The correct arrangement of the given soil types classified as CH, ML, SP, and SW in the decreasing order of hydraulic conductivity is:

Option A: SW, SP, ML, CH

In the Unified Soil Classification System (USCS):

SW (Well-graded sand) generally has the highest hydraulic conductivity due to its larger particle size and well-graded nature, allowing water to pass through it easily.

SP (Poorly-graded sand) also has high hydraulic conductivity but slightly lower than well-graded sand.

ML (Silt particles) have much lower hydraulic conductivity compared to sands because of their smaller particle size, which hampers water flow.

CH (High plasticity clay) has the lowest hydraulic conductivity among these soil types due to its very fine particles and high plasticity, making it almost impermeable.

Thus, the decreasing order of hydraulic conductivity is:

$$ \text{SW} > \text{SP} > \text{ML} > \text{CH} $$

This matches Option A: SW, SP, ML, CH.

Classification of Soils and Clay Mineralogy · Geotechnical Engineering · GATE CE

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