THE STRESS-STRAIN BEHAVIOUR OF THE PROTECTIVE PILLARS OF A SUBARRIER ZONE USING THE ORE DEPOSITS MINING COMBINED SYSTEM

Currently, two structural divisions of OJSC Apatit develop the Rasvumchorr Plateau deposit: by open pit mining - the Central mine (Central Quarry), commissioned in 1964; by underground mining - Rasvumchorrsky mine, since 1997 from the horizon + 600 m. The considered region is a heavily dissected mountain massif that rises above the surrounding terrain by 800 - 1000 meters. The stressstrained behaviour of the rock mass, containing the workings and excavation space of horizons 450 m and 470 m, was modeled in the ABAQUS software complex. The submodeling calculation method implies the estimation of the initial (before the beginning of underground purification works) of the stress-strain behaviour of the rock mass on the main model, followed by the transfer of borderline conditions to auxiliary partial models of specific objects. The stress behaviour of the mining horizons and pillars is subject to the influence of two factors. On the one hand, the pit excavation creates an unloading zone in the instrument area and removes some of the stresses from the horizon being developed; on the other hand, the excavation works form zones of stress concentration, in this case, they redistribute additional stresses to the surrounding pillars and into the interior of the massif. The article presents the results of numerical modeling of the rock mass in the excavating horizons located in the impact zone of the quarry at +450 m and +470 m. The model implemented allows one to take into account the redistribution of the stress field, and the influence of the existing pit digging, as well as the phased management of the excavation works at these horizons. The diagrams of the maximum and minimum principal stresses are given at the time of the development workings and the completion of the excavation works. The analysis of the current results of the stress state of the models makes it possible to predict the slow growth of compressive stresses in the control pillars as the front of the excavation works develops.