Study On The Propagation Law Of Hidden Fault Cracks In Floor Affected By Mining

Inrush accidents will happen in the process of coal mining,and most of the inrush accident reason and fracture structure exists a certain relationship,especially for the concealed fault,because of its relatively small size,it is hard to be totally and meticulous investigation,so the study of floor of concealed fault fissure extension law still exist many theory problems.Based on coal seam mining problem of the development of buried fault activation induced by theoretical analysis,simulation test specimens,similar material simulation experiment and FLAC3 D numerical simulation of the means of combining the analysis of concealed fault induced inrush mechanism and regularity of concealed fault in the process of coal mining research,study the general rule of coal floor of concealed fault fissure extension.The main conclusions are as follows:(i)The empirical formula for the minimum safe distance H from coal floor fault to coal seam in the presence of concealed fault is derived by means of mechanical analysis and considering the effect and influence of mining stress on concealed fault.(ii)Through the physical and mechanical tests,the expansion law of the fractured rock mass of the macroscopic concealed fault under the influence of the mining of the specimens containing prefabricated fault-like rock materials under uniaxial compression loading is obtained.The edge cracks(simulated working face)and the oblique cracks(simulated fault)are mainly in the shear failure form of the inclined surface,which is accompanied by the fracture tensile failure form as a whole.The shear crack developed by the edge crack and the oblique crack develops in the same direction,and the direction of development is the shortest path direction for the crack penetration.(iii)The law and mechanical analysis of fracture augmentation activation of buried fault rock mass were obtained by similar material simulation.The model has gone through the process of "original separation development--original separation compaction and airtight--new separation generation and expansion--new separation compaction and airtight".With the gradual advance of the working face,the fracture development of the fault is more affected.When the working face is pushed to the vicinity of the fault 25 cm,the development of the fault is sharply increased by mining,and the direction of fault fracture development changes with the advance of the working face.(iv)Combined with the simulation test model of similar materials,based on the engineering example of the 6303 working face of jining daizhuang coal mine,a numerical simulation model was established by using FLC3 D numerical simulation software to monitor the failure depth of coal seam floor and simulate the development and extension process of hidden fault fractures under coal seam floor during continuous mining.Through the analysis of the plastic zone,the vertical stress and the vertical displacement,the development law of the floor fault during mining,the stress state of the fault crack and the dynamic change of the expansion activation are summarized.The calculation and simulation results show that the failure depth of coal floor is 15m(before 25 m from the fault),which is consistent with the actual observation results of 6303 working face.