  The soil compaction by vehicles is a major factor responsible for physical
degradation of cultivated soils. Uniaxial confined compression tests are
usually performed to characterise the compaction properties of soil. Two main
forms of compression curve have been observed: (i) the bi-linear curve having
an elastic rebound curve at low stresses and a linear virgin compression curve
at higher stresses; (ii) the S-shaped curve having deviation of the virgin
compression curve at high stresses. In the present work, uniaxial confined
compression tests were performed on four soils having various textures and
different plasticity. Tests were performed on undisturbed and remould samples,
at various initial dry bulk densities and water contents. The S-shaped
compression curves were observed more frequently when the clay content and/or
the initial water content were high. In addition, the S-shaped curves were
observed more frequently on remould soils than on undisturbed soils. The
difference between the compression of air-filled pores and that of meso-pores
storing water subjected to high capillary forces could explain the observed
S-shaped curves.
