Study On Mechanical Properties And Failure Mechanism Of Coal-rock Under Different Intermediate Principal Stresses

Through the true triaxial test,the mechanical properties,failure characteristics and mechanism of rock under different three-dimensional stress field conditions are studied,which is of great engineering significance to scientifically evaluate the stability of surrounding rock and prevent the occurrence of major geological disasters.In this paper,through uniaxial compression test,conventional triaxial loading test,true triaxial loading test and true triaxial loading and unloading test,combined with acoustic emission monitoring technology,the mechanical characteristics and failure characteristics of coal-rock under different intermediate principal stress conditions are deeply studied,and the evolution mechanism of rock internal crack initiation,expansion and failure caused by mine excavation and other engineering activities is revealed Main achievements:(1)The conventional triaxial loading test and true triaxial loading test were carried out by the self-developed DTRB-1000 ground acoustic process simulation testing machine.The influence of different intermediate principal stresses on the mechanical properties of coal-rock under loading failure was discussed.Combined with acoustic emission technology,the damage evolution law and failure mechanism of coal-rock under loading were revealed.Based on the experimental results,a three-dimensional cubic mechanical model of coal-rock with fractures is established,which explains the failure mechanism of shear fractures formed along the direction of intermediate principal stress in general.The strength analysis of coal-rock failure process under loading is carried out by using Mogi-Coulomb strength criterion,and the relationship between coal-rock strength variation and intermediate principal stress is discussed.(2)In order to solve the complex three dimensional stress field change caused by the excavation of the geological disasters,in conventional triaxial loading test,true triaxial loading test as the basis,to carry out the coal-rock true triaxial unloading test,to explore different intermediate principal stress effect on coal-rock and mechanical characteristics of unloading process,also combined with acoustic emission technology,reveals the loading and unloading coal-rock damage evolution rule and two phase failure mechanism.In order to verify the good applicability and universality of the Mogi-Coulomb strength criterion,the strength of coal-rock under loading and unloading conditions was fitted.The influence of intermediate principal stress on the fracture degree and fracture characteristics of coal-rock after failure is analyzed.Through the three-dimensional model of coal-rock,the "effect of intermediate principal stress" summarized by predecessors is verified,and the effect of intermediate principal stress on the mechanical properties and failure mechanism of rock is illustrated with a practical engineering case.(3)In order to verify the accuracy of acoustic emission monitoring data in true triaxial tests,the fractal theory is introduced to study and analyze the impact count collected by acoustic emission.It is found that the acoustic emission impact count has good fractal characteristics and its fractal correlation dimension can describe the whole process of coal-rock loading failure.It is proved that there is a relationship between the m-value of phase space and the correlation dimension,that is,the larger the m-value is,the larger the correlation dimension is.(4)In order to verify the coal-rock true triaxial test the correctness of the conclusion,through own structural unit of Abaqus library and model library to establish the coal-rock materials constitutive model,set up the corresponding stress path,and use the material nonlinear analysis,the structure statics analysis and contact problem analysis,obtained the coal-rock failure process and mechanism of the numerical simulation test.The effectiveness of ABAQUS in coal-rock modeling was verified by comparative analysis with laboratory tests,which provided support and supplement for the accuracy of laboratory test results.