China is a big coal country, but there are also some safety problems while exploiting and utilizing coal resources. After large-scale coal mining, the surface will move, deform and destroy, which will have adverse effects on the surrounding buildings and environment. Therefore, it is a hot issue to analyze and evaluate the geological stability of coal mined-out areas to determine the treatment of subsequent mines, which has important economic and safety significance.

    In this paper, No.15, No.20 and No.30 coal seams in Shanlei expansion area of Lingdong mining area, Shuangyashan City, Heilongjiang Province are taken as the research objects. Through field investigation and data collection, 3D geological modeling and numerical simulation analysis are carried out based on Surfer and FLAC^3D software, respectively, and the deformation laws of overlying strata stability, surface movement period and ground deformation are summarized, so as to analyze and evaluate the geological stability of coal mine goaf and provide scientific information guarantee and new theoretical basis for mine management in the later period of goaf.

    With the help of Surfer software, the top and bottom depth data of No.15, No.20 and No.30 coal seams are processed in three dimensions. By arranging the top and bottom depth data of these three layers in EXCEL and saving them as *.csv format, the data includes X, Y coordinates and Z coordinates, where the X axis represents weft distance, the Y axis represents warp distance and the Z axis represents top and bottom depth. The files saved as *.csv format are respectively imported into Surfer software and gridded by Kriging interpolation method, and saved as *.grd data file format which can be directly mapped by Surfer software, and then contour maps of each layer are drawn and simple three-dimensional modeling is carried out, and contour maps of each layer are integrated with 3D surface maps to establish a three-dimensional goaf comprehensive model, which intuitively and truly reflects the development characteristics of coal seam top and bottom.

    Using FLAC^3D software, the three-dimensional model is numerically simulated and analyzed, and the geological stability of coal mine goaf is analyzed and evaluated from three aspects: the stability of overlying strata, the ground movement period and the ground deformation. By comparing the numerical simulation results with the actual data, the geological stability of the coal mine goaf is summarized according to the comparison results, which provides a new theoretical basis for mine mining management. The conclusions are as follows:

    First, the stability analysis of overlying strata. In the process of mining, the changes of mining sequence, mining mode and overlying strata properties of minable coal seams have great influence on the surface deformation of overlying strata in goaf. Using FLAC^3D software to draw the contour map of surface subsidence in goaf and the curve map of surface subsidence in each coal seam under different mining sequences and mining methods, and determine the degree of surface subsidence and its influence on surface subsidence. Under the same mining sequence and specific mining mode, the influence of roof and floor lithology of overlying strata on surface deformation is analyzed by FLAC^3D software.

   Second, the analysis of surface movement period. The stability of surface movement is an important aspect of analyzing and evaluating geological stability. Surface movement can be divided into three stages: initial stage, active stage and declining stage. Using FLAC^3D software to draw the curve of surface subsidence time, and then simulate the duration of surface movement and deformation, so as to calculate the surface movement period and determine the stability of goaf.

    Third, the ground deformation analysis. Determine the critical value of mining depth and mining thickness ratio in goaf, use FLAC^3D software to draw the comparison diagram between the critical value and the simulation analysis results, and then compare it with the simulation analysis of mining depth and mining thickness ratio in goaf, and finally summarize the types of ground deformation.

   To sum up, large-scale mining in mines will cause a series of geological disasters, such as deformation of mined-out areas and surface subsidence. Therefore, it is very necessary to study and analyze the geological stability of mined-out areas to control the subsequent mining. The results show that this study can provide some new theoretical basis for controlling mined-out areas caused by mining.