Raffaldi Michael Jon, Seymour Joseph Bradford, Richardson Jerald, Zahl Eric, Board Mark
Spokane Mining Research Division, National Institute for Occupational Safety and Health (NIOSH), 315 E. Montgomery Ave, Spokane, WA 99207, USA.
Present Address: RESPEC, 146 E. Third St., Lexington, KY 40508, USA.
Rock Mech Rock Eng. 2019 Dec;52(12):4925-4940. doi: 10.1007/s00603-019-01850-4. Epub 2019 Jun 10.
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.
下向分层充填采矿法已使许多在软弱岩石或高应力、易发生岩爆的地面条件下作业的矿山能够安全地开采矿石。然而，安全的充填底切设计通常基于矿山作业的历史经验以及从解析梁方程得出的强度要求。充填体中的现场测量并不常见，这主要是由于在恶劣的采矿环境中进行仪器安装存在挑战。在深部窄脉矿山中，大变形和诱导应力会使胶结充填体破裂，常常损坏仪器并妨碍长期测量。赫克拉矿业公司与美国国家职业安全与健康研究所（NIOSH）的斯波坎矿业研究部门合作了数年，以更好地量化胶结膏体充填（CPB）的地质力学特性，从而提高下向采场的安全性。这项工作的一个重要重点是开展广泛的现场充填体仪器监测计划，以监测采场的长期闭合情况和诱导的充填体应力。开发了坚固耐用的定制闭合仪，能够对多达五个连续的底切进行测量，测量的闭合量超过50厘米，水平充填压力高达5.5兆帕。这些大的采场闭合量要求在设计中考虑充填体的应力应变响应，而不是仅仅依赖基于完整充填体强度的传统充填跨度设计方法。此外，长期的仪器响应表明，在应变达到13 - 14%后行为发生了变化，这表明从完整胶结材料的剪切屈服转变为砂粒间孔隙的压实，这是未胶结砂充填体的典型特征。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护和应力重新分布而言。这些定量测量有助于证明关于充填体在地面支护中作用的长期假设是合理的，并且对其他在类似条件下作业的矿山也将有用。
