This paper examines mining of a flooded deposit safeguarded by a roof pillar using traditional mining methods and by hydraulic borehole mining. The ratio of ore extraction (proportion of ore mined) serves as an optimization parameter in the model of the rock mass stress-strain state. The purposes of optimization are efficient nature management and ecological safety of iron-ore fields development. The model estimations done in the paper determine the ore extraction ratio that ensures geomechanical safety (stability of above-ore strata), safety of hydro-geological conditions (including the natural regime of groundwater flow) in the overlain aquifer, and development of the ore field without environmental damage.
More than 50% of the iron-ore deposits in Russia mined underground are flooded. One of the more effective ways of mining such deposits is to leave a safeguard rock layer in the roof to prevent water inrushes and flooding of the mine workings. At the Gubkin Mine (Korobkovo Iron Ore Deposit, Russia) this method was applied through traditional technologies incorporated into the mining operations. An alternative method, Hydraulic Borehole Mining (HBM), has also been developed and used to help preserve the natural hydro-geological conditions, both underground and on surface. A HBM mining operation will be efficient if subsidence of the safeguard roof pillar bridging over the excavations does not surpass the limiting size for which the induced stresses exceed the rock mass strength of the roof pillar. Thanks to this method, the final product is of high quality and there is an opportunity for later traditional mining because of the geological conditions. Furthermore, negative influences on the environment are rather low. In all stages of the mining works, forecasting is a necessary condition for successful application.
2 PROBLEM DEFINITION AND ANALYTICAL SOLUTIONS