Fabric, rheology, and shear strength for risk reduction in tailings impoundment management

造成灾难性后果的尾矿库坍塌事件时有发生。2015年在巴西和2014年在不列颠哥伦比亚省(波利山)发生的尾矿坝坍塌和相关的环境灾难只是最广为人知的两起事件：巴西的尾矿坝坍塌造成了超过70亿美元的损失，波利山的尾矿流入了奎斯奈尔湖，这是世界上最大的原始淡水湖之一，也是不列颠哥伦比亚省鲑鱼渔业水道的重要组成部分。尽管之前采取了几项改善尾矿库安全和尾矿库管理的举措，但这些失败仍在继续发生。 大坝坍塌的灾难性后果，即溃决后尾矿移动的距离，至少可归因于两个因素：i)尾矿顶部的水可能会推动尾矿，以及ii)尾矿本身在溃坝后应力状态突然变化时容易出现强度损失和高流动性。关于这两个因素的相对贡献，在实践中有很多猜测。最近的研究表明，尾矿很容易坍塌到高应力水平和相对高的密度。此外，众所周知，尾矿的流变性，即控制尾矿在破坏后流动多远的材料特性，在高剪切率下很容易退化，正如在大坝坍塌期间可能预期的那样。此外，尾矿的结构或尾矿颗粒的排列会影响坍塌行为。例如，众所周知，干燥会引起面料变化，从而导致更高的强力。 因此，拟议的研究计划调查了影响尾矿坝后坍塌或溃坝变形行为的各种因素。这将涉及：i)使用现有的大型土壤测试设施来物理模拟大坝的破坏，以及ii)使用大型物理测试作为校准/验证工具的数值模拟，iii)改变模拟沉积物中的几个因素(气候冻结/融化或干燥)、固结程度、年龄、沉积类型、使用改进剂(废石、胶结尾矿层)，以及iv)用多个载荷路径进行织物测量和剪切强度测试，以解释大型测试。拟议的研究将有助于更好地了解导致尾矿流失的因素，从而改进实践中的方法，以减少或消除这类事件的灾难性后果。

The failure of tailings dams with catastrophic results continues to occur with regularity. The recent tailings dam failures and associated environmental disasters in Brazil in 2015 and in British Columbia (Mount Polley) in 2014 are only two of the most well-publisced occurrences: the failure in Brazil resulted in excess of $7 billion dollars in damages, with the tailings from Mount Polley flowed into Quesnel lake, one the largest pristine freshwater bodies in the world, and an important component of the water way for British Colombia's salmon fishery. These failures continue to occur despite several previous initiatives to improve tailings dam safety and tailings impoundment management. The catastrophic consequences of dam failure, namely the distance the tailings travel after the breach, or runout, can be attributed to at least two factors: i) the presence of water on top of the tailings may push the tailings, and ii) the susceptibility of the tailings themselves to strength loss and high flowability upon the sudden change in stress state following dam breach. Much speculation exists in practice concerning the relative contribution of these two factors. Recent research has shown that tailings are susceptible to collapse up to high stress levels and relatively high densities. Also, it is known that the rheology of the tailings, the material properties that control how far the tailings flow after failure, are susceptible to degradation following high rates of shear, as might be expected during dam failures. Further, the fabric of the tailings, or the arrangement of tailings particles, influences collapse behaviour. For instance, it is known that desiccation induces a fabric change that leads to higher strength. Therefore, the proposed research program investigates the various factors that influence the deformation behaviour of tailings post-dam collapse or dam breach. This will involve: i) use of an existing large earth testing facility to physical simulate dam failures, and ii) numerical modelling, using the large-scale physical tests as a calibration / verification tool, iii) varying several factors in the simulated deposits (climate freeze/ thaw or desiccation), degree of consolidation, age, type of deposition, use of amendments (waste rock, layers of cemented tailings), and iv) to conduct measurements of fabric and shear strength test with multiple load paths to interpret large-scale tests . The proposed research will lead to improved understanding of the factors contributing to tailings runouts and therefore to improved methods in practice to reduce or eliminate the catastrophic consequences of such events.