below freezing long enough to create ice lenses, the culprit behind potholes is the soil itself. Soil beneath the asphalt gets wet and softens. The weakened soils cannot carry the wheel loads transmitted by the asphalt, so when cars and trucks drive over the road the asphalt collapses into the area of weakened soil and a pothole forms.
Fixing a pothole correctly requires getting deep under the asphalt surface and providing materials to support the asphalt that drain well like sands and gravels. This way water does not build up under the pavement.
The best way to prevent potholes from forming is to build the entire substucture of the road out of free draining material and keep the pavement surface sealed. However, both of these methods cost lots of money, so instead you will continue to see potholes appearing and being fixed in many of the same places.