Grouting sleeve/bird’s nest anchor cable anchoring capacity characteristics and numerical simulation study

• Influence of grouting pressure on bearing characteristics of combined structures of grouting anchor cables . • Analyzed the failure modes of the bird’s nest anchor cable anchorage bodies. • Performed a simulation analysis of the stress distribution and failure of the bird’s nest anchor cables. • Explored the failure mechanisms of grouted bird’s nest anchor cable anchor bodies through numerical simulation. With the deepening of coal mining resources, the safety issues of broken soft coal seams become increasingly prominent, severely affecting the safety of deep mining operations and workers. Traditional anchoring methods alone are ineffective in achieving secure anchorage. Therefore, the grouting anchor cable composite structure is explored to address the safety of roadway excavation in deep broken soft coal seams. Indoor grouting anchorage tests and pull-out tests for grouted anchorages are conducted to study their bearing characteristics and failure mechanisms. Discrete element numerical simulation methods are employed to verify the findings from indoor tests. Research indicates that the ultimate pull-out forces at grouting pressures of 0.5, 1.0, 1.5, and 2.0 MPa are 87, 104, 118, and 131 kN, respectively. The pull-out force of the grouted anchorage is positively correlated with the grouting pressure. At the loading end, shear stress and axial force reach their maximum values of 1.8 MPa and 106 kN, respectively, under 2.0 MPa grouting pressure. The distribution patterns of shear stress and axial force decrease gradually with increasing anchoring depth. Microscopic analysis reveals that the failure of the anchor body model is primarily due to the tensile cracks formed by the particle flow code in two dimensions. This finding is consistent with the failure mode observed in indoor tests, which involves the slip and debonding failure of the anchor cable. Crack evolution is categorized into three stages: initiation, continuous propagation, and anchor failure. As the inter-particle contact forces within the anchor body model decrease, the region of chain fracture expands. These results provide technical support for understanding the bearing characteristics of grouting anchor cable composite structures.