Bulking of sand is caused due to 

Explanation:

Bulking of Sand

Bulking of sand refers to the increase in its volume when moisture is present. This phenomenon occurs due to the formation of a thin film of water around the sand particles, which causes them to move apart.

Reason for Bulking

The primary cause of bulking is surface moisture. When sand contains surface moisture, it creates a layer around each particle, preventing them from coming into close contact. This increases the overall volume of the sand.

Analyzing the Given Options

1. Option 1: Surface Moisture

   • As explained, surface moisture is the primary reason for bulking of sand. It forms a water film around sand particles, leading to increased volume.

2. Option 2: Air Voids

   • Air voids do not contribute significantly to the bulking of sand. Bulking is primarily caused by moisture, not air trapped between particles.

3. Option 3: Viscosity

   • Viscosity relates to the flow properties of fluids and has no direct impact on the bulking of sand.

4. Option 4: Clay Contents

   • While clay content may affect the characteristics of sand, it is not the primary cause of bulking. Bulking mainly depends on surface moisture.

5. Option 5: None of the Above

   • This option can be ruled out as the correct answer is already identified as surface moisture.

Conclusion

The correct answer is Option 1: Surface Moisture, as it is the primary cause of bulking of sand due to the formation of a water film around sand particles.