A fully saturated soil is best described as which phase system?

• A. One-phase system consisting of soil solids
• B. Two-phase system consisting of soil solids and air
• C. Two-phase system consisting of soil solids and water
• D. Three-phase system consisting of soil solids, water, and air

Answer: (C)

A fully saturated soil is best described as a two-phase system consisting of soil solids and water. In a fully saturated condition, all the void spaces within the soil are filled with water, and there is no air present in those voids.

In this context, "soil solids" refer to the particles that make up the structure of the soil. When the soil is fully saturated, the water takes the place of the air that would normally be present in the pores. Therefore, the primary distinction is the complete occupancy of the void space by water, signifying that the soil's condition allows it to be represented as comprising just two components: the soil particles and the water filling the voids.

When examining other options, they do not characterize a fully saturated soil accurately. A one-phase system comprising only soil solids ignores the presence of water entirely, while a two-phase system that includes both soil solids and air would be applicable to unsaturated or partially saturated conditions. A three-phase system would include soil solids, water, and air, which describes a state of partial saturation rather than full saturation. Thus, the choice that describes fully saturated soil as consisting solely of soil solids and water reflects the correct interpretation of the soil's phase state.