Soil phase relationships — the ratio of the volume of voids to the volume of soil solids in a given soil mass is called:

Introduction / Context:
Two foundational volumetric indices in soil mechanics are porosity (n) and void ratio (e). They quantify how much of the total space is empty (air and/or water) relative to solids and are indispensable in consolidation, permeability, and compaction analyses. Correctly distinguishing e from n is vital when converting between laboratory measurements and design parameters.

Given Data / Assumptions:

• Total volume V consists of Vv (voids) and Vs (solids): V = Vv + Vs.
• Void space may be partially or fully saturated with water.
• Representative elementary volume is considered.

Concept / Approach:

The void ratio is defined as e = Vv / Vs. Porosity is defined as n = Vv / V. The two are related by n = e / (1 + e) and e = n / (1 - n). Engineers use e to link volumes to masses through Gs and unit weights, for example in the equation gamma_d = (Gs * gamma_w) / (1 + e) for dry unit weight (symbol meanings as usual).

Step-by-Step Solution:

Verification / Alternative check:

Cross-validate using mass-based measurements: if gamma_d and Gs are known, rearrange gamma_d = (Gs * gamma_w) / (1 + e) to solve for e and compare with volumetric determination.

Why Other Options Are Wrong:

Porosity uses total volume V, not solids volume. Specific gravity compares weights of equal volumes of solids and water. Water content is mass of water over mass of dry soil. Degree of saturation is volume of water over volume of voids.

Common Pitfalls:

Interchanging e and n; mixing inconsistent units; using bulk volumes that include container voids.

Final Answer:

void ratio