Soil three-phase system: select the correct statements about voids in saturated and dry conditions.
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AVoids between soil grains are filled partly with air and partly with water (partially saturated)
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BIn perfectly saturated soil, all voids are fully filled with water
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CIn dry soil, all voids are filled with air
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DAll the above
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ENone of the above
Answer
Correct Answer: All the above
Explanation
Introduction / Context:The soil mass is modeled as a three-phase system: solids, water, and air. Whether a soil is dry, partially saturated, or fully saturated directly affects unit weight, compressibility, and strength. This question checks basic but essential definitions of saturation states.
Given Data / Assumptions:
- Voids = total volume not occupied by solids.
- Degree of saturation S_r varies from 0 to 100%.
- Idealized states: dry (S_r = 0), saturated (S_r = 100%).
Concept / Approach:
Partially saturated soils contain both air and water within the voids. Fully saturated soils have voids completely filled with water, while dry soils have voids completely filled with air. These are the standard textbook definitions and underpin formulas for bulk unit weight, buoyant unit weight, and relationships among e, n, and S_r.
Step-by-Step Solution:
Recognize three-phase composition.Map S_r to void filling: partial (air + water), saturated (water only), dry (air only).Confirm all three statements are correct → choose “All the above”.Verification / Alternative check:
Phase diagrams and standard relationships (e.g., γ_sat, γ_dry) rely on these exact definitions.
Why Other Options Are Wrong:
Since (a), (b), and (c) are all correct, “None” is false.
Common Pitfalls:
Assuming trapped air cannot exist in saturated conditions; in practice, saturation may be slightly less than 100% unless special saturation procedures are used in lab tests.
Final Answer:
All the above