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GATE 2025 CE (CE1) – Question 18

Geotechnical Engineering · Three-phase system, phase relationships, index properties and soil classification · 1 mark · Multiple choice

The standard plasticity chart for the classification of a fine-grained soil is shown in the figure. As per the Indian standard soil classification system, X represents

A plasticity chart with the liquid limit (%) on the horizontal axis and the plasticity index (%) on the vertical axis. The A-line starts at a liquid limit of 20 and rises to the right. Dashed vertical lines mark liquid limits of 35 and 50. The point X lies to the right of the 50 line and above the A-line.
  1. inorganic clay with medium plasticity
  2. inorganic silt with medium plasticity
  3. inorganic clay with high plasticity
  4. inorganic silt with high compressibility

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Correct answer: (C) inorganic clay with high plasticity

Explanation

Points above the A-line are clays and points below it are silts or organic soils. Under IS classification a liquid limit below 35 % is low plasticity, 35 to 50 % is medium and above 50 % is high. X is above the A-line and to the right of the 50 % line, so it is an inorganic clay of high plasticity (CH).