Study on cracking evolution characteristics of pre-fractured coal and rock mass based on DIC technology

In order to study the cracking network structure and the surface cracking evolution development process of the coal and rock mass,a triaxial loading test was conducted based on the mining stress path of the coal and rock mass.A loading operation was stopped when the stress was just over the peak stress and the pre-fractured coal and rock mass under the mining stress role were obtained.Then the DIC technology was introduced,an uniaxial loading was continued and the cracking evolution development process was observed and recorded.In combination with the fractal geometry,a fractal dimension of the surface cracking on the coal and rock in different loading stage was calculated.The study result showed that under the real mining stress path,with the influence of the surrounding pressure released,the loading capacity of the coal and rock was reduced over 40%.Due to the different roughness of the cracking surface and the heterogeneity and insitu defects,except for the continuous deformation and failure along the pre-fractured cracking surface,the pre-fractured coal and rock mass would occur new secondary cracking.Under the condition of the uniaxial compression,the fractal dimension of the cracking on the surface of the coal and rock mass would be increased from 1.12 to 1.60,and the completed tendency of the cracking evolution would be slow to rapid developed to steady stable.