Difficulty: Medium
Correct Answer: 0.60
Explanation:
Introduction / Context:
The paraffin (clod) method measures the bulk volume of an irregular soil clod by displacement after coating with a thin paraffin film. Knowing the dry mass and particle specific gravity allows determination of the volume of solids and thus the void ratio e = Vv / Vs. This problem exemplifies careful accounting for the paraffin shell volume.
Given Data / Assumptions:
Concept / Approach:
External volume from displacement includes soil + paraffin. Subtract the paraffin volume to get the bulk soil volume. Then compute Vs from dry mass and Gs. The void volume is Vv = V − Vs, and e = Vv / Vs.
Step-by-Step Solution:
Verification / Alternative check:
Dimensional consistency: volumes in cm^3 and masses in g with water at 1 g/cm^3 yield a dimensionless e. The value e ≈ 0.60 is typical for a medium-dense sandy silt/sand mixture, providing a reasonableness check.
Why Other Options Are Wrong:
0.55, 0.65, 0.70 deviate from the precise computation; 0.48 is too low given the volumes.
Common Pitfalls:
Forgetting to subtract the paraffin volume; using wet mass instead of dry mass for Vs; mixing units; rounding too early.
Final Answer:
0.60
Discussion & Comments