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

尾矿坝灾难性溃坝事件有规律地持续发生。最近发生在2015年巴西和2014年不列颠哥伦比亚省（波利山）的尾矿坝垮塌和相关环境灾难只是其中最广为人知的两起事件：巴西的垮塌造成了超过70亿美元的损失，波利山的尾矿流入了世界上最大的原始淡水水体之一的奎斯内尔湖，也是不列颠哥伦比亚鲑鱼渔业的重要组成部分。尽管以前采取了一些措施来改善尾矿坝安全和尾矿蓄水管理，但这些失败仍在继续发生。******溃坝的灾难性后果，即溃坝后尾砂移动的距离或跳动，至少可以归结为两个因素：1)尾砂顶部存在水可能对尾砂产生推动作用；2)溃坝后应力状态突然变化时尾砂本身对强度损失和高流动性的敏感性。关于这两个因素的相对作用，在实践中存在着许多猜测。最近的研究表明，尾矿在较高的应力水平和相对较高的密度下容易坍塌。此外，众所周知，尾矿的流变学，即控制尾矿在破坏后流动程度的材料特性，在大坝破坏期间可能预期的高剪切率下容易退化。此外，尾矿的结构或尾矿颗粒的排列也会影响坍塌行为。例如，众所周知，干燥会引起织物的变化，从而导致更高的强度。******因此，提出的研究方案研究了影响尾矿溃坝后或溃坝后变形行为的各种因素。这将涉及：1)利用现有的大型土方试验设施物理模拟大坝溃坝；ii)利用大规模物理试验作为校准/验证工具进行数值模拟；iii)改变模拟沉积物（气候-冻结/解冻或干燥）中的若干因素、固结程度、年龄、沉积物类型、修正剂的使用（废石、胶结尾砂层）；iv)进行多载荷路径下的织物测量和抗剪强度试验，对大型试验进行解释。拟议的研究将使人们更好地了解导致尾矿跳动的因素，从而改进实践中的方法，以减少或消除此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.