How many PDA tests are normally required in the USA?
For highway projects, the American Association of State Highway Transportation Officials (AASHTO) LRFD guideline is 2% of the total number of piles on the job, or 2 piles, whichever is larger (2 piles is usually larger because most bridges have very few piles in each pier), resulting in higher resistance factors (lower equivalent safety factors) than projects controlled by static analysis, dynamic formula, or even wave equation analysis; testing then lowers the overall cost of the foundation. Testing 100% of the piles results in even higher resistance factors (lower equivalent safety factors) under AASHTO's LRFD code, and thus results in even more economic benefit - this is now common in Florida for example.
For private sector projects, the IBC code treats dynamic testing (ASTM D4945) and static testing (ASTM D1143) as equivalent and provides no general guidance on the amount of testing; however, testing 5% of piles is reasonable (and even 10% is not unreasonable).
The Australian code LRFD code AS2159 gives higher resistance factors (lower equivalent safety factors) when higher percentages of piles are tested, yielding a larger benefit. Testing 5 to 10% of piles does not seem unusual. There is no additional benefit for testing more than 25% of the piles in the Australian code.