Long-term Monitoring And Evaluation Of Shaft Stability In Thick Overburden Area

Non-mining rupture of shaft in thick overburden is a mine geological hazard arising from 1980 s,The mechanism is that when the deep aquifer consolidated after dehydration,the unconsolidated layers sinked relative to shaft lining,and the interaction between soil and shaft lining causing additional stress spoils the shaft lining.Taking the main shaft of Xinglongzhuang Coal Mine as the research object,this paper investigates the fracture characteristics of the vertical shaft in eastern china coal mine,and monitors the water level of the bottom aquifer,the deformation of the loose layer and the compression of the stress relief slot.Monitoring data show that the dehydration and consolidation of bottom aquifer is the fundamental reason for the compression of loose layer,and the compression of bottom sand layer accounts for more than 80% of the compression of the whole loose layer,while the clay aquifer is basically non-deformed.Based on the interaction theory between pile and soil,an elastic-plastic analytical equation is established to study the influence of the change of relative displacement between loose layer and shaft wall on the additional stress of shaft wall,and the connection between shaft wall and soil layer.The elastic-plastic boundary depth Zp and the maximum vertical stress value of the shaft lining are caculated,and the most dangerous section is checked according to the first strength theory.The three-fluid-solid coupling effect is established by FLAC3 D software to verify the analytical results,and the stability of the main shaft in Xinglongzhuang is evaluated according to the results.The results show that:(1)The deformation of loose layer is consistent with the change of bottom water level.The compression of stress relief slot is a logarithmic function of time,but the correlation between the compression material and the three water levels is not high due to the creep characteristics of compression material.(2)Additional stress can be several times of the self-weight stress of the wellbore,which is the main reason for the damage of the wellbore.(3)Vertical pressure relief and transverse sleeve wall is the best way to control the non-mining damage of vertical shaft.Compression material pine is arranged with transverse compression plane.Stress accumulation value of pressure relief trough is stable when compression rate is less than 30%.