Mining Influence On Change Of Water Filling Conditions Of Coal Seam Floor

Many karst districts in north China are facing the threat of Ordovician confinedwater．Some failure appears in coal seam floor under the influence of mining．As aresult，the thickness of effective aquifuge is decreased；the stress field，medium fieldand hydrodynamic field of floor strata in natural conditions are changed．Meanwhile，the water disaster threat to mine where seam floor is subjected to water pressure isintensified．Therefore，it is significant to grasp the influence of mining on water fillingconditions accurately．In this paper，by means of hydro-geological survey，data collection，indoor testanalysis，mathematical model and numerical simulation methods，etc., the waterfilling conditions of coal seam floor were elaborated and the failure depth of floorstrata was predicted．All in all，mining influence on change of water filling conditionsof coal seam floor was analyzed comprehensively．The main results achieved are asfollows：The medium of floor strata was analyzed through the indoor test experiments，such as X-ray diffraction experiment， pressured-mercury testing and SEMobservation．The results show that floor strata consist of a series of aquifer andaquifuge which are K2limestone，mudstone and siltstone and so forth．Among them，there are mainly micro pores and ultra micro pores in K2limestone．Similarly，ultramicro pores mainly develop in mudstone and siltstone．K2limestone stratum is weakaquifer where fractures do not develop mostly．But local runoff conditions arebetter．It is conducive to inhibit water inrush under the condition of that the aquifugeis composed of hard rock and soft rock apart．Based on the statistical data of typical working face，GA-SVR model wasestablished to predict the failure depth of floor strata．It demonstrates that theprediction accuracy of GA-SVR model is higher than the methods of PSO-SVR，GS-SVR and empirical formula in this thesis．FLAC3Dsoftware was used to simulate the failure circumstances of floor strata in2-112working face．The results indicate that with the working face advancing．coalseam floor experiences stress increasing before mining and stress reduction andrecovering stage after mining successively．The failure depth of coal seam floorwithout buried fault is10m．Thus，effective aquifuge is still71m．It shows that thewater inrush coefficient is0.056Mpa/m which is less than critical water inrush coefficient．So，it is predicted that there is no water inrush risk during mining．Mining influence on water filling conditions is also reflected in that manyfissures appear after the failure of floor strata．Water may flow out from floor underthe combined action of high water pressure and high stress．Then，the balance ofgroundwater system is broke and a new hydrodynamic field is graduallyformed．Groundwater runoff conditions also change correspondingly．Hence，groundwater quality in aquifers will be affected．Water inrush from seam floor of2-112working face was simulated through theuse of FLAC3Dsoftware while the formation process of water inrush channel wassimulated．It is speculated that there is a buried fault near the water inrush point．Thewater inrush is induced by the combined effects of high ground stress，high waterpressure and buried fault in floor．...