How is the soil classification affected by the group index?

The group index is a numerical value used in the classification of soils, particularly within the Unified Soil Classification System (USCS) and AASHTO soil classification systems. It plays a significant role in assessing the engineering properties of soil, specifically related to its stability and suitability for construction projects.

When the group index increases, it typically signifies poorer soil characteristics related to stability. Soils with higher group index values often exhibit additional properties such as greater plasticity, higher moisture content, or lower load-bearing capacity. These factors can critically affect the stability of structures built on or with the soil, making the group index a vital tool for engineers when determining soil suitability for foundations, roadways, and other infrastructure.

While other options mention various aspects of soil characteristics, such as types, cost, and workability, they do not capture the direct relationship between the group index and the soil's stability. The group index is distinctively meant to provide insights into soil conditions that influence its mechanical behavior under load, thus supporting the interpretation of soil stability for engineering applications.