Specimen configuration effect on interface characterization using element anchor

Pullout test of element anchor specimens have been increasingly adopted to characterize the interface behavior of ground anchors. The effect of the configuration conditions of element anchor specimens on their interface characterization were investigated combining the laboratory tests and numerical simulations. Forty-eight element anchor specimens, reinforced with rebar tendons, were prepared using multiple bond/free length ratios and tested using consistent loading modes to quantify interface shear. The peak average interface shear strength was almost insensitive to configuration conditions when the ratio between bond length and grout diameter exceeded 2.10 or the ratio between free length and grout diameter exceeded 0.53. Additionally, the normalized peak average interface shear strength measured in the interface characterization was found to grow linearly with the increasing free/bond length ratio of the specimen. An interface shear displacement zone with a spindle-shaped distribution was found to develop within the soil surrounding the element anchor specimens when reaching the peak interface shear strength. However, the soil deformation zone developed a uniform distribution along the entire interface once testing reached the residual shear phase. Use of the reserved anchorage method to achieve a consistent interface shear area was found to effectively improve the uniformity of interface shear displacement throughout the interface.