Failure surface and pullout resistance of GFRP screw anchors

This study investigates the pullout resistance of glass fiber reinforced polymer (GFRP) screw anchors through laboratory experiments and numerical simulations, considering variations in H / D ( H and D are the embedment depth and diameter of the anchor plate, respectively). A generalized unified failure surface and calculation formulas for the ultimate pullout capacity were proposed. The research findings indicate that: (i) The pullout load-displacement curve of GFRP screw anchors can be divided into three stages: elastic, localized plastic, and through-failure stages. Correspondingly, the anchored soil can be partitioned into an active zone, a transition zone, and a passive zone; (ii) The failure surface shape of the anchored soil dynamically evolves following the sequence of "trumpet", "Wide-mouthed cup", "bulb" configurations as H / D gradually increases. The critical embedment depth ratio ( H / D ) cr varies with soil type, with typical values of 7 for clay and 11 for sand, highlighting the necessity of soil-specific design criteria for GFRP screw anchors. Both ultimate pullout capacity, Q u , and ultimate displacement ratio, u / D ( u refers to ultimate displacement) of GFRP screw anchors exhibit approximately linear positive correlations with H / D ; (iii) Increasing slope inclination angle reduces the ultimate pullout capacity, Q u , transitioning failure surfaces shape from symmetrical vertical propagation to asymmetrical slope-oriented deviation. The differences between the measured and calculated ultimate pullout capacity, Q u of GFRP screw anchors are within 20 %, demonstrating the rationality and accuracy of the proposed formulas.