Question

When the degree of saturation is zero, the soil mass under consideration represents

• A. One phase system with only soil solids
• B. Two phase system with soil solids and air
• C. Two phase system with soil solids and water
• D. Three phase system with soil solids, water and air

Hint:

In soil mechanics, understanding the phase relationships is fundamental. A soil can exist in three states: dry (solids + air, $S=0%$), saturated (solids + water, $S=100%$), or partially saturated (solids + water + air, $0%<S<100%$).

Answer 1

The Correct Option is B

Step 1: Understand the definition of degree of saturation.
The degree of saturation (\( S \)) of a soil is defined as the ratio of the volume of water (\( V_w \)) to the total volume of voids (\( V_v \)). It is usually expressed as a percentage: $$S = \frac{V_w}{V_v} \times 100%$$
Step 2: Analyze the condition when the degree of saturation is zero.
If the degree of saturation \( S = 0 \), it means that the volume of water \( V_w \) in the soil mass is zero.
$$0 = \frac{V_w}{V_v} \times 100% \quad \Rightarrow \quad V_w = 0$$ This implies that there is no water present in the voids of the soil.
Step 3: Identify the phases present in the soil mass.
A soil mass is generally considered a three-phase system, comprising:

• Soil solids (the solid particles)
• Water (filling some part of the voids)
• Air (filling the remaining part of the voids)

When \( V_w = 0 \), the water phase is absent. Therefore, the soil mass consists only of soil solids and air.
Step 4: Conclude the type of system.
Since the soil mass contains only two components, soil solids and air, it is classified as a two-phase system. This state describes a completely dry soil.
Step 5: Select the correct option.
Based on the analysis, when the degree of saturation is zero, the soil mass represents a two-phase system with soil solids and air. $$\boxed{\text{Two phase system with soil solids and air}}$$