Abstract: This study aims to analyze the anchoring characteristics of 2G-NPR anchor rods and determine the reasonable matching range between the anchor rod diameter and the anchoring aperture. Based on laboratory pull-out tests, the failure modes of the anchoring system under different anchoring apertures were analyzed. A mechanical model was established to match the anchor body and anchor aperture, and theoretical formulas for axial force and interface shear stress along the anchoring direction were derived. Using the finite difference program FLAC3D, pull-out models for different anchoring apertures were established, and the stress distribution of the anchoring system was analyzed. The results indicate that: 1) Under different anchoring apertures, with a diameter matching difference of 8 mm as the boundary, the failure interface of the anchoring system at maximum bearing capacity differs. 2) The load-displacement curve of the anchoring system during loading can be categorized into five stages: preloading, elastic deformation, plastic deformation, interface debonding initiation, and complete debonding. 3) Under a pulling force of 30 kN, as the anchoring aperture increases, the shear stress distribution at the anchor rod-anchoring agent interface shows little variation with hole diameter, but exhibits significant stress concentration at the spiral rib. At the same position, the shear stress at the anchor rod-anchoring agent interface is 2-3 times that at the anchoring agent-surrounding rock interface. Additionally, the shear stress distribution at the anchoring agent-surrounding rock interface decreases significantly with increasing hole diameter. 4) The optimal anchoring aperture difference for diameter of 18 mm 2G-NPR anchor rods has been determined to be 8-12 mm.

Key words: pullout test, 2G-NPR anchor blot, anchor aperture, anchor performance, anchorage body failure modes