Abstract: With the development of modern mining techniques,the steeply inclined vein deposits are transitioning from the traditional shallow hole mining method to the large section stage caving method. This change has altered the disturbance pattern of the rock mechanics environment,especially during the transition period when the two mining methods are replaced, which may result in a blind spot in the distribution pattern of the rock mechanics environment in the mining area. This paper simulated the changing characteristics of the surrounding rock in the transitional mining section using FLAC3D software based on the initial ground stress field determined by acoustic emission measurement. The results show that:① After the upper mining area is mined out by the shallow hole mining method,the surrounding rocks of the upper and lower plates of the mining area are subject to tensile stress and there is a tendency for the side gang of the mining area to be loosened,and the surrounding rocks between the single vein mining areas are subject to uneven stress leading to staggered distribution of the displacement of the upper and lower ends,and the surrounding rocks of the upper and lower plates of the mining area and the surrounding rocks between the single vein mining areas are mainly in the shear plastic zone,with the risk of shear damage. ② After the lower mining area is mined out by the large section stage caving method,the stress concentration phenomenon in the mining area is more obvious,the top plate of the mining area has a tendency to settle,the surrounding rocks of the upper and lower plates of the mining area are deformed in the vertical direction and the displacement of the two mining areas is more continuous,the top and bottom plates of the mining area are mainly tensile plastic zone and there is a large range of shear plastic zone in the surrounding rocks of the upper and lower plates,which indicates that the surrounding rocks of the mining area may have the risk of tension and shear damage at the same time. ③ The timely filling of waste rock in the quarry area can effectively suppress the stress concentration phenomenon. The mine should strictly control the timing of mining and filling of the adjacent quarries above and below when mining the transition area to avoid over mining,thus maximally suppressing the adverse effects of surrounding rock deformation and destabilization caused by stress concentration.

Key words: sharply inclined vein group ore,mining transition phase,surrounding rock,mechanical environment,numerical simulation