ABSTRACT
In contrast to agriculturists, engineers normally view soil merely in terms of unconsolidated sediments and deposits of solid particles derived from the disintegration of rock. Therefore in civil engineering the concept of soil includes all regolith material, and a sharp distinction between rock and soil is no longer made. In fact, the engineer is normally more concerned with what the agriculturist would term the C and D horizons than with the upper A and B horizons. From the engineering standpoint soil can be regarded as a three-phase system in some state of dynamic equilibrium. The three phases are soil (particulate organic and inorganic material), liquid (consisting of soil solutions containing various salts) and a gas
280 Soils and landforms phase containing soil air with changing amounts of oxygen, nitrogen and carbon dioxide. Plant cover and rooting systems are significant as stabilizers of soil conditions, but the engineer has few if any other interests in life within the soil.
