Study On The Multi-factor Influence Mechanism Of Coal Damage And Crack Evolution Under The Blasting

With the increasing depth of coal mining in China,various engineering disasters,such as coal and gas outburst,rock burst,rock instability and high temperature,has become increasingly serious,and coal and gas outburst is at the top of the list.Therefore,deep-hole controlled blasting technology,as one of the effective measures to prevent coal and gas outburst,aims to increase permeability,the key study of which is the coal damage and crack evolution mechanism under the action of blasting.However,nowadays most studies mainly focus on the increasing permeability effects of deep-hole controlled blasting by the measurement of gas drainage volume,drainage rate and gas pressure of coal seam,blasting equipment and blasting parameter design in the field of engineering practice.Research on the evolution mechanism of coal damage and crack under the action of blasting,especially in terms of the different geostress,different gas pressure,control hole and other factors in the coal damage and crack evolution under the action of blasting,is less.Therefore,it is necessary to launch an in-depth study of various influencing factors,such as different geostress,different gas pressure and control hole etc.,in the coal damage and crack evolution under the action of blasting.The research can provide a theoretical basis for the prevention of coal and gas outburst by using deep-hole controlled blasting,and will play an important role in guaranting mine safety and effective mining.Basing on previous research findings,this thesis adopts theoretical analysis,experimental investigation,numerical simulation and combination of multi methods to study the influence mechanism of different geostress,different gas pressure and control hole on the coal damage and crack evolution under the action of blasting.Firstly,the thesis analyses the mechanism of increasing permeability effect of deep-hole controlled blasting.The explosive energy is applied to the coal and rock medium to form the crushing zone and fracture zone.The crushed zone is formed by shock wave,explosive gas of high temperature and high pressure,and the fracture zone is formed by the compressive stress wave,the unloading wave and detonation gas.The explosive load of the column charge,the rock failure criterion,and the scope of the crushing and the fracture zone are calculated.Through the analysis of the multi influencing mechanism,including the geostress of coal crack evolution,the gas pressure,control hole,under the action of blasting,Geostress has an inhibitory effect on crack propagation;gas pressure has a positive effect on crack propagation,and the control hole plays a guiding role.Secondly,on the strength of the research of coal’s physical and mechanical properties,the composition and ratio of the coal materials in the blasting simulation are determined,and the blasting simulation coal can take the place of the real coal in the blasting simulation experiment.Next,similar simulation test device of coal damage and crack evolution under the blasting is built.It can simulate coal specimen of 300mm×300mm×300mm blasting.Two kinds of control-hole blasting simulation test model were designed and fabricated.Experiments on increasing-permeability of coal deep-hole controlled blasting were studied by using the test device under the condition of different geostress,different gas pressure and control-hole.The influence mechanism of multi-factor that including different geostress,different gas pressure and control hole in the coal damage and crack evolution under the blasting are studied.The results show that the geostress has obvious inhibition effect on the coal’s microscopic damage and crack under the explosion load,that the geostress and resistivity damage factor has a relationship of negative exponent,and that the resistivity damage factor and time shows a negative exponential relationship when the cracks after the blasting are continuously affected by geostress.When the gas in balance gets into the disturbulance crack caused by explosive load in the median or far zone of the blasting coal,the crack is expanded further.The control hole transformed all stress waves into tensile waves,making coal form fish scalling fall in the inner side from the free face.Finally,6 mathematical models of different holes’ layout(blasting holes and control holes)are established.Numerical simulation is conducted by the software ANSYS/LS-DYNA.The influence of control hole on the crack growth of coal is further studied.The research results can offer a further understanding of the multi-factor influence mechanism of coal damage and crack evolution under the blasting,provide a theoretical basis and research foundation for the application of deep-hole control blasting to prevent coal and gas outburst,and improve the gas drainage rate.