Acceptance of Timber Piles Based on Equivalent Driving Energy-Paper

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At JFK Airport’s Terminal 3 extension, variable ground conditions caused many timber piles to break, stop short, or fail the original acceptance criteria of minimum depth and final driving resistance. Of 874 timber piles installed, only 477 initially met those criteria, while conventional replacement piling led to further difficulties.<br /><br />The paper presents an alternative acceptance method based on Equivalent Driving Energy (EDE). Rather than judging a pile by its final blow count alone, the method uses cumulative driving resistance through the founding Glacial Sand to estimate the total energy required to advance the pile. EDE was calibrated against pile capacities measured by dynamic testing, including restrike tests that captured capacity gains from soil setup. The adopted criterion required at least 293 blows-ft of EDE and a minimum embedment of 7 feet in Glacial Sand (termination depth of at least 27 feet).<br /><br />Of 223 piles that failed the original criteria, 122 met the EDE criterion and were accepted; 12 failed it. Together with 132 piles accepted based on PDA results or nearby test-pile capacity, the alternative assessments rescued 254 piles. In total, 733 piles—84% of those installed—were accepted through the original criterion, PDA-based assessment, EDE, or a capacity downgrade.<br /><br />The case history indicates that EDE can help evaluate piles when variable soil conditions make final driving resistance or depth alone unreliable. Its use depends on representative dynamic testing for calibration and should retain minimum embedment and other safeguards.

Keywords

JFK Airport

Terminal 3 extension

timber piles

Equivalent Driving Energy

pile acceptance criteria

Glacial Sand

dynamic pile testing

pile capacity

soil variability

driving resistance