Civil Engineering PE Shallow and Deep Foundations 4 — Questions and Answers
Question 1: A 2.5-ft wide strip footing is founded 3 ft below grade in clay with Su = 800 psf. Using Hansen's bearing capacity factors (Nc = 5.14, sc = 1.0 for strip), the gross ultimate bearing capacity is approximately:
- 4,112 psf + overburden (Correct answer)
- 5,140 psf + overburden
- 3,600 psf + overburden
- 6,200 psf + overburden
Correct answer: 4,112 psf + overburden
q_ult = Su × Nc = 800 × 5.14 = 4,112 psf (net), plus the overburden pressure γDf = 120 × 3 = 360 psf for gross capacity.
Question 2: The wave equation analysis (WEAP) for driven piles is used primarily to:
- Predict driving resistance and evaluate hammer-pile-soil system performance during installation (Correct answer)
- Calculate long-term consolidation settlement under pile loads
- Design the pile cap reinforcement for punching shear
- Determine lateral pile stiffness using p-y curves
Correct answer: Predict driving resistance and evaluate hammer-pile-soil system performance during installation
WEAP models stress wave propagation to predict blow counts at refusal, check driving stresses, and confirm pile capacity during installation.
Question 3: For a rectangular footing with dimensions B × L, the Meyerhof shape factor for the cohesion term (sc) is:
- 1 + 0.2(B/L)Kp (Correct answer)
- 1 + (B/L)tan(φ)
- 1 + 0.4(B/L)
- 1 + 0.3(B/L)
Correct answer: 1 + 0.2(B/L)Kp
Meyerhof's shape factor for cohesion is sc = 1 + 0.2(B/L)Kp, where Kp = tan²(45 + φ/2).
Question 4: An H-pile driven to rock refusal develops its load primarily through:
- End bearing at the pile tip with minimal skin friction contribution (Correct answer)
- Skin friction along the full pile length
- A combination of 50% skin friction and 50% end bearing by code
- Lateral earth pressure on the flanges
Correct answer: End bearing at the pile tip with minimal skin friction contribution
H-piles driven to rock refusal rely almost entirely on end bearing since the relatively small tip area concentrates stress at the rock surface.
Question 5: The Davisson offset limit method for determining pile capacity from a static load test uses an offset of:
- 0.15 in + pile diameter/120 (Correct answer)
- 0.25 in + pile length/200
- 1% of pile diameter
- 0.5 in fixed offset for all pile sizes
Correct answer: 0.15 in + pile diameter/120
Davisson's criterion defines failure at a settlement equal to the elastic compression of the pile plus an offset of 0.15 in + D/120 (where D is diameter in inches).
Question 6: Immediate settlement of a footing on saturated clay under undrained loading is calculated using:
- Elastic theory with undrained modulus Eu and Poisson's ratio νu = 0.5 (Correct answer)
- Terzaghi's 1-D consolidation equation with Cv
- The stress distribution method with Cc and e0
- SPT-based empirical correlations with N60
Correct answer: Elastic theory with undrained modulus Eu and Poisson's ratio νu = 0.5
Immediate (elastic) settlement under undrained conditions uses elasticity theory with the undrained Young's modulus (Eu) and νu = 0.5 for incompressible behavior.
Question 7: When eccentricity of loading on a footing exceeds B/6, the pressure distribution beneath the footing:
- Develops tensile stress on one side, meaning only part of the footing is in contact with soil (Correct answer)
- Remains uniform but shifts toward the load resultant
- Causes immediate punching shear failure by code definition
- Is ignored and replaced with a uniform pressure
Correct answer: Develops tensile stress on one side, meaning only part of the footing is in contact with soil
When e > B/6, the resultant falls outside the kern, causing uplift (tension) on the far edge — since soil cannot take tension, the effective footing area reduces.
Civil Engineering PE Shallow and Deep Foundations 4
A 2.5-ft wide strip footing is founded 3 ft below grade in clay with Su = 800 psf.
Using Hansen's bearing capacity factors (Nc = 5.14, sc = 1.0 for strip), the gross ultimate bearing capacity is approximately: