Study On The Activation Mechanism Of Secondary Fault In Floor Induced By Mining On Working Face

Coal mine floor water inrush accident is mostly caused by the existence of fault structure.Near the fault zone in the process of fault formation,it may contain some secondary fault,and the secondary fault with strong concealment,is not easy to detect,and the characteristics of mining impact resistant ability is weak,therefore,in the mining and confined water under the dual function of the secondary fault is used into daily life,when the secondary fault activation extension through from the main fault and form water inrush channel area,destruction of the floor plate confined water along the water inrush channel into working face,water bursting accidents.Based on the actual geological conditions of wugou coal mine,this paper studies the disaster caused by the activation of secondary faults in the floor induced by mining in the working face by using theory,similar material test and numerical simulation,and obtains the following research results:(1)Through the collection,arrangement and summary of the research results on the disaster caused by activation of secondary faults in floor,the research status of water inrush from floor,water inrush from activation of fault and activation of secondary faults is understood.(2)The characteristics of activated water inrush from floor secondary fault are summarized by analyzing the cases of activated water inrush from floor.The factors affecting the activation of secondary faults are given and the activation propagation of secondary faults is deduced and analyzed by means of fracture mechanics theory.(3)Based on the test of similar materials containing secondary faults in the floor,the damage and failure characteristics of the floor,the activation characteristics of the secondary faults and the stress evolution rules of the working face during the stoping process were studied.It was concluded that the stress change rules of the secondary faults were that the closer to the working face,the greater the stress change and the more obvious the influence of mining.When approaching the secondary fault,under the influence of the superposition of the supporting pressure and the confined water,the rock strata around the secondary fault appear the fissure expansion,which forms the conduction fissure with the secondary fault,and provides the condition for the confined water to break into the working face along the activation expansion of the secondary fault.The secondary fault activation is more advanced than the main(DF68)fault activation,and the secondary fault promotes the main(DF68)fault activation.(4)FLAC3D numerical simulation software was used to numerically simulate the secondary faults with different dip angles,the morphology of the combined secondary faults and 8 models without water pressure.The activation of the floor secondary faults was studied from three aspects:failure characteristics of plastic zone,stress distribution characteristics and seepage characteristics.It is concluded that the smaller the secondary fault dip Angle is,the greater the influence of concentrated stress on the main fault will be,and the more concentrated the rock mass stress between the secondary fault and the working face is,the more prone the fractures in the secondary fault are to activate and expand,and the more serious the plastic failure of the secondary fault will be.The existence of the combined secondary fault makes the stress propagation in front of its working face more blocked and concentrated,and speeds up the activation rate of the combined secondary fault,leading to the inrush of confined water into the working face through the plastic failure area of the combined secondary fault.The greater the water pressure,the greater the water vector and the faster the activation rate of secondary faults.