BCE Geotechnical 2 — Questions and Answers
Question 1: What is the primary purpose of a consolidation test (oedometer test) in geotechnical engineering?
- Determine shear strength of soil
- Measure permeability of coarse-grained soils
- Determine compressibility and rate of consolidation of cohesive soils (Correct answer)
- Classify soil by grain size distribution
Correct answer: Determine compressibility and rate of consolidation of cohesive soils
The oedometer test measures how much a saturated cohesive soil compresses under load and how quickly excess pore pressure dissipates.
Question 2: Which of the following best describes the coefficient of consolidation (Cv)?
- Ratio of void ratio change to effective stress change
- Parameter combining permeability and compressibility that governs consolidation rate (Correct answer)
- Ratio of shear stress to normal stress at failure
- Volume of water expelled per unit area per unit time
Correct answer: Parameter combining permeability and compressibility that governs consolidation rate
Cv = k/(mv·γw), combining hydraulic conductivity and volume compressibility to describe how fast consolidation proceeds.
Question 3: A soil has a liquid limit of 60% and a plastic limit of 30%. What is the plasticity index?
- 90%
- 30% (Correct answer)
- 60%
- 45%
Correct answer: 30%
Plasticity Index (PI) = Liquid Limit − Plastic Limit = 60 − 30 = 30%.
Question 4: In Terzaghi's bearing capacity equation for a strip footing, which factor accounts for the depth of embedment?
- Nc
- Nq (Correct answer)
- Nγ
- Depth factor Fd
Correct answer: Nq
Nq is the bearing capacity factor associated with the surcharge term (q = γDf), which represents the overburden pressure from footing embedment depth.
Question 5: What type of failure surface does Rankine's earth pressure theory assume?
- Circular arc
- Log-spiral
- Planar (straight line) slip surface (Correct answer)
- Parabolic curve
Correct answer: Planar (straight line) slip surface
Rankine's theory assumes a planar failure surface inclined at 45 + φ/2 degrees from horizontal for active conditions.
Question 6: Which in-situ test provides continuous soil profiling by measuring cone resistance (qc) and sleeve friction (fs)?
- Standard Penetration Test (SPT)
- Vane Shear Test (VST)
- Cone Penetration Test (CPT) (Correct answer)
- Pressuremeter Test (PMT)
Correct answer: Cone Penetration Test (CPT)
The CPT pushes an instrumented cone into the ground at a constant rate, continuously recording qc and fs to classify soil layers.
Question 7: What does a negative value of the pore pressure parameter B indicate in a triaxial test?
- Fully saturated soil condition
- Partially saturated or dilative soil behavior (Correct answer)
- High preconsolidation pressure
- Excessive shear strain
Correct answer: Partially saturated or dilative soil behavior
B < 1 indicates partial saturation or dilative dense sand behavior where pore pressure decreases under shear.
BCE Geotechnical 2
What is the primary purpose of a consolidation test (oedometer test) in geotechnical engineering?