Deep Foundations Load Testing Using the Top-Loaded Bi-Directional Test

The Top-Loaded Bi-Directional Test ("TLBT") is a new method to apply bi-directional loads to a deep foundation element with the loading source located above the foundation head. In the TLBT reusable load assembly, loads are applied to the foundation using the R-System which consists of two stacked steel plates located at the geotechnical resistance balance point or at the foundation base connected to the load assembly via vertical elements. The top plate or the Shaft Bearing Plate ("SBP") will transfer loads to the foundation upper portion, and the bottom plate or the Base Bearing Plate ("BBP") will transfer loads to the foundation lower portion as well as the foundation base. At the surface, above the foundation head, a hydraulic jack is located between a Top ("TLA") and Bottom ("BLA") load assembly. The TLA and BLA are connected to vertical elements which are consequently connected to the R-system. As the jack is pressurized and expanded at the surface, the R-System plates are separated, and the foundation is bi-directionally loaded. Like the conventional Bi-Directional Load Tests ("BDLT"), from instrumentations, strains within the foundation element, the R-System upward and downward movement, and the jack pressures are measured. From the measured values, loads and displacements are calculated. Due to the test method practical constructability, the TLBT provides a foundation testing system with lower risk of creating challenges during the foundation construction and installation. This paper presents the description of the TLBT method including benefits and challenges during the foundation testing. In addition, comparison results from full-scale load tests performed by both bi-directional load testing methods on adjacent test shafts are included.