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5-question demo · FCI Assistant Grade III - Civil Engineering - Soil Mechanics

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Question 1 of 5
The relationship between **void ratio (e)** and **porosity (n)** for a soil sample is given by:
A A. \( n = \frac{e}{1+e} \)
B B. \( e = \frac{n}{1-n} \)
C C. \( n = \frac{e}{1-e} \)
D D. \( e = \frac{n}{1+n} \)
Why: The **void ratio (e)** is the ratio of volume of voids to volume of solids: \( e = \frac{V_v}{V_s} \). **Porosity (n)** is the ratio of volume of voids to total volume: \( n = \frac{V_v}{V_t} = \frac{V_v}{V_v + V_s} \). Substituting \( V_v = e V_s \) gives \( n = \frac{e V_s}{e V_s + V_s} = \frac{e}{1+e} \). Rearranging for e: \( e = \frac{n}{1-n} \). Thus, option B is correct.[1]
Question 2 of 5
For a given soil sample, if the **porosity** increases while keeping the **volume of solids** constant, what happens to the **void ratio**?
A A. Void ratio decreases
B B. Void ratio increases
C C. Void ratio remains constant
D D. Cannot be determined
Why: From the relationship \( e = \frac{n}{1-n} \), as **porosity (n)** increases (more voids relative to total volume), the **void ratio (e)** must increase since the denominator \( 1-n \) decreases. For constant solids volume, higher porosity means larger voids volume, directly increasing e. Option B is correct.[1]
Question 3 of 5
**MCQ:** A soil sample is saturated when:
A) Degree of saturation S = 0
B) Degree of saturation S = 50%
C) Degree of saturation S = 100%
D) Water content w = 0
A Degree of saturation S = 0
B Degree of saturation S = 50%
C Degree of saturation S = 100%
D Water content w = 0
Why: Saturated soil means all voids are filled with water, so degree of saturation S = 100% or 1. This is the definition used in all soil mechanics problems[1][2][5].
Question 4 of 5
Which of the following represents the **specific gravity** of quartz soil grains?
A. 1.0
B. 2.65
C. 3.5
D. 4.0
A 1.0
B 2.65
C 3.5
D 4.0
Why: Specific gravity of quartz (common soil mineral) is standardly 2.65. Option B matches this value. Others: 1.0 is water, 3.5-4.0 for heavier minerals like iron oxides.
Question 5 of 5
What is the definition of void ratio (e) in soil mechanics?
A Ratio of volume of voids to volume of solids
B Ratio of volume of solids to total volume
C Ratio of volume of voids to total volume
D Ratio of volume of solids to volume of voids
Why: Void ratio (e) is defined as the ratio of the volume of voids to the volume of solids in a soil sample.