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

摘要

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.