Triaxial mechanical behaviour and energy conversion characteristics of deep coal bodies under confining pressure

Abstract

To understand more about damage, failure, and transformation of coal, this paper performed triaxial loading tests on coal samples obtained from a deep coal mine in China. Results showed that the brittle failure characteristics of the specimens were obvious under single-axis loading, and that the ductile failure characteristics of the specimens increased as confining pressure increased. The ultimate strength and residual strength of the samples exhibited a sound linear growth relationship with confining pressure. And according to the change trend of damage variable with axial strain, the damage process of coal body is divided into four stages: initial damage stage, stable damage stage, rapid damage stage and damage failure stage. The energy conversion characteristics of the samples were thoroughly analysed and it was found that with the increase of confining pressure, the proportion of elastic energy of coal samples increases, while the proportion of dissipated energy decreases, indicating that confining pressure can inhibit the expansion of fractures and strengthen the energy storage capacity of coal samples. It was also discovered that the greater the confining pressure, the greater the ultimate elastic energy of the samples. This study is of great significance for mastering high energy level disasters in deep mines.