Unplanned dilution back analysis in an underground mine using numerical models

Abstract In underground mines, stability problems can cause unplanned dilution, increasing the costs of mining operations, such as loading, transport, crushing and grinding. This is usually dealt with by simply increasing investments with support. However, the design geometry of stopes and drifts also has a great effect on a stope’s stability. The use of empirical stability methods is a very common practice, however because of their few input parameters, it cannot predict the actual performance related to each stope and drift design. This study has as main goals a back analysis of the actual dilution, using the Equivalent Linear Overbreak Slough (ELOS) method and analysis in the drift developments at the hanging wall contact, using numerical models. The case study is an underground hard rock gold mine, with a pillar-less Transversal Stope method. The hanging wall failure was quantified using a database from 19 stopes measured by the Cavity Monitoring System (CMS). Numerical finite elements models (FEM) were used, and 5 primary stopes were selected to calibrate models. The volumes of actual dilution showed a good correlation with the volumes of the relaxation zones produced by the models. Then, new optimized drift geometry layouts at the hanging wall contact were proposed, showing a decrease in 2.35 times in the relaxation zone of the numerical models, therefore justifying the use of these models as a dilution optimization tool. This methodology also proved to be useful in the definition of cable bolt length.

摘要 在地下矿山中，围岩失稳问题可引发非计划贫化，增加装载、运输、破碎及磨矿等采矿作业的成本。过往此类问题通常仅通过增加支护投入进行应对，但采场与巷道的设计几何参数同样对采场稳定性具有显著影响。经验稳定性方法是当前极为常用的技术手段，然而由于其输入参数有限，无法针对单个采场与巷道设计预测其实际表现。本研究的核心目标为：采用等效线性超挖坍塌法（Equivalent Linear Overbreak Slough, ELOS）对实际贫化情况开展反演分析，并结合数值模型对上盘接触带的巷道掘进展开研究。案例研究对象为一座采用无矿柱横向采场采矿法的地下硬岩金矿。研究人员借助空腔监测系统（Cavity Monitoring System, CMS）实测的19个采场数据库，对上盘破坏情况进行量化分析。本研究采用有限元数值模型（FEM），并选取5个主采场对模型进行校准。实际贫化体积与模型生成的松弛区体积呈现出良好的相关性。随后研究团队提出了上盘接触带的优化巷道几何布局方案，该方案可使数值模型中的松弛区体积降低2.35倍，从而验证了将此类模型用作贫化优化工具的合理性。此外，该方法在锚索锚固长度的确定方面也展现出实用价值。