Enhanced Load-Transfer Analysis for Friction Piles Using a Modified Borehole Shear Test

This study discusses the development and use of a modified borehole shear test (mBST) to improve the prediction of the load-displacement and load-distribution responses for axially loaded friction piles in cohesive soils using the load-transfer analysis method (i.e., t–z analysis). Unlike available approaches that rely on empirical or semi-empirical correlations to generate the shear stress displacement at the soil–pile interface (i.e., t–z curves), the mBST enables direct field measurement of the t–z curves at the soil–pile interface. As part of this study, three full-scale vertical static load tests (SLTs) were conducted on instrumented steel H piles. The t–z analysis was carried out utilizing the TZPILE software with measured t–z curves via the mBST (i.e., the TZ-mBST model). When comparing results of the analysis with the measured responses for the three test piles, it was found that: (1) the TZ-mBST provides proper prediction for the initial part of the measured load-displacement response from SLT results, with a difference not exceeding 10 %; (2) the TZ-mBST analysis provides acceptable prediction of the pile capacity; (3) the TZ-mBST analysis matches the load distribution along the pile length with a maximum difference of 8.3 %; and (4) the analysis with directly measured t–z curves using the mBST provide improved predictions of the pile response when compared to the empirical CPT-based analysis.