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Systems by size and plasticity; ISSCS chart

Short answer

ISSCS plasticity chart plots Ip against wL with A-line; vertical lines at 35% and 50% give low, intermediate, high plasticity. Above A-line are clays, below are silts/organics; hatched zone gives CL-ML.

Write down the names of soil classification systems based on particle size and plasticity of soil. Define the plasticity chart of a soil based on ISSCS (Indian Standard Soil Classification System).

Systems based on particle size and plasticity

  • Unified Soil Classification System (USCS)
  • Indian Standard Soil Classification System (ISSCS, IS 1498)
  • AASHTO classification system
  • British Soil Classification System (BSCS)

Plasticity chart of ISSCS

The plasticity chart is a graph of plasticity index IpI_p (y-axis) against liquid limit wLw_L (x-axis), used for classifying the fine-grained soils (passing 75 micron).

  • A-line: Ip=0.73(wL−20)I_p = 0.73(w_L - 20). Inorganic clays (C) lie above it; silts (M) and organic soils (O) lie below it.
  • Vertical lines at wL=35%w_L = 35\% and 50%50\% divide the soils into low (L, wL<35w_L < 35), intermediate (I, 35 - 50) and high plasticity (H, wL>50w_L > 50).
  • The hatched area above the A-line with IpI_p between 4 and 7 gives dual symbol CL-ML.

The resulting groups are CL, CI, CH (clays), ML, MI, MH (silts), and OL, OI, OH (organic soils).

✓ Answer checked by Claude Opus 5.5 (high effort)

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