Investigation of Mining-Induced Fault Reactivation Associated with Sublevel Caving in Metal Mines

The long-term deformation of the Jinshandian Iron-ore Mine in China was monitored in situ, and the failure characteristics of the underground roadways and ground surface were analyzed. The mechanisms responsible for the mining-induced fault reactivation associated with non-pillar sublevel caving were subsequently revealed. When the quality of the overlying strata above the mined-out areas is relatively good, columns in the surrounding rock masses in the abutment pressure zone that are cut by joints with high dip angles will be subject to collapse, which causes significant reactivation of the faults. The failure of the surrounding rock masses in the abutment pressure zone has three distinct stages: failure of the columns, fault reactivation, and caving of the fault rock mass. In this event, the fault suffers large-scale reactivation which causes large-scale movement of the overlying strata. However, if the overlying strata are of relatively poor quality, the mining of the orebodies induces the roof strata to cave and this caving rapidly extends to the ground level. In this case, only the faults in the overlying strata above the mined-out areas are subjected to reactivation, and the scale of the movement observed in the overlying strata and ground surface is small. Due to the distinctive nature of the collapse and destruction that occurs in the columns in the abutment pressure zone, the scope of the fracturing in the surrounding rock masses is significantly larger than the scope of the mined-out areas (especially in the horizontal direction). Because of this, the ground movement angle associated with non-pillar sublevel caving in metal mines needs to be redefined. It is thus defined as the angle between the horizontal direction and an oblique line drawn from the bottom corner point of the actual fractured zone of the surrounding rock mass to an extended point on the ground surface movement curve.