北方草原区露天煤矿外排土场平台土体裂缝形态特征

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

煤炭资源的开采不仅能够带来经济的快速发展,也会产生严重的生态环境问题,其中以露天开采最为严重。频繁不合理的采矿活动破坏土地资源,诱发矿区地质灾害。土体裂缝是煤矿区地质灾害中最直观的一种,也是危害最大的一种,其数量多、分布广、危害重,严重影响矿区生态安全。土体裂缝的产生极大程度地影响着排土场地表径流、入渗、蒸发等水文循环过程,也增加排土场泻溜、崩塌、滑坡等水土流失灾害发生的可能性。研究排土场平台土体裂缝形态特征可为认识矿区水分快速运动、植被恢复与重建提供科学依据。以内蒙古锡林郭勒盟锡林浩特市大唐国际胜利东二号露天煤矿南排土场为研究对象,通过现场调查、野外试验、室内分析、图像处理等研究方法,系统地研究北方草原区露天煤矿外排土场平台土体裂缝形态规律及其分形特征。结果表明:排土场平台土体裂缝发育严重,多为直线型,走向平行于等高线,集中在排土场平台前缘5 m内;排土场平台土体裂缝长度主要集中在0~500 cm,占80%以上;土体裂缝宽度在4.3~40.4 cm,深度在5.7~55.3 cm。土体裂缝尺寸的差异较大,但可以根据裂缝宽度W将其划分为小裂缝(W<15 cm)、中裂缝(15 cm<W<30 cm)和大裂缝(W>30 cm)3个等级;GFⅠ,GFⅡ,GFⅢ裂缝宽度依次为9.85,2.86,5.77 cm,各裂缝之间差异显著(P<0.05)。GFⅠ,GFⅡ,GFⅢ裂缝深度依次为29.00,30.67,28.67 cm,各裂缝之间无显著差异(P>0.05)。随着裂缝宽度不断扩张,松散的砂质壤土会在裂缝开裂过程中坍塌而回填裂缝,影响裂缝深度。裂缝宽深比与裂缝深度之间具有较好的幂函数关系,两者达到极显著水平(P<0.001)。GFⅠ,GFⅡ,GFⅢ分形维数为1.437,1.240,1.309,回归方程的决定系数为0.986~0.994,P<0.001,排土场土体裂缝分布具有明显的自相似性。分形维数越大,裂缝的形态特征越复杂,对土壤及植被的扰动作用也越大。

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 cm<W<30 cm),and large fissures(W>30 cm)according to the fissure width W in the dump.The ground fissure width of GFⅠ,GFⅡ,and GFⅢwas 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 GFⅢwere 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,GFⅢwere 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.