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AASHTO Soil Classification System
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<p>The AASHTO Soil Classification System was developed by the <a href="/facts/American_Association_of_State_Highway_and_Transportation_Officials/IlB1BuPQ">American Association of State Highway and Transportation Officials</a>, and is used as a guide for the <a href="/facts/Soil_classification/gru7kDvL">classification of soils</a> and soil-aggregate mixtures for <a href="/facts/Highway_construction/3aadH4s3">highway construction</a> purposes. The classification system was first developed by Hogentogler and <a href="/facts/Karl_von_Terzaghi/tcUP6LoG">Terzaghi</a> in 1929, but has been revised several times since. </p> AASHTO Soil Classification System (from AASHTO M 145 or ASTM D3282)<table><tbody><tr><th>General Classification</th><th colspan="7">Granular Materials (35% or less passing the 0.075 mm (No. 200) sieve)</th><th colspan="4"><a href="/facts/Silt/HAxJkhDP">Silt</a>-<a href="/facts/Clay/xnwouEkB">Clay</a> Materials (>35% passing the 0.075 mm (No. 200) sieve)</th></tr><tr><td rowspan="2">Group Classification</td><td colspan="2">A-1</td><td rowspan="2">A-3</td><td colspan="4">A-2</td><td rowspan="2">A-4</td><td rowspan="2">A-5</td><td rowspan="2">A-6</td><td>A-7</td></tr><tr><td>A-1-a</td><td>A-1-b</td><td>A-2-4</td><td>A-2-5</td><td>A-2-6</td><td>A-2-7</td><td>A-7-5 A-7-6</td></tr><tr><td><a href="/facts/Sieve_Analysis/ISBCHmjh">Sieve Analysis</a>, % passing</td><td colspan="11"></td></tr><tr><td>2.00 mm (No. 10)</td><td>50 max</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td></tr><tr><td>0.4255 mm (No. 40)</td><td>30 max</td><td>50 max</td><td>51 min</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td><td>…</td></tr><tr><td>0.0755 mm (No. 200)</td><td>15 max</td><td>25 max</td><td>10 max</td><td>35 max</td><td>35 max</td><td>35 max</td><td>35 max</td><td>36 min</td><td>36 min</td><td>36 min</td><td>36 min</td></tr><tr><td>Characteristics of fraction passing 0.425 mm (No. 40)</td><td colspan="11"></td></tr><tr><td><a href="/facts/Liquid_Limit/vVBMPgoH">Liquid Limit</a></td><td colspan="2">…</td><td>…</td><td>40 max</td><td>41 min</td><td>40 max</td><td>41 min</td><td>40 max</td><td>41 min</td><td>40 max</td><td>41 min</td></tr><tr><td><a href="/facts/Plasticity_index/vVBMPgoH">Plasticity index</a></td><td colspan="2">6 max</td><td>N.P.</td><td>10 max</td><td>10 max</td><td>11 min</td><td>11 min</td><td>10 max</td><td>10 max</td><td>11 min</td><td>11 min1</td></tr><tr><td>Usual types of significant constituent materials</td><td colspan="2">stone fragments, gravel and sand</td><td>fine sand</td><td colspan="4">silty or clayey gravel and sand</td><td colspan="2">silty soils</td><td colspan="2">clayey soils</td></tr><tr><td>General rating as a subgrade</td><td colspan="7">excellent to good</td><td colspan="4">fair to poor</td></tr></tbody></table> <p>Plasticity index of A-7-5 subgroup is equal to or less than the LL - 30. Plasticity index of A-7-6 subgroup is greater than LL - 30. </p>