Top-Loaded Bidirectional Test, a New Approach to Deep Foundations Load TestingÂ-Paper

Paper

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The paper introduces the Top-Loaded Bi-Directional Test (TLBT), a method for testing deep foundations that applies bidirectional loads from a reusable assembly at the foundation head. Surface hydraulic jacks connect through vertical bars to an embedded R-System: two steel plates that transfer loads to the upper and lower portions of the foundation. The plates are positioned at the geotechnical resistance balance point or foundation base.<br /><br />Unlike conventional bi-directional load tests (BDLT), TLBT does not require hydraulic jacks or hydraulic lines embedded within the foundation. Its R-System also has a central opening for a Tremie concrete-placement line, allowing standard construction practices and reducing the risk of concrete integrity problems. Surface-accessible equipment can be inspected or repaired, and most components are reusable; only the R-System is sacrificial.<br /><br />A full-scale proof-of-concept test on a 48-inch-diameter, 40-foot-deep drilled shaft reached a maximum bidirectional load of 970 kips. Instrumentation produced load-displacement and load-strain results, including an equivalent top-loading curve. The authors report that the results and load transfer were consistent with the expected behavior of a bidirectional test.<br /><br />The authors conclude that TLBT may offer a more practical, lower-risk alternative that can simplify installation, reduce the chance of abandoning a test foundation, and enable more tests with the same equipment. Additional testing and direct comparisons with conventional BDLT and top-loaded tests are needed to confirm its reliability and address remaining limitations.

Keywords

Top-Loaded Bi-Directional Test

TLBT

deep foundations

bidirectional load testing

drilled shaft

foundation testing

R-System

load-displacement response

load transfer

proof-of-concept test