Development of New Shaft Resistance Models for Piles Driven in the Puget Sound Lowlands-Paper

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The study develops region-specific shaft-resistance models for driven piles in the Puget Sound Lowlands, Washington. Researchers compiled End-of-Driving (EOD) and Beginning-of-Restrike (BOR) CAPWAP records for 85 piles and matched their shaft-resistance profiles to soil classifications and effective stresses. This produced 1,216 observations from which β coefficients were calculated.<br /><br />Eight soil groups were defined using the Unified Soil Classification System (USCS), including a locally used mixed silty sand/silt category. For each group, separate EOD and BOR models were fitted using a three-parameter exponential function describing β as a continuous variation with depth. The fitting process targeted a mean prediction bias of one to support reliability-based design and load and resistance factor design (LRFD).<br /><br />The models capture general depth-related trends and provide designers with empirical estimates that account for soil type and pile setup. BOR models generally showed lower variability than EOD models, consistent with reduced scatter after setup. However, uncertainty remained substantial: coefficients of variation ranged from 62% to 180%, reflecting variability in soil conditions, CAPWAP shaft-resistance interpretation, and the use of broad soil categories. The organic-soil group had the smallest sample, with 26 observations.<br /><br />The models are intended to inform preliminary pile-capacity and drivability analyses in the Puget Sound Lowlands. Because they were calibrated using data from this specific geological region, application elsewhere requires validation or recalibration.

Keywords

shaft-resistance models

driven piles

Puget Sound Lowlands

CAPWAP records

EOD

BOR

Unified Soil Classification System

β coefficients

load and resistance factor design

pile setup