Ask the Foundation Expert Blog

According to the Unified Soil Classification System (USCS), a soil classification
system used in geology and engineering to describe texture and grain size of soil, there are 15 soil types.

1. Well Graded Gravel/Fine to Course Gravel (GW) - Clean gravel with greater than 50% of coarse fraction retained on No. 4 sieve.
2. Poorly Graded Gravel (GP) - Clean gravel with greater than 50% of coarse fraction retained on No. 4 sieve.
3. Silty Gravel (GM) - Gravel with greater than 12% fines and 50% of coarse gravel fraction retained on No. 4 sieve.
4. Clayey Gravel (GC) - Also Gravel with greater than 12% fines and 50% of coarse gravel fraction retained on No. 4 sieve.
5. Well Graded Sand/Fine to Course Sand (SW) - Clean sand with greater than or equal to 50% of coarse fraction retained on No. 4 sieve.
6. Poorly-Graded Sand (SP) - Clean sand with greater than or equal to 50% of coarse fraction retained on No. 4 sieve.
7. Silty Sand (SM) -  Sand with greater than 12% fines and greater than or equal to 50% of coarse fraction retained on No. 4 sieve.
8. Clayey Sand (SC) - Inorganic silt and clay with less than 50% liquid limit.
9. Silt (ML) - Inorganic silt and clay with less than 50% liquid limit also in higher division of  fine grained soils in which more than 50% passes No.200 sieve
10. Clay (CL) - Inorganic silt and clay with less than 50% liquid limit also in higher division of  fine grained soils in which more than 50% passes No.200 sieve.
11. Organic Silt/Organic Clay (OL) -  Organic silt and clay with less than 50% liquid limit also in higher division of  fine grained soils in which more than 50% passes No.200 sieve.
12. Silt of High Plasticity/Elastic Silt (MH) - Inorganic silt and clay with greater than or equal to 50% liquid limit also in higher division of  fine grained soils in which more than 50% passes No.200 sieve.
13. Clay of High Plasticity/Fat Clay (CH) - Inorganic silt and clay with greater than or equal to 50% liquid limit also in higher division of  fine grained soils in which more than 50% passes No.200 sieve.
14. Organic Clay/Organic Silt (OH) - Organic silt and clay with greater than or equal to 50% liquid limit also in higher division of  fine grained soils in which more than 50% passes No.200 sieve.
15. Peat (Pt) - Highly organic soils.