Question

With reference to the compaction test conducted on soils, which of the following is INCORRECT?

• A. Peak point of the compaction curve gives the maximum dry unit weight and optimum moisture content
• B. With increase in the compaction effort, the maximum dry unit weight increases
• C. With increase in the compaction effort, the optimum moisture content decreases
• D. Compaction curve crosses the zero-air-voids curve

Hint:

The compaction curve never crosses the zero-air-voids line because complete removal of air voids is practically impossible.

Answer 1

The Correct Option is D

Step 1: Understanding compaction curve.
In a soil compaction test, dry density is plotted against moisture content. The peak point represents the maximum dry density (MDD) and the corresponding water content is the optimum moisture content (OMC).

Step 2: Effect of compaction effort.
When compaction effort is increased: - The maximum dry unit weight increases because higher energy reduces voids.
- The optimum moisture content decreases because less water is needed for lubrication under higher energy.

Step 3: Zero-air-voids (ZAV) curve.
The ZAV curve represents the condition of 100% saturation (no air voids). In reality, soils always contain some air, so the compaction curve will approach the ZAV curve but never cross it. \[ \boxed{\text{Hence, statement (D) is incorrect.}} \]