The spatiotempora variations rules of Songzao coal mining subsidence based on numerical simulation

Abstract. With the increasing demand of coal, coal mining at Songzao makes the area of land subsidence growing larger. Land subsidence in coal mining area not only made large subsided farmland out of production and caused the enormous loss to local agricultural production, but also brought a number of serious problems to the local social economy and ecology Environment. To use Probability-integral Method based on numerical simulation of Songzao Mine, its subsidence simulation data from 1999 to 2009 was obtained. Hence, overlay analysis between Goaf data and the simulation data in 2009, and between field investigation and the simulation data in 2009 were carried out. After the coal mining underground was identified as the crucial cause of surface subsidence. Therefore, the accuracy and feasibility of the simulation data had been verified, and the spatial pattern and spatiotemporal variations conforming to the actual values have been obtained. The results show five main findings. The first indicated that the surface subsidence is mostly located at the top of the Goaf, where the overlap areas between Goaf data and subsidence simulation data have accounted for 93.05 % of Goaf and 65.19 % of subsidence simulation data respectively. The second finding indicated that by end of 2009, the mining subsidence extent had reached about 5087.50 hm². This area accounts for about 40 % of total of the mining area. The third finding indicated that within 10 years from 1999 to 2009, the influence range of subsidence has expanded about 2340.54 hm², and the coal mining subsidence rate in Songzao Mine has increased gradually with time. Moreover, average increasing speed of the extent area in the second five years was larger than the first five years (about 75.08 hm² yr⁻¹ more). The fourth finding indicated that maximum subsidence has increased from 2.0 m in 1999 to 2.5 m in 2004, and then 3.0m in 2009 with subsidence rate of about 0.1 m yr⁻¹. At the same time, the area affected by the subsidence 2.0 m in 1999 was more than twice the area affected by subsidence in 2004. This in return, it was more than 7 times larger than the area affected by subsidence in 2009 of the one affected by subsidence in 2004. Extent of the area affected by the 2.5 m subsidence has also enlarged rapidly. This area has expanded by about 40 times in 2009 than its value in 2004. In addition, the area of subsidence of value 3.0 m has reached about 0.44 hm² in 2009 from zero value. Finally, the fifth finding indicated that the overall extend of the mining subsidence was much more serious in southern than in northern side of the Songzao Mine. Moreover, it was indicated that the increasing rate of mining subsidence in the western side of the study area was as bigger as in the eastern side between 1999 and 2009. The spatiotemporal variations rules of songzao coal mining subsidence based on numerical simulation could provide reference for the subsequent subsidence prevention and land consolidation.