Why won't rubber tires stay buried?
Most people, having never tried to bury a tire, are not aware that one will not stay in the ground. In fact, if you bury a tire five feet below the surface, it will—under normal conditions—rise to the top in about ten years.
The reason for this is as follows. The rubber tire, being resilient, is constantly pushing back against the soil around it. And since the pressure above the tire is less than that below it, the tire has more success pushing up than it does pushing down. As this pushing proceeds, small particles of soil around the tire are dislodged and fall down through cracks and crevices too small for the tire itself to fit through, a process that is accelerated somewhat by the slight movement of the tire as it expands and contracts with changes in temperature. Thus, as the tire pushes upward and the soil around it slowly moves down, the tire migrates toward the surface.
~source used: "Ever Wonder Why?" by Douglas B. Smith
.This story is like a rubber tire. I first posted it 4 years ago, now it has resurrected itself.