Which feature indicates Expansive Soils during evaluation?

The presence of slickensides is a key indicator of expansive soils during evaluation. Slickensides are a type of soil structure that forms when soil undergoes significant movement due to swelling and shrinking cycles related to moisture changes. This movement often occurs in soils with high clay content, particularly those rich in expansive clay minerals such as montmorillonite. As these soils expand when wet and contract when dry, they can create slickensides, which are often characterized by polished surfaces and linear features that form as soil particles slide past each other.

This physical evidence of soil movement and expansion directly correlates to the behavior of expansive soils, helping identify areas significantly impacted by these soil characteristics. While other factors like high sand content, a low resilience to moisture, or the absence of clay minerals may influence soil behavior, they do not provide the direct visual evidence of the expansive nature as slickensides do. Therefore, the visibility of slickensides in a field assessment is a crucial feature for identifying expansive soils.