Analysis of Bi-directional Static Load Tests on Large Barrettes-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines bi-directional static load testing (BDSLT) of large barrettes using the Osterberg Cell (O-Cell) method and compares its results with conventional top-loading tests (TLTs).<br /><br />An O-Cell is installed within the pile before construction. During testing, it pushes upward against the pile above it and downward against the pile below it, allowing shaft resistance and toe resistance to be assessed separately. The method can provide very high test loads and is useful where conventional reaction systems are impractical, including restricted sites, underwater construction, inclined piles, and tests targeting particular soil or rock layers. Its limitations include advance installation and design, a sacrificial cell, more complex interpretation, and unsuitability for certain pile types and small test loads.<br /><br />The presentation explains how strain-gauge measurements are used to calculate load transfer and displacement. An equivalent TLT load–settlement curve is then estimated by combining the upward and downward load–displacement responses. This estimate relies on assumptions about pile rigidity, movement, shaft-friction reversal, and elastic shortening; it is therefore not a directly measured TLT response.<br /><br />A case study applies the method, supported by RSPile analysis, to three test barrettes for a 105-storey tower. Maximum cell loads were about 90,000 kN, corresponding to estimated equivalent top loads of roughly 180,000 kN. Results examine shaft-friction distribution, segment shortening, displacement, and estimated TLT curves. Comparisons with working barrettes and numerical analysis show that predicted TLT behavior may require adjustment.<br /><br />The key conclusion is that O-Cell testing provides valuable insight into pile and barrette behavior, but equivalent TLT curves do not consistently match actual top-loading results. The author recommends systematic calibration of soil-transfer (T-z) curves—and toe-response (Q-z) curves where available—using measured test behavior. Further research is needed to make these estimates more reliable and less dependent on engineering judgment.

Keywords

bi-directional static load testing

BDSLT

Osterberg Cell

O-Cell method

barrettes

top-loading tests

shaft resistance

toe resistance

load settlement curve

RSPile analysis