# Soil Mechanics Questions and Answers – Soil as Three Phase System

This set of Soil Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Soil as Three Phase System”.

1. A soil mass in a three-phase system consists of ______
a) solids, water and air
b) sand, gravel and air
c) solids and water only
d) solids and air only

Explanation: Solids and water, solids and air are two-phase systems. Sand, gravel and air are not the phases. Solids, water and air are considered to be a three-phase system of the soil mass.

2. When the soil is fully saturated, then there are no air voids present in it.
a) True
b) False

Explanation: The air voids get filled with water leaving no air voids when the soil is fully saturated. When the soil is completely dry, then the soil will contain only air voids.

3. The volume of voids Vv is equal to the sum of ______
a) the volume of air and volume of solids
b) the volume of air and volume of water
c) the volume of water and volume of solids
d) the volume of water and the weight of water

Explanation: The voids in soil mass are occupied by air and water. Hence, the volume of voids equals to the volume of air and volume of water.

4. The phase diagram is also known as _______
a) soil grain diagram
b) block diagram
c) constituents diagram
d) element diagram

Explanation: It is always convenient to show the constituents occupying separate spaces as blocks. In the phase diagram, the soil occupies the bottom position. Water and air occupy the middle and top positions.

5. The weight of total voids is equal to the weight of Water.
a) True
b) False

Explanation: The weight of total voids Wv is equal to the sum of weights of Water Ww and air Wa. Wv=Ww+Wa. Here, the weight of air is considered to be negligible. ∴ Wa=0
Therefore, Wv=Ww , i.e., weight of total voids is equal to the weight of Water.

6. In the phase diagram, volumes are represented on the ________
a) left side
b) right side
c) top
d) bottom

Explanation: Volumes are represented on the left side whereas weights are represented on the right side of the block diagram.

7. The volume of solids is represented as _______ in the phase diagram.
a) Vv
b) VW
c) VS
d) Va

Explanation: The volume of voids, water and air are represented as Vv, VW and Va. The volume of solids is represented as Vd or VS in the phase diagram.

8. The weight of solids is represented as _______
a) Wd
b) WW
c) Wa
d) W

Explanation: The weights of Water, air and total weight are represented as WW, Wa and W. The weight of solids is represented as Wd or WS in the phase diagram.

9. The total weight of the moist sample is the sum of _______
a) WW+Wd
b) Wa+WW
c) Wa+Wd
d) Wv

Explanation: The sum of the weight of voids Wv and weight of solid is the total weight. The weight of total voids is equal to the weight of Water and weight of air. Since the weight of air is considered to be negligible, the weight of total voids is equal to the weight of Water. Therefore, the total weight of the moist sample is the sum of WW+Wd.

10. For a fully saturated soil sample, the volume of voids is equal to _______
a) volume of air
b) volume of water
c) the volume of air and volume of water
d) the volume of water and volume of solids

Explanation: In a fully saturated sample, the volume of voids gets completely filled by water leaving no air voids present in the sample. Hence, volume of voids equals the volume of water.

11. A soil sample weighs 190kN. After oven drying it weighs 150kN. What will be the weight of Water before oven drying?
a) 35 kN
b) 40 kN
c) 30 kN
d) 45 kN

Explanation: Given,
Weight of soil sample W=190kN
Weight after oven drying Wd=150kN
Weight of Water WW=W-Wd
WW=190-150
WW=40kN.

12. In wet soil mass, air occupies one-seventh of its volume and Water occupies one- eighth of its volume. What will be the ratio of volume of voids with respect to the total volume?
a) 0.329
b) 0.279
c) 0.432
d) 0.286

Explanation: Given,
Volume of Water Va= (1/7) total volume V
Volume of Water VW= (1/8) total volume V
Volume of voids Vv= Va + VW
Vv=(1/7)V+(1/8)V
Vv=(15/56)V=0.268V.

Sanfoundry Global Education & Learning Series – Soil Mechanics.

To practice all areas of Soil Mechanics, here is complete set of 1000+ Multiple Choice Questions and Answers.

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