Experimental study on characteristics of strain and acoustic emission in the process of coal rock expansion and fracture

In order to solve the problem that there are few researches on the acoustic emission characteristics in the process of coal rock expansion and fracture, experiments on coal rock expansion and fracture are carried out to analyze the change law of strain and acoustic emission signals during the whole process of coal rock expansion and fracture. The results show that: ① the coal-rock expansion and fracture process can be divided into micro-fracture stage (Ⅰ), macro-fracture generation and expansion stage (Ⅱ) and splitting stage (Ⅲ). ② the strain evolution of coal and rock samples in the expansion process is consistent, showing the trend of 'slow change→acceleration→extreme value'. However, the acoustic emission signals of the two samples at each stage are quite different. ③ the acoustic emission ringing counts are more abundant in the coal samples at stages Ⅰ and Ⅱ, and the cumulative ringing counts increase exponentially near stage Ⅲ; while the acoustic emission ringing counts are less in the rock samples at stages Ⅰ and Ⅱ, and the cumulative ringing counts show a 'sudden increase - calm' trend near stage Ⅲ. ④ there is deformation localization in the process of both coal and rock expansion and fracture. The sudden change of strain variation coefficient and the increase of acoustic emission peak frequency range can be used as the precursor characteristics of coal rock expansion,fracture and instability. The research results can provide a basis for monitoring and early warning of coal rock fractures and other projects.