What does a high plasticity index suggest about a soil's behavior?

A high plasticity index indicates that the soil has the ability to undergo significant changes in volume with variations in moisture content. This property is crucial in assessing the behavior of soil when it interacts with water. Soils with high plasticity are typically associated with clayey materials, which can absorb water and swell, or dry out and shrink considerably. This characteristic can lead to challenges in construction and engineering applications, as the soil's ability to change volume can impact the stability and integrity of structures built upon it.

In the context of the other options, while a soil with a high plasticity index may also shrink significantly when dry and may be less stable under load, these are secondary effects of its primary characteristic of significant volume changes with moisture. The statement regarding its use in construction does not necessarily relate to the plasticity index; rather, it can reflect a soil's overall suitability for construction, which is influenced by multiple factors beyond just plasticity.