Integration of underground mapping, petrology, and high-resolution microseismicity analysis to characterise weak geotechnical zones in deep South African gold mines
Integration of underground mapping, petrology, and high-resolution microseismicity analysis to characterise weak geotechnical zones in deep South African gold mines
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DOI：
10.1016/j.ijrmms.2018.10.003
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发表时间：
2019-02-01
影响因子：
7.2
通讯作者：
Ishida, A.
中科院分区：
文献类型：
--
作者：
Mngadi, S. B.;Durrheim, R. J.;Ishida, A.
高应力井筒煤柱易发生大地震、地面福尔斯坍塌和岩爆，这可能会造成人员伤亡和生产损失，特别是在岩土软弱地带。因此，重要的是要确定薄弱的岩土工程区，以减轻风险。在这项研究中，我们提出了综合研究（地下测绘，岩石学，岩石力学和高分辨率微震分析），以了解不同的岩土工程区在南非库克4矿的轴柱。残余竖井柱的下盘包括Mondeor组的上Elsburg礁，而Venterspost组的Ventersdorp接触礁（VCR）和Westonaria组的软/弱熔岩形成上盘。井下测绘和显微分析结果表明，该井矿柱由石英岩、含砾石英岩、泥质石英岩和砾岩组成。地下测绘进一步表明，竖井支柱的特点是有几个不连续性，这些不连续性从小到大规模的裂缝不等。室内单轴抗压强度试验表明，石英岩的强度最高，其次是含砾石英岩、泥质石英岩和砾岩。高分辨率声发射（AE）集群的分析表明，大多数AE与采矿范围的脸。集群显示的Ortlepp剪切形成的范围提前，这是由开挖引起的应力场。微地震资料进一步揭示了断裂转折点发生在软弱地层（软弱上盘熔岩）中。这些数据集的整合使我们能够开发不同岩土区域的断裂模型，这与以前为类似地下环境开发的模型一致（即，弱/软熔岩上盘和石英岩/砾岩下盘）。这对未来的采矿、支持、生产和安全具有重大影响。
A highly-stressed shaft pillar is prone to large seismic events, falls of ground and rockbursts, which may cause injuries and loss of production, especially in weak geotechnical zones. It is thus important to identify weak geotechnical zones in order to mitigate risks. In this study, we present integrated studies (underground mapping, petrology, rock mechanics and high-resolution microseismicity analysis) to understand the different geotechnical zones in the shaft pillar of Cooke 4 mine in South Africa. The footwall of the remnant shaft pillar comprises the Upper Elsburg reef of the Mondeor Formation, while the Ventersdorp Contact Reef (VCR) of the Venterspost Formation and soft/weak lavas of the Westonaria Formation form the hangingwall. Results from underground mapping and microscopic analysis show that the shaft pillar is composed of quartzites, pebbly quartzites, argillaceous quartzites and conglomerates. Underground mapping further shows that the shaft pillar is characterized by several discontinuities, which vary from minor to macro scale fractures. Laboratory uniaxial compressive strength (UCS) tests indicate that quartzite has the strongest strength, followed by pebbly quartzite, argillaceous quartzite and lastly, conglomerate. Analysis of high-resolution acoustic emissions (AEs) clusters indicates that the majority of AEs are associated with the mining scope faces. The clusters show the formation of Ortlepp shears ahead of the scope, which is caused by the excavation-induced stress field. Microseismic data further reveal that the fracture turning-point occurs in the soft strata (weak hangingwall lavas). The integration of these datasets has allowed us to develop the fracture model for different geotechnical zones, which concurs with previous models developed for the similar underground environment (i.e., weak/soft lava hangingwall and quartzite/conglomerate footwall). This has major implications for future mining, support, production and safety.