Refined Prediction of End Bearing through Multi-Level High Strain Dynamic Measurements

High strain dynamic testing (HSDT) has been used successfully as part of or the sole means of loading test programs on both driven pile and drilled foundations. Signal matching analysis of pile top force and velocity measurements allows for modeling of soil resistance and its distribution along the pile, determining not only the total static resistance, but also the end bearing component. While the estimation of total static resistance has been proven reliable with multiple published correlation studies performed, the accurate estimation of shaft resistance versus end bearing is limited. This limitation is caused by the lack of resolution of the measurements and relatedly the difficulty of distinguishing between the end bearing and shaft resistance near the pile bottom. This ability is further complicated on drilled foundations due to the non-uniform nature of these foundation types. The best available means of improving the accuracy of the calculated end bearing–shaft resistance distribution is making additional measurements of force and velocity near the toe. The analysis of these data requires a multi-level signal matching approach. This paper describes measurement and analysis techniques, which were developed for the purpose of improving the resistance distribution predictions of HSDT. Three case studies are presented, where pile top and pile toe measurements in combination were taken on various foundation types, which allowed for a more refined prediction of end-bearing through a multi-level analysis of the data at the pile toe and pile top. Limitations of this approach are also discussed.