Improvement of anchor structural unit in FLAC3D and its application to the 110 construction method

Numerical simulation is an important method for analyzing the behavior of supports under complex geological conditions. FLAC3D, a widely used analysis tool, assumes the anchor structural unit to be an ideal elastoplastic material, which limits its ability to simulate strength decay in situations involving large deformation. In this study, we enhanced the anchor structural unit in FLAC3D software by developing a nonlinear convergent model of the anchor structure. This modification improved the simulation accuracy of anchor behavior in real-world engineering scenarios. The new model was verified through careful numerical pullout tests. In the numerical pullout tests, the predicted engineering conditions, including the deformation, axial force, and failure conditions of the Poisson's ratio (PR) and negative Poisson's ratio (NPR) anchors corresponded to the actual conditions in both the elastic and plastic stages. The model was then applied to compare the stress distributions in the surrounding rock during back mining using the conventional 121 method and the 110 method. The peak stresses were generally higher for the 121 method compared with the 110 method. The shear stresses of the two methods differed by 2.48 times in the XZ direction and by 6.41 times in the YZ direction, while the vertical stress differed by 1.3 times. For the rock mass outside the roadway, the shear stresses differed by up to 6.7 times in the XZ direction and by up to 3.5 times in YZ direction, while the vertical stress differed by up to 1.88 times. These findings confirm the advantages of the 110 method and demonstrate the key role of NPR anchors in improving the stress distribution of the surrounding rock. This research provides a reliable strategy for the large-scale numerical simulation of NPR and PR anchors.