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USCS classification of soils A and B

Short answer

Soil A is CL, sandy lean clay; Soil B is MH, inorganic elastic silt. Both pass 75 micron more than 50%, so fine-grained. A has Ip=29 above A-line 18.25 and wL=45<50; B has Ip=15 below A-line 25.55 and wL=55>50.

Classify the soils A and B with the properties shown below according to the unified soil classification system.

SoilwLw_L (%)IpI_p (%)% passing through 4.75 mm sieve% passing through 75 µ sieve
A452910059
B551510085

Soils A and B have 59% and 85% passing the 75 micron sieve (more than 50%), so both are fine-grained. Use the plasticity chart with the A-line Ip=0.73(wL−20)I_p = 0.73(w_L - 20).

Soil A: wL=45%w_L = 45\%, Ip=29%I_p = 29\%

Ip,A-line=0.73(45−20)=18.25%I_{p,A\text{-line}} = 0.73(45 - 20) = 18.25\%

Ip=29>18.25I_p = 29 > 18.25, so the soil lies above the A-line (clay), and wL=45<50w_L = 45 < 50 (low plasticity).

Soil A: CL, inorganic clay of low plasticity (lean clay). It is also sandy, since 41% is coarse.

Soil B: wL=55%w_L = 55\%, Ip=15%I_p = 15\%

Ip,A-line=0.73(55−20)=25.55%I_{p,A\text{-line}} = 0.73(55 - 20) = 25.55\%

Ip=15<25.55I_p = 15 < 25.55, so the soil lies below the A-line (silt), and wL=55>50w_L = 55 > 50 (high plasticity).

Soil B: MH, inorganic silt of high plasticity (elastic silt).

(Both are taken as inorganic, since no data on organic content is given.)

✓ Answer checked by Claude Opus 5.5 (high effort)

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