What are the three phases of soil and how are they related?

Soil consists of three phases: solid particles (mineral grains), water (pore water), and air (pore air). Key relationships include: void ratio (e) = volume of voids/volume of solids, porosity (n) = volume of voids/total volume, degree of saturation (S) = volume of water/volume of voids. For saturated soil, S = 100% and all voids are filled with water. These relationships are fundamental for calculating unit weights and understanding soil behavior.