Field and numerical investigations on the lower coal seam entry failure analysis under the remnant pillar

摘要

Extraction of multiple seam using fully mechanized coal mining technology caused severe de-formations in the lower coal seam roadways in Zhaiyadi Coal Mine in Shanxi Province, China. Understanding the characteristics of the lower coal seam entry failure mechanism under the remnant pillar is the first step in determining a reasonable location of the lower coal seam entry. Characteristics of the lower coal seam entry failure mechanism under the remnant pillar are investigated by means of numerical simulations and in-situ observations. To improve the relia-bility of the numerical simulations, the global model is validated by comparing the surrounding rock deformation of 3905 headgate with the in-situ observation data due to the extraction of Panel 3805. The numerical simulation results of the global model indicate that the original 3905 headgate under the remnant coal pillar is located in the vertical stress concentration zone and horizontal stress concentration zone. Firstly, the peak vertical stress concentration factor in the coal seam 9# (the lower coal seam) is 4.9, located 100 m behind the active Panel 3805 while the peak horizontal stress concentration factor in the coal seam 9# is 2.1, and located 30 m behind the active Panel 3805. When the delay distance to the active Panel 3805 is 80 m, the stress transmission angle reaches a constant value of 30.9 degrees. Secondly, both the ratio of coal pillar rib deformation to solid coal rib and the ratio of roof subsidence to floor heave increase as the delay distance to the active Panel 3805 increases. Finally, numerical results show that the designed 3905 headgate located 25 m to 30 m away from the middle of the remnant coal pillar would be an alternative scheme, located out of the floor horizontal stress concentration and vertical stress concentration in the coal seam 9#. The findings in this study will help to provide a basis to select a reasonable location for lower coal seam roadways under similar mining and geological con-ditions.