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ISSCS classification, 55% passing 200

Short answer

CH, inorganic clay of high plasticity (fat clay). Fine-grained because 55% passes No. 200; wL=68>50 gives high plasticity. Ip=46 exceeds A-line value 35, so clay.

A soil has the following characteristics: a) Percentage of soil passing No. 200 sieve = 55 b) Percentage of coarse fraction passing No. 4 sieve = 60 c) Liquid limit = 68% d) Plastic limit = 22% Classify the given soil according to ISSCS.

Given

Passing No. 200 =55%= 55\%; wL=68%w_L = 68\%; wP=22%w_P = 22\% (the percentage of coarse fraction passing No. 4 is not needed).

Ip=68−22=46%I_p = 68 - 22 = 46\%

Step 1: Coarse or fine?

Since 55% passes the 75 micron sieve (more than 50%), the soil is fine-grained.

Step 2: Plasticity group (IS 1498)

  • wL<35%w_L < 35\%: low (L); 35−50%35 - 50\%: medium (I); >50%> 50\%: high (H).
  • wL=68%>50%w_L = 68\% > 50\%: high plasticity (H).

Step 3: Position relative to the A-line

Ip,A-line=0.73(wL−20)=0.73(68−20)=35.0%I_{p,A\text{-line}} = 0.73(w_L - 20) = 0.73(68 - 20) = 35.0\%

Ip=46>35.0I_p = 46 > 35.0: the soil plots above the A-line, so it is a clay (C) (inorganic).

Answer: CH, inorganic clay of high plasticity (fat clay). Because 45% is coarse, it may be described as a sandy or gravelly clay.

✓ Answer checked by Claude Opus 5.5 (high effort)

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