Compaction theory — the theoretical maximum dry density at a given water content is referred to as:

Introduction / Context:
In laboratory compaction (Proctor) tests, the dry density–water content curve approaches an upper theoretical limit called the zero air-voids (ZAV) line. This line represents the maximum possible dry density at a given water content if all air were removed from the voids, which is not practically achievable during normal compaction.

Given Data / Assumptions:

• ZAV condition implies percentage air voids na = 0.
• Specific gravity G and water content w govern the ZAV line.
• No collapse or particle crushing is considered.

Concept / Approach:
The ZAV dry density is given by the relation:
gamma_d(ZAV) = gamma_w / (w + 1/G)
where gamma_w is unit weight of water, w is decimal water content, and G is the specific gravity of solids. Actual compaction curves lie below this line due to trapped air and energy limitations. The ZAV concept provides a benchmark for evaluating compaction results and moisture control strategies in the field.

Step-by-Step Solution:

Verification / Alternative check:
Plotting the ZAV line with Proctor data shows the experimental curve approaching but never crossing the ZAV limit.

Why Other Options Are Wrong:

• Option A: Generic term; not necessarily the theoretical maximum.
• Option C: The phrase “saturation dry density” is ambiguous; at full saturation, dry density is not defined as “maximum” without the ZAV context.
• Option D/E: Overbroad or imprecise.

Common Pitfalls:
Confusing ZAV with optimum water content (OMC) where peak measured dry density occurs; the ZAV is a theoretical upper bound, not necessarily achieved at OMC.

Final Answer:
Zero air-voids dry density (airless condition)