In pile driving, one of the most important quality control activities is recording the pile driving blow count, often called the pile driving log or driving record. This record helps engineers verify that the pile has reached the required bearing capacity and design depth.
During installation, the hydraulic hammer repeatedly strikes the pile while an inspector records the pile penetration for a specific number of blows—commonly 10 blows. As the pile reaches denser soil, penetration per blow decreases.
How the blow count is taken
- Mark the pile with scale intervals (e.g., every 10 cm or 25 cm).
- Near the final driving stage, count 10 hammer blows.
- Measure the total penetration after those 10 blows.
- Calculate the average penetration per blow.
- Continue recording until the pile reaches the specified final set, indicating the required capacity has been achieved.
For example:
- 10 hammer blows = 20 mm penetration
- Average penetration = 2 mm per blow
A smaller penetration per blow generally indicates increasing soil resistance, but final acceptance should always be based on the project’s design criteria and the engineer’s specifications.
Accurate blow count records are essential for:
- Verifying pile bearing capacity
- Monitoring installation quality
- Ensuring compliance with project specifications
- Providing documentation for quality assurance
Every hammer blow tells a story about the ground beneath our feet—and accurate records help ensure a safe and reliable foundation.