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AASHTO soil classification flowchart systematically categorizes soils from A-1 (excellent) to A-7 (poor) based on particle size, plasticity index, and sieve analysis. The diagram evaluates soil stability under traffic loads and determines suitability for road bases, subbases, and subgrades using the No. 200 sieve threshold and plasticity criteria. Engineers use this classification to predict soil behavior, select appropriate materials, and design durable pavement structures that meet highway standards. Fork this diagram to customize soil group criteria, add local specifications, or integrate into geotechnical reports and design documentation. The advanced A-7 subgroup distinction (A-7-5 vs. A-7-6) reflects volumetric change potential critical for long-term pavement performance.

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How do I classify soil using the AASHTO system for road construction?

The AASHTO classification system categorizes soils A-1 (excellent) through A-7 (poor) using sieve analysis (No. 200 threshold), plasticity index, and liquid limit. Granular materials (≤35% passing No. 200) are groups A-1 to A-3; silt-clay materials (>35% passing) are A-4 to A-7, with A-7 subdivided into A-7-5 and A-7-6 based on volumetric change potential.