CCI Foundation & Soil Analysis 3 — Questions and Answers
Question 1: Which condition describes 'quick condition' or 'quicksand' in cohesionless soils?
- Upward seepage force equals the effective weight of the soil (Correct answer)
- Soil liquefies due to seismic shaking alone
- Pore pressure drops below atmospheric pressure
- Cohesion becomes greater than friction angle
Correct answer: Upward seepage force equals the effective weight of the soil
Quick condition occurs when upward hydraulic gradient causes seepage force to equal the buoyant weight of soil, eliminating effective stress.
Question 2: A geotechnical inspector observes 'heave' at the bottom of an excavation in soft clay. The most likely cause is:
- Insufficient passive resistance against base instability (Correct answer)
- Excessive dewatering of the excavation
- Over-compaction of subgrade soils
- High coefficient of permeability in the clay
Correct answer: Insufficient passive resistance against base instability
Bottom heave in soft clay excavations results from inadequate shear strength to resist the net vertical stress difference at the base.
Question 3: In a soil boring log, the abbreviation 'SP' under USCS refers to:
- Poorly graded sand (Correct answer)
- Sandy peat
- Silty peat
- Saturated pumice
Correct answer: Poorly graded sand
SP = Poorly Graded Sand in the Unified Soil Classification System, indicating uniform or gap-graded sand with insufficient fines.
Question 4: Which laboratory test determines the maximum dry density and optimum moisture content of a soil?
- Proctor compaction test (Correct answer)
- Consolidation test
- Triaxial shear test
- Hydrometer analysis
Correct answer: Proctor compaction test
The Proctor compaction test (standard or modified) establishes the compaction curve to find maximum dry density at optimum moisture content.
Question 5: What is the primary purpose of a surcharge load applied near an existing foundation?
- It increases lateral earth pressure on the foundation or retaining structure (Correct answer)
- It reduces the factor of safety against bearing capacity failure
- It accelerates consolidation settlement below the foundation
- It improves drainage around the footing
Correct answer: It increases lateral earth pressure on the foundation or retaining structure
A surcharge near a foundation or retaining wall increases the lateral earth pressure that must be resisted by the structure.
Question 6: For a driven steel H-pile, 'plugging' refers to:
- Soil trapped inside the flanges acting as part of the pile toe (Correct answer)
- Corrosion blocking the hollow section
- Grout injected to seal the tip
- Driving refusal before reaching design depth
Correct answer: Soil trapped inside the flanges acting as part of the pile toe
Plugging occurs when soil becomes trapped between the flanges of an H-pile, effectively increasing the end-bearing area.
Question 7: Which of the following best describes 'differential settlement'?
- Unequal settlement between two points on a structure causing distortion (Correct answer)
- Total settlement at the center of a footing
- Settlement that occurs only during construction
- Elastic rebound after load removal
Correct answer: Unequal settlement between two points on a structure causing distortion
Differential settlement is the difference in settlement between two points, which can cause structural distortion, cracking, or tilting.
CCI Foundation & Soil Analysis 3
Which condition describes 'quick condition' or 'quicksand' in cohesionless soils?