Under a wheel,
the load is covered by the soil. Inside the soil, zone of the same pressure (isobars)
can be drawn like onion peels. Directly under the wheel the forces follow
gravity and form a compaction. But to the left and right of the main vertical
push, the soil can relax against the neighboring soil particles; the vectors
turn around. The parts of the soil near the surface give way to the pressure
and are lifted.
Thus, ruts
are not only the result of compaction, but also of lateral lifting of
the soils beneath the ruts.
