PDA Testing and Analysis: Utilizing Test Results with a Focus on Capacity-Paper

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The paper explains how Pile Driving Analyzer (PDA) testing, combined with CAPWAP signal-matching analysis, can assess driven-pile performance and ultimate capacity. PDA instruments measure pile strain and acceleration during hammer impacts, providing information on hammer efficiency, driving stresses, and soil resistance. CAPWAP analysis of selected blows estimates total static resistance, separates shaft resistance from end bearing, and shows how shaft resistance varies along the pile.<br /><br />Test piles are commonly driven before production piles, with results used to establish installation criteria. Reported capacities are nominal ultimate resistances—not design capacities—so engineers must apply the applicable safety or resistance factors. The paper notes that testing levels can affect the LRFD resistance factor; more extensive dynamic testing may permit a higher factor. Project documents should specify testing requirements and applicable factors.<br /><br />A case history describes a 125-foot steel H-pile driven through sand and gravel into hard silt with sand. At end of driving, CAPWAP estimated 710 kips of capacity: 505 kips from shaft resistance and 205 kips from end bearing. After a 1.25-hour wait, restrike testing indicated a mobilized capacity of 1,000 kips, with shaft resistance increasing by about 290 kips—evidence of soil setup.<br /><br />The restrike result was a lower bound rather than a definitive maximum: pile movement was very small, suggesting that the soil’s full available resistance may not have been mobilized. The paper emphasizes that dynamic test results reflect conditions at the time of testing; restrike testing can reveal capacity changes over time, while limited mobilization must be considered when interpreting results.

Keywords

Pile Driving Analyzer

CAPWAP

driven pile capacity

dynamic pile testing

shaft resistance

end bearing

restrike testing

soil setup

LRFD resistance factor

pile driving analysis