Adjacent Top-Loaded Bi-Directional Test And Conventional Bi-Directional Load Test Results

Paper

Pdf Summary

The paper compares conventional bi-directional load testing (BDLT) with a newer top-loaded bi-directional test (TLBT) using adjacent 3-foot-diameter, 30-foot-long drilled shafts at a site in Solon, Ohio. Both methods load embedded bearing plates in opposite directions. BDLT uses an embedded hydraulic jack, while TLBT applies load through reusable high-strength threaded bars connected to an above-grade jack and loading assembly.<br /><br />The BDLT shaft reached a maximum unidirectional load of 240 kips, with upper and lower bearing-plate movements of 0.5 and 3.8 inches. The TLBT reached 300 kips, with movements of 1.0 and 5.9 inches. The greater TLBT capacity reflected, in part, stiffer base materials at its location and its jack’s longer stroke, so the results should not be interpreted as a direct measure of method performance alone.<br /><br />Equivalent top-loading curves were broadly similar at loads available from both tests. At 377 kips, estimated shaft-top displacement was 0.54 inches for BDLT and 0.43 inches for TLBT. Additional TLBT instrumentation indicated generally uniform load transfer, though one of three mobilizer bars carried less load than the other two; at maximum load, the difference between jack load and average bar load was 12%.<br /><br />The authors conclude that TLBT can provide a practical alternative for moderate-size shafts. Its reusable loading components may reduce costs, and eliminating embedded hydraulic jacks and lines may lower construction risks. However, the comparison is affected by differences in subsurface resistance and construction conditions.

Keywords

bi-directional load testing

BDLT

top-loaded bi-directional test

TLBT

drilled shafts

load transfer

bearing plates

shaft displacement

load capacity

Solon Ohio