Geotechnical

USCS Soil Classification (ASTM D2487)

Unified Soil Classification System group symbol and name from gradation (percent gravel/sand/fines or sieve passing percents, D10/D30/D60 or Cu/Cc) and Atterberg limits (LL, PL or PI), following the ASTM D2487 flowchart: 50% fines split, A-line plasticity chart, dual symbols at 5–12% fines, CL-ML hatched zone. Use for: 'classify this soil (USCS)', group symbol from sieve + Atterberg data. Not for: AASHTO classification (separate solver) or organic-soil (OL/OH) identification.

Direct solving is free and needs no account. Have a word problem instead? Submit it as text.

Inputs

Units

Load a sample problem:

gravel percent (optional)Percent gravel (coarser than the No. 4 sieve), 0–100sand percent (optional)Percent sand (passing No. 4, retained on No. 200), 0–100fines percent (optional)Percent fines (passing the No. 200 sieve), 0–100passing no4 (optional)Percent passing the No. 4 sieve (alternative to gravel/sand/fines percents)passing no200 (optional)Percent passing the No. 200 sieve (alternative to finesPercent)d10 (optional)Grain size D10 (10% passing) [dimension: length]d30 (optional)Grain size D30 (30% passing) [dimension: length]d60 (optional)Grain size D60 (60% passing) [dimension: length]cu (optional)Coefficient of uniformity Cu = D60/D10, if given directly instead of D-valuescc (optional)Coefficient of curvature Cc = D30²/(D10·D60), if given directly instead of D-valuesliquid limit (optional)Liquid limit LL of the fines (percent, e.g. 40)plastic limit (optional)Plastic limit PL of the fines (percent, e.g. 18)plasticity index (optional)Plasticity index PI = LL − PL, if given directly

Worked examples

These are the solver's own reference problems — the answers come from published sources or independent hand computation, never from the solver itself. The solution below is the live solver output for each.

Example 1

SW-SM dual symbol: sand, 8% fines, Cu=8, Cc=1.5, ML fines

Given

gravel percent: 10
sand percent: 82
fines percent: 8
cu: 8
cc: 1.5
liquid limit: 30
plastic limit: 26

Assumptions

Classification follows the ASTM D2487 (USCS) flowchart for inorganic soils; organic soils (OL/OH/PT) are not evaluated.
Result: SW-SM (well-graded sand with silt)

Solution steps

Gradation summary
Fines (passing the No. 200 sieve) decide the top-level split: 50% or more fines is fine-grained, less is coarse-grained.
fines = 8 %; sand = 82 %; gravel = 10 %
Coarse-grained soil: gravel or sand?
With less than 50% fines the soil is coarse-grained; the larger coarse fraction names it.
fines = 8 % < 50 %; gravel = 10 % ≤ sand = 82 % → sand
Borderline fines: dual symbol
Fines between 5% and 12% take a dual symbol: gradation (W/P) first, fines type (M/C) second.
5 % ≤ fines = 8 % ≤ 12 %
Gradation shape: well or poorly graded?
Well-graded sand requires Cu ≥ 6 with Cc between 1 and 3.
Cu = D60/D10 and Cc = D30² / (D10·D60)
Cu = 8 and Cc = 1.5; limits: Cu ≥ 6 and 1 ≤ Cc ≤ 3 → well graded
Plasticity chart (A-line) check
The A-line PI = 0.73(LL − 20) separates clays (on or above) from silts (below); the hatched CL-ML zone is PI between 4 and 7 on or above the A-line.
PI_A-line = 0.73·(LL − 20)
A-line at LL = 30: PI_A = 0.73 × 10 = 7.3; soil PI = 4 (below the A-line)
Classification: SW-SM
Group symbol SW-SM — well-graded sand with silt (ASTM D2487 group name).

Results

Fines content (passing No. 200)

Gravel fraction

Sand fraction

Coefficient of uniformity Cu = D60/D10

Coefficient of curvature Cc = D30²/(D10·D60)

1.5

Plasticity index PI = LL − PL

Where this answer was checked

source: ASTM D2487 flowchart criteria (as tabulated in the NCEES FE Reference Handbook) — 5–12% fines → dual symbol; Cu ≥ 6 and 1 ≤ Cc ≤ 3 → SW; PI below A-line → M
verified by: hand-recomputed
derivation: Fines 8% < 50 → coarse; sand 82 > gravel 10 → S. 5 ≤ 8 ≤ 12 → dual. Gradation: Cu = 8 ≥ 6 and Cc = 1.5 in [1,3] → W. Fines: PI = 30 − 26 = 4; A-line = 0.73(30−20) = 7.3; 4 < 7.3 → below A-line → ML → M. Symbol SW-SM, name 'well-graded sand with silt' (gravel 10% < 15% adds no modifier).

Example 2

sandy lean clay CL: 65% fines, LL=40, PL=18

Given

fines percent: 65
sand percent: 30
gravel percent: 5
liquid limit: 40
plastic limit: 18

Assumptions

Classification follows the ASTM D2487 (USCS) flowchart for inorganic soils; organic soils (OL/OH/PT) are not evaluated.
Result: CL (sandy lean clay)

Solution steps

Gradation summary
Fines (passing the No. 200 sieve) decide the top-level split: 50% or more fines is fine-grained, less is coarse-grained.
fines = 65 %; sand = 30 %; gravel = 5 %
Fine-grained soil
Half or more of the soil passes the No. 200 sieve, so the group is decided entirely on the plasticity chart.
fines = 65 % ≥ 50 %
Plasticity index
PI is the plastic range of the fines.
PI = LL − PL
PI = 40 − 18 = 22
= 22
Plasticity chart (A-line) check
The A-line PI = 0.73(LL − 20) separates clays (on or above) from silts (below); the hatched CL-ML zone is PI between 4 and 7 on or above the A-line.
PI_A-line = 0.73·(LL − 20)
A-line at LL = 40: PI_A = 0.73 × 20 = 14.6; soil PI = 22 (on or above the A-line)
Classification: CL
Group symbol CL — sandy lean clay (ASTM D2487 group name).

Results

Fines content (passing No. 200)

Gravel fraction

Sand fraction

Plasticity index PI = LL − PL

Where this answer was checked

source: ASTM D2487 flowchart criteria (as tabulated in the NCEES FE Reference Handbook) — ≥50% fines → plasticity chart; PI > 7 and above A-line, LL < 50 → CL
verified by: hand-recomputed
derivation: Fines 65 ≥ 50 → fine-grained. PI = 40 − 18 = 22; A-line = 0.73(40−20) = 14.6; 22 > 14.6 and 22 > 7 → CL; LL 40 < 50 → low plasticity. Coarse fraction 35% ≥ 30% with sand 30 ≥ gravel 5 → 'sandy lean clay'.

Example 3

GW from D-sizes: gravel 70%, 3% fines, D10=0.3, D30=2, D60=9 mm

Given

gravel percent: 70
sand percent: 27
fines percent: 3
d10: 0.3 mm
d30: 2 mm
d60: 9 mm

Assumptions

Classification follows the ASTM D2487 (USCS) flowchart for inorganic soils; organic soils (OL/OH/PT) are not evaluated.
Result: GW (well-graded gravel with sand)

Solution steps

Gradation summary
Fines (passing the No. 200 sieve) decide the top-level split: 50% or more fines is fine-grained, less is coarse-grained.
fines = 3 %; sand = 27 %; gravel = 70 %
Coarse-grained soil: gravel or sand?
With less than 50% fines the soil is coarse-grained; the larger coarse fraction names it.
fines = 3 % < 50 %; gravel = 70 % > sand = 27 % → gravel
Clean coarse soil
Under 5% fines: the fines are ignored and gradation alone decides the second letter.
fines = 3 % < 5 %
Gradation shape: well or poorly graded?
Well-graded gravel requires Cu ≥ 4 with Cc between 1 and 3.
Cu = D60/D10 and Cc = D30² / (D10·D60)
Cu = 9 mm / 0.3 mm = 30; Cc = 2 mm² / (0.3 mm × 9 mm) = 1.48; limits: Cu ≥ 4 and 1 ≤ Cc ≤ 3 → well graded
Classification: GW
Group symbol GW — well-graded gravel with sand (ASTM D2487 group name).

Results

Fines content (passing No. 200)

Gravel fraction

Sand fraction

Coefficient of uniformity Cu = D60/D10

Coefficient of curvature Cc = D30²/(D10·D60)

1.48

Where this answer was checked

source: ASTM D2487 gradation criteria; Cu and Cc closed forms — Cu = D60/D10 = 30, Cc = D30²/(D10·D60) = 1.481 → GW; sand 27% ≥ 15% → 'with sand'
verified by: hand-recomputed
derivation: Fines 3% < 5 → clean; gravel 70 > sand 27 → G. Cu = 9/0.3 = 30 ≥ 4; Cc = 2²/(0.3·9) = 4/2.7 = 1.48148 in [1,3] → GW, 'well-graded gravel with sand'.