Study On The Mechanism Of Mining Activation Of Overburden Fault In Fully Mechanized Mining Face

The mine water inrush accident has brought great harm to the safety of coal mine production.One of the urgent problems to be solved is that the coal mining leads to the activation of faults and causes the mine water inrush.In this paper,theoretical analysis,numerical simulation experiment and similar material simulation experiment are used to study the change rule of vertical stress,shear stress,horizontal displacement and settlement of surrounding rock under the action of coal mining.According to the characteristics of fracture development of fault surrounding rock,the disaster mechanism of fault activation is obtained.The main conclusions are as follows:(1)Using FLAC3D numerical simulation software,the numerical model of footwall mining of normal fault is established.The vertical stress,shear stress,horizontal displacement and settlement of the fault caused by the advance of the working face are simulated and analyzed under the conditions of different dip angle,different drop and different coal seam depth.It is concluded that the fault with smaller dip angle is more likely to produce water diversion channel,which results in activated water inrush;the fault with large drop is more likely to be damaged in the coal seam roof,which increases the possibility of activated water inrush;the deep buried fault is prone to increase the permeability of the fault and the accident of activated water inrush.(2)According to the theory of mine pressure and strata control,the mechanical criterion of fault activation and the critical dip angle of fault activation are established.That is to say,when the main stress and dip angle of fault meet certain conditions,the fault will develop life.According to the limit equilibrium theory and Mohr Coulomb yield failure criterion,the formula for calculating the maximum water pressure of mining fault water inrush is derived.When the data of four variables are taken into the maximum water pressure formula,it can be seen that with the increase of fault dip angle,the increase of internal friction angle,the decrease of fault cohesion and the decrease of working face distance L2 from fault,the fault is more easily activated.(3)By analyzing the distribution and direction of the main stress,we can know that the fracture field is affected by the change of stress path.According to the different fracture mechanism,the fracture field can be divided into four areas,i.e.original rock stable area(?),micro fracture area(?),fracture opening area(?)and collapse area(?).Compared with the fault with large dip angle,the fault with small dip angle is easy to be affected by type ?fracture area,which makes the fault easier to activate water inrush.