Control Measure And Its Numerical Analysis For Slope Safety During Hanging-wall Ore Mining Below A Landslide

Xiangbishang open pit of Daye Iron Mine has already closed and the ore outside its pit limit will be mined by underground method. In order to facilitate the smooth transfer from open pit mining to underground mining, hanging-wall ore was planned to be mined by open pit. A landslide once happened in the North Slope of the pit, whether the slide will be reactivated and how to prevent possible safety problems are problems having to be solved during hanging-wall ore mining. Considering the short term of mining operation, it's irrational to make systematic reinforcement to the slope. So how to predict the slope safety correctly and how to maintain the safety of human and facilities when the slope is not sufficiently safe are key to the success of hanging-wall ore retraction. In this dissertation, a measure is suggested, which uses high-quality iron ore as retaining wall to control the slope deformation and to maintain its stability. Flac-3D is employed to analyze the problem and verify the feasibility of the measure.Firstly, a state of art review is made on the open pit mine slope stability and hanging-wall ore mining techniques. Possible mining schemes and their potential problems are analyzed. Based on the geological investigation of the slope and the analysis of its historical landslide event, a measure is proposed, using the intact, high-quality iron ore as retaining wall to control the slope deformation and maintain its safety during mining operation.Secondly, a 3D model is established, which make some simplification to the slope geology and is used to analyze the efficiency of the iron-ore retaining wall and the effects of different mining sequence by FLAC-3D code. Results demonstrate that the wall can reduce the slope deformation for at least one order and effectively shrink the extent of yield zones.Thirdly, The effect of subground water is analyzed by FLAC-3D code. Results show that subground water level will greatly influence the deformation and stability of the fault zone. As the water level rises, the deformation will increase gradually and the extent of yield zones expands. However, under sufficient drainage condition the wall can effectively control the slope deformation and stability, being favorable for the hanging wall ore retraction.Fourthly, deformation monitoring is executed during mining operation. Based on the feedback of the monitored deformation, mining technique and measure are adjusted to make the mining operation continue safely. When the mining work is completed, a deformation of nearly 10m happens in the slope. However the retaining wall remains unbroken, effectively holding back the landslide.