Soil Classification MCQ with answer and solution

Concept

Well-Graded Sand Classification

Formula

Cu = D60 / D10 and Cc = (D30)² / (D10 × D60)

Step-by-step solution

1. Recall the criteria for Well-Graded Sand (SW): Coefficient of Uniformity (Cu) \> 6 and Coefficient of Curvature (Cc) between 1 and 3. 2. Check the given condition: Cc is already between 1 and 3. 3. Determine the remaining condition required for SW: Cu \> 6 (Option A).

Explanation

For a soil to be classified as well-graded sand (SW), it must meet two conditions: its coefficient of curvature (Cc) must be between 1 and 3, and its coefficient of uniformity (Cu) must be greater than 6. Since the question states that Cc is already between 1 and 3, the remaining requirement for SW classification is Cu > 6.

Shortcut

Remember SW = Sand Well-graded: Sand needs Cu > 6 (higher ratio than Gravel which needs Cu > 4). Both require 1 ≤ Cc ≤ 3. Memory trick: "Sand" has higher Cu requirement than Gravel (6 > 4).

Common mistake

Students often confuse the requirement for well-graded sand (SW, Cu > 6) with well-graded gravel (GW, Cu > 4) and mistakenly select option C (Cu > 4).