Investigation of Geomechanical Features of the Rock Mass in Mining of Two Contiguous Deposits under Tectonic Stresses

The paper presents the results of research about the stress-strain state in the eastern part of the Khibiny massif (the Kola Peninsula, North-Western Russia) where the Niorkpahk and Oleniy Ruchey contiguous deposits are being mined by open technologies. There are plans to develop the Oleniy Ruchey deposit by underground methods in the near future. The underground mining operations will be restricted by protecting pillars because of nearby open-pits. High horizontal stresses and brittle rock have a significant influence on mining operations and indicate rockburst hazardous conditions.For estimating mutual influence of open-pit and underground mining in progress, the authors have designed a numerical geomechanical model which includes basic geological and mining-engineering factors. Based on the results of numerical modeling it has been found that the mutual influence occurs when underground mining reaches the rock mass under the open-pit. This conclusion suggests that the protecting pillars' boundaries can be revised for the purpose of the further decrease. This will increase volume of reserves mined and efficiency of underground mining.