Case Study: H-Piles Driven Into Shale Rock for Compression and Uplift Resistance-Article

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The case study evaluates four HP360x174 steel H-piles driven into fractured shale for a bridge project in western New York. The piles had to meet both compression and uplift requirements, including a nominal uplift resistance of 1,334 kN. Because the shallow sand-and-silt overburden provided little uplift resistance, capacity depended on pile penetration into the shale and friction along the pile.<br /><br />Each pile was driven with a diesel hammer and a protective shoe flush with the pile flanges. Dynamic testing under ASTM D4945, including PDA measurements and CAPWAP analysis, was used to assess resistance. Rock penetration ranged from 0.98 to 2.31 m. The piles reached practical refusal at about 50 blows per 25 mm; measured driving stresses remained below the specified limit.<br /><br />Assuming a plugged pile section, the tests yielded an average unit side resistance of approximately 706 kPa and average unit tip resistance of 24.9 MPa. The side resistance was broadly consistent with the Illinois DOT AGMU 10.2 recommendation for shale (about 576 kPa), while the measured tip resistance was roughly four times the recommended value. The findings also show that calculated unit resistances depend substantially on whether the pile is treated as plugged or unplugged.<br /><br />At this site, dynamic test results indicated that approximately 1.5 m of shale penetration was sufficient to achieve the required uplift resistance. The authors emphasize that empirical design estimates alone may not reliably predict pile behavior in rock. Site-specific dynamic testing, together with pre-construction wave-equation analysis to verify the pile and hammer selection, is therefore important for confirming capacity and drivability.

Keywords

HP360x174 steel H-piles

fractured shale

bridge foundation

uplift resistance

compression capacity

dynamic testing

ASTM D4945

CAPWAP analysis

PDA measurements

pile penetration