What measure is needed to calculate the void ratio (e)?

• A. Mass of water
• B. Volume of solids
• C. Volume of voids
• D. Mass of soil

Answer: (C)

To calculate the void ratio (e), you need to understand that it is defined as the ratio of the volume of voids to the volume of solids in a soil sample. The formula for void ratio is given by:

[ e = \frac{V_{voids}}{V_{solids}} ]

This means that the void ratio provides insight into the relative proportions of open space compared to the solid particles within the soil. By focusing on the volume of voids, which includes all the spaces between the solid particles, you can specifically assess how much of the soil is not occupied by solid material.

While other measures like the mass of water, volume of solids, and mass of soil are critical to various calculations in soil mechanics, they do not directly provide the information needed to quantify the void ratio itself. Instead, the volume of voids is essential because it serves as the numerator in the void ratio calculation, allowing for an understanding of the soil's structure and its potential drainage characteristics.