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Karst collapse columns (KCCs) are channels where groundwater and gas gather, and they pose a great threat to mining safety. In this study, a mechanical model and criterion for the roof collapse of KCCs were established, and simulations were performed to analyze the formation mechanism of KCCs in the Huainan coalfield of Northern China. The results showed that the roof collapse and upward development of KCCs were facilitated by increasing the cave radius of the KCC basement and decreasing the groundwater pressure, single-layer thickness of the roof strata, lateral pressure coefficient of the rock mass, and cohesion and internal friction angle between fractures. The KCC formation process in the Huainan coalfield could be divided into four stages: (I) early collapse, (II) middle-early rapid collapse, (III) middle-late slow collapse, and (IV) late filling compaction. The simulation results were generally consistent with actual KCCs observed in the Huainan coalfield, which verified the theoretical analysis. The results of this study provide an important reference for the formation mechanism and evolution of KCCs in Northern China.

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This paper discusses the effect of parameters in MIG based wire and arc additive manufacturing (WAAM) using stainless-steel wire and Q235 as substrate. The response surface methodology (RSM) and ANOVA were used to determine the effects of current, voltage, and welding velocity on the responses of bead height and width. It was found that voltage had the largest effect on the bead width, followed by welding velocity and current. But on the bead height, welding velocity is the most significant parameter, followed by current and voltage. The genetic algorithm (GA) was utilized to optimize the parameters to obtain the maximum ratio of weld bead width to height for multi-layer single-pass arc additive deposition.