Atterberg limits applicability — the liquid limit and plastic limit are meaningful primarily for which soil type?

Introduction / Context:
Atterberg limits quantify the consistency changes of fine-grained soils as water content varies. They underpin classification systems (USCS, BIS/IS) and correlate with engineering behavior such as compressibility and undrained shear strength. Understanding for which soils these limits are meaningful prevents misclassification and misuse of index properties.

Given Data / Assumptions:

• Liquid limit (LL) and plastic limit (PL) require cohesive, fine-grained behavior.
• Tests rely on plasticity and remoldability characteristics typical of clays.
• Silty soils may exhibit low plasticity but often yield less reliable limits.

Concept / Approach:

Clay soils (with significant clay mineral content) display distinct plastic and liquid states over a range of water contents. Their plate-like particles and electrochemical interactions enable rolling at PL and flow at LL. Coarse-grained soils (sands, gravels) lack plasticity; their measured “limits” are not meaningful. Silts can show borderline or low plasticity, but classical Atterberg limit interpretation is strongest and most diagnostic for clays.

Step-by-Step Solution:

Verification / Alternative check:

Plasticity chart (PI versus LL) reliably classifies clays into low, intermediate, high plasticity; sands and gravels plot as nonplastic.

Why Other Options Are Wrong:

Sands and gravels are nonplastic; Atterberg limits are not applicable. Silts may have marginal plasticity, but the question asks where the limits exist meaningfully — clays.

Common Pitfalls:

Assuming measurable LL/PL in silty sands implies cohesive behavior; misusing limits for coarse soils.

Final Answer:

clay soils