What constitutes a good PDA test?

High strain dynamic pile testing (HSDPT) is routine practice, and has many benefits that make its use highly attractive. However, it requires careful preparation, attention to detail and testing engineer skill to properly perform these tests. Depending on his or her experience level, the test engineer may or may not realize when results are valid, or when capacity results may be only a lower bound. It is widely known that the capacity of driven piles may change with time after installation and for that reason restrike tests are generally recommended. It is also generally stated that the set per blow should be at least 2 mm, or otherwise the dynamic test may only yield a lower bound solution. To investigate the validity of these recommendations, GRL's database of dynamic test results is compared with static load tests, and various comparisons are made for both driven and drilled piles. Conclusions from this study and recommendations for practice are drawn.