CREEP BEHAVIOR AND ACOUSTIC EMISSION CHARACTERISTICS OF COAL SAMPLES WITH DIFFERENT MOISTURE CONTENT

Abstract

The acoustic emission (AE) test of step-loaded samples of coal with different moisture contents was conducted using an AG-X250KN rock servo test system and an AE21C AE-monitoring system to study the influence of moisture content on the creep characteristics of coal. The results show that the moisture content influences the creep characteristics of coal samples, in that the greater the moisture content, the greater the creep deformation of the coal and the lower the creep threshold, creep strength, and creep coefficient values. The improved Burgers model can better describe the mechanical properties of creep in coal. In the transient creep stage, the coal micropores and fractures are gradually expanded, and AE activity gradually increased. In the stable creep stage, the creep deformation rate of coal tended to be stable, while new fractures and AE events and energy were all decreased. In the accelerated creep stage, a large number of fractures were generated in the coal, which gradually developed into unstable macrofractures. The stored energy was released rapidly in a relatively short time span, and the number and energy of AE events reached their maximum value. Therefore, the AE characteristics of coal reflect the evolutionary process of damage during creep.