Reference
Modified Unified Soil Classification System
Typical descriptions on this chart are what Earthtec Log writes into the borehole log. Dual symbols are required if fines are 5–12%, or if the soil plots above the "A" line with 4 < Ip < 7.
Gravels
Coarse-grained — more than half of coarse grains larger than 4.75 mm (#4 sieve). More than 50% retained on the No. 200 sieve.
| Sym | Typical description | Fines | Grading / plasticity |
|---|---|---|---|
GW | WELL GRADED GRAVEL Well graded gravels, gravel-sand mixtures, little or no fines | 0–5% | Cu > 4 and 1 < Cc < 3 |
GP | POORLY GRADED GRAVEL Poorly graded gravels, gravel-sand mixtures, little or no fines | 0–5% | Not satisfying requirements for GW |
GM | SILTY GRAVEL Silty gravels, gravel-sand-silt mixtures | >12% | Below "A" line or Ip < 4 |
GC | CLAYEY GRAVEL Clayey gravels, gravel-sand-clay mixtures | >12% | Above "A" line and Ip > 7 |
Sands
Coarse-grained — more than half of coarse grains smaller than 4.75 mm. More than 50% retained on the No. 200 sieve.
| Sym | Typical description | Fines | Grading / plasticity |
|---|---|---|---|
SW | WELL GRADED SAND Well graded sands, gravelly sands, little or no fines | 0–5% | Cu > 6 and 1 < Cc < 3 |
SP | POORLY GRADED SAND Poorly graded sands, gravelly sands, little or no fines | 0–5% | Not satisfying requirements for SW |
SM | SILTY SAND Silty sands, sand-silt mixtures | >12% | Below "A" line or Ip < 4 |
SC | CLAYEY SAND Clayey sands, sand-clay mixtures | >12% | Above "A" line and Ip > 7 |
Silts
Fine-grained — more than 50% passing the No. 200 sieve. Below the "A" line, negligible organic content.
| Sym | Typical description | Fines | Grading / plasticity |
|---|---|---|---|
ML | SILT Inorganic silts and very fine sands, rock flour, silty or clayey fine sands or clayey silts with slight plasticity | — | WL < 50% and below "A" line |
MH | ELASTIC SILT Inorganic silts, micaceous or diatomaceous fine sandy or silty soils | — | WL > 50% and below "A" line |
Clays
Fine-grained. Above the "A" line, negligible organic content. This modified system adds CI for medium plasticity.
| Sym | Typical description | Fines | Grading / plasticity |
|---|---|---|---|
CL | CLAY of low plasticity Inorganic clays of low plasticity, gravelly, sandy, or silty clays, lean clays | — | WL < 30% and above "A" line |
CI | CLAY of medium plasticity Inorganic clays of medium plasticity, gravelly clays, sandy clays, silty clays | — | 30% < WL < 50% and above "A" line |
CH | CLAY of high plasticity Inorganic clays of high plasticity | — | WL > 50% and above "A" line |
Organic silts & clays
Below the "A" line.
| Sym | Typical description | Fines | Grading / plasticity |
|---|---|---|---|
OL | ORGANIC SILT Organic silts and organic silty clays of low and medium plasticity | — | WL < 50% and below "A" line |
OH | ORGANIC CLAY Organic silts and organic clays of high plasticity | — | WL > 50% and below "A" line |
Highly organic & other
Peat, topsoil, and undifferentiated fill as used on borehole logs.
| Sym | Typical description | Fines | Grading / plasticity |
|---|---|---|---|
Pt | PEAT Peat and other highly organic soils | — | Strong colour and odour, and often fibrous texture |
TS | TOPSOIL Topsoil | — | — |
FILL | FILL Undifferentiated fill | — | — |
Pavement & geosynthetics
Constructed layers encountered in excavations. Select these instead of writing a free-form description.
| Sym | Typical description | Fines | Grading / plasticity |
|---|---|---|---|
ASPH | ASPHALT Asphalt pavement | — | Record the full thickness of the asphalt as the layer contact |
CONC | CONCRETE Concrete | — | Slab, curb, footing, or buried concrete remnant |
CEM | CEMENT Cement or cement-treated material | — | Cement paste, slurry, lean mix, or cement-treated base |
GG | GEOGRID Geogrid | — | Record as a discrete layer at the contact depth |
NWF | NON-WOVEN FABRIC Non-woven geotextile fabric | — | Record as a discrete layer at the contact depth |
Plasticity chart
Conforms to USCS / ASTM D2487 except for the intermediate clay category CI (30% < WL < 50%). The "A" line divides clays from silts and organic soils. The "U" line marks a typical upper limit.
- Cu = D60 / D10
- Cc = (D30)² / (D60 × D10)
- Ip = plasticity index (%) · WL = liquid limit (%)
- Dual symbols required if 5–12% fines, or above the "A" line with 4 < Ip < 7.