Distribution characteristics of the additional vertical stress on a shaft wall in thick and deep alluvium: a simulation analysis

In order to investigate the mechanisms of shaft lining deformation of coal mines in thick and deep alluvium, we selected Qianyinzi coal mine in the Huaibei mining area in the east of China as the research subject. The structure and stratigraphic composition of the shaft lining of the Qianyinzi coal mine and its geological and hydrogeological conditions and shaft lining deformation characteristics are comprehensively analyzed. The results preliminarily demonstrate that the water loss of the bottom aquifer is the major cause for the shaft lining deformation. On this basis, we designed and manufactured test system consisting of a similar material to simulate the decrease in the bottom aquifer water level and obtain the relationship between the decrease in the water level and the additional vertical stress of the shaft lining and the shaft lining depth. The numerical simulation results indicate a good fit for the equations. The fitting formula can be used to predict the additional vertical stress of the shaft lining based on data of the surface subsidence and bottom aquifer water level changes. The maximum additional vertical stress of the shaft lining is 39.4MPa. Taking into consideration the stress caused by the self-weight of the shaft lining and tower, which is approximately between 5.0 and 8.0MPa, the additional vertical stress range between the bottom aquifer and the bedrock interface is between 44.4 and 47.4MPa. If the additional vertical stress exceeds the allowable reinforced concrete strength of the shaft lining, it may result in shaft lining fractures. In other words, the similarity simulation results are roughly consistent with the numerical simulation results. The results of this study provide an important reference for the prevention of shaft lining fractures in coal mines with similar geological and hydrogeological conditions.