Construction methods · Driven piles

Driving control: sets, refusal, restrike and splicing

The rules that decide when a driven pile is done: the set (penetration per blow) that corresponds to the required capacity, the refusal limit that protects the pile, and the restrike that reveals setup in clay or relaxation in dense sand. Getting them wrong wastes piles or leaves capacity on paper.

How bridges get built · Driven piles · Driving control: sets, refusal, restrike and splicing

Also called: driving criteria, set per blow, refusal criteria, pile splicing

How it is done

Derive the driving criterion from a wave equation analysis and confirm it with a dynamic or static test on the first piles.
Record blows per 250 mm continuously; stop at the target set at the design toe level, or at refusal (typically 10 blows per 25 mm) with the engineer's approval.
Restrike 10-20 % of piles after 24-72 hours; clays gain (setup), dense sands may lose (relaxation).
Splice with full-penetration welds (steel) or welded end plates (PHC) inspected before further driving; keep splices out of the zone of maximum bending.

Where it fits

Every driven pile job.

Where it does not

Driving to a fixed length regardless of set; accepting refusal on a boulder as bearing on rock.

Plant, pace and money

PlantBlow counter, PDA, welding inspection.

ProductivityGoverns the piling programme more than the hammer does.

CostSmall; poor criteria cost far more.

Risks and controls

What goes wrong

Overdriving through the bearing layer, underdriving into a soft layer below the target, splice failure.

Quality assurance

Driving log for every pile, restrike programme, splice inspection records.

Examples

The game's load-test step models this: a test pile turns a weaker-than-expected layer into a re-sized group instead of a surprise.