Section 4: Soil and Water Conservation Engineering
Soil Physical Properties & Phase Relationships
Subtopic: Phase relations in soil mechanics
Question Statement:
Which of the following statements regarding soil phase relationships is/are TRUE?
Options:
(A) Porosity $n$ is strictly bounded between $0$ and $1$ ($0 < n < 1$), whereas void ratio $e$ can exceed $1$
(B) For fully saturated soil, degree of saturation $S_r = 100\%$ and air content $a_c = 0$
(C) Submerged unit weight $\gamma'$ is related to saturated unit weight $\gamma_{sat}$ by $\gamma' = \gamma_{sat} - \gamma_w$
(D) Water content $w$ defined on dry weight basis cannot exceed $100\%$ under any geological condition
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
1. Porosity $n = V_v / V < 1$ because void volume cannot exceed total volume. Void ratio $e = V_v / V_s$ can exceed $1.0$ (e.g. highly organic soils, bentonite clays have $e > 2$) (A is true).
2. Degree of saturation $S_r = V_w/V_v$; at full saturation $V_w = V_v$, so $S_r = 1$ and air content $a_c = 1 - S_r = 0$ (B is true).
3. Buoyant unit weight $\gamma' = \gamma_{sat} - \gamma_w$ by Archimedes principle (C is true).
4. Water content $w = W_w / W_s$; highly organic soils, peats, or sensitive clays frequently have water contents exceeding $100\%$ to $500\%$ (D is false).