Pile Driver Systems
2 hours
Learning Objectives
- •Identify the four major hammer types used in pile driving and state their operating principles
- •Describe the components of a pile driving leads system (fixed and swinging)
- •Distinguish the appropriate application of each pile type by material and driving method
- •Explain the function of the pile template, follower, and cushion in a pile driving system
Topics Covered
- •Drop hammer: gravity-powered, simplest type; stroke height determines energy
- •Single-acting diesel hammer: fuel ignited by compression; rated by ram weight and stroke
- •Double-acting / differential diesel hammer: downstroke assisted by combustion gases
- •Hydraulic hammer: variable energy settings; low vibration; preferred for sensitive sites
- •Vibratory hammer: eccentric weights create high-frequency vibration; reduces soil friction; effective in granular soils; not for capacity verification
- •Fixed leads: attached to crane base, hold hammer in precise alignment; required for batter piles
- •Swinging (free) leads: suspended from crane boom tip; more flexible; allow slight misalignment
- •Pile types: timber (round or square); pre-stressed concrete; steel H-pile; steel pipe pile; sheet pile (Z and U profiles)
- •Pile cushion: absorbs hammer blow and protects pile head; must be replaced when compressed
- •Hammer cushion: protects the helmet/cap; inspected every 500 blows or per manufacturer spec
- •Pile template: guides pile to exact location during initial driving; ensures plan accuracy
- •Follower: extension used when pile head is below leads reach; reduces accuracy; avoided when possible
- •Pile helmet (driving cap): transmits blow evenly to pile head; matched to pile type
- •Penetration rate and set: blows per foot tracked; final set recorded as blows per inch
Resources
Self-Check Questions
Question 1: Which pile driving hammer type works by reducing friction between the pile and soil through high-frequency vibration, rather than impact?
- A. Drop hammer
- B. Single-acting diesel hammer
- C. Hydraulic hammer
- D. Vibratory hammer(correct)
Show Explanation
Explanation:
The vibratory hammer uses rotating eccentric weights to create rapid oscillations that temporarily liquefy the surrounding soil, allowing the pile to sink. It does not measure bearing capacity the way impact hammers do.
Question 2: You are driving batter piles at a precise angle. Which leads type is most appropriate?
- A. Swinging (free) leads, because they allow flexible positioning
- B. Fixed leads attached to the crane base, because they hold a precise alignment(correct)
- C. Either type — angle does not affect the choice of leads
- D. No leads are required for batter piles
Show Explanation
Explanation:
Fixed leads are required for batter piles because they keep the hammer and pile at a consistent angle throughout driving. Swinging leads cannot maintain the precise geometry needed for accurate batter work.
Question 3: What is the primary purpose of the pile cushion in a driving system?
- A. To lift the pile from the storage yard to the leads
- B. To absorb the hammer blow energy and protect the pile head from damage(correct)
- C. To guide the pile to the correct grid location
- D. To prevent the hammer from rising into the head block
Show Explanation
Explanation:
The pile cushion (between the drive cap and the pile head) absorbs impact energy and distributes it evenly to avoid spalling or cracking the pile head. It must be replaced when it compresses past the manufacturer's limit.
Question 4: Which pile type would be best suited for a project requiring a continuous subsurface barrier to retain soil and water?
- A. Timber pile
- B. Pre-stressed concrete pile
- C. Steel sheet pile(correct)
- D. Steel H-pile
Show Explanation
Explanation:
Steel sheet piles (Z or U profiles) are designed to interlock and form a continuous wall, making them ideal for cofferdams, retaining walls, and waterfront shoring. H-piles and timber piles are bearing members, not barriers.
Question 5: A follower is used when driving piles. What is a key drawback of using a follower?
- A. A follower prevents the use of a diesel hammer
- B. A follower reduces driving accuracy because it introduces misalignment between the hammer and pile(correct)
- C. A follower is only usable with vibratory hammers
- D. A follower requires a separate licensed operator
Show Explanation
Explanation:
Followers extend reach when the pile head is below the bottom of the leads, but they reduce energy transfer efficiency and introduce the possibility of misalignment. Engineers avoid followers whenever possible for this reason.
Question 6: Final pile set is typically recorded as:
- A. Total feet driven per shift
- B. Blows per inch during the last few inches of driving(correct)
- C. Minutes required to drive each pile
- D. The distance from the pile head to grade after driving
Show Explanation
Explanation:
Final set — blows per inch (or per 25 mm) — is the standard measure of pile bearing capacity. The more blows required per inch, the greater the resistance and the closer the pile is to its design capacity.