Increased Axial Resistance of Small-Diameter Piles and Ground Anchors by Using Expander Bodies

An expander body (EB) is an element consisting of a folded steel sheet with a circular cross section that can be added to a relatively small diameter pile and ground anchor to increase axial resistance. During the injection of pressurized grout, the outer portion of the EB is expanded (inflated) from its original diameter of about 120 mm (4.75 in.) to about 400-800 mm (15.75-31.5 in.), depending on the model and stiffness of the in situ soil surrounding the device. Due to the controlled expansion process, the stress state is improved around the device and can be deduced from the recorded measurements; hence, the available axial resistance for these smaller diameter elements can be increased considerably due to the greater soil stiffness and shear strength around the device as well as to the larger cross-sectional area (i.e., end resistance) and larger surface area. This paper describes the general principles of the EB system as well as the construction, grouting operation, quality control, and select results from static axial compression load tests performed on continuous flight auger (CFA) + EB piles.