The Effect of Setup Time in Geotechnical Resistance Factor of Driven Steel Piles in Alberta: a Case Study-Article

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This study examines how pile setup—the increase in bearing capacity over time after driving—affects geotechnical resistance factors (GRFs) for steel pipe piles in Alberta. Setup occurs as excess pore-water pressure dissipates and soil resistance around the pile increases.<br /><br />The authors analyzed PDA test results from 346 piles, each tested at end of drive (EOD) and beginning of restrike (BOR), and used 28 static load tests to validate the dynamic measurements. Piles were classified as being in cohesive, cohesionless, or mixed soils. Monte Carlo simulation was used to calibrate GRFs for target reliability indices of 2.33 and 3.00. The study compared a single GRF for total BOR capacity with separate factors for EOD resistance and resistance gained through setup.<br /><br />Pile capacity increased between EOD and BOR in all soil types, with setup more pronounced in cohesive soils. The calibrated GRFs were generally lower for cohesive than cohesionless soils, reflecting greater uncertainty in pile behavior and setup in cohesive ground.<br /><br />Using separate EOD and setup factors produced higher factored resistance than applying one factor to total BOR capacity, improving design efficiency across all soil categories. At a reliability index of 2.33, the improvement was about 18% for cohesive soils and 13% for cohesionless soils; gains in mixed soils were smaller. The authors conclude that accounting for setup through separately calibrated factors can support more cost-effective pile design. They caution that the factors depend on the analysis method and that results for mixed soils are uncertain because the sample included only seven piles.

Keywords

pile setup

geotechnical resistance factors

steel pipe piles

bearing capacity

Alberta

dynamic testing

static load tests

cohesive soils

Monte Carlo simulation

pile design