The question each test answers
| Test | What it shows | Main limit |
|---|---|---|
| Static load test | Load-settlement behaviour under a sustained load | Slow and costly, so only a few piles are tested |
| Dynamic load test | Capacity estimated from the response to a hammer blow | Interpretation depends on analysis and correlation |
| Low-strain integrity test | Major defects and approximate length of the shaft | Limited on long piles; cannot measure capacity |
| Cross-hole sonic logging | Concrete quality between tubes cast into the pile | Tubes must be planned before concreting |
Static load tests
A static test loads the pile in steps with a hydraulic jack against a reaction system, such as kentledge or anchor piles, while settlement is measured. It is the most direct evidence of pile behaviour.
Preliminary test piles are loaded to high loads before the working piles are built, to confirm the design. Working piles are proof tested to a lower multiple of their working load.
Dynamic load tests
A dynamic test strikes the pile head with a heavy hammer while sensors record force and velocity. Signal-matching analysis estimates the capacity and how it is shared between shaft and base.
Dynamic tests are quick, so more piles can be covered. They are commonly correlated with static tests on the same site.
Integrity tests
A low-strain test taps the pile head with a hand-held hammer and reads the reflected wave. It is quick and cheap, and it is often carried out on all or most piles.
Cross-hole sonic logging sends a signal between tubes cast into the pile and profiles the concrete between them over the depth of the tubes. It suits large-diameter bored piles.
Building a testing plan
- Agree the number and type of tests with the consultant before piling starts.
- Decide early which piles need tubes for sonic logging.
- Choose which piles are tested with the consultant, including piles with unusual installation records.
- Allow the concrete to gain strength before testing.
- Agree what happens if a pile fails a test: further testing, redesign or replacement.