Which type of soil would likely require a higher plasticity index?

The plasticity index of soil is a key indicator of its behavior when wet and dry, particularly in how it responds to changes in moisture. Clay is the type of soil that typically has a higher plasticity index because it contains fine particles that allow it to retain water and change its consistency significantly between its plastic and liquid states. The high clay content provides this soil with the ability to be molded when moist and to become hard and brittle when dry.

In contrast, gravel and sandy soils have larger particle sizes which do not hold water or changeTheir consistency in the same way. Gravel, being coarser, does not exhibit plastic behavior at all, while sandy soil tends to drain quickly and lacks the cohesion needed to develop a plasticity index. Loam is a mixture of sand, silt, and clay, and while it may have some plasticity due to clay content, it does not reach the levels characteristic of pure clay. Therefore, clay stands out as the type of soil that requires a higher plasticity index due to its unique physical properties and its ability to undergo significant changes with moisture content.