CTQP Pile Driving Inspection 4 — Questions and Answers
Question 1: What does a 'pile refusal' condition indicate during driving?
- The pile has reached its design capacity and can no longer be driven (Correct answer)
- The hammer has run out of fuel and stopped operating
- The pile has deviated beyond allowable tolerance
- The driving cap has separated from the pile head
Correct answer: The pile has reached its design capacity and can no longer be driven
Pile refusal occurs when the pile meets resistance that prevents further penetration, typically indicating it has reached bearing capacity at or near design load.
Question 2: Which type of pile splice is generally considered the strongest for steel H-piles?
- Bolted splice plates
- Full penetration butt weld (Correct answer)
- Partial penetration fillet weld
- Mechanical friction sleeve
Correct answer: Full penetration butt weld
A full penetration butt weld develops the full strength of the pile section and is the preferred splice method for steel H-piles under high loads.
Question 3: When should a pile inspector record the 'set' measurement?
- At the start of each driving session
- After every 10 blows regardless of penetration
- During the final set of blows near the end of driving (Correct answer)
- Only when the pile reaches the design tip elevation
Correct answer: During the final set of blows near the end of driving
Set is measured during the final blows of driving — typically the last inch or fraction of an inch per blow — to determine bearing capacity using driving formulas.
Question 4: A concrete pile develops a longitudinal crack during driving. What is the most likely cause?
- Excessive tension stresses from hammer rebound (Correct answer)
- The pile cap is too soft for the pile size
- Driving through very loose sand layers
- The pile was cast with too high a water-cement ratio
Correct answer: Excessive tension stresses from hammer rebound
Longitudinal (horizontal or tension) cracks in concrete piles are typically caused by tensile stress waves reflecting back up the pile during hard driving or near refusal.
Question 5: Under FDOT CTQP requirements, who is responsible for maintaining the pile driving log?
- The geotechnical engineer of record
- The contractor's pile driving crew foreman
- The pile driving inspector assigned to the project (Correct answer)
- The FDOT district structures engineer
Correct answer: The pile driving inspector assigned to the project
The pile driving inspector is responsible for accurately maintaining the pile driving log, recording blow counts, penetration, and field observations throughout driving.
Question 6: What is the purpose of a 'follower' in pile driving operations?
- A secondary pile driven alongside for lateral support
- An extension used to drive a pile below the reach of the leads (Correct answer)
- A cushion material placed on top of the pile head
- A sensor attached to the pile to monitor driving stresses
Correct answer: An extension used to drive a pile below the reach of the leads
A follower is a structural member placed between the hammer and the pile top to extend the effective driving depth when the pile head is below the reach of the leads.
Question 7: When driving piles in a group, which sequence is typically recommended to minimize soil heave effects?
- Drive from the outside perimeter inward toward the center
- Drive from the center of the group outward (Correct answer)
- Drive in alternating rows from one side to the other
- Drive from the deepest design tip elevation piles first
Correct answer: Drive from the center of the group outward
Driving from the center outward allows displaced soil to move freely outward, reducing heave on previously driven piles and minimizing group effects.
CTQP Pile Driving Inspection 4
What does a 'pile refusal' condition indicate during driving?