Abstract
The macro-micro mining response of the surrounding rock and overlying strata towards the transformation from open-pit to underground mining is examined in the present study, based on the engineering background of the Jinning phosphate mine (Yunnan Phosphate Chemical Group Co., Ltd.) via simulations involving similar materials, digital photographic measurement technology, and numerical simulation. The mining deformation of the surrounding rock underground, and of the overlying strata, is shown to develop in three stages, namely: (1) small and local deformation, (2) continuous linear increase, and (3) the violent nonlinear collapse of the entire system. The internal distribution of stress in the surrounding rock and adjacent overlying strata of the inclined mined-out area is complicated. The degrees of pressure increase and pressure relief have an important relationship with the size of the mining space. The pressure relief is more complete close to the mined area, and the stress reduction decreases with increasing distance. The cracks propagate in arc shapes and have a tendency to penetrate into the upper and lower ends of the stope. The size of the excavation space plays a key role in the generation, propagation, and penetration of the cracks. Due to the disturbance of the first mining level and the increase in excavation depth, the rate of damage to the surrounding and overlying rock increases in the second mining level. This process generates more cracks, which accelerate the instability of the surrounding rock and overlying strata.
Highlights
Most of China’s open-pit mines were built in the 1950s
A mathematical model was established to describe the attenuation of peak particle velocity (PPV) in the open-pit slope, which is used to evaluate the influence of underground mine blasting on the slope stability [23]
Cheng et al used the Universal Distinct Element Code (UDEC) numerical method to simulate the movement of strata in the footwall caused by underground mining [24]
Summary
Most of China’s open-pit mines were built in the 1950s. After several decades of continuous high-intensity mining, the vast majority of open-pit mines have entered the deep open-pit mining stage and even underground mining. Researchers have used micro seismic monitoring, in situ monitoring, and true triaxial modeling [29–32] to investigate the deformation characteristics and failure mechanisms of the slope rock mass and the surrounding rock of the underground stope after the transition from open-pit to underground mining. Due to major differences in the conditions, mining techniques, mining methods, and complexity of the open-pit slope and underground mining environments, it is necessary to study the macro-micro response characteristics of the surrounding rock and overlying strata to the transition from open-pit to underground mining. Taking the open-pit to underground mining project of the Jinning phosphate mine belonging to the Yunlin Group as an example, experiments on similar materials, numerical simulations, and theoretical analyses are used in the present study to investigate the mining response characteristics of the surrounding rock and overlying strata during such a transition
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