Soil Consistency Limits – Order of liquid, plastic, and shrinkage limits for cohesive soils Choose the correct inequality among liquid limit (LL), plastic limit (PL), and shrinkage limit (SL).

Introduction / Context:Atterberg limits define moisture contents at which a fine-grained soil changes state. The liquid limit (LL) marks the transition from plastic to liquid behavior, the plastic limit (PL) from semi-solid to plastic, and the shrinkage limit (SL) from solid to semi-solid with volume change ceasing. Understanding their correct order is essential for classification and prediction of engineering behavior.

Given Data / Assumptions:

• Cohesive (clayey/silty) soil exhibiting measurable plasticity.
• Standard test methods for LL, PL, SL.
• Water contents are expressed in percent by mass.

Concept / Approach:

As water content decreases from a very wet state, soil passes through liquid, plastic, semi-solid, and solid states. Therefore: LL is highest, followed by PL, and then SL as the lowest. This yields LL > PL > SL. The plasticity index PI = LL − PL and shrinkage index IS = SL relations are then used for classification and volumetric change assessment.

Step-by-Step Solution:

Verification / Alternative check:

Typical values for clays: LL in the range 30–80% (or more), PL perhaps 15–40%, SL generally lower than PL. Field experience and lab databases satisfy LL > PL > SL across most cohesive soils.

Why Other Options Are Wrong:

Options A, C, D invert or mix the inequalities; Option E suggesting equality is physically unrealistic because each limit corresponds to a different moisture state and mechanism.

Common Pitfalls:

Confusing the order when moving from wet to dry states, or misreporting units. Also, assuming SL means zero water content—SL is a finite moisture content at which further drying does not reduce volume.

Final Answer:

LL > PL > SL