Impermeability Analysis And Experimental Study About Coal Bed Floor In Workings

Mechanics of floor water invasion in coal mining above confined aquifer in North China type coal field are all based on the general recognized floor aquifuge taking no account of the water resistance properties of certain layers in Ordovician limestone which is generally deemed as highly inhomogeneous aquifer。As depth of coal mining increases rapidly,the water pressure on bed floor of under-group coal becomes even greater,if we again restricted floor aquifuge in finite thickness of coal measure strata,many percents of under-group coal seams and even some upper and lower groups are not safe for exploitation according to industry standard。So it's necessary to carry out detailed research on the water resistance properties of Fengfeng Group at the top of Ordovician limestone and revaluate the condition of mining above aquifer。The water resistance properties analysis and experimental study about Fengfeng Group is set in Sihe coal mine of Jincheng Anthracite Mining Group,results are as follows:(1) Experimental study on water resistance properties of Fengfeng Group has been done by field geological surveying,pumping test,hydrochemical survey,water pressure test on bed floor and borehole flow survey,conclusions which proves characteristics of confining layer is held by Fengfeng Group shows that the water abundance of it is far less than upper Majiagou Group。(2) Comprehensive research about Paleozoic evolution background,cause of formation of paleo-weathering crust,development and filling state of Karst fissure and lithological associations export a conclusion that Fengfeng 2 member and upper part of Fengfeng 1 member can be seen as relative aquifuge when considering a safety factor。(3) Research about destruction rule of coal bed floor was done on macro-scale, medium-scale and micro-scale in Sihe coal mine,results show that water resistance properties of coal bed floor is the interaction of stress field and the own characteristics of rock。(4) Based on fluid-solid coupling by using FLAC3D program,when considering relative aquifuge,concentrated stress in rib of workings and mined-out area releases easier and yield region is reduced。The influence of ordovician water pressure on rib distortion is almost constant and has no relation to the length of mining field,while in the mined-out area,the value increases with a acceleration。That means the floor in mined-out area gets more sensitivity upon ordovician water pressure than that in rib area。The floor damage include mining-induced fracture of direct floor and fluid-solid coupling caused yield region in Fengfeng Group,which may get a coalescence and cause a water inrush into 15# seam from floor without the relative aquifuge。(5) The condition of mining above aquifer in east zone of Sihe coal mine was evaluated by method of coefficient of water inrush,recalculated value considering the relative aquifuge was generally below critical value and safety mining become possible。...