ASCE Geotechnical and Foundation Engineering 4 — Questions and Answers
Question 1: For a strip footing on saturated clay under undrained (φ = 0) conditions, the Prandtl/Meyerhof bearing capacity factor Nc is:
- 1.00
- 3.14
- 5.14 (Correct answer)
- 5.70
Correct answer: 5.14
Nc = π + 2 ≈ 5.14 for φ = 0; Terzaghi's original value is 5.7.
Question 2: A footing of width B carries a load with eccentricity e in one direction. Meyerhof's effective width used in bearing capacity calculations is:
- B - e
- B - 2e (Correct answer)
- B + 2e
- B/(1 + 6e/B)
Correct answer: B - 2e
Meyerhof's method uses B' = B - 2e so the load acts at the center of the reduced area.
Question 3: To avoid tension (loss of contact) beneath a rectangular footing under one-way eccentric loading, the eccentricity must not exceed:
- B/3
- B/4
- B/6 (Correct answer)
- B/12
Correct answer: B/6
Keeping e ≤ B/6 keeps the resultant within the kern and the minimum bearing pressure non-negative.
Question 4: When the groundwater table rises to the base of a shallow footing in sand, how should the Nγ term of the bearing capacity equation be modified?
- No modification is needed
- Replace γ with the buoyant unit weight γ' in the Nγ term (Correct answer)
- Replace γ with the saturated unit weight
- Set the Nγ term to zero
Correct answer: Replace γ with the buoyant unit weight γ' in the Nγ term
Soil below the base is submerged, so the effective (buoyant) unit weight is used in the Nγ term.
Question 5: Which method is commonly used to estimate immediate settlement of shallow foundations on sand using CPT cone resistance and a strain influence factor diagram?
- Terzaghi's consolidation method
- Schmertmann's method (Correct answer)
- Casagrande's method
- Converse-Labarre method
Correct answer: Schmertmann's method
Schmertmann's method integrates a strain influence factor with modulus derived from CPT qc.
Question 6: What factor of safety is typically applied to the ultimate bearing capacity of shallow foundations in allowable stress design?
- 1.0
- 1.5
- 3.0 (Correct answer)
- 6.0
Correct answer: 3.0
A factor of safety of about 3 is customary to account for uncertainty and limit settlement.
Question 7: A fully compensated mat foundation is designed so that:
- The mat thickness equals the excavation depth
- The weight of excavated soil approximately equals the building load, so net added stress is near zero (Correct answer)
- Piles carry all of the structural load
- The water table is permanently lowered below the mat
Correct answer: The weight of excavated soil approximately equals the building load, so net added stress is near zero
Removing soil equal in weight to the structure leaves little net stress increase, minimizing settlement.
ASCE Geotechnical and Foundation Engineering 4
For a strip footing on saturated clay under undrained (φ = 0) conditions, the Prandtl/Meyerhof bearing capacity factor Nc is: