Improving Prediction of the Load-Displacement Response of Axially Loaded Friction Piles

This paper describes a Modified Borehole Shear Test (mBST) and a Modified Direct Shear Test (mDST) and their use to improve the prediction of the load-transfer (or t-z) analysis of axially loaded friction piles. The mBST and mDST enable direct measurement of the t-z curves along the soil-pile interfaces for cohesive soils in the field and for cohesionless soils in the laboratory, respectively, thereby improving the prediction of load-displacement response of piles. As part of this study, two full-scale instrumented static vertical load tests were conducted on steel H-piles and the t-z analysis was used to model these piles utilizing the TZPILE software. In these models, t-z curves established from the mBST and mDST as well as those currently used based on Cone Penetration Test (CPT) data were used to predict the pile load-displacement response. By comparing to the measured responses from static load tests (SLTs), the mBST- and mDST-based models produced closely comparable load-displacement responses. In contrast, the CPT-based models over predicted the loads at a given target displacement, underscoring the benefits of the mBST and mDST.