顶板导水裂隙高度随采厚的台阶式发育特征

Stepped development characteristic of water flowing fracture height with variation of mining thickness

传统导水裂隙发育高度预计方法对顶板岩性进行均化,忽略了具体条件关键层结构差异所造成的影响,认为导水裂隙的发育高度随采厚是呈近线性增大的,有时会导致较大的判别误差。针对该问题,采用理论分析、现场探测等方法,研究了关键层结构影响下顶板导水裂隙发育高度随采厚的变化特征。结果表明,导水裂隙的发育高度同时受到采厚和覆岩关键层结构的影响。在覆岩关键层结构的控制作用下,导水裂隙的发育高度随采厚呈现台阶式突变而非连续的近线性变化。关键层厚度及其所控制的岩层厚度越大,导水裂隙高度随采厚变化时的台阶落差越大,突变越明显。一定关键层结构条件下,如果采高变化范围没有超出导水裂隙高度产生台阶的范围,则采高变化并不导致导水裂隙高度的变化,也就是说此时降低采高并不能减少导水裂隙高度,增加采高也并不会增大导水裂隙高度。研究结果得到了亭南煤矿导水裂隙高度实际探测结果的验证,在二盘区206工作面开采条件下,采厚7.5和9.0 m时对应的导水裂隙高度分别为140.2和148.3 m,均发育至宜君组底界,采厚在一定范围增加并未引起导水裂隙高度的明显变化,该工作面在保证导水裂隙高度不明显增大的前提下,最大采厚理论上可以达到14 m。基于研究成果形成了考虑关键层结构的洛河组砂岩含水层下合理采厚确定方法,指导了亭南煤矿二盘区综放工作面洛河组砂岩水防治实践。根据亭南煤矿207工作面附近钻孔柱状的关键层结构,以导水裂隙高度不直接沟通洛河组为限,提出207工作面在设计采厚7.5 m基础上,可以将顶煤全部放出的方案。工作面实际总采厚平均达9.0 m,多放顶煤1.5 m,多回收煤炭资源约71万t,有效提高了采出率。

The traditional predicting method of water flowing fracture height sometimes makes some discriminating errors because of its homogenization classification of roof lithology,its ignorance of the influence of different key stratum structure,and near-linear relationship between mining thickness and height of water flowing fracture based on the traditional formula.In this study,the variation characteristics of water flowing fracture with changing mining thickness were investigated by way of theoretical analysis and engineering detection.Results showed that both mining thickness and key stratum structure could influence the height of water flowing fracture,which showed a stepped development characteristic but not continuous or even near-linear variation when mining thickness changed.The thicker the key stratum and the layer it controlled was,the larger the drop height was,and the more obvious the mutagenicity the height of water flowing fracture was.According to some key strata structures with certain characteristic,the height of water flowing fracture wouldn’t change with changing mining thickness if the changed ranges of mining thickness didn’t exceed the drop height range of water flowing fracture.Namely,the decrease of mining thickness couldn’t reduce the height of water flowing fracture,and vice versa.The research results were verified by the engineering detection result obtained from Tingnan coal mine.The height of water flowing fracture was 140.2 m and 148.3 m with the mining thickness 7.5 m and 9.0 m respectively in No.206 working face,and the fracture have both reached the bottom of Yijun aquifer.These results convincingly proved that the increase of mining thickness in a certain range did not significantly change the height of water flowing fracture.On the premise that the height of water flowing fracture didn’t increase obviously,the maximum mining thickness could be increased to 14 m theoretically in the mining condition of No.206 working face.Determination method of reasonable mining thickness using fully mechanized top-coal caving mining method under aquifer should be pro-posed,and then guided the practice of preventing roof water disaster at Tingnan coal mine.According to the characteristic of key stratum structure in No.207 working face,the scheme that the top coal could be entirely mined out was proposed.Finally,the actually total mining thickness of No.207 working face was 9.0 m and about 710 thousand ton of additional coal was mined,and the coal recovery rate was effectively improved.