Cemented Paste Backfill Design under States of Low Confining Stress

现代地下采矿方法依靠回填在高岩石应力条件下安全地继续挖掘。水泥膏体回填（CPB）是一种工程材料，可重复使用“废弃”产品（尾矿），并产生可高速输送到地下空隙的厚稠度回填材料，紧密填充所有空隙空间，固化时具有可根据特定矿山设计要求定制的均匀材料特性。 两个关键的设计方案涉及评估当邻近空隙被挖掘时（侧壁稳定性）或当CPB被底切时（门槛垫稳定性）所需的CPB强度。这两种情况的设计方法都是在20世纪80年代开发的，在回填设计不重要的情况下，这些方法很好地服务于工业。然而，越来越多的人认为这些方法过于保守，需要寻求更详细的工程方法。合理的工程设计的一个主要障碍是用于模拟回填行为的本构模型的形式，特别是在这些暴露面的情况下，围压可能非常低，甚至在拉伸范围内。本建议书中描述的研究计划旨在解决这一问题，并开发基本的理解以及实用的设计工具，以便更好地评估侧壁稳定性或门槛垫稳定性的CPB强度要求。 将开发新的CPB实验室技术，以允许在“限制”的拉伸状态下进行测试。在测试CPB时，将使用非破坏性波浪技术来表征渐进性损坏。本构模型纳入弹性以及脆性和韧性塑性机制将开发和实施的数值代码。将与加拿大工业伙伴协商，以建立一个侧壁和窗台垫案例历史数据库，用于反分析目的。用于研究目的的复杂建模方法对于基本了解侧壁和窗台垫暴露条件下的CPB行为至关重要，但这些方法对于常规设计不实用;因此，将开展额外工作，以根据更严格的反分析开发简化分析和设计方法，并将与合作矿山一起进行测试。 共有3个博士和3个硕士项目将得到研究的支持。他们将与UofT更大的土壤和岩石力学团队以及咨询和采矿业务的行业合作伙伴进行互动。通过这种方式，学生也将成为技术转让机制的一部分，以便研究成果能够为加拿大带来利益。

Modern underground mining methods rely on backfill to safely continue excavation under high rock stress conditions. Cemented Paste Backfill (CPB) is an engineered material that reuses “waste” products (mine tailings) and creates a thick consistency backfill that can be delivered at high rates to the underground voids, tightly filling all void spaces and curing with uniform material properties that can be tailored to specific mine design requirements. Two critical design scenarios involve assessing the CPB strength required when an adjacent void is excavated (sidewall stability), or when the CPB is undercut (sill mat stability). Design methods for both of these scenarios were developed in the 1980's and served the industry well in situations where backfill design was not critical. Increasingly, however, these methods are thought to be overly conservative and more detailed engineering approaches are sought. A major impediment to rational engineering design is the form of constitutive model used to simulate backfill behaviour, especially under these exposed-face scenarios where the confining stresses can be very low and even in the tensile range. The research program described in this proposal aims to address this problem and develop basic understanding as well as practical design tools that allow a better assessment of CPB strength requirements for sidewall stability or sill mat stability. New CPB laboratory techniques will be developed to allow testing under tensile states of “confinement”. Non-destructive wave techniques will be used to characterize progressive damage as the CPB is tested. A constitutive model incorporated elastic as well as brittle and ductile plastic mechanisms will be developed and implemented in a numerical code. Canadian industrial partners will be consulted to develop a database of sidewall and sill mat case histories for back-analysis purposes. The sophisticated modeling approaches used for research purposes will be critical to developing basic understanding of CPB behaviour under sidewall and sill mat exposure conditions, but these will not be practical for routine design; hence, additional work will be undertaken to develop simplified analysis and design approaches based on the more rigorous back-analyses, and they will be tested against ongoing design work with the partner mines. A total of 3 PhD and 3 MASc projects will be supported by the research. They will interact with the larger soil and rock mechanics group at UofT, as well as with industry partners in consulting and in mining operations. In this way the students will also become part of the technology transfer mechanism so that the fruits of the research can be brought to bear for the benefit of Canada.