Underhand cut-and-fill mining has allowed for the safe extraction of ore in many mines operating in weak rock or highly stressed, rockburst-prone ground conditions. However, the design of safe backfill undercuts is typically based on historical experience at mine operations and on the strength requirements derived from analytical beam equations. In situ measurements in backfill are not commonplace, largely due to challenges associated with instrumenting harsh mining environments. In deep, narrow-vein mines, large deformations and induced stresses fracture the cemented fill, often damaging the instruments and preventing long-term measurements. Hecla Mining Company and the Spokane Mining Research Division of the National Institute for Occupational Safety and Health (NIOSH) have worked collaboratively for several years to better quantify the geomechanics of cemented paste backfill (CPB), thereby improving safety in underhand stopes. A significant focus of this work has been an extensive in situ backfill instrumentation program to monitor long-term stope closure and induced backfill stress. Rugged and durable custom-designed closure meters were developed, allowing measurements to be taken for up to five successive undercuts and measuring closures of more than 50 cm and horizontal fill pressures up to 5.5 MPa. These large stope closures require the stress–strain response of the fill to be considered in design, rather than to rely solely on traditional methods of backfill span design based on intact fill strength. Furthermore, long-term instrument response shows a change in behavior after 13–14% strain, indicating a transition from shear yielding of the intact, cemented material to compaction of the porosity between sand grains, typical of uncemented sand fills. This strain-hardening behavior is important for mine design purposes, particularly for the use of numerical models to simulate regional rock support and stress redistribution. These quantitative measurements help justify long-standing assumptions regarding the role of backfill in ground support and will be useful for other mines operating under similar conditions.

中文翻译：

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窄脉地下挖填矿的水泥浆回填土力学

在许多在脆弱岩石或高应力、易发生岩爆的地面条件下作业的矿山中，地下挖填式采矿允许安全提取矿石。然而，安全回填底切的设计通常基于矿山运营的历史经验和从分析梁方程得出的强度要求。回填中的现场测量并不常见，这主要是由于与严苛采矿环境仪表相关的挑战。在深、窄矿脉的矿井中，大变形和诱导应力会使胶结填充物破裂，通常会损坏仪器并妨碍长期测量。Hecla 矿业公司和美国国家职业安全与健康研究所 (NIOSH) 的斯波坎矿业研究部多年来一直合作，以更好地量化胶结膏体回填 (CPB) 的地质力学，从而提高地下采场的安全性。这项工作的一个重要重点是广泛的原位回填仪器计划，以监测采场长期关闭和诱发的回填压力。开发了坚固耐用的定制设计闭合计，最多可以测量五个连续的底切，测量超过 50 厘米的闭合和高达 5.5 MPa 的水平填充压力。这些大型采场封闭要求在设计中考虑填充物的应力应变响应，而不是仅仅依靠基于完整填充强度的传统回填跨度设计方法。此外，长期仪器响应显示在 13-14% 应变后行为发生变化，表明从完整的胶结材料的剪切屈服转变为砂粒之间孔隙的压实，典型的未胶结砂填充。这种应变硬化行为对于矿山设计目的很重要，特别是对于使用数值模型来模拟区域岩石支撑和应力重新分布。这些定量测量有助于证明关于回填土在地面支持中的作用的长期假设，并将对在类似条件下运营的其他矿山有用。表明从完整的胶结材料的剪切屈服转变为砂粒之间孔隙度的压实，典型的未胶结砂充填。这种应变硬化行为对于矿山设计目的很重要，特别是对于使用数值模型来模拟区域岩石支撑和应力重新分布。这些定量测量有助于证明关于回填土在地面支持中的作用的长期假设，并将对在类似条件下运营的其他矿山有用。表明从完整的胶结材料的剪切屈服转变为砂粒之间孔隙度的压实，典型的未胶结砂充填。这种应变硬化行为对于矿山设计目的很重要，特别是对于使用数值模型来模拟区域岩石支撑和应力重新分布。这些定量测量有助于证明关于回填土在地面支持中的作用的长期假设，并将对在类似条件下运营的其他矿山有用。