Analysis of Floor Stability under the Coupled Influence of Mining-Induced Disturbance and Confined Water

This study investigates floor stability in underground coal mining, considering the coupled effects of backfilling and confined aquifer pressure. Using a North China coal mine’s 9101 fully mechanised mining face as a case study, a formula for maximum floor failure depth under confined water pressure was derived using the zero-position failure principle and superposition. A numerical model was developed to analyse how vertical stress, permeability, porosity, and pore water pressure in the floor evolve with varying backfill rates. The interrelationship of these parameters at different floor locations was analysed to determine how backfilling impacts the effective impermeable layer thickness and overall floor stability. Results show the theoretical formula accurately predicts the plastic zone height; increasing mining face advancement increases maximum vertical stress, but this stress negatively correlates with backfill rate; higher backfill rates reduce permeability (up to 45%); at 120 m advancement, the increased porosity zones in the caving method aquiclude and the Ordovician aquifer show a connection, but higher backfill rates significantly reduce overall porosity; increased backfill rates lower pore water pressure, reducing the plastic zone and confined water rise; floor stress and permeability are negatively correlated, while porosity increases due to mining; and the water inrush face experienced both pore water pressure increase and recovery zones. This research provides a theoretical foundation for safely mining coal above deep confined aquifers.