Understanding Soil Volume Ratios: Porosity Explained

Soil is typically considered a three-phase material consisting of solid particles, water, and air. The spaces between the solid particles are called voids, which can be filled with either water or air, or both.

Different ratios are used in soil mechanics to describe the proportions of these phases. The question asks about the ratio of the volume of voids to the total volume of soil, expressed as a percentage.

Analyzing the Options

Let's examine each option based on its standard definition:

• Void ratio ($e$): This is defined as the ratio of the volume of voids ($V_v$) to the volume of solid particles ($V_s$). Mathematically, $e = \frac{V_v}{V_s}$. It is usually expressed as a decimal.
• Air Content ($A_c$): This is defined as the ratio of the volume of air ($V_a$) to the volume of voids ($V_v$). Mathematically, $A_c = \frac{V_a}{V_v}$. It is usually expressed as a decimal or percentage.
• Water Content ($w$): This is typically defined as the ratio of the weight of water ($W_w$) to the weight of solid particles ($W_s$), expressed as a percentage. Mathematically, $w = \frac{W_w}{W_s} \times 100\%$. There is also a definition based on total weight, but the standard is based on solid weight.
• Porosity ($n$): This is defined as the ratio of the volume of voids ($V_v$) to the total volume of the soil ($V$). The total volume is the sum of the volume of voids and the volume of solids ($V = V_v + V_s$). Mathematically, $n = \frac{V_v}{V}$. When expressed as a percentage, it is $\frac{V_v}{V} \times 100\%$.

Identifying the Correct Term

Comparing the definition given in the question (Volume of voids to total volume of soil expressed in percentage) with the definitions above, we see that it exactly matches the definition of Porosity ($n$).

The formula for porosity is:

\( n = \frac{V_v}{V} \)

Where:

• \( V_v \) is the volume of voids
• \( V \) is the total volume of the soil

When expressed as a percentage, it is \( n (\%) = \frac{V_v}{V} \times 100\% \).

Therefore, the term for the ratio of the volume of voids to the total volume of soil, expressed in percentage, is Porosity.