In soil mechanics, what does the term 'consistency limits' refer to?

• A. The range of moisture content in soils
• B. The limit of soil shear strength
• C. The boundary between liquid and plastic states of soil
• D. The effective stress state of the soil

Answer: (C)

The term 'consistency limits' refers specifically to the boundaries that define the various physical states of soil, particularly the transition between liquid and plastic states. These limits are crucial in understanding the behavior of cohesive soils, which can exhibit significantly different characteristics depending on their moisture content.

The liquid limit is the moisture content at which the soil transitions from a viscous (liquid) state to a plastic state, while the plastic limit is the point at which the soil changes from plastic behavior to a semi-solid state. The difference between these two points is known as the plasticity index, which quantifies the range of moisture content over which the soil remains workable. Consistency limits are key indicators of how a soil will behave under various loading and environmental conditions, thus playing a vital role in geotechnical engineering design and analysis.

Understanding these limits helps engineers predict performance in applications such as earthworks, slope stability, and foundation design.