If the pores of a soil are completely full of air only, the soil is said to be..........
Try it first: pick an option, then read the explanation.
Correct answer: C. Dry soil
Detailed Explanation
If all the pore space (voids) in a soil mass contains only air, with no water present at all, the soil is classified as dry soil. In this state, the degree of saturation S = 0, the water content w = 0, and the phase diagram consists of only two phases: solid particles and air — the water block simply vanishes from the diagram.
This is the opposite extreme from saturated soil (all voids water-filled, no air, S = 1); most natural soils in the field sit somewhere between these two extremes, i.e., partially saturated.
Key Concepts for Students
- Dry soil: voids contain only air; S = 0, w = 0.
- Saturated soil: voids contain only water; S = 1 (100%), no air present.
- Partially saturated soil: the general, most commonly encountered case — voids contain a mix of air and water, 0 < S < 1.
- The phase diagram for dry soil reduces to just two blocks (solid and air), since the water phase has zero volume.