This paper assesses the fracture development characteristics of the rock mass around the sublevel and shrinkage stopes under steep thick orebody using 3DEC and Surpac, and redetermines the boundary of the protective pillar area for the dressing plant. A 3D solid model was constructed using a laser detector and Surpac, transformed it into a 3DEC numerical model, and then the settlements and failure zones of the rock mass around the stopes were analyzed using generalized Hoek–Brown failure criterion. At that time, the mining characteristics of the orebody are 50–100m long, the bed height is 50m, the ore body thickness (M) is 10–30m and the slope angle is 60°. From the simulation results, the relative error between the simulated and the measured data was less than 10%. Finally, the mineable reserves of more than about 2 million tons in the protective pillar area can be obtained.
The target mine is extracting the apatite, a raw material for the production of phosphorus fertilizer. The deposit region is widely exposed to sedimentary rocks, basic and ultramafic rocks and granitoids, mostly consisting of biotite schist, metaclastic gneiss, garnet biotite gneiss, hornblende schist, quartz schist, etc. In addition, this region has developed faults in the northwest and northeast directions, and the northeast faults cut and transformed the northwest faults and ore bodies.
At present, production activities are not properly carried out in this mine due to the collapse of stopes and the stability problem of the dressing plant by surface subsidence in the area of the mine's protective pillar.
There are many mining space areas due to the production activities of more than 10 years in the area, which deteriorates mining conditions and causes deformation failure of rock mass around the stopes. Hence, the maintenance of stopes and openings is difficult and there is a risk of subsidence even to the surface buildings such as the dressing plant.
Therefore, the exploration and stability of the mined-out spaces (i.e. gobs) is of great importance in ensuring the normal productivity of the mine.
