Influence factors on the ground temperature recovery process of an open-pit coal mine backfill in the permafrost area of northeastern China

Open-pit coal mine backfill is an effective method for ecological environment recovery in permafrost areas. Quantitative analyses for ground temperature changes are lack and the main influence factors affecting the ground temperature recovery remains unknown. The numerical simulation method is implied to analyze the open coal mine backfill effects on the thermal status of permafrost in the Gulian area. The results show that the main factors influencing the ground temperature recovery is the depth of the backfilling soil and the filling soil temperature. The backfilling soil tends to decrease and then increase in 50 years under the climate warming background. The underneath and lateral heat effect is about 5 m and it will recover in 5 years in any condition. The backfill area will froze in about 27, 21, 16, and 10 years with different soil temperatures of 20℃, 15℃,10℃ and 2℃, respectively. With the filling back depth of 2.6, 10, 20, 30 and 40 m, the corresponding temperature of the backfill area depress to negative after 1, 9, 27, 65 and 114 years. The reliability of the model is validated through the statistical regression model compared with the numerical analysis results of the backfill depth of 80 m. On the basis of the above study, we give a suitable backfill solution such as the proper construction season and backfill practice ways.