西山煤田岩溶陷落柱柱体形态与组构特征

Morphological and fabric characteristics of Karst collapse pillars in Xishan coalfield

岩溶陷落柱柱体形态与组构特征严重影响着华北煤田的物探解译、采掘工作开展和水文地质预测预报。通过野外观测、井下编录、叠置对比和统计分析,以例证的形式,表征了太原西山岩溶陷落柱柱体高度、跨度、柱壁角和柱体组成,归纳了岩溶陷落柱柱体形态特征,在煤层开采界面上直径多为30~50 m,自奥灰顶面算起高度多在150~350 m,柱壁角为82°~85°,高低参差不齐,在柱顶上覆软岩层上多发育直径10 m左右“锅底”状构造的柱状岩块堆积体;总结了其柱体组构特征,柱体顶部往往空洞发育、富水、多生长次生矿物晶体;自柱顶以下的柱体组构密实、干燥,岩块镶嵌接触或碎屑流以基质形式填充于大岩块之间,大岩块与大岩块之间分段相间,岩块表面多发育镜面及擦痕构造;柱体下部岩块分选变好,块度变小,密实镶嵌;柱体中最大岩块直径可达3 m,一般岩块直径多在20~30 cm,最小岩块直径多在1 cm左右,棱角分明;柱体边缘煤层多向柱体倾斜、煤质变差、倾向柱体的裂隙发育;柱体岩块最大塌落距多在40~200 m。在华北克拉通破坏的过程中,不同区域构造地貌演化的历程不同,导致不同区域地壳表层岩溶水系统演化的进程不同,进而导致不同煤田岩溶陷落柱的形成时间、发育密度、柱体形态与组构特征也各异;陷落柱分布于沿先成弱面发育的岩溶水系统径流路径上,多期岩溶水系统演化的叠置会导致一些先成岩溶陷落柱柱体活化;柱体岩块风化是陷落柱柱体活化的重要表现,柱体活化是陷落柱导水的重要因素之一。寻找与对比岩溶陷落柱柱根位置,可作为地球物理方法探测与分辨区域煤系新老陷落柱的依据。

The morphological and fabric characteristics of Karst collapse pillars seriously influence the interpretation of the geophysical data,mining process,and the prediction of hydrogeology situations in North China coalfield.The field observation on the surface and in the roadway,overlay comparison,and statistical analysis were used to study the morphology characteristics of the collapse pillars in the Xishan coalfield including its height,span,pillar wall angle,and composition.The diameters of most pillars in mining roadways are 30-50 m,the heights of pillars from the top of Ordovician limestone are uneven,from 50 m to 350 m,and the pillar wall angles are 82°-85°.The‘pot-bottom’structure of stacked rocks can be seen on the soft rock layer which covers the top of the pillars.The structure and composition characteristic of collapse pillars is divided into three parts.In the top of the pillars,it is observed that the development of caves,high water content as well as secondary minerals crystals.In the middle of the pillars,the pillar body is highly dense and dry.Fragment rocks with slickenside surface or scratch structure exhibit inlaid structure.And the gap of large blocks is filled by fabrics as debris flow.In the bottom of the pillars,the sorting changes better,the particle size decreases,and fragments connect closely when compared with other parts of the pillars.The diameters of the irregular edges fragment rocks are 20-30 cm on average(maximum to 3 m,minimum to 1 cm).Closing to the margin of the collapse pillars,the dip direction of the coal seam incline to the pillars,the coal quality clearly become lower,and many fractures inclined to the pillars appear.The maximum falling distance of the blocks in pillars is 40-200 m.In the destruction process of the North China Craton,the evolution process of the structure and geomorphology in different areas is different,which leads to the different evolution process of the Karst water system in the subsurface system,and further leads to the different formation time,distribution density,morphology and fabric characteristics of pillars.The distribution of the pillars is in the path of the Karst underground water which formed in the weak layers.The evolution of multi-terms of Karst underground water could lead to the overlaid of the pillars which will cause the activation of the previous pillars.The weathering of the fabrics in pillars is the critical signal of the activation which is one of the key factors of water transportation in pillars.Finding and comparing the root of Karst collapse pillars will provide some insights into detecting and distinguishing the younger and elder pillars when using geophysical methods.