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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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A soil having liquid limit 60 % and plasticity index 40 % can be defined as
CL
CH
SM
CL-ML
CH
According to the Unified Soil Classification System (USCS), soils are classified based on the A-line chart in the plasticity chart. A soil with a liquid limit (LL) of 60% (which is > 50%) is classified as high plasticity (H), and since it plots above the A-line, it is identified as CH (Inorganic Clay of high plasticity).
According to the Unified Soil Classification System (USCS), soils are classified based on the A-line chart in the plasticity chart. A soil with a liquid limit (LL) of 60% (which is > 50%) is classified as high plasticity (H), and since it plots above the A-line, it is identified as CH (Inorganic Clay of high plasticity).
Ip=wL−wP — Plasticity Index definition
A−line:Ip=0.73(wL−20) — Boundary equation between clay and silt
The plasticity chart uses the A-line, defined by Ip=0.73(wL−20), to separate inorganic clays (C) from inorganic silts (M) or organic soils (O). Soils with wL>50% are designated as high plasticity (H), while those with wL<50% are designated as low plasticity (L). Here, wL=60%>50% and Ip=40%>0.73(60−20)=29.2%, confirming it is CH.
CH represents inorganic clays of high plasticity.
CL represents inorganic clays of low to medium plasticity (wL<50%).
Liquid Limit of 60% falls into the 'High' (H) category.
Plasticity Index of 40% ensures the soil plots well above the A-line.
Simple classification system based on Atterberg limits.
Provides reliable correlation with soil engineering properties like compressibility and shear strength.
Does not account for soil structure or fabric.
Less effective for soils with high organic content.
Foundation design and settlement analysis.
Subgrade suitability assessment for highways.
The A-line is the empirical line separating clays from silts.
Option A (CL) is incorrect because wL<50% is required for low-plasticity classification.
Option C (SM) is a coarse-grained soil classification, requiring < 50% passing the 0.075mm sieve.
B is correct — A soil with wL=60% and Ip=40% is classified as inorganic clay of high plasticity (CH) because it falls above the A-line and has a high liquid limit.
Remember the boundary wL=50% as the primary pivot for differentiating between 'L' (Low) and 'H' (High) plasticity in the USCS system.