CCI Foundation & Soil Analysis 2 — Questions and Answers
Question 1: A soil sample has a liquid limit of 45 and a plastic limit of 20. What is the plasticity index?
- 25 (Correct answer)
- 65
- 45
- 20
Correct answer: 25
Plasticity index (PI) = Liquid Limit − Plastic Limit = 45 − 20 = 25.
Question 2: Which field test is commonly used to estimate the in-situ undrained shear strength of cohesive soils?
- Vane shear test (Correct answer)
- Standard Penetration Test
- Plate load test
- Proctor compaction test
Correct answer: Vane shear test
The field vane shear test directly measures undrained shear strength in soft to medium cohesive soils.
Question 3: A mat (raft) foundation is most appropriate when:
- Individual footings would cover more than half the building area (Correct answer)
- Rock is encountered at shallow depth
- Soil is highly permeable
- Loads are very light and widely spaced
Correct answer: Individual footings would cover more than half the building area
When individual footings would overlap or cover more than 50% of the plan area, a mat foundation is more economical and effective.
Question 4: Which soil classification group under USCS is described as 'poorly graded gravel with little or no fines'?
- GP (Correct answer)
- GW
- GM
- GC
Correct answer: GP
GP (Poorly Graded Gravel) has a wide range of particle sizes missing, resulting in a poor gradation curve.
Question 5: During pile driving, a 'set' refers to:
- Penetration per blow at final driving (Correct answer)
- The total depth of pile embedment
- The rate of hammer blows per minute
- The pile's allowable load capacity
Correct answer: Penetration per blow at final driving
Set is the permanent penetration of a pile per blow measured at final driving, used in pile driving formulas to estimate capacity.
Question 6: What does a negative skin friction on a pile indicate?
- Surrounding soil is settling and dragging the pile downward (Correct answer)
- The pile has insufficient embedment depth
- The pile toe is bearing on compressible clay
- Skin friction exceeds end bearing capacity
Correct answer: Surrounding soil is settling and dragging the pile downward
Negative skin friction (downdrag) occurs when consolidating soil surrounding a pile settles, imposing additional downward load on the pile.
Question 7: The allowable bearing capacity of a soil differs from ultimate bearing capacity in that it:
- Includes a factor of safety and accounts for acceptable settlement (Correct answer)
- Is always twice the ultimate bearing capacity
- Excludes the weight of the foundation itself
- Is determined solely by laboratory testing
Correct answer: Includes a factor of safety and accounts for acceptable settlement
Allowable bearing capacity = ultimate bearing capacity divided by a factor of safety (typically 2–3), also considering tolerable settlement limits.
CCI Foundation & Soil Analysis 2
A soil sample has a liquid limit of 45 and a plastic limit of 20.
What is the plasticity index?