Moisture (water) content calculation from weighing data A soil sample is tested for water content with: container weight = 260 g; container + wet soil = 320 g; container + dry soil = 310 g. Compute the moisture content (percent, by mass of dry soil).
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A15%
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B18%
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C20%
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D25%
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E12.5%
Answer
Correct Answer: 20%
Explanation
Introduction / Context:Water content (moisture content) is defined as the mass of water divided by the mass of dry soil, expressed as a percentage. It is a core parameter for compaction, consistency limits, and phase-relationship calculations in geotechnical engineering.
Given Data / Assumptions:
- W_c (container) = 260 g.
- W_c+w (container + wet soil) = 320 g.
- W_c+d (container + dry soil) = 310 g.
- No mass loss from soil solids during drying.
Concept / Approach:
Compute masses of wet and dry soil by subtracting container mass, then obtain water mass as the difference. Water content w(%) = (mass of water / mass of dry soil) * 100.
Step-by-Step Solution:
Wet soil mass: 320 − 260 = 60 g.Dry soil mass: 310 − 260 = 50 g.Water mass: 60 − 50 = 10 g.w(%) = (10 / 50) * 100 = 20%.Verification / Alternative check:
Cross-check: Container cancels; water mass equals difference between wet and dry combined weights (320 − 310 = 10 g), consistent with the calculation.
Why Other Options Are Wrong:
15%, 18%, 25%, and 12.5% arise from using wet mass in the denominator or arithmetic slips.
Common Pitfalls:
Dividing by wet soil mass instead of dry; forgetting to subtract the container mass correctly.
Final Answer:
20%