GATE CE 2023 Set 1 Geotechnical Engineering - Compaction of Soil Question 1 English Explanation

The incorrect statement is Option D: Compaction curve crosses the zero-air-voids curve.

Let's break down why the other options are correct and why option D is incorrect.

Option A: Peak point of the compaction curve gives the maximum dry unit weight and optimum moisture content

This statement is correct. The compaction curve is a graphical representation of the relationship between the dry unit weight of the soil and the moisture content. The peak point of this curve represents the maximum dry unit weight that can be achieved for that particular soil and compaction effort. The corresponding moisture content at this peak point is called the optimum moisture content (OMC).

Option B: With increase in the compaction effort, the maximum dry unit weight increases

This statement is also correct. Increasing the compaction effort (like using a heavier hammer or more compactive blows) generally leads to a higher dry unit weight. This is because more energy is being applied to the soil, pushing the particles closer together and squeezing out more air voids.

Option C: With increase in the compaction effort, the optimum moisture content decreases

This statement is correct. As the compaction effort increases, the OMC tends to decrease. This is because at higher compaction energies, the soil particles are more tightly packed, and less water is needed to fill the void spaces.

Option D: Compaction curve crosses the zero-air-voids curve

This statement is incorrect. The zero-air-voids curve represents a theoretical condition where there are no air voids in the soil. In reality, achieving a completely zero-air-voids condition is practically impossible. The compaction curve will always be below the zero-air-voids curve because there will always be some air voids present in the soil, even after compaction.

Here's a table summarizing the key concepts:

Concept	Explanation
Compaction Curve	Plots the relationship between dry unit weight and moisture content for a soil.
Peak Point	Represents the maximum dry unit weight achievable for a given compaction effort. The corresponding moisture content is the optimum moisture content (OMC).
Zero-air-voids curve	A theoretical curve representing a soil with absolutely no air voids.
Compaction Effort	The amount of energy applied to the soil during compaction (e.g., number of blows, weight of the hammer).

Compaction of Soil · Geotechnical Engineering · GATE CE

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