Soil phase interaction diagram maps the three-phase composition of soil—solid mineral particles, pore water, and air voids—and their mechanical behavior under loading. The flowchart traces how relative proportions and particle contact govern soil deformation, distinguishing saturated and unsaturated conditions and their distinct stress-strain responses. Key concepts include normal and tangential forces at particle contacts, effective stress calculation (σ' = σ − μ), and consolidation driven by drainage and volume reduction. This educational framework helps geotechnical engineers predict soil behavior under foundation loads and design appropriate remediation strategies. Fork and customize this diagram on Diagrams.so to build your own soil mechanics reference or embed it in course materials and technical reports.