In roadway construction, which factor does NOT determine the economical thickness of subgrade?

The thickness of subgrade in roadway construction is primarily influenced by factors that directly affect the structural integrity, load distribution, and overall performance of the roadway. These include the embankment, base, and surfacing. Each of these factors plays a crucial role in determining the required thickness for stability and load-bearing capacity.

Embankment height impacts the total load on the subgrade, requiring an adequate thickness to support that load without significant deformation. The base layer provides support and distributes loads to the subgrade, necessitating consideration of its thickness to ensure proper performance. Surfacing relates to the load applied on the subgrade; different materials and thicknesses will require different subgrade thicknesses for adequate support.

Soil color, however, does not inherently affect the mechanical or physical properties of the soil in relation to load-bearing capacity or stability. While soil characteristics such as type, moisture content, and density are essential for evaluating subgrade performance, color merely indicates surface characteristics or organic content without a direct correlation to structural requirements. Therefore, it does not impact the economical design of subgrade thickness.