Strips Secondary Steep Mining Method for End-slope of Seasonally Frozen Soil Area

In order to make full use of the difference of seasonal freeze-thaw strength of the soil on the free face of the slope to improve the recovery rate of the coal under the end-slope, the mechanism of the improvement of the shear strength of the frozen soil is analyzed by using shear plane microstructure model. Two kinds of strips mining methods for the secondary steep mining in the freezing period are proposed, and the optimal strips width analysis flow is designed. A case study on the south end-slope of Western Shengli No.1 open-pit mine is carried out. The results show that the stability factors of the south end-slope in the non freezing period and freezing period are 1.06 and 1.14, respectively. The second steep mining can be carried out in the freezing period, and the optimal strips width is determined to be 60 m by analysis. The secondary steep mining realized that the south end-slope angle was raised from 30° to 33° and the end-slope residual coal was recovered by 171 500 t. In the seasonal frozen soil area, the implementation of the strips secondary steep mining can ensure the safety of the slope and further improve the recovery rate of resources.