This document discusses soil mechanics concepts including:
1) Soil can exist as a three phase system (solids, water, air), two phase dry system, or two phase wet system. Volume and weight relationships are provided.
2) Key terms are defined including void ratio, porosity, degree of saturation, dry density, bulk density, unit weights, specific gravity, and relative compaction.
3) Functional relationships are shown between void ratio, degree of saturation, porosity, dry density, saturated density, unit weights, and specific gravity. Approximation equations for relative compaction are also provided.