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

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The presentation compares a conventional bi-directional load test (BDLT) conducted in 2017 with a top-loaded bi-directional test (TLBT) conducted in 2021 at Site II, where the shafts encountered stiff clay and glacial till. The TLBT uses top and bottom load assemblies and mobilizer bars to apply load to the shaft.<br /><br />The two methods produced comparable results. At the maximum BDLT load of 240 kips, the equivalent top-loading (ETL) responses were very similar, allowing for differences in base-material resistance and normal construction variability. The BDLT reached 240 kips, with upper and lower bearing-plate displacements of 0.5 and −3.8 inches. The TLBT reached 300 kips, with corresponding displacements of 1.0 and −5.9 inches.<br /><br />Additional TLBT instrumentation assessed load distribution through the base mobilizer bars and lower bearing plate. At maximum load, two of the three bars carried nearly identical loads; the third carried 8.3% less than their average. Despite this variation, the difference between hydraulic-jack load and average bar load was 12%. The findings support the TLBT as a method that can produce results comparable to a conventional BDLT.

Keywords

bi-directional load test

BDLT

top-loaded bi-directional test

TLBT

shaft load testing

Site II

glacial till

stiff clay

load distribution

equivalent top-loading