Macro-Meso Failure Characteristics And Energy Evolution Of Granite Under Uniaxial Compression

To reveal the macro-and micro-failure characteristics and energy evolution of granite under uniaxial compression,the mineral composition,content and morphology of granite were observed by polarizing microscope.Then uniaxial and Brazilian tests of granite and were conducted to obtain the stress-strain curves and mechanical parameters.The failure characteristics of the granite under uniaxial compression were analysed from macro-and microscope,the mineral composition image and morphology features of the damage fractures by FESEM.Finally,the energy evolution characteristics of granite during uniaxial compression were analyzed based on energy theory and numerical simulation.The research results are as follows:(1)The rock sample selected for this paper is a medium-coarse-grained black mica diorite granite,which contains four main mineral compositions with the contents of Quartz(30%),Quartz(30%),respectively.The uniaxial compressive stress-strain curves of these granites are typical inhomogeneous rocks with almost no yielding stage and instantaneous bursting after the peak stress in the elastic stage,and no residual strength.The average uniaxial compressive strength of the rock samples is 146.24 MPa,the average splitting tensile strength is 7.91 MPa,and the compression-tension ratio is 18.5,which is typical of brittle rocks.(2)From a macroscopic perspective,the uniaxial compression of granite presents an X-shaped conjugate inclined plane shear failure mode(conical failure),and its failure mechanism is shear-tensile coupling failure.The tensile failure is distributed around the specimen,which is manifested as lateral bursting and peeling of the specimen side.Shear failure is distributed in the upper and lower conical areas of the specimen,which is manifested as inclined shear slip and produces a large amount of rock debris and powder.From the mesoscopic perspective,the failure modes of rock samples can be divided into intrachrystalline and intergranular failure,which include shear failure and tensile failure respectively.(3)The rock sample has a high energy storage limit during uniaxial compression.A large amount of elastic strain energy is stored inside the rock before reaching the strength limit,and is rapidly released after the strength limit and transformed into surface energy and kinetic energy required for rock bursting.The dissipated energy during uniaxial compression of rock samples shows three stages,a nonlinear increasing stage,a smooth or small decreasing stage and a rapid increasing stage,corresponding to the three stages of damage evolution,the initial damage period,the damage calming period and the damage acceleration period,respectively.There is no deceleration damage and residual damage phase in the energy evolution during uniaxial compression of granite,which is the main cause of rock explosion.(4)The three-dimensional granite numerical model constructed by "randomly generated particle cluster method" can realize the quantitative control and non-uniform distribution of the main minerals of granite,and better reproduce the mechanical properties,damage characteristics,crack expansion and energy evolution law of granite in indoor compression and tensile tests.The crack types in the uniaxial compression of granite in the numerical model are mainly tensile cracks,and the tensile cracks appear earlier than shear cracks.The total strain energy gradually increases during the uniaxial compression of the numerical model and reaches the maximum at the peak stress point,showing the characteristics of accelerated accumulation before the peak and rapid release after the peak,while the dissipation energy increases slowly before the peak stress and increases sharply after the peak,which is consistent with the energy evolution law of the indoor test.