The influence of backfilling of a caved zone and magma intrusion-type faults on surface deformation in a metal mine caused by sublevel caving mining

Based on monitoring data and engineering geological conditions, the surface deformation patterns caused by sublevel caving mining in the Dahongshan iron mine were analyzed. By interpreting the four stages of development of the surface fractured zone, namely, the formation, full unilateral development, asymmetric expansion and backfilling of the caved zone, it was found that the magma intrusion-type fault F2 had an inhibitory effect on the expansion of the surface fractured zone and that backfilling of the caved zone was an effective measure for controlling surface movement. The fault acted as a barrier, limiting the propagation of damage in the surrounding deep rock but allowing it to spread outward in the shallow rock, resulting in damage and a sliding zone of approximately 60 degrees from the horizontal plane in the shallow rock. A zonal characterization method for the lateral support force of a loose medium was proposed. After backfilling the caved zone, the active and passive lateral pressures generated by the critical medium column helped suppress the deformation of the deep surrounding rock. However, in the noncritical medium column segment, the active lateral pressure failed to prevent damage and sliding of the shallow rock. The lower strength of the diabase in the shallow part of the fault, caused by weathering and alteration, compared to that of the gabbro in the deep part, led to bending deformation and damage in the shallow part of the fault due to weaker lateral support forces. A thicker fault, higher inclination angle, and smaller range of tensile damage resulted in stronger inhibition of movement in shallow rock. These findings offer valuable insights for similar metal mines with comparable engineering and geological conditions.