Soils Classification

Question 1

1. The system commonly used in civil engineering for soil classification is ___.
   A. AASHTO B. Unified Soil Classification System (USCS) C. ASTM D. NSCP

Answer 1

✅ Answer: B – Unified Soil Classification System (USCS)
USCS is widely used for foundation and design works.

Question 2

2. The USCS classifies soils primarily by ___.
   A. Color and smell B. Grain size and plasticity C. Density and moisture D. Depth and origin

Answer 2

✅ Answer: B – Grain size and plasticity
Key parameters affecting strength and behavior.

Question 3

3. In USCS, coarse-grained soils are those with more than __ fine fraction passing No. 200 sieve.
   A. 10% B. 25% C. 35% D. 50%

Answer 3

✅ Answer: D – 50%
If >50% retained → coarse-grained.

Question 4

4. Fine-grained soils are those with ___.
   A. More than 50% passing No. 200 sieve B. Less than 50% C. Equal 50% D. None

Answer 4

✅ Answer: A – More than 50% passing No. 200
Classified as silts or clays.

Question 5

5. Gravels are particles larger than ___.
   A. 0.075 mm B. 2.0 mm C. 4.75 mm D. 75 mm

Answer 5

✅ Answer: C – 4.75 mm
Standard boundary between sand and gravel.

Question 6

6. Sands are particles smaller than 4.75 mm but larger than ___.
   A. 0.075 mm B. 0.01 mm C. 0.002 mm D. 0.5 mm

Answer 6

✅ Answer: A – 0.075 mm
Passing No. 4 sieve but retained on No. 200 sieve.

Question 7

7. Clays are particles smaller than ___.
   A. 0.002 mm B. 0.075 mm C. 0.01 mm D. 0.005 mm

Answer 7

✅ Answer: A – 0.002 mm
Finest soil size per ISS and ASTM.

Question 8

8. The liquid limit (LL) and plasticity index (PI) are plotted on the ___.
   A. Casagrande Chart B. Mohr’s Circle C. Flow Curve D. Flow Net

Answer 8

✅ Answer: A – Casagrande Chart
Used to classify silts vs clays.

Question 9

9. The A-line equation in the plasticity chart is ___.
   A. PI = 0.73(LL – 20) B. PI = 0.7(LL + 20) C. PI = 0.75(LL – 10) D. PI = LL / 2

Answer 9

✅ Answer: A – PI = 0.73(LL – 20)
Boundary between clays (above) and silts (below).

Question 10

10. In USCS, symbol “G” stands for ___.
    A. Gravel B. Ground C. Granular D. Graded

Answer 10

✅ Answer: A – Gravel
Used for coarse-grained materials.

Question 11

11. In USCS, symbol “S” stands for ___.
    A. Silt B. Sand C. Saturated D. Soft

Answer 11

✅ Answer: B – Sand
Used for coarse-grained group.

Question 12

12. In USCS, symbol “M” denotes ___.
    A. Moist B. Medium C. Silt D. Mixed

Answer 12

✅ Answer: C – Silt
“M” stands for micaceous/silt fraction.

Question 13

13. In USCS, “C” refers to ___.
    A. Clay B. Coarse C. Clean D. Crushed

Answer 13

✅ Answer: A – Clay
Represents plastic cohesive fines.

Question 14

14. “W” in soil symbol (GW, SW) means ___.
    A. Wet B. Well-graded C. Weak D. Wide

Answer 14

✅ Answer: B – Well-graded
Indicates a good range of particle sizes.

Question 15

15. “P” in soil symbol (GP, SP) means ___.
    A. Plastic B. Poorly graded C. Partly saturated D. Permeable

Answer 15

✅ Answer: B – Poorly graded
Uniform-sized particles, poor interlock.

Question 16

16. A soil classified as CL in USCS means ___.
    A. Coarse Loam B. Clay of Low Plasticity C. Clayey Loam D. Clean Loam

Answer 16

✅ Answer: B – Clay of Low Plasticity
Below 35% plasticity index.

Question 17

17. A soil classified as CH in USCS means ___.
    A. Clay of High Plasticity B. Coarse High C. Clean Hard D. Clayey Sand

Answer 17

✅ Answer: A – Clay of High Plasticity
High PI → compressible and expansive.

Question 18

18. A soil classified as ML indicates ___.
    A. Medium Loam B. Silt of Low Plasticity C. Mixed Loam D. Moist Loam

Answer 18

✅ Answer: B – Silt of Low Plasticity
Fine-grained, below A-line.

Question 19

19. The letter “O” in USCS classification means ___.
    A. Organic B. Ordinary C. Open D. Overconsolidated

Answer 19

✅ Answer: A – Organic
e.g., OL = organic silt, OH = organic clay.

Question 20

20. In USCS, a dual symbol (e.g., SW-SC) means ___.
    A. Two layers of soil B. Borderline classification C. Non-cohesive D. Unknown

Answer 20

✅ Answer: B – Borderline classification
Transitional soil showing mixed characteristics.

Question 21

21. The AASHTO system primarily classifies soil for ___.
    A. Building foundations B. Highway subgrades C. Earthen dams D. Water channels

Answer 21

✅ Answer: B – Highway subgrades
AASHTO = American Association of State Highway & Transportation Officials.

Question 22

22. In AASHTO system, soil groups range from ___.
    A. A-1 to A-7 B. A-1 to A-8 C. G-1 to G-10 D. C-1 to C-7

Answer 22

✅ Answer: A – A-1 to A-7
Used for pavement and road design.

Question 23

23. The best soil group for road foundation in AASHTO is ___.
    A. A-1 B. A-2 C. A-3 D. A-7

Answer 23

✅ Answer: A – A-1
Excellent subgrade quality.

Question 24

24. The worst soil group for road foundation in AASHTO is ___.
    A. A-1 B. A-7-6 C. A-3 D. A-4

Answer 24

✅ Answer: B – A-7-6
Highly plastic clay, poor drainage.

Question 25

25. The group index (GI) in AASHTO provides a measure of ___. A. Plasticity B. Strength C. Performance rating D. Drainage

Answer 25

✅ Answer: C – Performance rating Higher GI = poorer quality soil.