Compaction MCQ with answer and solution

Concept

Higher compactive energy yields a higher maximum dry density (MDD) at a lower optimum moisture content (OMC).

Step-by-step solution

1. Understand the effect of compactive energy: Increased compactive energy compresses air voids more effectively, which increases the maximum dry density (MDD). 2. Understand the effect on lubrication: Greater mechanical energy reduces the requirement of water for lubrication between particles, so the peak dry density is achieved at a lower moisture content. 3. Therefore, as compactive effort increases, maximum dry density increases and optimum moisture content (OMC) decreases.

Explanation

Increasing the compactive effort drives the soil particles closer together, expelling more air voids and thereby increasing the maximum dry density (MDD). Because a higher compactive energy can overcome particle friction at lower moisture contents, less water is required to lubricate the soil particles, resulting in a lower Optimum Moisture Content (OMC). Consequently, the compaction curve shifts upward and to the left.

Why the other options are wrong

A: OMC decreases with higher compactive effort, it does not increase. B: OMC decreases because less water lubrication is required under higher mechanical force; it does not remain unchanged. D: Maximum dry density always increases with higher compactive effort.

Shortcut

More effort = curve moves UP and LEFT (MDD increases, OMC decreases).

Common mistake

Candidates often think that since density increases, more water is required for lubrication, mistakenly picking increase in OMC.