Mechanical Response and Crack Evolution Law of Coal and Rock Mass Under Different True Triaxial Stress

Abstract In order to study the mechanical response and crack evolution law of surrounding rock under different stress environments in deep high ground stress mines, the true triaxial disturbed unloading rock test system was used to realize the original rock stress occurrence environment, and the mechanical properties of coal and rock mass with different intermediate principal stresses were studied. The intermediate principal stress deviatoric stress model was established to analyze the crack evolution law of coal and rock mass under different stress environments. The results show that when the intermediate principal stress is 3MPa, 6MPa, 10MPa and 14MPa, with the increase of intermediate principal stress, the deformation in this direction is further inhibited, and the elastic modulus and peak strength of coal and rock mass are enhanced, but the increase of coal is weaker than that of sandstone. The lateral expansion of rock mainly appears along the direction of minimum principal stress, and the development of cracks appears on the plane of σ1-σ3 and expands along the direction of σ2. From the proportion of RA-AF value, it is found that the increase of intermediate principal stress aggravates the development of shear cracks in coal and reduces the development of shear cracks in sandstone. Based on the acoustic emission signal (ringing count, cumulative energy), it is found that with the increase of intermediate principal stress, the acoustic emission signal of coal and rock mass gradually tends to be stable in the elastic stage, and the cumulative energy curve of sandstone shows ladder-like fluctuation. When the failure occurs, the acoustic emission signal of coal and rock mass increases with the increase of intermediate principal stress. The acoustic emission signal is very active when the coal and rock mass is close to failure, and the ringing count and cumulative energy increase suddenly, which indicates that the rock is about to fail. The acoustic emission activity can be used as a precursory information for judging the rock failure. The research results can provide an experimental basis for the sudden instability of deep high ground stress roadway.