Explanation:

When discussing the behavior of soil, it is important to understand the concept of swell. Swell refers to the increase in volume that occurs when soil absorbs water. This increase in volume can have significant impacts on engineering structures, such as buildings, roads, and foundations.

Water Content and Swell

The water content of soil plays a crucial role in determining its swell potential. Swell is typically measured by conducting laboratory tests on soil samples and observing the increase in volume as water is added. The water content at which the soil stops swelling is known as the shrinkage limit.

Shrinkage Limit

The shrinkage limit is the water content below which a soil sample will no longer shrink in volume upon further drying. It represents the minimum water content required to maintain the soil in a stable state. At the shrinkage limit, the soil has reached its maximum dry density.

Relation to Swell

When the water content of a soil sample exceeds the shrinkage limit, it will begin to swell as it absorbs water. The soil particles absorb the water and expand, causing an increase in volume. As more water is added, the volume of the soil sample continues to increase until it reaches a point where it can no longer swell.

Shrinkage Limit and Water Content

The water content at which free swell ceases is the shrinkage limit. This is because the shrinkage limit represents the maximum water content that the soil can absorb while maintaining its stability. Beyond this point, any additional water will not be absorbed by the soil, and the swelling will stop.

Other Options

The other options provided in the question are not correct answers because they do not represent the water content at which free swell ceases. The liquid limit and plastic limit are properties used to characterize the plasticity of soil, while the plasticity index is a measure of the range of water content within which the soil behaves as a plastic material.

In conclusion, the correct answer to the question is option (c) shrinkage limit. This is the water content at which free swell ceases, as it represents the maximum water content that the soil can absorb while maintaining its stability.