Abstract: In order to further study on the failure mechanism of vertical shaft in loose strata, an industrial test has been carried out in loose strata around west breeze well in Dongtan Coal Mine and the Fiber Bragg Grating system was used to monitor the change of strain in loose strata. In addition, additional stress of shaft lining was calculated theoretically based on the theory of retaining wall and the criterion of shaft wall fracture model was built based on the fourth strength theory. Pumping water test shows that water reduction led to consolidation of clayey and increment of compressive stress in lower coal group aquifer, it also led to clayey be in a state of tension in middle coal group aquifer because that movement of clayey in middle coal group aquifer lags behind that in lower coal group aquifer. Supplying water test shows that for each 1000m3 water increase, there was 1.61με increased strain variation of the clayey, and with the increment of water, the compressive strain decreased obviously, which shows the clayey is heavily influenced by the change of flow; For calculating the additional stress of shaft, it is found that the angel between slip line and horizontal plane decreases with the loss of aquifer, which lead to increase in size of soil centrum, causing increment of additional stress of shaft.

Key words: loose strata, shaft lining, failure mechanism, additional stress