Zero-air-voids (saturation) unit weight – dependent variables At zero air voids (100% saturation), the unit weight of soil depends on which of the following basic quantities?

Introduction:
The zero-air-voids concept provides an upper bound for the dry density (or unit weight) a soil can theoretically attain at a given water content if it were fully saturated with no entrapped air. This line is frequently plotted on compaction curves to judge compaction efficiency and realistic targets in the field.

Given Data / Assumptions:

• Fully saturated soil mass (Sr = 100%).
• Specific gravity of solids Gs given for the soil mineralogy.
• Water content w expressed as mass of water to mass of solids.
• Unit weight of water gamma_w known (≈ 9.81 kN/m^3).

Concept / Approach:

The zero-air-voids unit weight gamma_zav (or corresponding dry unit weight) is derived from phase relationships under Sr = 1. The expression includes Gs, w, and gamma_w; therefore, all three variables govern the result. Intuitively, heavier mineral grains (higher Gs) and higher water content (at full saturation) affect the total mass per unit volume, while gamma_w provides the link from water mass to weight.

Step-by-Step Solution:

Verification / Alternative check:

Typical compaction charts plot the zero-air-voids line using the above inputs; changing Gs or gamma_w shifts the curve, and different w values trace the line.

Why Other Options Are Wrong:

Any single parameter alone is insufficient; ‘‘none’’ contradicts the derivation.

Common Pitfalls:

Confusing the zero-air-voids line with the line of optimum moisture contents; assuming gamma_w is always constant regardless of temperature (minor variation exists).

Final Answer:

all the above