Failure prediction from crack evolution and acoustic emission characteristics of coal-rock sandwich composite samples under uniaxial compression

Predicting and preventing the occurrence of catastrophic accidents in rock engineering have always been a long-term goal pursued by scientists and engineers. The failure of rock begins with hollow nucleation, and after the cavity is oriented, microcracks form and develop into macro-cracks until the entire sample is destroyed. In order to predict its failure of roof rock-coal-floor rock (RCF) sandwich composite samples, uniaxial compression tests were performed by numerical simulation tests firstly. Secondly, the evolution of microcracks and failure characteristics of RCF are studied. And based on the evolution of microcracks, an index for the failure prediction of RCF-K is proposed. Finally, the accuracy of K was verified through laboratory tests. The results show that when the coal thickness increases from 10 to 60 mm, the number of cracks first increase, then decrease, and then increase. The fracture of RCF is mainly concentrated in the coal body, and becomes more and more obvious with the increase of coal thickness. The crack ratio K changes little with the initial strain, increases rapidly before the peak strength, and reaches the maximum increase to 1 at the peak strength. Therefore, when the crack ratio K increases rapidly and approaches equal to 1, it can be considered a precursor to the failure of the RCF. The failure prediction ratio K given in this paper has certain engineering reference value for the monitoring, and prediction of disasters such as rock scaling, roof fall, and rock bursts.