Leakage mechanism and stability control for overburden grout injection induced by mining

Underground slurry inrush directly constrains the effectiveness of subsidence mitigation and threatens underground safety, representing a major challenge in the engineering application of overburden grout injection technology. The issue of slurry leakage occurring during overburden grout injection in the field was investigated through theoretical analysis, engineering practice, and on-site monitoring. The factors influencing the stability of the slurry reserve were systematically analyzed, and the formation mechanism of bed separation was elucidated through an analysis of deflection rates. A mechanical model for the deflection of the grout-separating layer was established, considering its deformation characteristics during the grouting process. The stability of the grout-separating layer under different conditions was then evaluated. A risk assessment system for underground slurry inrush was established. The results indicate that the stability of the grout-separating layer in the original grouting plan is insufficient, and it is prone to rupture under grouting pressure, which is the primary cause of slurry leakage. The grouting scheme optimized through risk assessment yields safety factors of 0.42 and 0.15 for the grout-separating layer, ensuring its structural integrity. Monitoring results of underground water inflow volume and tracer ion concentrations indicate that adjusting the grouting layer effectively resolved the grout leakage issue underground. Subsequent to overburden grout injection, the maximum surface subsidence measured 649.8 mm, corresponding to a subsidence reduction rate of approximately 80.77%, thereby achieving a significant control effect. The findings provide insights for the broader application of overburden grout injection and for subsidence control in mining under analogous geological settings. Underground slurry inrush multi-factor coupling mechanism was explained. Bed separation formation mechanism was clarified; grout-separating layer stability criteria proposed. Overburden grout injection slurry inrush risk system was established for grout reserve evaluation.