Compute degree of saturation from given phase data: For a soil with void ratio e = 0.67, water content w = 0.188 (18.8%), and specific gravity of solids G = 2.68, determine the degree of saturation Sr (expressed as a percentage).

Introduction / Context:
Phase relationships connect the volumetric and gravimetric properties of soils. The degree of saturation Sr is a key descriptor for seepage behavior, compressibility, and compaction performance. This problem illustrates the direct use of a fundamental identity to compute Sr from e, w, and G.

Given Data / Assumptions:

• Void ratio e = 0.67.
• Water content w = 0.188 (decimal form; 18.8%).
• Specific gravity of solids G = 2.68.
• Standard definitions and consistent units; ρw cancels in the identity used.

Concept / Approach:
The fundamental relation between degree of saturation, water content, specific gravity, and void ratio is:
Sr = (w * G) / e
where w is decimal water content. This follows from standard phase-relationship derivations using volumes and masses of water and solids.

Step-by-Step Solution:

Verification / Alternative check:
Using porosity n = e / (1 + e) = 0.67 / 1.67 ≈ 0.401; water ratio by volume Vw/V ≈ Sr * n ≈ 0.752 * 0.401 ≈ 0.302, consistent with a moist but not fully saturated soil.

Why Other Options Are Wrong:

• 25%, 40%, 60%, 90%: Do not match the computed value from the fundamental identity and are inconsistent with the given w and e.

Common Pitfalls:
Forgetting to convert w from percent to decimal; mixing e and n; or assuming full saturation when Sr must be computed.

Final Answer:
75%