Plastic zone evolution law and enhanced support technology of surrounding rock in gateway retained along goaf with double gateway layout

In order to solve the surrounding rock instability problems occurred in the gateway retained along the goaf in a layout of the double gateways of Hongqin gliang Mine, the numerical simulation was applied to the study on the distribution features of the principal stress difference value under the influences of two mining as well as the plastic zone features of the gateway retained along the goaf under the different stress stage. The results showed that the principal stress difference value of the surrounding rock along the gateway retained along the goaf would have five stages under the influences of the first mining and the second mining and would have t he stage increased features. During the first mining period, the plastic zone of the roof in the surrounding rock along the gateway retained was increased from 1.2m to 2.1 m, the plastic zones in the sidewall of the coal wall and the coal pillar were increased from 0.5 m to 2.0 m and 1.5 m individually. After the influences of the second mining stress, the plastic zone would be expanded with asymmetric features, the plastic zone in the roof at the sidewall of the coal pillar would have many plastic failure s, the failure depth could be 3.0 m, the plastic failure of the two sidewalls would be in symmetry and the scope of the plastic failure could be 2.5 m. Finally, the related e nhanced support measures were provided. After the site application, the convergence between the roof and floor of the surrounding rock was reduced by 38%, the conv ergence between the two sidewalls was reduced by 36% and the stability of the surrounding rock along the gateway was kept.