A pile-driving cap is the protective cap placed over the pile head during driving, between the hammer and the pile. The cap guides the blow of the hammer to the pile head, spreads the pressure evenly and cushions the impact, so that the pile head does not split or crack.
Construction
A pile-driving cap usually consists of two parts:
- Driving cushion — an insert of hardwood (such as azobé), nylon or aluminium that spreads the hammer blows and reduces noise
- Packing — a softwood filling (often pine) that absorbs the impact; it is soft and has a short service life
Function
The cap acts as a physical, pressure-spreading guide of the blow from the hammer to the pile head. In doing so, it:
- protects the pile head from splitting and cracking
- spreads the pressure evenly across the head
- lengthens the duration of the blow and cushions the impact before it reaches the pile
Points to watch
- Replacing the packing — the softwood filling is replaced regularly, typically after about 800 to 1,000 blows or when it is compressed to about a third of its original thickness
- Correct size — the cap must match the pile diameter, otherwise the pressure distribution does not work well
Related terms
- Piling
- Driven pile
- Pile-driving hammer
- Piling rig
- Pile foundation
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