Evaluation of Tangent Bearing Element Axial Load Response-Article

Article

Pdf Summary

The paper evaluates Tangent Bearing Elements (TBEs), bundles of two or more augered cast-in-place (ACIP) piles installed tangent to one another. TBEs offer a way to construct large-capacity foundations where individual ACIP pile diameters are limited, and may be installed substantially faster than equivalent large bored piles. Their unconventional geometry, however, raises questions about how they perform under axial load.<br /><br />The author compares bi-directional static load test results from three projects, each including a single-pile element and one or more multi-pile TBEs. For analysis, the TBE’s effective side-shear and end-bearing areas are based on its enveloping perimeter—the outline around the bundle. Test loads are normalized against the single-pile results.<br /><br />Across the case histories, the normalized unit side-shear response of TBEs was broadly comparable to that of individual ACIP piles. In one case, the four-pile element’s normalized end-bearing resistance also compared reasonably with the single pile at large, plunging displacements. Its initial stiffness differed, but the difference was broadly consistent with the expected influence of a larger effective diameter. Another comparison with a nearby bored pile showed similar behavior at small displacements, with greater divergence at larger movements.<br /><br />The findings are encouraging but preliminary: only a few projects were available, and differences may reflect scale effects, construction-related soil disturbance, installation methods, or natural ground variability. The author recommends load testing for significant TBE projects and further full-scale testing and finite-element studies to validate the enveloping-perimeter assumption. Overall, the results suggest TBEs can provide axial resistance comparable to conventional piles when their effective area is evaluated appropriately, while potential scale effects should be considered in design.

Keywords

Tangent Bearing Elements

TBEs

augered cast-in-place piles

ACIP piles

axial load

static load test

side-shear resistance

end-bearing resistance

enveloping perimeter

pile foundations