Where does the zero voids curve lie in relation to the Proctor test curve?

The zero voids curve represents the relationship between moisture content and dry density for a fully saturated soil, indicating the maximum density achievable without any voids in the soil. In contrast, the Proctor test curve illustrates the relationship between moisture content and dry density for soil subjected to compaction, showing the optimum moisture content at which maximum dry density is achieved for a given compactive effort.

The zero voids curve lies above the Proctor test curve because, at any given moisture content below saturation, the Proctor test accounts for the presence of air voids that the zero voids curve does not consider. Thus, the maximum dry density obtained from the Proctor test is lower than that indicated by the zero voids curve at the same moisture content, given that the latter assumes complete saturation and no air voids. This relationship highlights the importance of moisture content in achieving the desired density in soils through compaction, reinforcing the understanding of soil behavior under varying conditions.

In summary, the zero voids curve lies above the Proctor test curve because it represents the theoretical maximum density without air voids, while the Proctor test reflects real-world conditions where voids are present, thus yielding a lower density for the same moisture content.