Static And Dynamic Stability Of Bauxite Orepillars In Strip Mining

Strip mining is used widely among three-undergound mining dued to its low cost and simple process.The stability of orepillar of bauxite is directly related to the safety of the gob and the surface, so the study on the stability of the orepillar is very important. This paper focusing on the strength of orepillars, static and dynamic stability in strip mining, and the analysis and conclusions are followed:(1)The test specimen results are analyzed after the uniaxial compression test of bauxite mine pillar.Based on the research on domestic and foreign strength theory of orepillars and especially the discussion of A. H. Wilson strength theory, a mechanical model concered about the stress distribution and the formula of the orepillar width is proposed.(2)The stress distribution of orepillars in different width and mining-out areas between them are anylyzed:The central pillars are bearing larger forces than the pillars at the edges of the mining areas; the stress distribution of wide pillar which is in good stability is saddle shaped, however the narrow pillar is in poor stability which stress distrution is platform shaped or arched.Therefore the design of wide pillar is beneficial to improve the stability in strip mining.(3)The numerical model is set up and the numerical simulation is applied.The stress distribution and the plastic strain of pillars with different width showed that stability of wide ore pillars is better than narrow ones, but I will cause stress concentration increasing and lead to the uneven subsidence of ground surface if it id too wide. (4) The elasticity plane wave theory is introduced to discuss the mechanism of orepillar instability caused by seismic wave. Accompanied by the crack propagation, the enlarging fracture zone, narrowing kernel elastic zone and the plastic zone moving inside finally induced the failure of the pillar under the increasing additional dynamic stress proportional to the velocity of the particle.(5)Stress and plastic strain are analyzed in vertical and transverse earthquake respectively under three different intensity.The results show that microearthquake and moderate earthquake have little impact on given model, severe earthquake in transverse direction will induce the shear failure thoroughly and bad consequences to the stability of the mining-out areas than in the other direction.(6)Through the contrast of stability of pillar in different working conditions, the conclusions reveal that transverse earthquake and biaxial loading earthquake will cause redistribution of stress dramatically and asymmetric distribution of stress whereas the vertical earthquake have little impact on the distribution of stress; the microearthquake and moderate earthquake has little influence of pillar stress, and the amplitude of stress will amplify drastically in severe earthquake.