Compaction

Question 1

1. Soil compaction is the process of ___.
   A. Reducing water content B. Increasing density by expelling air C. Increasing pore water D. Consolidation under load

Answer 1

✅ Answer: B – Increasing density by expelling air
Short-term densification by mechanical means.

Question 2

2. The main purpose of compaction is to ___.
   A. Reduce permeability B. Increase strength C. Reduce settlement D. All of the above

Answer 2

✅ Answer: D – All of the above
Compaction improves soil performance

Question 3

3. Compaction differs from consolidation because ___.
   A. Compaction is rapid B. Air is expelled C. Consolidation expels water D. All are correct

Answer 3

✅ Answer: D – All are correct
Compaction = air removal; consolidation = water removal.

Question 4

4. The maximum dry density (MDD) is obtained at ___.
   A. Zero water content B. Optimum moisture content C. Full saturation D. 50% saturation

Answer 4

✅ Answer: B – Optimum moisture content (OMC)
Ideal water for best packing of particles.

Question 5

5. The OMC is the moisture content at which ___.
   A. Void ratio is maximum B. Dry density is maximum C. Saturation is minimum D. Water content is zero

Answer 5

✅ Answer: B – Dry density is maximum
Best compaction efficiency.

Question 6

6. The relationship between dry density and moisture content is called ___.
   A. Flow curve B. Compaction curve C. Consolidation curve D. Void ratio line

Answer 6

✅ Answer: B – Compaction curve
Parabolic shape; peak = MDD.

Question 7

7. The laboratory test for compaction is ___.
   A. Plate load test B. Standard or Modified Proctor test C. Triaxial test D. Shear box test

Answer 7

✅ Answer: B – Proctor test
Determines MDD and OMC.

Question 8

8. In the Standard Proctor test, compaction energy = ___.
   A. 600 kN-m/m³ B. 592 kN-m/m³ C. 595 kN-m/m³ D. 600 J/m³

Answer 8

✅ Answer: B – 592 kN-m/m³
Based on 2.5 kg hammer, 305 mm drop.

Question 9

9. In the Modified Proctor test, energy = ___.
   A. 2700 kN-m/m³ B. 2700 J/m³ C. 594 kN-m/m³ D. 1800 kN-m/m³

Answer 9

✅ Answer: A – 2700 kN-m/m³
Heavier hammer, higher compaction effort.

Question 10

10. The MDD of soil depends on ___.
    A. Type of soil B. Compaction effort C. Moisture content D. All of the above

Answer 10

✅ Answer: D – All of the above
Denser soils or higher energy → higher MDD.

Question 11

11. The line joining points of zero air voids is called ___.
    A. Saturation line B. Zero air void line (ZAV) C. Compaction line D. Air–water line

Answer 11

✅ Answer: B – Zero air void line (ZAV)
Represents theoretical 100% saturation.

Question 12

12. The dry density (γ_d) is related to bulk density (γ) by ___.
    A. γ / (1 + w) B. γ(1 + w) C. γ + w D. γ – w

Answer 12

✅ Answer: A – γ_d = γ / (1 + w)
Eliminates water weight for comparison.

Question 13

13. The degree of compaction in field = ___.
    A. (γ_field / γ_lab) × 100 B. (γ_lab / γ_field) × 100 C. (γ_d / γ_sat) × 100 D. None

Answer 13

✅ Answer: A – (γ_field / γ_lab) × 100
Target: ≥ 95% of lab MDD.

Question 14

14. For highway embankments, minimum field compaction required is ___.
    A. 85% B. 90% C. 95% D. 100%

Answer 14

✅ Answer: C – 95%
Standard requirement for structural fill.

Question 15

15. For earth dams, required compaction = ___.
    A. 90% B. 95% C. 98%–100% D. 85%

Answer 15

✅ Answer: C – 98–100%
Critical for watertight core.

Question 16

16. Compaction control in the field is verified by ___.
    A. Sand cone test B. Proctor test C. Triaxial test D. Core cutter test

Answer 16

✅ Answer: A – Sand cone test
Used to measure in-situ density.

Question 17

17. Another field test for compaction control is ___.
    A. Plate load test B. Nuclear density gauge C. Atterberg limit test D. Grain size test

Answer 17

✅ Answer: B – Nuclear density gauge
Modern method for density + moisture.

Question 18

18. The dry side of compaction curve gives soil that is ___.
    A. Flocculated B. Dispersed C. Soft D. Fully saturated

Answer 18

✅ Answer: A – Flocculated
High strength but higher voids.

Question 19

20. Increasing compactive effort shifts the compaction curve ___.
    A. Up and left B. Down and right C. Up and right D. Down and left

Answer 19

✅ Answer: A – Up and left
Higher MDD and lower OMC.

Question 19

19. The wet side of compaction curve gives soil that is ___.
    A. Dispersed B. Flocculated C. Dry D. Rigid

Answer 19

✅ Answer: A – Dispersed
Lower strength due to lubrication.

Question 20

21. Compaction of clay soils is more effective with ___.
    A. Impact rollers B. Pneumatic rollers C. Sheepsfoot rollers D. Vibratory rollers

Answer 20

✅ Answer: C – Sheepsfoot rollers
Penetrate and knead cohesive soil.

Question 21

22. Compaction of granular soils is best achieved using ___.
    A. Vibratory rollers B. Sheepsfoot rollers C. Hand tampers D. Static rollers

Answer 21

✅ Answer: A – Vibratory rollers
Vibration rearranges sand particles.

Question 22

23. Excessive compaction may lead to ___.
    A. Reduced permeability B. Soil crushing C. Lower strength in clays D. All of these

Answer 22

✅ Answer: D – All of these
Too much energy can degrade structure.

Question 23

24. The relative compaction (R.C.) = ___.
    A. γ_field / γ_max B. (γ_field / γ_max) × 100 C. γ_max / γ_field D. w_field / w_lab

Answer 23

✅ Answer: B – (γ_field / γ_max) × 100
Used to express field compaction level.

Question 24

25. Compaction energy (E) in Proctor test is proportional to ___. A. N × W × H / V B. W/H C. N × V / W D. None

Answer 24

✅ Answer: A – E = N × W × H / V N = number of blows, W = hammer weight, H = drop height, V = mold volume.