Analysis of the comprehensive influence of support timing and support parameters on the full section anchors of weakly cemented roadway surrounding rock

In response to the problems of anchors failure and roof collapse encountered during the construction of a green mine in a mining area in Western China, a full section anchoring mechanical model and numerical model of the roadway are developed. This model grounded in stress release theory and utilizing FLAC^3D software. The accuracy of the numerical model is validated through comparison with theoretical solutions. The paper analyzes the evolution of the plastic zone, stress field, and displacement field within the surrounding rock following roadway excavation. It explored how the timing of anchors installation influences the control of surrounding rock displacement and the axial force on the anchors, pinpointing the optimal timing for anchors support. Additionally, the impact of anchor density, anchor length, and pre-tension on the control of surrounding rock displacement is examined, all based on the established optimal support timing for the anchors. This research results indicate that excessive plastic deformation of the surrounding rock after roadway excavation is a principal cause of roadway failure. Therefore, the main objective of anchors support in roadways is to control the plastic deformation. The support timing significantly affects the performance of the anchors-surrounding rock system: early support will lead to excessive axial forces on the anchors, increasing the risk of breakage. Conversely, delayed support results in considerable deformation of the roadway, compromising its stability. In summary, the optimal support timing for the roadway, as determined by this study, is when the stress release rate with the surrounding rock reaches between 0.80 and 0.85. Optimization of support parameters: increasing the density of anchors support and enhancing the pre-tension force have a substantial effect on controlling the surrounding rock, whereas extending the length of the anchors does not significantly constrain the displacement of the surrounding rock. Consequently, when implementing anchors support for roadways, it is recommended to adopt a support scheme featuring short anchors, high density, and high preload force, after determining a reasonable support time.