Simulation analysis of the impact of excavation backfill on permafrost recovery in an opencast coal-mining pit

The article attempts to investigate the status of permafrost recovery after excavation backfill in an opencast coal mine. To do that, we forecast the permafrost recovery under certain initial temperatures and different boundary conditions by using the numerical simulation method. The results show that the filling temperature significantly influences permafrost recovery after backfilling. When the filling temperature decreases from +2.0 to -2.0 degrees C, the permafrost recovery rate will greatly accelerate, and the permafrost thickness will significantly increase. When the surface temperature of the filling is positive, the permafrost recovery at the bottom of the excavation will be more difficult than when the temperature is negative. The permafrost recovery rate will be slow, and the permafrost thickness will be thin. The permafrost recovery also gradually speeds up the thickening with decreasing natural surface temperature. Thus, backfilling should be conducted in the cold season, and cooling treatment should be applied to the filling before backfilling. The treatment will ensure that the permafrost recovery is faster and more stable. This measure is also conducive to the recovery of the ecological environment of the mine.