隔离层厚度对露天最终边帮破坏形式及稳定性影响研究

Effect of Isolation Layer Thickness on Stability and Failure Form of Final Pit Slope of Open Cut Mine

以霍各庄铁矿露天转地下首阶段开采为工程背景,选取典型勘探线剖面,建立二维有限元数值模型,运用有限元局部强度折减法计算不同隔离层厚度下地下首阶段开采时露天最终边帮破坏形式及安全系数。分析表明,霍各庄铁矿地下首阶段开采时,隔离层厚度低于19 m时会造成露天最终边帮失稳,隔离层厚度在19～28 m范围内时,顶帮塑性变形区由坡脚先向首阶段采空区上盘侧壁发展,再向坡顶扩展贯通,隔离层厚度在28～50 m范围时,顶帮塑性变形区直接由坡脚贯通至坡顶;顶帮安全系数随隔离层厚度增大而增大,但增长速率逐渐减小,隔离层厚度超过45 m时,顶帮安全系数变化不再显著;底帮塑性变形区由坡脚贯通至坡顶,且安全系数无变化,底帮破坏形式和稳定性受隔离层厚度影响较小;霍各庄铁矿考虑边帮稳定性时隔离层厚度应不低于25 m。研究结果可为霍各庄铁矿及类似露天转地下开采矿山合理隔离层厚度的选择提供指导。

Huogezhuang Iron Mine is in the first stage of mining after transition from open-pit mining to underground mining. In the study,a typical prospecting line profile of the iron mine was selected to establish a two-dimensional finite element numerical model. Then,finite element strength reduction (local) method was adopted to calculate the failure form and safety coefficient of final pit slope during the first stage of mining with different thickness of underground isolation layer. Analysis showed that in the first stage of underground mining,an isolation layer with the thickness less than 19 m will result in the failure of final pit slope. And when an isolation layer is 19~28 m in thickness,the plastic deformation zone of topwall will develop from the toe of slop to the hanging wall of the stope,then up to the crest. But with an isolation layer being 28~50 m in thickness,the plastic deformation zone of topwall will running through from the toe directly to the crest of the slope. Safety factor of topwall will increase with an increase in the thickness of isolation layer,with the rising rate in a gradual decline. However,when an isolation layer is over 45 m in thickness,there will be little change in the safety factor of topwall and the plastic deformation zone of the footwall will run through from the toe to the crest of slop with the safety factor unchanged,indicating the thickness of isolation layer will bring less impact on the stability and failure mode of footwall. Based on the study,the isolation layer was determined to be no less than 25 m in thickness for slope stability in Huogezhuang Iron Mine. This study may be of reference for selecting reasonable thickness of isolation layer for mines with similar practice of transition from open-pit mining to underground mining.