CTQP Pile Driving Inspection 5 — Questions and Answers
Question 1: What information must be verified on the pile driving equipment submittal before driving begins?
- Manufacturer's suggested retail price and delivery schedule
- Hammer type, rated energy, stroke, and cushion material specifications (Correct answer)
- Operator's years of experience and union certification
- Insurance policy number and equipment serial number only
Correct answer: Hammer type, rated energy, stroke, and cushion material specifications
The equipment submittal must confirm hammer type, rated energy, operating stroke, and cushion specifications to ensure compatibility with the pile type and driving requirements.
Question 2: A diesel hammer is operating with very short strokes and low blow counts. What does this likely indicate?
- The pile is encountering hard driving and high resistance
- The hammer is not developing full rated energy due to light resistance (Correct answer)
- The pile has achieved refusal and driving should stop
- The fuel injection system is operating at peak efficiency
Correct answer: The hammer is not developing full rated energy due to light resistance
A diesel hammer requires sufficient resistance from the pile to compress fuel and fire properly; light soil resistance causes short strokes and low energy transfer.
Question 3: What is the significance of the 'elastic compression' (C1 or Ec) value in the Engineering News (EN) formula?
- It accounts for the energy lost in compressing the pile cap and cushions (Correct answer)
- It measures the permanent set of the soil after each blow
- It represents the maximum allowable pile head movement
- It calculates the total weight of the hammer ram
Correct answer: It accounts for the energy lost in compressing the pile cap and cushions
Elastic compression in the EN formula accounts for temporary elastic shortening of the pile, cap, and cushion system, distinguishing it from permanent set of the soil.
Question 4: Which condition requires the inspector to immediately halt pile driving and notify the engineer?
- Blow count increases by 10% over the previous 12-inch interval
- The pile head rises (rebound) more than 1/8 inch between blows
- Driving deviation exceeds maximum allowable tolerance limits (Correct answer)
- The crane operator requests a scheduled break for equipment maintenance
Correct answer: Driving deviation exceeds maximum allowable tolerance limits
Exceeding maximum allowable pile deviation (out-of-plumb or out-of-position tolerance) requires stopping work and engineer notification to evaluate structural and design impacts.
Question 5: What is the primary purpose of PDA (Pile Driving Analyzer) testing during construction?
- To determine the chemical composition of soil at the pile tip
- To measure driving stresses and evaluate pile capacity using wave equation analysis (Correct answer)
- To verify the concrete strength of precast piles after driving
- To monitor groundwater table changes caused by pile installation
Correct answer: To measure driving stresses and evaluate pile capacity using wave equation analysis
PDA testing uses strain gauges and accelerometers to measure force and velocity during driving, enabling CAPWAP analysis to evaluate pile capacity and driving stresses in real time.
Question 6: When inspecting a timber pile, what visible defect would be cause for rejection before driving?
- Natural taper of more than 1 inch per 8 feet of length
- Knots that reduce the cross-sectional area by more than 33% at any section (Correct answer)
- Sapwood that is less than 1 inch thick on any face
- Slight discoloration of the wood surface from weathering
Correct answer: Knots that reduce the cross-sectional area by more than 33% at any section
Knots or defects that reduce the net cross-sectional area by more than one-third at any point compromise structural capacity and are grounds for rejection.
Question 7: What does 'driving criteria' for a pile project typically specify?
- The number of workers required on the driving crew per shift
- The minimum blow count per foot or required tip elevation, whichever is more restrictive (Correct answer)
- The maximum allowable noise level in decibels near the driving site
- The exact brand and model number of approved hammer equipment
Correct answer: The minimum blow count per foot or required tip elevation, whichever is more restrictive
Driving criteria establish the minimum blow count per unit penetration and/or the required tip elevation, and piles must satisfy the more restrictive of the two conditions to be accepted.
CTQP Pile Driving Inspection 5
What information must be verified on the pile driving equipment submittal before driving begins?