SHANSEP-Based Side Resistance of Driven Pipe Piles in Plastic Soils: Revision and LRFD Calibration

Abstract

The empirical approach adapting the Stress History and Normalized Soil Engineering Properties (SHANSEP) concept relates the average overconsolidation ratio (OCR) of plastic soils to the average pile side adhesion normalized to the effective overburden stress. Additional pile case histories were identified and used to expand an existing database and slightly revise the side adhesion design model. The data set then was used to calibrate resistance factors for the SHANSEP-based design model within the Load and Resistance Factor Design (LRFD) framework. The resistance factors derived provide a significantly greater nominal capacity than those presently available in the AASHTO code due to the accuracy of the SHANSEP-based design approach. For example, piles loaded in compression and for bridge spans with a dead-to-live load ratio of three returned resistance factors equal to 0.875 and 0.769 for reliability indexes of 2.33 and 3.09, respectively, in the absence of variability in OCR. Resistance factors then were calibrated in consideration of the uncertainty in OCR to allow the practitioner to directly consider the uncertainty in stress history in the reliability of the SHANSEP design approach. Reductions in the resistance factors ranged from 2% to 67% for coefficients of variability in OCR ranging from 5% to 50%. The reliability-based SHANSEP approach for side resistance represents a significant improvement over currently accepted design models in the AASHTO code and can be directly used to justify improved site investigation.