Abstract
In deep hard-rock mines, the failure of subsurface structures (e.g., tunnels, stopes, and shafts) has been a significant problem affecting mining safety due to the high-stress environment. In this paper, the mechanism of structural failure and instability is discussed, and optimized excavation methods are proposed for stress control in deep gold mines. Based on the field observation and investigation of the joints distribution and rock failure modes at 800–1200 m depth of several large gold mines and a typical ultradeep borehole (2017 m depth) in northwest Jiaodong Peninsula, three engineering methods for reducing stress, including the stress transferring by mining optimizations, pressure relief by boreholes, and energy release in advance by optimizations of excavation and support, are analyzed by numerical simulation and field monitoring. Results show that stress reduction by excavation alone is limited and the backfill mining method is more conducive to stress transfer than the opening stope method. Roof contacted backfill can produce an unloading zone around the stope and reduce the stress of the surrounding stope. Relief boreholes can reduce the stress concentration of stopes, but the effect of cutting seams generated by presplitting blasting on pressure relief is not significant. The technology “short excavation and short support” releases less energy. By increasing the bench height and the reasonable timing of support by calculating, the elastic strain energy of rock in the shaft is prereleased, which benefits the long-term stability of the shaft.
Highlights
In deep hard-rock mines, the failure of subsurface structures has been a significant problem affecting mining safety due to the high-stress environment
It is well known that the excavation activities change the stress field of rock and the mining method, excavation order, and support time have effects on the stress change [2]. erefore, some theoretical methods and practical technologies are proposed and developed to adjust the stress and energy in targeted areas, which improves the stability of rock mass in deep mines [3]
Scholars have proposed many methods to control high-stress hazards of subsurface structures, there is a well-justified need to understand these methods in practice for rock engineering in deep mines. e deformation and failure of rock are affected by many factors, but the dominant factors are stress level and energy evolution. erefore, it is of significance to adjust stress and energy for deep mining. is study is focused on employing some advanced engineering methods and practical management strategies for adjusting stress and energy in deep gold mines located in Jiaodong, China
Summary
After the ore body has been excavated in deep hard-rock mines, the original stress balance is destroyed. e stress in the surrounding rock of subsurface structures is redistributed, and it reaches a new balance. Once the stress exceeds the tensile strength or the compressive strength of rock mass, it causes joints and cracks to open or close [17, 18], leading to subsidence of stope roof, wedge caving, bottom swelling, spalling, slip, and even rockburst. All these phenomena are collectively known as ground behaviors caused by high stress [19]. E above analysis indicates that ground failures and instability are mainly affected by stress level, the structural plane of rock mass, and the mechanical properties of rock mass itself.
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