Abstract: In order to study the expansion of internal cracks in the deformation process of limestone under axial load,uniaxial loading tests were carried out. At the same time,the loading process of limestone was monitored in real time by using three-dimensional positioning acoustic emission technology and rock acoustic parameter testing technology. Combined with the evolution law of real-time wave velocity and acoustic emission signal,the process of crack propagation in the sample is revealed. The results show that the longitudinal wave velocity of the limestone sample is higher in the elastic deformation stage and the plastic deformation stage during the axial loading process,and the wave velocity fluctuates greatly in the plastic deformation stage,indicating that the crack propagation speed inside the rock sample is the fastest in the plastic deformation stage. However,the longitudinal wave velocity is low when it is close to failure. During the loading process,the amplitude of the acoustic emission signal is mostly less than 60 dB. The high amplitude signal will increase with the frequency of the sample failure,and the value will increase as a whole. The specimen cracks inside,and the cracks mainly extend to the edge of the specimen around the crack initiation position. The three-dimensional positioning acoustic emission signal can reflect the expansion of the internal cracks of the limestone sample during the axial loading process,and its position is obviously corresponding to the final failure crack. 

Key words: three-dimensional positioning acoustic emission,crack propagation,real-time wave velocity,signal amplitude, fractured crack