Question

24. Given below are two statements:
Statement (I): Values of void ratio are likely to be smaller in coarse grained soil than for fine grained soil.
Statement (II): The void ratio of a soil is 1 when soil is fully saturated.
In light of the above statements, choose the most appropriate answer from the options given below.

• A. Both Statement (I) and Statement (II) are true.
• B. Both Statement (I) and Statement (II) are false.
• C. Statement (I) is true but Statement (II) is false.
• D. Statement (I) is false but Statement (II) is true.

Hint:

Although individual pore spaces in sand are larger, the total volume of voids in clay is much greater due to its structural arrangement, resulting in higher void ratios for clay.
Always use the relationship \(Se = wG\) to analyze saturated soil behavior.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Void ratio (\(e\)) is defined as the ratio of the volume of voids (\(V_v\)) to the volume of solid particles (\(V_s\)) in a soil mass.
The degree of saturation (\(S\)) is the ratio of the volume of water (\(V_w\)) to the volume of voids (\(V_v\)), indicating how much pore space is filled with water.
Key Formula or Approach:
The fundamental relationship linking the void ratio, degree of saturation, water content (\(w\)), and specific gravity of soil solids (\(G\)) is given by:
\[ S \cdot e = w \cdot G \]

Step 2: Detailed Explanation:
Let us evaluate each of the given statements individually:
Statement (I): Coarse-grained soils (like gravels and sands) consist of large, bulky grains that pack together in a highly efficient manner, leaving relatively small cumulative void spaces.
Their void ratios typically range between \(0.4\) and \(0.8\).
Fine-grained soils (like clays and silts) consist of plate-like particles that form complex, flocculated arrangements under electrostatic forces, trapping a vast volume of water within their structures.
This causes fine-grained soils to have much larger cumulative void spaces, resulting in higher void ratios that typically range from \(0.6\) to \(1.5\) or even higher.
Therefore, the void ratio is smaller in coarse-grained soils than in fine-grained soils, making Statement (I) true.
Statement (II): When a soil is fully saturated, the degree of saturation is \(S = 1\).
Substituting \(S = 1\) into the soil relationship yields:
\[ e = w \cdot G \]
This indicates that the void ratio of a saturated soil depends entirely on its water content (\(w\)) and specific gravity (\(G\)).
Since water content can vary widely, the void ratio of a fully saturated soil can be any value (such as \(0.5\), \(0.8\), or \(1.3\)) and is not restricted to exactly \(1\).
Therefore, Statement (II) is false.

Step 3: Final Answer:
Statement (I) is true but Statement (II) is false.