Morphological characteristics of ground fissures at surface coal mine dump in northern grassland of China

The exploitation of coal resources can not only bring about a rapid economic development,but also cause some serious ecological and environmental problems,which seriously affect surface coal mining. Frequent and unreasonable mining activities destroy land resources and induce geological disasters in mining areas. Ground fissure is one of the most intuitive geological hazards in coal mining area,and also the most harmful one. It has a large number, extensive distribution and severe damage,and seriously affects the ecological security of mining area. The occurrence of ground fissures greatly affects the hydrological cycle processes such as surface runoff,infiltration,and evaporation, and also increases the possibility of soil and water loss disasters such as granular disintegration,collapse,and landslide in the dump. Studying the morphological characteristics in the ground fissure of dump may provide a scientific basic support for understanding the rapid movement of water and vegetation restoration and reconstruction in the mining area. Taking the south dump of the Shenglidong No.2 surface coal mine of Datang in Xilinhot City,Xilingol League,Inner Mongolia as the research object,the morphological characteristics and fractal dimension of ground fissures were systematically studied by field investigation,field test,indoor analysis and image processing in a surface coal mine dump of northern grassland China. The results indicate that the development of ground fissures was serious in the dump and most of them was linear. Ground fissures were concentrated within the first 5 m from the frontal edge of the dump and their trend was parallel to the contour line. The length of most fissures ranged from 0 to 500 cm; these fissures accounted for 80% of the total fissures. Ground fissure width was from 4.3 to 40.4 cm,and its depth was from 5.7 to 55.3 cm. The difference of ground fissures was relatively large. However,the ground fissures were classified into small fissures (W<15 cm),medium fissures (15 cm30 cm) according to the fissure width W in the dump. The ground fissure width of GFⅠ,GFⅡ,and GFⅢ was 9.85,2.86 and 5.77 cm respectively,and there were significant differences among three fissures (P <0.05). The ground fissure depths of GFⅠ,GFⅡ,and GF Ⅲ were 29.00,30.67 and 28.67 cm respectively. There was no significant difference among three ground fissures (P >0.05). The ground fissure width expanded continuously,and loose sandy loam would backfill the fissures during the cracking process of the fissures. The soil at the wall of the fissures would collapse,burying the fissures. There was a good power function relationship between the width-depth ratio and depth,which indicated that the two had reached a very significant level (P<0.001). The fractal characteristics of ground fissures of GFⅠ,GFⅡ,GFⅢ were 1.437,1.240 and 1.309 respectively,and the determinant coefficients were from 0.986 to 0.994 (P<0.001). That showed that the distribution of ground fissures had self-similarity in the dump. The larger the fractal dimension,the more complex the morphological characteristics of ground fissure and the greater the disturbance to soil and vegetation.