###### Abstract  
The instability of slopes and ground subsidence caused by the conversion from open-pit to underground mining are important aspects of mining disaster research. This study focuses on the instability of slopes and ground subsidence during the conversion from open-pit to underground mining in the Beiyi mining area of the Shilu iron ore mine. Using numerical simulation and analysis, this study establishes a mechanical analysis model to assess the rock stability and movement of rockfall. The research findings indicate that there are significant stress concentration phenomena in the surrounding and floor areas of the goat during the mining process. The collapse zone mainly develops in the western area before and after a certain level of mining and then shifts to the eastern part of Beiyi area. Surface subsidence expands after mining at a certain level, resulting in a large-scale disturbance area. Furthermore, the eastern slope experiences extensive landslides. This study suggests the continued monitoring of landslides and slope stability in specific areas of the mine. The research results can help us to understand the stability of the open-pit to underground rock mass in Hainan, judge the development trend of the surface subsidence range, and provide a reference for the stability evaluation of the rock mass mined by the open-pit-to-underground caving method. t +
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methods, as well as the net present value (NPV) obtained through mining. In the model, the NPV of the open-pit mine is compared with that of the underground mine to determine the optimal transition depth. [PERSON] et al. [12] established a thin plate model of a mining slope based on the reality of combined mining and underground mining and its interaction, analyzed the influence of underground mining on the slope, and obtained the deformation law of a mining slope under open-pit and underground mining conditions from the change in rock layer dip caused by roof deformation. [PERSON] et al. [13] conducted similar simulation experiments and used digital measurement techniques to analyze the deformation characteristics of surrounding rock using the room-and-pillar method during the open-pit-to-underground transition. This study found that the surrounding rock underwent three stages: localized micro-movement, linear large deformation, and overall nonlinear collapse after mining. Meanwhile, with an increase in the dip angle of the phosphate ore body, the failure angle decreased, and, at 50\({}^{\circ}\), the surrounding rock exhibited a feature of overall shear failure. [PERSON] et al. [14] conducted FLAC3D numerical simulations and similar physical model experiments to analyze the displacement and stress changes and the distribution of plastic zones in the composite mining system. They obtained a linear correlation between the displacement changes of overlying rock layers in the mining area and the variation in the mining-induced influence zone and excavation space. [PERSON] et al. [15] studied the failure characteristics of overlying rock masses during full extraction of the open-pit to an underground L-shaped panel in the Wuhai open-pit coal mine using numerical simulation methods. [PERSON] et al. [16] studied the slope stability before the transition to underground mining using limit equilibrium theory and FLAC3D v5.0. They analyzed the stress variation, distribution of plastic zones, and displacement changes under different mining levels and conditions with and without backfilling in the subsidence zone, defining the surface deformation as the criterion for delineating the surface movement range at different mining levels. [PERSON] et al. [17] analyzed the stability changes in the slope rock mass structure after the transition from open-pit to underground mining in the Ekati diamond mine from a geological survey perspective. [PERSON] et al. [18] established a three-dimensional finite difference numerical model of the Jinfeng gold mine using FLAC3D, including the surface topography, ore body, shafts, and major faults.